Aviation Safety: More Research Needed on the Effects of Air
Quality on Airliner Cabin Occupants (16-JAN-04, GAO-04-54).
Over the years, the traveling public, flight attendants, and the
medical community have raised questions about how airliner cabin
air quality contributes to health effects, such as upper
respiratory infections. Interest in cabin air quality grew in
2003 when a small number of severe acute respiratory syndrome
(SARS) infections may have occurred on board aircraft serving
areas that were experiencing outbreaks of the disease. In 2001, a
National Research Council report on airliner cabin air quality
and associated health effects recommended that additional
research be done on the potential health effects of cabin air.
GAO reviewed what is known about the health effects of cabin air,
the status of actions recommended in the 2001 National Research
Council report, and whether available technologies should be
required to improve cabin air quality.
-------------------------Indexing Terms-------------------------
REPORTNUM: GAO-04-54
ACCNO: A09134
TITLE: Aviation Safety: More Research Needed on the Effects of
Air Quality on Airliner Cabin Occupants
DATE: 01/16/2004
SUBJECT: Airline industry
Airline regulation
Commercial aviation
Respiratory diseases
Health hazards
Public health research
Air quality
******************************************************************
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GAO-04-54
United States General Accounting Office
GAO Report to the Ranking Democratic Member, Subcommittee on Aviation, Committee
on Transportation and Infrastructure, House of Representatives
January 2004
AVIATION SAFETY
More Research Needed on the Effects of Air Quality on Airliner Cabin Occupants
a
GAO-04-54
Highlights of GAO-04-54, a report to the Ranking Democratic Member,
Subcommittee on Aviation, Committee on Transportation and Infrastructure,
House of Representatives
Over the years, the traveling public, flight attendants, and the medical
community have raised questions about how airliner cabin air quality
contributes to health effects, such as upper respiratory infections.
Interest in cabin air quality grew in 2003 when a small number of severe
acute respiratory syndrome (SARS) infections may have occurred on board
aircraft serving areas that were experiencing outbreaks of the disease. In
2001, a National Research Council report on airliner cabin air quality and
associated health effects recommended that additional research be done on
the potential health effects of cabin air.
GAO reviewed what is known about the health effects of cabin air, the
status of actions recommended in the 2001 National Research Council
report, and whether available technologies should be required to improve
cabin air quality.
GAO recommends that FAA develop detailed plans for its research and
surveillance program on cabin air quality, improve the public's access to
information on the health risks of flying, and assess the costs and
benefits of requiring HEPA filters in commercial aircraft.
www.gao.gov/cgi-bin/getrpt?GAO-04-54.
To view the full product, including the scope and methodology, click on
the link above. For more information, contact Gerald L. Dillingham at
(202) 512-2834 or [email protected].
January 2004
AVIATION SAFETY
More Research Needed on the Effects of Air Quality on Airliner Cabin Occupants
Despite a number of studies of the air contaminants that airline
passengers and flight attendants are potentially exposed to, little is
known about their associated health effects. Reports on airliner cabin air
quality published by the National Research Council in 1986 and 2001
concluded that more research was needed to determine the nature and extent
of health effects on passengers and cabin crew. Although significant
improvements have been made to aircraft ventilation systems, cabin
occupants are still exposed to allergens and infectious agents, airflow
rates that are lower than those in buildings, and air pressures and
humidity levels that are lower than those normally present at or near sea
level.
The 2001 National Research Council report on airliner cabin air quality
made 10 recommendations, 9 of which directed the Federal Aviation
Administration (FAA) to collect more data on the potential health effects
of cabin air and to review the adequacy of its standards for cabin air
quality. FAA has addressed these 9 recommendations to varying degrees as
it attempts to balance the need for more research on cabin air with other
research priorities (e.g., passenger safety). However, some in the
aviation community, including some of the committee members who produced
the report on cabin air, do not feel that FAA's planned actions will
address these recommendations adequately. For example, most members were
concerned that FAA's plan for implementing the report's key
recommendations on the need for more comprehensive research on the health
effects of cabin air was too limited. FAA plans to address these
recommendations in two parts-the first, which started in December 2003,
and the second, which will start in December 2004 and end in late 2006 or
early 2007. However, FAA lacks a comprehensive plan, including key
milestones and funding needs. In addition, most committee members thought
that FAA's response to a recommendation for it to improve public access to
information on the health risks of flying was inadequate. We also had
difficulty accessing this information on FAA's Web site.
Several technologies are available today that could improve cabin air
quality, (e.g., increasing cabin humidity and pressure or absorbing more
cabin odors and gasses); however, opinions vary on whether FAA should
require aircraft manufacturers and airlines to use these technologies. GAO
found that one available technology, high-efficiency particulate air
(HEPA) filtering, was strongly endorsed by cabin air quality and health
experts as the best way to protect cabin occupants' health from viruses
and bacteria in recirculated cabin air. While FAA does not require the use
of these filters, GAO's survey of major U.S. air carriers found that 85
percent of large commercial airliners in their fleets that recirculate
cabin air and carry more than 100 passengers already use these filters.
However, the use of HEPA filters in smaller commercial aircraft that carry
fewer than 100 passengers is much lower. The cost to retrofit the smaller
aircraft to accept the HEPA filter, if it were made mandatory, could be
expensive.
Contents
Letter
Results in Brief
Background
Despite a Number of Studies, Data Are Lacking About the Effects of
Air Quality On Cabin Occupants FAA has Taken Action to Address Council
Recommendations On Cabin Air Quality, but These Efforts Could Be Improved
Some Technologies Exist for Improving Cabin Air Quality, but There
Are Questions About Whether They Should be Required Conclusions
Recommendations for Executive Action Agency Comments
1 3 6
11
17
32 39 40 41
Appendixes
Appendix I: Appendix II:
Appendix III:
Appendix IV: Appendix V:
Appendix VI:
Objectives, Scope, and Methodology
Biographical Information on the National Research Council Committee
Transmission of Severe Acute Respiratory Syndrome (SARS) on Board Aircraft
Is Rare and Associated with Proximity
European CabinAir Study: Scope and Methodology
Surveillance and Research Programs
Surveillance Program
Research Program
GAO Contacts and Staff Acknowledgments
GAO Contacts
Staff Acknowledgments
43
46
49
53
55 55 56
58 58 58
Selected Bibliography
Tables Table 1: Potential Air Quality Related Concerns on Aircraft
Cited by
the National Research Council in 2001 16
Table 2: Status of the National Research Council's 2001 Report
Recommendations on Airliner Cabin Air Quality 18
Table 3: Number of Large and Regional Aircraft of Top 28
Airlines
That Do or Do Not Recycle Cabin Air 44
Contents
Figures Figure 1: Passenger Cabin of Commercial Airliner 8
Figure 2: Overview of How Air Is Supplied on a Commercial
Airliner 10
Figure 3: A Typical HEPA Filter for Commercial Passenger
Aircraft 33
Contents
Abbreviations
AFA Association of Flight Attendants
APFA Association of Professional Flight Attendants
APL Applied Physics Laboratory (Johns Hopkins University)
ASHRAE American Society of Heating, Refrigerating and Air-Conditioning
Engineers AsMA Aerospace Medical Association ATA Air Transport Association
ATR Avions de Transport Regional BAe British Aerospace BRE Building
Research Establishment CAA Civil Aviation Authority (United Kingdom) CDC
Centers for Disease Control and Prevention CO carbon monoxide CO2 carbon
dioxide DOT Department of Transportation ECS Environmental Control System
EPA Environmental Protection Agency FAA Federal Aviation Administration
FARS Federal Aviation Regulations GAO General Accounting Office HEPA
high-efficiency particulate air IAPA International Airline Passengers
Association IATA International Air Transport Association JAA European
Joint Aviation Authorities NEJM New England Journal of Medicine NIOSH
National Institute for Occupational Safety and Health NRC National
Research Council O3 ozone RPM revenue passenger mile SARS severe acute
respiratory syndrome TB tuberculosis URI upper respiratory tract infection
WHO World Health Organization
Contents
This is a work of the U.S. government and is not subject to copyright
protection in the United States. It may be reproduced and distributed in
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separately.
A
United States General Accounting Office Washington, D.C. 20548
January 16, 2004
The Honorable Peter DeFazio
Ranking Democratic Member
Subcommittee on Aviation
Committee on Transportation and Infrastructure
House of Representatives
Dear Mr. DeFazio:
The quality of air in commercial airliner cabins has long been a concern
of
the traveling public, the medical community, and particularly flight
attendants, who fly often. Air quality, in the context of airliner cabins,
refers to the extent to which airflow, low humidity, and air pressure1 and
contaminants such as pollutants and infectious disease pathogens affect
the healthfulness of the air. Air travelers, flight attendants, and the
medical
community have raised questions about the extent to which cabin air
contributes to discomfort, such as dry eyes and nose, and to more serious
health effects, such as upper respiratory infections. Interest in cabin
air
quality heightened in 2003, with reports that a small number of severe
acute
respiratory syndrome (SARS) infections may have occurred on board
aircraft serving areas with SARS outbreaks.2 In 2001, the National
Research Council3 issued a report that assessed airborne contaminants in
commercial aircraft, including an evaluation of their toxicity and
associated health effects; addressed cabin pressure (oxygen supply) and
ventilation; and recommended approaches to improving data on cabin air
quality.4
1Although airliners are pressurized, the air pressure in an aircraft cabin
is lower than it is at sea level. Airliners are required to be pressurized
to an altitude that is not higher than 8,000 feet. This is about
three-fourths the air pressure at sea level.
2According to the World Health Organization (WHO), there is a very low
risk of catching SARS through an airplane's ventilation system. SARS is
believed to be transmitted based on proximity to an infected individual.
However, WHO reported that as of May 23, 2003, there were 29 probable
cases of in-flight SARS transmissions on four flights. See appendix III
for more information on SARS.
3The National Research Council is the principal operating arm of the
National Academy of Sciences and the National Academy of Engineering.
4National Research Council. The Airliner Cabin Environment and the Health
of Passengers and Crew, National Academy Press (Washington, D.C.:
Distributed electronically December 2001; bound report copyrighted 2002).
Given this backdrop, you asked us to provide information on steps that the
aviation community is taking to address concerns about cabin air quality.
Specifically, you asked us to address the following questions: (1) What is
known about the major potential health effects of air quality in
commercial airliner cabins on passengers and flight attendants? (2) What
actions has the National Research Council recommended to improve cabin air
quality, and what is the status of those actions? (3) What technologies
are available today to improve the air quality in commercial airliner
cabins, and which, if any, should be required?
To address these questions we reviewed the December 2001 National Research
Council report on airliner cabin air quality because it was the most
current and comprehensive work of its kind in this area. The Council is
the principal operating agency of the National Academy of Sciences, which
was chartered by Congress to advise the federal government on scientific
and technical matters. To produce the report, the Council convened a
committee of experts in the fields of industrial hygiene, exposure
assessment, toxicology, occupational and aerospace medicine, epidemiology,
microbiology, aerospace and environmental engineering, air monitoring,
ventilation and airflow modeling, and environmental chemistry. (App. II
lists the members of the committee.) The committee examined the existing
literature on this issue and made recommendations for potential approaches
for improving cabin air quality. We also independently reviewed other
studies on issues related to cabin air quality, paying particular
attention to those issued after the publication of the National Research
Council report.5 We also gathered information from airlines and the
governments of Australia, Canada, and the United Kingdom because of the
research these countries have done on airliner cabin air quality. We also
interviewed officials representing the World Health Organization (WHO),
the Centers for Disease Control and Prevention (CDC), the Federal Aviation
Administration (FAA), the National Institute for Occupational Safety and
Health (NIOSH), the Aerospace Medical Association (AsMA), the Air
Transport Association (ATA), the Association of Flight Attendants (AFA),
the International Airline Passengers Association (IAPA), and aircraft and
air filter manufacturers. We also interviewed several recognized experts
on cabin air quality issues. In
5See the Selected Bibliography at the end of this report and, in
particular, Hocking, Martin B., "Trends in Cabin Air Quality on Commercial
Aircraft: Industry and Passenger Perspectives," Reviews on Environmental
Health 17, 1 (2002): 1-49; and Rayman, Russell B., "Cabin Air Quality,"
Aviation, Space and Environmental Medicine 73 (2002): 211-215.
addition, we interviewed 11 of the 13 members6 of the National Research
Council Committee on Air Quality in Passenger Cabins of Commercial
Aircraft that produced the 2001 report to obtain their views on the status
of the report's recommendations and other cabin air quality issues,
including leveraging expertise outside of FAA, such as the Environmental
Protection Agency for its large body of research on indoor air quality and
NIOSH for its role in conducting public health and air quality research.
Finally, we contacted the 14 largest U.S. airlines that use Airbus,
Boeing, or McDonnell Douglas aircraft to determine the extent to which
their aircraft fleets use high-efficiency particulate air (HEPA) filters7
on recirculated cabin air. Twelve of these 14 airlines responded, allowing
us to determine HEPA filter usage rates for approximately 90 percent of
the aircraft in our study population. We also obtained information from an
aviation publication and the manufacturers of regional jets (typically
aircraft that seat 100 or fewer passengers) on the extent of HEPA filter
usage in these aircraft. We conducted our work from April 2003 through
December 2003 in accordance with generally accepted government auditing
standards. See appendix I for additional information on our objectives,
scope, and methodology.
Results in Brief Despite a number of studies of the air contaminants that
passengers and flight attendants are potentially exposed to in airliner
cabins and complaints by cabin occupants about health effects from poor
cabin air quality, little is known about the extent of associated health
effects. Reports published by the National Research Council in 1986 and
2001 on what was then known about airliner cabin air quality concluded
that more research was needed to determine the nature and extent of health
effects on passengers and cabin crew and that available air quality data
are not adequate to address critical questions on aircraft cabin air
quality and its possible effects on cabin occupant health. While aircraft
manufacturers
6The NRC committee consisted of 13 members. We attempted to contact all 13
members. We interviewed 11, and 8 members responded to cabin air quality
questions and the implementation status of their recommendations. Of the
11 committee members interviewed, 3 declined to address our questions,
stating that they did not follow the progress of FAA's implementation of
the recommendations. For example, 1 member stated that as a toxicologist,
he could not comment on the overall approach FAA is taking to address the
NRC recommendations.
7For purposes of this report, we use the Environmental Protection Agency's
definition of HEPA, which is a filtering efficiency of 99.97 percent.
have made significant improvements to aircraft ventilation systems,
passengers and cabin crews are still exposed to a number of air
contaminants, such as allergens and infectious agents. Passengers and crew
are also subjected to airflow rates that are lower than those recommended
for buildings and to air pressures and humidity levels that are lower than
those normally present at or near sea level. This exposure can pose a
health risk to passengers with certain medical conditions, such as lung,
heart, and circulatory disorders. In addition, poor cabin air quality has
been associated with such discomforts as eye and nasal passage irritation.
The 2001 National Research Council report on airliner cabin air quality
made 10 recommendations directed largely to the Federal Aviation
Administration (FAA) to collect more information on the potential health
effects of cabin air quality and to review the adequacy of its standards
for air quality in commercial airliner cabins. To varying degrees, the
agency has addressed the recommendations for which it is responsible. FAA
is attempting to balance the need for additional research on the potential
health effects of cabin air quality with other research priorities, such
as improving passenger safety. However, some in the aviation community,
including members of the Council committee who prepared the report, do not
feel that FAA's planned actions will adequately address all of its
recommendations on cabin air quality. For example, several of the Council
committee members were particularly concerned about FAA's approach to
implementing the committee's principal recommendations that more
comprehensive research on the health effects of cabin air qualityis
needed. In response to the committee's recommendations in this area, FAA
is leading the development of a surveillance and research program intended
to relate perceptions of discomfort or health-related symptoms of flight
attendants and passengers to possible causal factors, such as air
contaminants, reduced air pressures and airflows, jet lag, low humidity,
or inactivity. However, FAA has not yet developed a detailed plan with key
milestones and funding estimates for conducting the planned surveillance
and research program. In addition, of the 8 committee members who
discussed the recommendations with us,8 all said that FAA's program was
much more limited than the Committee had envisioned. For example, 2 of the
8 said that FAA's program does not include an adequate number and
cross-section of aircraft types and flights for accomplishing its
objective.
8Of the 11 members interviewed, 8 agreed to address our questions
concerning the committee recommendations (see app. I).
One committee member was also concerned that the program is too heavily
tied to the aircraft industry to ensure objectivity and independence. In
addition, another committee member believes that although FAA has a
committee to oversee the selection of the contractor for the program, it
has not assembled an advisory committee to review the research design and
monitor the implementation of the program. In addition, 3 committee
members are concerned that the research effort may not be adequately
funded. Furthermore, 6 of the committee members felt that FAA's approach
for addressing its recommendation that increased efforts be made to
provide cabin crew, passengers, and health professionals with information
on health issues related to flying by creating links on the FAA Web site
to relevant information from health organizations was inadequate because
the links are difficult to navigate and need to be supplemented with other
information dissemination methods, such as providing physicians with
brochures to share with patients who are planning air travel.
Several technologies are available today that could improve cabin air
quality (e.g., by filtering or removing contaminants, increasing cabin
humidity and raising cabin pressure, or absorbing more cabin odors and
gasses), but opinions vary on whether FAA should require aircraft
manufacturers and airlines to use these technologies. Aircraft
manufacturers contend that unless future research proves otherwise, the
ventilation systems in the aircraft that they have produced provide ample
amounts of relatively clean air. Most aircraft currently in production
have ventilation systems that recirculate cabin air. In addition, all of
the new large commercial airliners in production that carry more than 100
passengers and have ventilation systems that recirculate cabin air come
equipped with high-efficiency particulate air (HEPA) filters, which are
highly effective (99.97 percent) at capturing airborne contaminants, such
as viruses, when properly fitted and maintained. According to our survey
of major U.S. air carriers, 85 percent of commercial airliners in the
current U.S. fleet that recirculate cabin air and carry more than 100
passengers use HEPA filters. However, we found that only a small portion
of the smaller regional jets that recirculate cabin air are using these
filters. According to the manufacturers, most of these aircraft have no
provision for installing any type of filter for their recycled air and
could not be retrofitted with HEPA filters without extensive
modifications. Nevertheless, given the proven effectiveness of HEPA
filters, some National Research Council committee members and health
officials believe that FAA should require them on all aircraft with
recirculation systems. GAO also found that HEPA filters are relatively low
cost when their use does not require modifying the
existing ventilation system. In addition, airflow rates could be increased
in some aircraft by adjusting settings on the ventilation system to reduce
the effects of some airborne contaminants by diluting their concentration.
However, this would be done at the expense of higher fuel consumption,
increased engine emissions, and lower cabin humidity. Finally, both Boeing
and Airbus-the world's two largest airframe manufacturers-are considering
using air quality improvement technologies (e.g., increasing cabin
humidity) to improve passenger comfort on the long-range commercial
aircraft that they are developing.
To help ensure that FAA's research and surveillance efforts on airliner
cabin air quality answer critical outstanding questions about the nature
and extent of potential health effects of cabin air quality on passengers
and flight attendants, GAO recommends that the FAA Administrator (1)
develop a detailed plan for the research and surveillance efforts,
including key milestones and funding estimates; (2) appoint a committee of
acknowledged experts in the fields of aircraft ventilation and public
health, including representatives of EPA and NIOSH, to assist in planning
and overseeing the research and surveillance efforts; (3) leverage the
findings of international counterparts' research on airliner cabin air
quality to inform FAA's surveillance and research efforts; and (4) report
to Congress annually on the progress and findings of the research and
surveillance efforts and funding needs.
In addition, to help improve the healthfulness of cabin air for passengers
and cabin crews, GAO also recommends that the FAA Administrator assess the
costs and benefits of requiring the use of HEPA filters on commercial
aircraft with ventilation systems that recirculate cabin air. GAO also
recommends that FAA should go farther in addressing the Council
recommendation to increase efforts to provide the public with information
on the health risks of flying by taking additional steps to improve its
methods for disseminating this information, such as improving the ease
with which the public can access this information on FAA's Web site and
systematically disseminating such information to physicians and their
patients through various medical associations.
Background Since people began traveling in pressurized,
climate-controlled aircraft more than 40 years ago, questions have arisen
about the quality of air inside aircraft cabins and its effect on the
health of passengers and cabin crews. In addition, the number of people
traveling by commercial aircraft has increased dramatically over the
years, with more than 600 million
passengers flown by U.S. carriers in 2002 alone. Despite a downturn in air
travel following the events of September 11, 2001, FAA expects demand to
recover and then continue a long-term trend of 3.6 percent annual growth.
As air travel has become more accessible, the flying public mirrors the
general population more closely than in years past. Therefore, it includes
more young and elderly passengers who can be more susceptible to potential
health risks associated with air travel. This diverse group of passengers,
as well as the cabin crew, experiences an environment in the aircraft
cabin that in some ways is similar to that of homes and buildings but in
other ways is distinctly different. The National Research Council (the
Council)-the principal operating agency of the National Academy of
Sciences-has issued two reports at the request of Congress on the air
quality in aircraft cabins, one in 1986 and another in 2001.9 The 2001
Council report notes that the aircraft cabin is a unique environment in
which the occupants are densely confined in a pressurized space. The
report goes on to note that airline passengers encounter environmental
factors that include low humidity, reduced air pressure, and potential
exposure to air contaminants, including ozone, carbon monoxide,
pesticides, various organic chemicals, and biological agents that can have
serious health effects. The report concluded that there are still many
unanswered questions about how these factors affect cabin occupants'
health and comfort and about the frequency and severity of incidents in
which heated oils or hydraulic fluids release contaminants into the cabin
ventilation system. Figure 1 shows the passenger cabin of a commercial
aircraft.
9National Research Council, The Airliner Cabin Environment: Air Quality
and Safety, National Academy Press (Washington, D.C.: 1986) and National
Research Council, The Airliner Cabin Environment and the Health of
Passengers and Crew, National Academy Press (Washington, D.C.: Distributed
electronically December 2001; bound report copyrighted 2002).
Figure 1: Passenger Cabin of Commercial Airliner
Source: Markus Wechselberger.
As depicted in figure 2, supplying air to modern jet airliner cabins is a
complex process that varies somewhat among airplane models but has
essential characteristics that are shared by most airliners. Basically,
some of the outside air that enters the aircraft engines is diverted and
processed for use in the cabin in order to achieve an air pressure and
temperature closer to that experienced on the earth's surface. FAA
requires that air supplied to aircraft be designed to maintain a cabin
pressure equivalent to that at an elevation of no more than 8,000 feet,
which is similar to the elevation of Mexico City (7,500 ft.).
Nevertheless, the air pressures inside aircraft cabins are much higher
than the extremely low outside air pressures at normal cruising altitudes
of 25,000 to 40,000 feet. After flowing through the engines, the air
enters an intricate system of cooling devices and ducts and is distributed
throughout the cabin and cockpit.
Airlines that fly in areas where ozone levels are high10 are required to
take steps to ensure that ozone levels do not exceed prescribed standards
(e.g., by having a device that converts the ozone pollutant into oxygen
before it enters the cabin and cockpit). The Council reported that
unacceptable high ozone levels can occur in passenger cabins of commercial
aircraft in the absence of effective controls. On most modern aircraft, an
average of about 56 percent of the outside air supplied to the cabin is
vented out of the aircraft through valves that help regulate cabin
pressure. The remaining air is then recirculated through the cabin; this
recirculation allows the engines to use less fuel for air supply and
pressurization. In addition to less fuel and pressurization, recirculation
also provides the benefit of higher airplane cabin humidity, improved
airflow patterns, and minimized temperature gradients. On most large
aircraft, the recirculated air typically passes through filters that are
designed to remove harmful particulates, such as viruses and bacteria.11
FAA requires that aircraft ventilation systems for aircraft designs
certified after June 1996 be designed to supply at least 10 cubic feet per
minute of outside air per person under standard operating conditions. This
compares with the standard minimum rate of 15 cubic feet per minute per
person for buildings recommended by the American Society of Heating,
Refrigerating and Air-Conditioning Engineers (ASHRAE).12 However,
according to FAA officials, there is currently no standard for cabin
ventilation rate, and it has yet to be determined if it is appropriate to
compare building and aircraft ventilation rates because outside air at
altitude is very clean, while air sources for buildings are often
contaminated by pollution. Furthermore, in rare instances, oil leaks or
other engine malfunctions can cause contaminants such as carbon monoxide
to be released into the cabin ventilation system. The 2001 Council report
noted that questions about the frequency and significance of such
incidents remain unanswered. In February 2002, FAA published a report that
discussed many of the issues in the Council report, including an
10The 2001 Council study reported that the effects of ozone vary with
latitude, altitude, and season and that the concentration of ozone is much
higher at cruise altitudes in high latitudes (greater than approximately
60DEGN) than at low latitudes (approximately 30DEGN), resulting in higher
concentrations of ozone on polar flights.
11FAA does not require these filters; however, our survey of U.S. airlines
found that 85 percent of the large aircraft (those that carry 100
passengers or more) currently use HEPA filters.
12The American Society of Heating, Refrigerating and Air-Conditioning
Engineers (ASHRAE) advances the arts and sciences of heating, ventilation,
air conditioning, refrigeration, and related human factors to serve the
evolving needs of the public.
estimate of 416 air contaminant events (or 2.2 events every 1,000,000
aircraft hours) that may have taken place in commercial transports within
the United States between January 1978 and December 1999.
Figure 2: Overview of How Air Is Supplied on a Commercial Airliner
(1) Outside air continuously enters the engine, where it is compressed.
(2) It then passes through a catalytic ozone converter (in some aircraft)
to air-conditioning packs.
(3) The air passes through cooling packs to a mixing manifold.
(4) Outside air entering the mixing manifold is mixed with recirculated
air that has been cleaned with high-efficiency filters.
(5) The makeup of air in the mixing manifold is approximately 50 percent
outside and 50 percent filtered, recirculated air.
(6) Air from the mixing manifold is then supplied to the cabin on a
continuous basis from overhead outlets.
(7) As outside air enters the airplane, air is continuously exhausted from
the airplane.
(8) Mixed outside and filtered recirculated air is provided to the flight
deck from the mixing manifold.
FAA is responsible for setting design standards for aircraft ventilation
systems. To fulfill its responsibilities, FAA requires that manufacturers
design and build their large commercial airplanes to meet specific
engineering standards, which limit the amounts of certain air quality
contaminants (e.g., carbon monoxide, carbon dioxide, and ozone) that can
be present in an airliner cabin. Manufacturers comply with these
engineering standards in order to have FAA certify their airplanes as
airworthy.13 However, while FAA monitors overall aircraft system
operations, it does not require airlines to monitor cabin air quality
during their operations to determine if air quality during routine flight
operations is meeting the agency's engineering standards. According to
FAA, the certification requirements combined with the monitoring of
overall aircraft system operations are sufficient. However, the 2001
Council report stated that because of a lack of data it was not able to
answer questions about the extent to which aircraft ventilation systems
are operated properly.
Despite a Number of Studies, Data Are Lacking About the Effects of Air
Quality On Cabin Occupants
Passengers and flight attendants have had long-standing concerns about
negative health effects from the quality of air in airliner cabins;
however, research to date, including two reports by the Council, has not
been able to definitively link the broad, nonspecific health complaints of
passengers and flight attendants to possible causes, including cabin air
quality. In its most recent report, the Council concluded that critical
questions about the potential effect of cabin air quality on the health of
cabin occupants remain
13According to FAA officials, FAA regulations have always required
limitations on certain contaminants (e.g., carbon monoxide and carbon
dioxide). Later amendments added ozone and changed the ventilation
requirements. However, these officials stressed that airplanes are
certified to the regulations in effect at a certain time prior to their
manufacture. Only the latest certified airplanes will have had to meet the
latest amendment level for the regulations governing the cabin
environment, such as a 1996 amendment which added the requirement that
each occupant be provided with 0.55 pounds (equivalent to 10 cubic feet)
of fresh air per minute under standard operating conditions.
unanswered because existing data are inadequate, and it recommended
further research to narrow this knowledge gap.
Passengers and flight attendants (cabin occupants) have long complained of
acute and chronic health effects during and after flying. Many complaints
made by cabin occupants are relatively minor, such as dry eyes and nose,
or the onset of colds soon after flying, but others are much more serious.
According to the Association of Flight Attendants, its members have
reported such health problems as respiratory diseases, nausea, dizziness,
muscle tremors, nervous system damage, and memory loss.14 The association
notes that these illnesses are consistent with exposure to carbon
monoxide, pesticides, reduced oxygen levels, neurotoxins, and ozone gas,
all of which can be present in the cabin itself or in cabin air supplies,
depending on the flight. In addition, passengers with certain medical
conditions can be at higher risk from the quality of cabin air than the
general population due to air contaminants, lowered oxygen levels in the
body (hypoxia), and changes in cabin pressure. Such medical conditions
include limited lung capacity (e.g., asthma) and cardiovascular and
circulatory disorders. Those who fly soon after surgery are particularly
vulnerable to changes in cabin pressure. However, according to the Council
report, many of the complaints made by cabin occupants are so broad and
nonspecific that they could have many causes, and it is difficult to
determine a specific illness or syndrome.
Although numerous studies have been conducted on cabin air quality issues,
there are insufficient data to determine the nature and extent of cabin
air quality's effect on cabin occupants. Council reports published in 1986
and 2001 reviewed the literature on cabin air quality issues and concluded
that the studies had not collected data in a systematic manner that would
conclusively address many of the questions about potential exposures in
aircraft cabins and their health effects. Both reports recommended actions
for improving what is known about cabin air quality, including the need to
collect better data on the potential effect of cabin air quality on
passenger and cabin crew health. The 2001 report concluded that available
data on air quality and its possible negative effects on cabin
14ATA officials noted that these symptoms are also consistent with a host
of other causes, such as lack of sleep (perhaps due to difficulty in
adjusting to different time zones), dehydration (possibly from drinking
too much caffeine or alcohol and not enough water during a long flight),
the effect of changes in climate, or exposure to contaminants in other
settings.
occupant health have left three critical outstanding questions unaddressed
and that additional research is needed:
o Do current aircraft as operated comply with FAA design and operational
limits for ventilation rate and for chemical contaminants, including
ozone, carbon monoxide, and carbon dioxide, and are the existing air
quality regulations adequate to protect health and ensure the comfort of
passengers and cabin crew?
o What is the association, if any, between exposure to cabin air
contaminants and reports or observations of adverse health effects in
cabin crew and passengers?
o What are the frequency and severity of incidents when air contaminants
enter the cabin due to nonroutine conditions such as oil leaks or other
engine malfunctions?
Following the 1986 report, the Department of Transportation sponsored a
study to evaluate the health risks posed by exposures to contaminants on
randomly selected flights. In addition, various researchers conducted a
number of studies of cabin air quality issues, including eight
investigations of biological agents, such as viruses and bacteria, on
commercial aircraft. However, these and other studies were not able to
link the broad, nonspecific health complaints that passengers and cabin
crew continued to make to possible causes, including cabin air quality.
Recognizing the need for more data on the issue, Congress directed FAA, in
AIR-21,15 to request that the Council perform another independent
examination of cabin air quality. The Council's report, issued in 2001,
concluded that when operated properly, the environmental control system16
should provide an ample supply of air to pressurize the cabin, meet
general comfort conditions, and dilute or reduce normally occurring odors,
heat, and contaminants. However, the Council also found
15The Wendell H. Ford Aviation Investment and Reform Act for the 21st
Century (AIR-21), Public Law 106-181, April 5, 2000.
16The environmental control system includes devices that pressurize the
cabin in flight, control thermal conditions in the cabin, and ventilate
the cabin with outside air to prevent a buildup of contaminants that might
cause discomfort or present a health hazard.
that the design standard for ventilation rates17 in aircraft required by
FAA was less than one-half to two-thirds the rate recommended by ASHRAE
for buildings. The Council noted that whether the building ventilation
standard is appropriate for the aircraft cabin environment has not been
established.18 Studies have shown that low ventilation rates in buildings
have contributed to "sick building syndrome," which causes fatigue,
headache, and throat irritation. However, FAA officials told us that a
sick building syndrome comparison is not applicable, in part because HEPA
filtration results in much cleaner recirculated air than in a building
environment.
The 2001 Council report also found that although the environmental control
system in aircraft is designed to provide adequate air pressure and
minimize the concentration of contaminants in the cabin, passengers and
cabin crew are potentially exposed to air quality-related health risks.
The Council was particularly concerned about two cabin air characteristics
and suggested that they be given high priority for further investigation.
The first is reduced oxygen partial pressure, which results from the lower
air pressures present in aircraft cabins at cruise altitudes. Most healthy
individuals are unaffected by reduced oxygen partial pressure, but those
with health problems such as cardiopulmonary disease and infants can
experience serious health effects from a lack of oxygen (e.g., respiratory
stress). The other concern of the Council was elevated concentrations of
ozone, which can occur at high cruise altitudes over certain areas of
earth, such as the Arctic. The Council reported that unacceptably high
ozone levels could occur in passenger cabins of commercial aircraft in the
absence of effective controls. FAA allows aircraft operators to maintain
cabin ozone concentrations at or below prescribed limits through flight
planning that avoids areas with ozone concentrations exceeding those
limits or the installation of devices that convert ozone to oxygen.
However, FAA does not have a process in place to ensure that ozone
converters are
17The ventilation rate is the flow of outside air supplied to the cabin
for ventilation and it does not normally include recirculated air even
though recirculated air may be used for cabin ventilation.
18According to FAA officials, a comparison of ventilation rates for
buildings and aircraft is not valid and that "sick building syndrome"
should not be applied to aircraft. Furthermore, both FAA and Boeing
officials told us that the new ASHRAE standards for buildings create two
sets of building standards for ventilation-one for high density buildings
and another for low density buildings. Boeing officials said that under
this standard, high density buildings would have lower airflow rates per
occupant, and that high density buildings are most comparable to airplanes
with high density occupancy.
installed in all aircraft that fly routes where ozone may pose a risk or
that converters in service are operating properly.
The Council also had what it termed moderate concern about several other
potential air quality-related exposures on aircraft, but it noted that
there were little data available on the frequency at which they occur. For
example, according to the Council, infectious agents, such as viruses and
bacteria, were likely present on aircraft, and high occupant densities
could increase the risk of transmittal. The Council observed, however,
that air recirculation did not increase the risk of transmittal,
especially in systems using HEPA filters. Likewise, the Council noted that
airborne allergens, such as cat dander, could pose problems for passengers
with sensitivities. In addition, when aircraft are on the ground,
according to the Council, passengers can be exposed to contaminants from
engine exhaust, such as carbon monoxide and other outdoor air pollutants,
including ozone and particulate matter, when they are pulled into the
aircraft through the ventilation system. Also of some concern to the
Council were incidents when lubricating and hydraulic fluids seep into the
aircraft ventilation system during engine and other system malfunctions.
Although such occurrences are rare, and the actual exposure to
contaminants resulting from them is unknown, lubricating and hydraulic
fluids contain substances that can pose neurological health risks to
passengers and cabin crew if they are present in sufficient concentrations
and for a sufficient length of time. Finally, the Council was somewhat
concerned about exposures to the pesticide spraying that takes place on
some international flights,19 which can cause skin rashes and other health
effects. Table 1 summarizes information presented by the Council on the
potential air quality-related exposures on aircraft.
19Disinsection is the process of spraying the aircraft cabin with
insecticide to prevent the conduction of insects such as mosquitoes from
one country to another. The spraying is often done while passengers and
crewmembers are still on board. The United States terminated this practice
in 1979 because of health concerns and doubts about the effectiveness of
the spraying. Over the years, a number of countries have changed their
policies regarding the spraying of pesticides. The Department of
Transportation is studying alternative technological methodologies,
including air curtains to prevent airborne insects from flying into the
aircraft cabin.
Table 1: Potential Air Quality Related Concerns on Aircraft Cited by the
National Research Council in 2001
Characteristic Potential health impacts Exposure frequency Availability of
information
High concern
Cabin pressure Serious health Reduced cabin Reliable
effects may occur in pressure measurements are
infants and those occurs on nearly available; health
with cardio- all flights. effects in some
respiratory diseases sensitive groups are
from lack of uncertain.
oxygen. Temporary
discomfort or
pain from gas
expansion in middle
ears or sinuses.
Ozone Airway irritation and Elevated Few systematic
reduced lung concentrations are measurements made
function. expected primarily since 1986 Council
on aircraft report.
without ozone
converters.
Moderate
concern
Airborne Irritated eyes and nose,
allergens sinusitis,
Not known. Only self-reported data are available.
acute increases of asthma, or anaphylaxis.
Carbon Headaches and High concentrations Reliable measurements
monoxide lightheadedness could are available
occur at low occur during for normal operating
concentrations, more air-quality conditions, but
serious health incidents. Frequency no data are available
effects result from of for incidents.
higher incidents is highly
concentrations. uncertain but
is believed to be
low.
Hydraulic fluids Mild to severe health effects can Frequency of incidents
in which No quantitative data are available. result from exposure to these
fluids. these fluids enter the cabin is Little information is available on
uncertain but is expected to be health effects related to smoke,
relatively low. mists, or odors in aircraft cabins.
Pesticides Skin rashes can result from skin or Exposure likely on some
Only self-reported data are available. inhalation exposure. international
flights.
Low concern
Carbon Indicator of Concentrations are Reliable measurements
dioxide ventilation adequacy. generally are available
Elevated below FAA only for normal
concentrations regulatory limits. operating conditions.
associated
with increased
perceptions of poor
air quality.
Nuisance Annoyance and mucous Can be present on Reliable information is
odors membrane any flight. available from
irritation can occur. surveys of cabin
occupants.
Relative humidity Temporary drying of skin, eyes, and Relative low
humidity occurs on Reliable and accurate measurements mucous membranes can
occur at most flights. in aircraft are available. relative low humidity
(10 to 20%).
Source: National Research Council.
Since the issuance of the 2001 Council report, some limited studies have
examined specific air quality issues, such as infectious disease
transmission, but they have raised as many questions as they have
answered. For example, according to a revised 2003 WHO report on
tuberculosis (TB) and air travel, as of August 2003, no case of active TB
has
been identified as resulting from exposure while on a commercial
aircraft.20 The report did note, however, that there is some evidence that
transmission of TB may occur during long flights (i.e., more than 8 hours)
from an infectious source (passenger or crew) to other passengers or
crewmembers. In 2002, the American Medical Association21 did not find any
evidence that aircraft cabin air recirculation increases the risk for
upper respiratory tract infection (URI) symptoms in passengers traveling
aboard commercial jets. However, passengers had higher incidents of URI
infections than the general public within a week after completing their
trips. One of the study's authors noted that the research indicated that
while flying increases the risk of getting colds or other infections, an
aircraft's ventilation system may not be a key factor. A 2003 study
appearing in the New England Journal of Medicine found that SARS
transmissions may occur on flights carrying people in the symptomatic
stages of the disease. (See app. II for more details on this study.22)
FAA has Taken Action to Address Council Recommendations On Cabin Air
Quality, but These Efforts Could Be Improved
The December 2001 Council report on airliner cabin air quality made 10
recommendations about air quality standards for the cabins of commercial
airliners and the need for more information concerning the health effects
of cabin air. Nine of these recommendations were directed to FAA, and it
has implemented them to varying degrees. The Council report's 10
recommendations focused on five aspects of cabin air quality and its
environment: (1) the establishment of cabin air quality surveillance and
research programs, (2) FAA's oversight of the operation of aircraft
ventilation systems, (3) exposures on aircraft due to the transport of
small animals in aircraft cabins, (4) distribution of health related
information, and (5) recommended procedures as a result of a ventilation
system shutdown. Although one recommendation asked Congress to designate a
lead federal agency for conducting airliner cabin air quality research,
most of the recommendations were directed at or involved FAA. Table 2
describes each of the Council report recommendationsand FAA's response.
20World Health Organization, Tuberculosis and Air Travel: Guidelines for
Prevention and Control (Geneva, Switzerland: Aug. 27, 2003).
21Zitter, Jessica, Peter Mazonson, Dave Miller, Stephen Hulley, and John
Balmes, "Aircraft Cabin Air Recirculation and Symptoms of the Common
Cold," Journal of the American Medical Association 288 (2002): 483-486.
22Olsen, Sonja J. et al., "Transmission of the Severe Acute Respiratory
Syndrome on Aircraft," The New England Journal of Medicine 349; 25 (2003):
2416-2422.
Table 2: Status of the National Research Council's 2001 Report Recommendations
on Airliner Cabin Air Quality
Council Report Recommendations FAA's Response
Cabin Air Quality Surveillance and Research Programs
Surveillance program FAA is addressing this recommendation
To be consistent with FAA's mission to promote aviation safety, an air
quality and through a joint research effort combining the
health-surveillance program should be established. The objectives and
approaches resources of FAA and the American Society
of this program are summarized in appendix V of this report. The health
and air of Heating, Refrigerating and Air
quality components should be coordinated so that the data are collected in
a Conditioning Engineers (ASHRAE).
manner that allows analysis of the suggested relationship between health
effects or
complaints and cabin air quality.
Research program FAA is addressing this recommendation
To answer specific questions about cabin air quality, a research program
should be through a joint research effort combining the
established. See appendix V of this report for a summary of research
questions, resources of FAA and ASHRAE.
objectives, and research program approach.
Research program lead agency Congress has designated FAA as the lead
The Council committee recommends that Congress designate a lead federal
agency to direct the cabin air quality
agency and provide sufficient funds to conduct or direct the research
program research program, but, according to FAA
recommendation (see above), which is aimed at filling major knowledge gaps
officials, has not appropriated sufficient
identified in this report. An independent advisory committee with
appropriate funds to support it.
scientific, medical, and engineering expertise should be formed to oversee
the
research program to ensure that its objectives are met and the results
publicly
disseminated.
FAA Oversight of Aircraft Ventilation Systems
Air quality regulations
FAA should rigorously demonstrate in public reports the adequacy of
current and proposed Federal Aviation Regulations (FARs) related to cabin
air quality and should provide quantitative evidence and rationales to
support sections of the regulations that establish air quality-related
design and operational standards for aircraft (standards for carbon
monoxide, carbon dioxide, ozone, ventilation, and cabin pressure). If a
specific standard is found to be inadequate to protect the health and
ensure the comfort of passengers and crew, FAA should revise it. For
ventilation, the committee recommends that an operational standard
consistent with the design standard be established.
Necessary data to implement this recommendation will be available upon
completion of the ASHRAE study in late 2006 or early 2007.
Regulations for ozone
FAA should take effective measures to ensure that the current FAR for
ozone (average concentrations not to exceed 0.1 ppm above 27,000 ft; and
peak concentrations not to exceed 0.25 ppm above 32,000 ft.) is met on all
flights, regardless of altitude. These measures should include a
requirement that either ozone converters be installed, used, and
maintained on all aircraft capable of flying at or above those altitudes,
or strict operating limits be set with regard to altitudes and routes for
aircraft without converters to ensure that the ozone concentrations are
not exceeded in reasonable worst-case scenarios. To ensure compliance with
the ozone requirements, FAA should conduct monitoring to verify that the
ozone controls are operating properly (see also surveillance program
recommendation).
Necessary data to implement this recommendation will be available upon
completion of the ASHRAE study.
(Continued From Previous Page)
Council Report Recommendations FAA's Response
Air cleaning equipment Necessary data to implement this
FAA should investigate and publicly report on the need for and feasibility
of installing recommendation will be available upon
air cleaning equipment for removing particles and vapors from the air
supplied by completion of the ASHRAE study.
the environmental control system (ECS) on all aircraft to prevent or
minimize the
introduction of contaminants into the passenger cabin during ground
operation,
normal flight, and air quality incidents.
Carbon monoxide monitoring Necessary data to implement this
FAA should require a carbon monoxide monitor in the air supply ducts to
passenger recommendation will be available upon
cabins and establish standard operating procedures for responding to
elevated completion of the ASHRAE study.
carbon monoxide concentrations.
Exposures on Aircraft, Health Information, and Ventilation Shutdown Procedures
Allergens
Because of the potential for serious health effects related to exposures
of sensitive people to allergens, the need to prohibit transport of small
animals in aircraft cabins should be investigated, and cabin crews should
be trained to recognize and respond to severe, potentially
life-threatening responses (e.g., anaphylaxis, severe asthma attacks) that
hypersensitive people might experience because of exposure to airborne
allergens.
FAA issued an advisory circular providing guidance regarding air carrier
passenger handling procedures for allergen-sensitive people, but did not
prohibit the transport of animals on aircraft, particularly service
animals. Agency officials do not think that a prohibition on animals in
the cabin would be effective in minimizing animal allergens because they
believe that these allergens are brought on board aircraft primarily on
the clothes of passengers.
Health information
Increased efforts should be made to provide cabin crew, passengers, and
health professionals with information on health issues related to air
travel. To that end, FAA and the airlines should work with such
organizations as the American Medical Association and the Aerospace
Medical Association to improve health professionals' awareness of the need
to advise patients on the potential risks of flying, including risks
associated with decreased cabin pressure, flying with active infections,
increased susceptibility to infection, or hypersensitivity.
The FAA's Office of Aerospace Medicine made health information and
recommendations available to passengers and crews through its Web site and
linked the site to other health-related organizations. The agency also
developed a brochure on the potential risk of developing a condition known
as deep vein thrombosis (DVT), in which blood clots can develop deep in
the veins of the legs after extended periods of inactivity. This brochure
has been distributed to aviation medical examiners and cited in the
Federal Air Surgeon's Bulletin.
Ventilation shutdown FAA concurred with the objective of the
The committee reiterates the recommendation of the 1986 Council report
that a recommendation and advised air carriers,
regulation be established to require removal of passengers from an
aircraft within through advisory circulars, to deplane
30 minutes after a ventilation failure or shutdown on the ground and
ensure the passengers as long as operational safety is
maintenance of full ventilation whenever on-board or ground-based air
conditioning not compromised.
is available.
Sources: National Research Council and GAO analysis of FAA documents.
Note: Federal Aviation Regulations are legal requirements and rules for
the aviation industry set by the Federal Aviation Administration.
FAA formed the Airliner Cabin Environment Report Response Team to review
the findings of the NRC report on airliner cabin air quality and
published a planned response in February 2002. However, many of the
actions included in this plan were contingent on the formation of an
aviation rulemaking advisory committee, on which the agency has deferred
action. FAA subsequently updated its plans, as reflected above.
We reviewed FAA's approach for addressing the recommendations and found
that the agency has made progress on implementing some of them, including
those relating to making information available on potential health issues
related to cabin air quality and the risks posed to sensitive people by
allergens from small animals transported in aircraft cabins; however
action on others is pending. For example, recommendations to improve FAA
oversight of aircraft ventilation systems are pending until completion of
the ASHRAE study in late 2006 or early 2007. In implementing the Council
report recommendations, FAA is attempting to balance the need to conduct
additional research on the healthfulness of cabin air quality with other
research priorities, such as improving passenger safety. Our prior work on
airliner cabin safety and health has underscored the importance of setting
risk-based research priorities, in part by establishing cost and
effectiveness estimates to allow direct comparisons among competing
research priorities. In commenting on this prior work, FAA cautioned that
if too much emphasis is placed on cost/benefit analyses, potentially
valuable research may not be undertaken.23 We concur in that caution.
Similarly, we found that many members of the Council committee on airliner
cabin air quality question FAA's approach to implementing some of the
recommendations it made, particularly those related to the committee's
principal finding that more comprehensive research on the health effects
of cabin air quality is needed. Specifically, some in the aviation
community have raised concerns that FAA's planned actions for implementing
the Council recommendations on cabin air quality, including its research
and surveillance efforts, will not be adequate to answer long-standing
questions about the nature and extent of potential health effects posed by
cabin air.
Council Recommendations To address the need for more information on the
health effects of cabin air Calling for Cabin Air Quality quality, the
2001 Council report made three recommendations regarding the Surveillance
and Research establishment of cabin air quality surveillance and research
programs.
FAA, in coordination with ASHRAE, has begun to develop a program
toPrograms monitor air quality on some flights and correlate this
information with
23U.S. General Accounting Office, Aviation Safety: Advancements Being
Pursued to Improve Airliner Cabin Safety and Health, GAO-04-33
(Washington, D.C.: October 3, 2003).
Council Concluded That Surveillance and Research Programs Needed to Answer
Outstanding Questions Concerning Cabin Air Quality
health data collected from passengers and cabin crews. Although this
effort can provide a foundation for future research, members of the
committee that produced the report are concerned that its scope is too
limited to adequately answer long-standing questions concerning the
association between cabin air quality and health effects.
According to a committee member, the Council report's most important
recommendations are those pertaining to the establishment of cabin air
quality surveillance and research programs. The report concluded that
available air quality data are not adequate to address three critical
questions on aircraft cabin air quality and its possible effects on cabin
occupant health:
o Do current aircraft, as operated, comply with FAA design and
operational limits for ventilation rate and for chemical contaminants,
including ozone, carbon monoxide, and carbon dioxide, and are the existing
air quality regulations adequate to protect the health and ensure the
comfort of passengers and the cabin crew?
o What is the association, if any, between exposure to cabin air
contaminants and reports or observations of adverse health effects in
cabin crew and passengers?
o What are the frequency and severity of incidents when air contaminants
enter the cabin due to nonroutine conditions such as oil leaks or other
engine malfunctions?
To answer these questions, the Council report recommended a dual approach
that includes a routine surveillance program and a more focused research
program. The report said that the surveillance program should continuously
monitor and record chemical contaminants, cabin pressure, temperature, and
relative humidity in a representative number of flights over a period of 1
to 2 years. Thereafter, the program should continue to monitor flights to
ensure accurate characterization of air quality as existing aircraft
equipment ages or is upgraded. In addition to air quality monitoring, the
report said the surveillance program should also include the systematic
collection, analysis, and reporting of health data, with the cabin crew as
the primary study group. The report said a detailed research program to
investigate specific questions about the possible association between air
contaminants and reported health effects should supplement the
surveillance program. Among the subjects suggested for research are
the factors that affect ozone concentration in cabin air and the adequacy
of outside air ventilation flow rates.
FAA Has Taken the Lead in In order to implement the surveillance and
research programs, the report
Developing Surveillance and recommended that Congress designate a lead
federal agency and provide
Research Programs sufficient funding to conduct or direct the research
program to fill the major knowledge gaps. It also called for an
independent advisory committee with appropriate scientific, medical, and
engineering expertise to oversee the programs to ensure that the research
program's objectives are met. In response, as a part of FAA's
reauthorization, Congress designated FAA as the lead federal agency.24
Prior to this, FAA acted in this capacity and allocated limited funding
for this effort, although, according to FAA officials, Congress provided
no additional funding through fiscal year 2003 for air quality
surveillance and research; however, pending legislation for fiscal year
2004 would provide $2.5 million for this effort. In addition, on March 4,
2003, FAA announced the creation of a voluntary program for air carriers,
called the Aviation Safety and Health Partnership Program. Through this
program, the agency intends to enter into partnership agreements with
participating air carriers, which will, at a minimum, make data on their
employees' injuries and illnesses available to FAA for collection and
analysis. According to FAA officials, this program has a reporting system
and database available to capture air quality incidents.
In taking the lead for implementing the recommendations for surveillance
and research programs, FAA has undertaken a joint effort with ASHRAE.
According to FAA, this joint effort will build on a previous study
conducted for FAA by NIOSH, which identified and characterized potential
health issues, including respiratory effects, related to the aircraft
cabin
24Vision 100-Century of Aviation Reauthorization Act,'' passed by Congress
in November 2003, requires that FAA, at a minimum: 1) conduct surveillance
to monitor ozone in the cabin on a representative number of flights and
aircraft to determine compliance with existing regulations for ozone, 2)
collect pesticide exposure data to determine exposures of passengers and
crew, 3) analyze samples of residue from aircraft ventilation ducts and
filters after air quality incidents to identify potential exposure of
contaminants to passengers and crew, 4) analyze cabin air pressure and
altitude, and 5) establish an air quality incident reporting system. The
FAA administrator is to report the findings to Congress no later than 30
months after the date of the act's enactment.
environment, but did not link the health issues to cabin conditions.25 The
joint effort includes a surveillance and research initiative whose
principal aim is to relate perceptions of discomfort or health-related
symptoms that flight attendants and passengers have had to possible causal
factors, including cabin and outside air quality and other factors, such
as reduced air pressure, jet lag, inactivity, humidity, flight attendant
duty schedule and fatigue, disruptions to circadian rhythm,26 stress, and
noise. While FAA's fiscal year 2004 appropriation in the research and
development budget includes $2.5 million for cabin air research-including
identifying bacterial and pesticide contamination and monitoring air
quality incidents-it is unclear which of the cabin air quality projects
outlined in the FAA reauthorization bill will be funded.27 Additionally,
ASHRAE officials stated that the surveillance and research initiative
would support ASHRAE's ongoing efforts to develop air quality standards
for commercial aircraft.
According to FAA, the surveillance and research program is to be carried
out in two parts; the first started in December 2003 and the second will
start in December 2004 and end in late 2006 or early 2007. In part I, air
quality data will be collected on four to six flights on a minimum of two
different types of aircraft, and the data will then be compared with
health information gathered from surveys of passengers and crew on the
flights. According to FAA and ASHRAE, the protocol and procedures
developed in part I of the study will be the basis for conducting
on-ground and in-flight monitoring in part II of the initiative. In part
II, air quality monitoring will be conducted on different models of
commercial jet airplanes representing a large section of the world fleet
and will include a minimum number of
25NIOSH conducted the study over 2 years on 33 commercial flights on 10
different types of airplanes owned by four air carriers. NIOSH initially
surveyed female flight attendants on reproductive health, but the survey
was later expanded to include respiratory effects. The study did not
include direct linkage to measurement of cabin environment conditions. The
survey respondents flew on a wide variety of aircraft in which the cabin
environment was not sampled.
26Circadian rhythm is the body's internal resting or wakefulness schedule
over the course of a day. Outside influences, such as jet lag, can disrupt
the circadian rhythm temporarily.
27FAA's fiscal year 2004 facilities and equipment budget includes $8.5
million to develop and demonstrate a chemical/biological detection and
mitigation capability and decontamination procedures for aircraft
occupants and for returning the aircraft to service.
flights that has not yet been determined.28 However, according to FAA
officials, the level of funding that will be available for part II is
uncertain. FAA and ASHRAE have assembled a committee which is responsible
for selecting a contractor to conduct the monitoring and health
surveillance in part I and overseeing the contractor's performance. The
committee consists of aircraft, health, and air quality experts, including
five members of the Council committee, as well as representatives from
FAA, the Association of Professional Flight Attendants, and the Boeing
Commercial Airplane Group. In September 2003, the committee chose a
contractor for part I, and work began in December 2003. FAA and ASHRAE
have not yet selected a contractor for part II, although the estimated
completion date for the entire program is late 2006 or early 2007.
ASHRAE officials stated that to date FAA, Boeing, and two major U.S.
airlines are supporting this effort. FAA has provided $50,000 of the
estimated $250,000 it will cost to conduct air quality surveillance on two
aircraft. Boeing is the major source for the balance of the funding for
the surveillance program. FAA had previously reported that it was seeking
a $500,000 contract with the Johns Hopkins University Applied Physics
Laboratory (APL) to develop devices to monitor the aircraft cabin
environment as part of the research and surveillance program. However, the
contract was not finalized because APL determined that the project would
cost significantly more than $500,000 and FAA reprogrammed the funds. FAA
said that it has not yet funded part II, while ASHRAE officials noted that
they are planning to solicit the part I contributors again for part II
once part I is under way.
Despite FAA's efforts to date, we found that the agency has not developed
a detailed plan for the research and surveillance program, including key
milestones and funding estimates, in keeping with generally accepted
practices for oversight and independence. In addition, the agency has not
created an independent panel of experts in the areas of aircraft
ventilation, air quality, and public health to help plan and oversee this
effort. Furthermore, FAA's plans do not explicitly include leveraging the
findings of international research on cabin air quality.
28The minimum number of flights to be included will depend on the
recommendations of part I and on the availability of research funds and
will be specified in the solicitation for part II to be released by ASHRAE
in the future.
Committee Members Concerned about Scope, Independence, and Funding of FAA
Surveillance and Research Program
Members of the committee that produced the 2001 Council report are
concerned that the FAA/ASHRAE surveillance and research program, as
designed, will fall short of answering the long-standing questions about
the effect of cabin air quality on passenger and cabin crew health and
comfort. We contacted the 13 members of the committee, and 8 agreed to
comment on FAA's response to their recommendations on cabin air quality
surveillance and research. We refer to these 8 individuals from here
forward as commenting committee members. Although 5 of 8 commenting
committee members said that the initiative should shed some light on cabin
air quality's effects on health, all said that it was much more limited
than the committee had envisioned. Two of the 8 commenting committee
members thought that the air quality and health surveillance initiative
should be a continuous undertaking in which air quality and health
information is taken from a representative sample of commercial aircraft
and flight routes. They also said that it appears the FAA and ASHRAE
program will not include a broad enough cross-section of aircraft and
flights to determine the full range of air quality problems and relate
them to health effects. Two commenting committee members said that part I
of the FAA and ASHRAE program will extensively monitor cabin air quality
on two aircraft types; however, part I will not provide information that
is generalizable to the U.S. commercial airliner fleet. According to
Boeing officials involved in this study, part I research is designed to
validate test equipment and study protocols and is not designed to be
generalized to the airliner fleet. One committee member said that although
more aircraft are to be included in part II, it is doubtful that enough
information will be collected to adequately answer the key questions the
agency's research and surveillance program was designed to address.
According to Boeing officials, part II includes plans for information
collection to address the key question of the agency surveillance and
research program, provided sufficient funds are available. Another
commenting committee member said that the FAA and ASHRAE program would
also yield little or no information on air quality incidents that occur
when cabin air is contaminated by oil or hydraulic fuel leaks. According
to the member, these incidents are rare and can be monitored only if
simple, inexpensive equipment (e.g., devices that can "grab" samples) is
available to cabin crew on a large number of flights to use in the event
that an incident occurs. FAA officials said that issues of sampling
adequacy and specimen handling could complicate the grab sample approach.
These officials also noted that a voluntary injury and illness reporting
system that it has in place could capture air quality incidents if it were
made mandatory.
Seven of the eight commenting committee members also noted that FAA has
not adequately addressed the Council report's recommendations regarding
cabin air surveillance and research programs. FAA has indicated that its
program responds to the report's recommendations calling for surveillance
and research efforts. However, these committee members believe that the
program focuses only on surveillance and does not include in-depth
research of air quality issues as outlined in the committee's
recommendation calling for a separate comprehensive research program.
One of the commenting committee members said that a cabin air quality
study currently under way in Europe contains many of the elements that the
committee had hoped to see in the U.S. surveillance and research efforts.
As part of the ongoing surveillance and research study, the European cabin
air study29 is currently coordinated by Building Research Establishment,
Ltd. (BRE).30 The study focuses on three major goals: (1) advancing the
industry's understanding of what is known about air quality issues by
assessing the current level of air quality found in aircraft cabins; (2)
identifying the technology (i.e., environmental control systems including
filtration and air distribution) that is available to improve cabin air
quality; and (3) assessing and determining potential improvements to
existing standards and performance specifications for the cabin
environment. (The scope and methodology for Europe's cabin air study is
found in appendix IV). The cabin air study partnered (to various degrees)
with 16 organizations, including Boeing, Airbus Deutschland, Honeywell
(manufacturer of environmental control systems), Pall Aerospace (filter
manufacturer), British Airways, United Kingdom's Civil Aviation Authority
(CAA), European Joint Aviation Authorities (JAA), and other organizations
representing Austria, France, Germany, Greece, Norway, Poland, and Sweden.
The European cabin air study began on January 2001 with an
29The European cabin air study is known as CabinAir.
30Building Research Establishment, Ltd. (BRE) is a high-level
research-based consultancy organization, owned by a not-for-profit entity
headquartered in the United Kingdom. BRE provides the aviation industry
with expert advice on cabin environment issues and, particularly, on air
quality in passenger aircraft.
estimated cost of $8 million and is expected to disclose its findings in
2004.31
Of the eight commenting committee members, three addressed the funding of
the FAA and ASHRAE surveillance and research programs. These members said
that the amount of funding available for U.S. efforts might be
insufficient to conduct surveillance and research programs of the scope
they envisioned in their recommendations. For example, one of the
committee members stated that to conduct a surveillance and research
program of the scope the Council had in mind, Congress would have to
provide funding levels comparable to that of the European cabin air study.
One commenting committee member, National Institute for Occupational
Safety and Health (NIOSH) officials, and airline flight attendant
representatives we interviewed expressed concern that the extensive
involvement of aircraft manufacturers and airlines in the design and
implementation of the FAA and ASHRAE program could threaten the
independence of the effort. However, with the exception of the flight
attendant representatives,32 they agreed that any surveillance and
research programs require participation by these groups. Nonetheless, they
point to the fact that much of the available funding for the initiative
($200,000 of the $250,000) is coming from the aviation industry, which has
a stake in the outcome, and that this might give the impression that the
study lacks the necessary objectivity. The commenting committee member
suggested that the research money provided by the aviation industry be
placed in a special fund that would be managed by FAA or an independent
research group. According to ATA officials, due to a lack of public
funding on a scale comparable to what has been provided for Europe's cabin
air study, the financial support and cooperation of aircraft manufacturers
and airlines is essential if FAA is to conduct this research. In addition,
Boeing officials stressed that the project funding is currently controlled
by ASHRAE and the project oversight committee is led by the chairman of
the Council study.
31In addition to Europe's cabin air study (CabinAir), Australia has
addressed cabin air quality issues through the creation of a Reference
Group on Cabin Air Quality. The Reference Group is responsible for
following the progress of and analyzing the outcomes of international
research and development. The Reference Group comprises government
agencies, industry representatives, employee/union representatives, and
representatives of aircraft and engine manufacturers.
32The flight attendant groups have actively lobbied for independent
research that is not funded and controlled by companies that have a
financial interest in the outcome.
Five of the commenting committee members also discussed the status of
their recommendation concerning the need for Congress to designate a lead
federal agency and advisory committee for the air quality research effort.
Although Congress designated FAA as the lead agency in November 2003, FAA
had already assumed responsibility for implementing the research and
surveillance-related recommendations. In commenting on the Council
recommendation to designate a lead federal agency, several members said
they thought that the lead agency should be one that is experienced in
conducting scientific research on air quality and environmental health
issues. Some noted that the Environmental Protection Agency (EPA) has
supported a large body of research into air quality issues, and another
pointed out that NIOSH has performed studies of air quality in buildings
and the workplace. Several commenting members indicated that although it
is FAA's mission to promote aviation safety, they had reservations about
whether the agency was well suited to oversee a large air quality research
program on its own. Several members thought that, as an alternative, FAA
might be part of a cooperative federal effort to perform airliner cabin
air quality research. In addition, another committee member believes that
although FAA has a committee to oversee the selection of the contractor
for the program, it has not assembled an advisory committee to review the
research design and monitor the implementation of the program.
Council's Recommendations Concerning FAA Oversight of Aircraft Ventilation
Systems
Four of the Council recommendations pertain to FAA's oversight of the
operation of aircraft ventilation systems. These recommendations call for
FAA to (1) demonstrate in public reports the adequacy of its regulations
related to cabin air quality and establish operational standards for
ventilation systems, (2) ensure that standards for ozone levels are met on
all flights, (3) investigate the need for and feasibility of installing
equipment to clean the air supplied to aircraft ventilation systems, and
4) require carbon monoxide monitors in air supply ducts to passenger
cabins and establish procedures for dealing with elevated carbon monoxide
concentrations. According to FAA officials, the agency originally planned
to have an aviation rulemaking advisory committee assess whether current
standards were appropriate for ensuring that aircraft ventilation systems
adequately prevent contamination of cabin air. However, FAA decided to
defer this action until data is available from the surveillance and
research study, as well as the European cabin air study. Additionally, FAA
believes that data from this study will aid in the reconsideration of air
quality standards for commercial aircraft. However, most of the commenting
committee members questioned the need for delay in addressing some of the
recommendations.
Four of the eight commenting committee members said that they recommended
that FAA demonstrate, in public records, the rationale for the established
design standards for carbon monoxide (CO), carbon dioxide (CO2), ozone
(O3), ventilation, and cabin pressure because FAA was unable to explain
the reasoning for these standards. For example, FAA has not documented the
reasons for setting the ventilation rate standard for aircraft cabins of
new aircraft types at .55 pounds of outside air per minute per occupant.
The American Society of Heating, Refrigerating and Air-Conditioning
Engineers (ASHRAE)33 recommends that ventilation rates inside a building
environment be at least 1.1 pounds of outside air per minute per occupant,
which is about 50 percent more than the current FAA requirement for
aircraft. In addition, FAA has not documented the reasons for requiring a
design for cabin air pressure altitude of not more than 8,000 feet air
pressure, which is about three-fourths of the air pressure found at sea
level. Members of the research community, including the Aerospace Medical
Association (AsMA) and CAA, state that the loss of air pressure and oxygen
may pose serious health risks for infants whose lungs have not fully
developed and for older adults who may have upper respiratory problems.
In response to the committee members' comments, FAA provided us the
following explanations for the design standards in question. The
ventilation rate standard was based on a regulatory value established
decades ago, which has been shown to be acceptable, and ASHRAE has formed
a subcommittee to develop a standard specifically for airplanes. The limit
for carbon monoxide concentration of 1 part in 20,000 parts air (0.005
percent) was adopted from the Occupational Safety and Health
Administration (OSHA) and ASHRAE standards. The limit of maximum allowable
carbon dioxide concentration in occupied areas of transport category
airplanes was reduced to 0.5 percent in part due to a recommendation from
the National Academy of Sciences to review the carbon dioxide limit in
airplane cabins; it provides a cabin carbon dioxide concentration level
representative of that recommended by some
33ASHRAE writes standards and guidelines in its fields of expertise to
guide industry in the delivery of goods and services to the public.
Currently, it has some 87 active standards and guideline project
committees, addressing such broad areas as indoor air quality, thermal
comfort, energy conservation in buildings, reduction of refrigerant
emissions, and the designation and safety classification of refrigerants.
authorities for buildings. The ozone limits were based on studies
conducted by the FAA Civil Aerospace Medical Institute and are comparable
to standards adopted by the Environmental Protection Agency and the
Occupational Safety and Health Administration. The cabin pressure altitude
standard was based on the accepted industry practice of maintaining the
health and safety of occupants while considering the structural
limitations of the aircraft.
A commenting committee member also expressed concern that FAA certifies
aircraft ventilation systems that are designed to meet certain standards,
such as those for ventilation rates, but it does not require that systems
operate in accordance with these standards. The practical effect is that
aircraft are not monitored to determine if they meet the design standards.
According to another commenting committee member, FAA did not need data
from the planned research project to provide a rationale for ventilation
system standards, or to require that ventilation systems operate according
to standards. Some committee members also said that FAA could begin to
take steps to ensure that ozone standards are met on all flights
regardless of altitude and require monitors for dangerous carbon monoxide
vapors in air supply ducts to passenger cabins before the completion of
the planned research study. FAA officials said that although it does not
conduct recurrent system design compliance checks, the agency uses various
reporting systems to monitor aircraft system performance and takes
appropriate mandatory action when an unsafe condition is found.
Council Recommendation Concerning Airborne Allergens
Because of the potential for serious health effects for people sensitive
to allergens, the 2001 Council report also recommended that FAA
investigate the need to prohibit the transport of small animals in
aircraft cabins and provide training to cabin crews to deal with allergic
reactions. However, FAA does not think that prohibiting animals in the
cabin would be effective because it believes that most animal allergens
are brought onboard aircraft on the clothes of passengers rather than by
the animals themselves. Instead, the agency issued an advisory circular
highlighting the effective procedures that passengers can use when
carrying animals and guidance on how to train crewmembers to recognize and
respond to in-flight medical events that result from exposure to
allergens. Additionally, FAA will enhance its Internet site to provide
general information related to FAA and air carrier policy concerning the
transport of animals in aircraft cabins. Commenting committee members
generally supported FAA's approach to this recommendation.
Council Recommendation Concerning Health Information
In response to the Council report recommendation calling for FAA to
increase efforts to provide cabin crew, passengers, and health
professionals with information on health issues related to air travel, FAA
modified the general information section of its Web site; however, we
found that the traveler health information is not easy to access. FAA
created hyperlinks to other Web sites, such as those of the Aerospace
Medical Association and Centers for Disease Control and Prevention, which
include information on potential health risks of flying, particularly for
healthchallenged individuals. However, we found it difficult to locate the
section of the FAA Web site that deals with traveler health information
and when we did, it required several steps to reach the hyperlinks. Some
commenting committee members also noted how difficult it is to access
health-related information on the FAA Web site. In addition to citing the
need for FAA to increase the accessibility of health-related information
on its Web site, six of the eight committee members also mentioned that
FAA should take further steps to make health information available to the
flying public. Suggestions included having airlines include health related
information on their Web sites and establishing a program to provide
flying-related heath risk information to physicians that they could then
share with their patients (e.g., through brochures).
Council Recommendation Concerning Aircraft Ventilation System Shutdown
FAA responded to the 2001 Council report recommendation that it establish
a regulation to require removal of passengers from an aircraft within 30
minutes after a ventilation failure or shutdown on the ground by issuing
an advisory circular to airlines. Some commenting committee members viewed
this action as insufficient. This recommendation reiterated one made in
the 1986 Council report, which FAA did not act on. The committees that
produced both the 1986 and 2001 reports noted that environmental
conditions in an aircraft cabin respond quickly to changes in ventilation
system operation. The committees felt that the ventilation system should
not be shut down for a long period when the aircraft is occupied, except
in the case of an emergency, because excessive contaminant concentrations
and uncomfortably high temperatures can occur quickly. Several commenting
committee members told us that they felt strongly that FAA should require
passenger removal in the event of ventilation system shutdown of more than
30 minutes and that advising airlines that this should be done was
insufficient to accomplish the committee's objective. FAA, on the other
hand, said that airlines pay close attention to advisories. The agency
decided against issuing a regulation because there are situations when an
evacuation within 30 minutes is not
possible due to operational necessity, such as when a ventilation system
breakdown occurs on a taxiway far from a gate.
Some Technologies Exist for Improving Cabin Air Quality, but There Are
Questions About Whether They Should be Required
Several technologies exist today that could improve cabin air quality, but
opinions vary on whether requiring the use of improved technologies in
commercial airliner cabins is warranted. We found one of these
technologies, HEPA filters, is strongly endorsed by cabin air quality and
health experts as providing the best possible protection against one cabin
air problem-the presence of particulates, bacteria, and viruses in
recirculated air. While FAA does not currently require HEPA filters, some
health experts believe these filters should be required, given their
demonstrated effectiveness in cleansing cabin air. Figure 3 illustrates a
typical HEPA filter for commercial passenger aircraft.
Figure 3: A Typical HEPA Filter for Commercial Passenger Aircraft
According to many in the aviation community, several technologies are
available today, and more are in the planning stages, that could improve
the air quality in commercial airliner cabins. However, some in the
aviation industry question whether requiring their use is warranted.
Filtering particulates, bacteria, viruses, and gaseous pollutants and
removing ozone can improve the healthfulness of cabin air, and increasing
cabin humidity and absorbing more cabin odors and gasses can increase the
comfort of passengers and cabin crews. While aircraft manufacturers
acknowledge that a few technologies are available today that could further
improve air quality and comfort in airliner cabins and that more are
possible in the future, they believe that unless future research proves
otherwise, the ventilation systems in the aircraft they have produced
provide ample
amounts of relatively clean air. One technology with proven effectiveness
is HEPA filtering of recycled cabin air. All new large commercial
airliners in production with ventilation systems that recirculate cabin
air come equipped with these filters, which, when properly fitted and
maintained, are effective at capturing airborne contaminants such as
viruses that enter the re-circulation system. However, some regional jets,
which have fewer than 100 seats, are not equipped with filters, and some
older large aircraft still use less efficient filters. FAA does not
require the filtration of recirculated air, but health experts and members
of the committee that produced the 2001 report on cabin air quality
believe that given their proven effectiveness, HEPA filters should be
required for all aircraft that recirculate cabin air. In addition, airflow
rates could be increased in some aircraft by adjusting settings on the
ventilation system, thereby dissipating the effects of some contaminants.
However, this would be done at the expense of higher fuel consumption,
increased engine emissions, and lower cabin humidity.
High Efficiency Particulate Filters Are an Effective Technology for
Cleaning Recirculated Air
HEPA filters are a readily available and affordable technology for
providing the best possible protection against one cabin air problem-the
presence of particulates, bacteria, and viruses in recirculated air.
However, HEPA filters will not filter gaseous contaminants. These filters
have become widely available for aircraft since the late 1990s. According
to EPA, HEPA filters can remove nearly all particulate contaminants, such
as airborne particles and infectious agents including bacteria and
viruses, from the recirculated air that passes through them.34 A
manufacturer of HEPA filters, as well as health authorities such as CDC,
NIOSH, and WHO, believe that HEPA filters are highly effective in
preventing the transmission of bacteria and viruses through aircraft
ventilation systems. However, they emphasize that HEPA filters clean only
the air that is recirculated through aircraft ventilation systems, so
transmissions from an infected person to others nearby are still possible.
HEPA filters are available for most large commercial airliners in the U.S.
fleet, but some aircraft with recirculation systems are equipped with less
effective filters. However, not all commercial aircraft recirculate air
through their ventilation systems. For example, some smaller jets, such as
34The Environmental Protection Agency states that HEPA filters are to be
99.97 percent efficient for the removal of Particulate Matter (PM) that is
greater than or equal to 0.3 micrometer (mm) in diameter.
the Boeing 717 and Bombardier CRJ-200s, which typically fly shorter
routes, as well as older models of some longer-range aircraft, such as the
Boeing 737-200 and the DC-10, provide 100 percent outside air to the
passenger cabins instead of recirculating air and, therefore, would not
need HEPA filters. Nevertheless, most commercial airliners in use today
recirculate between 30 and 55 percent of the air provided to the passenger
cabin. Officials from Boeing and Airbus, the world's two largest
manufacturers of commercial aircraft, told us that all their aircraft with
recirculation systems currently in production are equipped with HEPA
filters. The ventilation systems in many older commercial aircraft were
designed to use the less effective filters available at the time, and some
of these aircraft still use these types of filters. However, according to
Boeing and Airbus officials, HEPA filters can be used on these older
aircraft with little or no retrofitting required.35 According to a filter
manufacturer, a HEPA filter costs about twice as much (e.g., $400 to $600
for the smaller narrow-body aircraft) as the non-HEPA models that are less
effective in trapping particulates. Some regional jets, such as the
Embraer ERJ-145 recirculate air but are not equipped with filters.
In fact, FAA does not require the filtration of recirculated air on
aircraft. However, when manufacturers voluntarily equip their aircraft
models that recirculate cabin air with HEPA or other filters when they are
certified for flight by FAA, as most do, the aircraft are required to
continue operating with the filters. The schedule for changing the filters
is also included in the FAA certification process. Airlines typically
change HEPA filters after 4,000 to 12,000 hours of service to maintain
good airflow and in accordance with manufacturers' recommendations.
Little information has previously been available on the extent of HEPA
filter usage in commercial aircraft ventilation systems, though the
Council report and many in the health community have pointed to the
importance of HEPA filters in preventing the spread of bacteria, viruses,
and other contaminants in aircraft cabins. As noted earlier in this
report, the 2001 Council report recommended that FAA investigate and
publicly report on the need for installing equipment to clean the air
supplied to aircraft cabin ventilation systems. In the report, the
committee did not determine how many larger aircraft were equipped with
HEPA filters, and regional jets were not within the scope of its study.
However, the report concluded that HEPA filters are highly effective in
removing all airborne pathogens and
35Installing HEPA filters on the A300 would require some modification.
other particulate matter that pass through them. The report further stated
that the use of recirculated air in aircraft cabins when combined with
effective HEPA filtration does not contribute to the spread of infectious
agents. Members of the research community, including those from NIOSH, as
well as the Association of Flight Attendants, have noted that given the
proven effectiveness of HEPA filters in capturing contaminants such as
infectious viruses and bacteria, FAA should require their use on all
aircraft with recirculation systems.
To determine the extent of HEPA filter usage in the United Stares, we
surveyed the largest 14 airlines36 in the United States that had Airbus,
Boeing, or McDonnell Douglas aircraft that recirculate cabin air, and we
received responses from 12 airlines. Of the 3,038 aircraft for which we
were able to obtain survey results, 15 percent (454 aircraft)37 did not
use HEPA filters. All of the aircraft that did not use HEPA filters were
older out-of-production models that used less effective filters. One
airline has plans to retrofit a small number of these aircraft with HEPA
filters.
We were also able to obtain some information on HEPA filter usage in the
U.S. regional aircraft fleet by contacting the manufacturers of these
aircraft. We found that 69 percent of these regional aircraft recycle
cabin air (1,087 of 1,584), and only a handful of these aircraft are
equipped with HEPA filters. The manufacturer of a new regional jet model38
offers HEPA filters as an option. Information we obtained from two
airlines that had 29 of these aircraft indicated that about half (14 of
29) were equipped with HEPA filters.
36We used revenue passenger miles (RPM) as reported in Aviation Daily for
May 2003 to identify the largest U.S. carriers. This list identified the
largest 28 airlines, 14 of which had the larger aircraft that recirculate
cabin air. The other 14 airlines only had smaller regional aircraft or
larger aircraft that did not recycle cabin air. An RPM is a standard unit
of passenger demand for air transport, defined as one fare-paying
passenger transported one mile. We obtained the model information for
these carriers from data published in Air Transport World (July 2003).
37We obtained information on 3,038 larger aircraft that recycled cabin
air, 454 of which did not have a HEPA filter. We were not able to obtain
survey results for another 384 aircraft. Of these 384, 56 (15 percent) of
the aircraft were older models that most airlines had not retrofitted with
HEPA filters. Our study included 3,770 larger aircraft, of which 348 did
not recycle cabin air.
38HEPA filters are available for the CRJ700 manufactured by Bombardier.
We also found that 90 percent of the regional aircraft (973 of 1,087
aircraft) that recycled cabin air would require modifications to be
retrofitted with HEPA filters. Most of these aircraft (73 percent) had no
provision for installing filters in their air ducts.
Consideration has also been given to filtering outside air entering an
aircraft's ventilation system. Outside air at cruise altitudes is mainly
free of pollutants, except for ozone. However, in the event of an engine
or hydraulic system malfunction, outside air can become contaminated
before it enters the ventilation system. In addition, when an aircraft is
at the gate or taxiing, the available outside air contains pollutants
normally present around the airport, including exhaust from other aircraft
on the runway. For these reasons, the 2001 Council report recommended that
FAA investigate the need for and feasibility of installing air-cleaning
equipment for removing particles and vapors from the air supplied to the
ventilation system. As previously noted, FAA has put off consideration of
this recommendation until the completion of FAA's and ASHRAE's air quality
research and surveillance program in 2006 or 2007. One manufacturer did
begin installing outside air filtering equipment on one of its models in
1992. British Aerospace began equipping its BAe 146 aircraft (now out of
production) with outside air filters as part of an effort to reduce cabin
odors. Other manufacturers, including Boeing and Airbus, contend that
outside air filtration is not necessary unless U.S. and European research
indicates a problem with the quality of air entering aircraft ventilation
systems.
Technology is Available to Remove Ozone from the Air Brought in from
Outside the Aircraft
Technologies are currently available for removing ozone from outside air.
Ozone is present in the air at high altitudes on some routes, particularly
those over the polar regions, and FAA requires that the airlines that fly
these routes take measures to maintain cabin ozone levels at or below
prescribed limits (e.g., using devices that convert ozone to oxygen).
According to ATA officials, nearly all commercial aircraft that fly on
these routes are so equipped. However, the Council report said that
although FAA requires that ozone concentrations in aircraft cabins be
maintained within specified limits, surveillance programs with accurate
and reliable equipment are needed to ensure compliance and that the ozone
converter equipment works properly. One study attributed elevated ozone
levels that exceeded FAA limits to temporary ozone plumes that can appear
unexpectedly. In November 2000, the British House of Lords, in a study of
health issues in aircraft cabins,39 made a recommendation that airlines
fit their aircraft that fly on routes where these plumes occur with ozone
converters to minimize potential health problems. The Council report also
identified the need for FAA to take effective measures to ensure that
ozone does not exceed levels specified in FAA regulations, regardless of
altitude. As noted earlier, FAA plans to monitor ozone levels in selected
aircraft as part of its surveillance and research program. However, some
committee members told us that the effort will be too limited to enable
FAA to determine if ozone is present on aircraft not fitted with
converters or whether ozone converters are working properly.
Increasing Ventilation Rates in Aircraft Cabins Poses Challenges
Increasing ventilation rates on aircraft to levels approximating those
currently required in buildings would pose technological challenges, and
aircraft manufacturers believe such increases are not necessary. Raising
ventilation rates would reduce the effects of some airborne contaminants
by diluting their concentration.
According to Boeing and Airbus officials, airflow rates on their aircraft
could be slightly increased by adjusting settings on the ventilation
systems, but such adjustments would increase fuel consumption and result
in higher operating costs. According to Boeing officials, to achieve the
same airflow rates recommended for buildings, aircraft ventilation
systems, and possibly the aircraft themselves, would have to undergo
expensive modifications. Boeing and Airbus believe that unless the U.S.
and European research and surveillance initiatives prove otherwise,
ventilation rates in commercial aircraft are sufficient to sustain
passenger and cabin crew comfort and health.
Boeing and Airbus officials told us that they are always seeking to
improve the aircraft they build, but they believe that the ventilation
systems in the aircraft they produce provide a healthy and relatively
comfortable environment for passengers and cabin crew. Nevertheless,
Boeing is considering increasing the air pressure and humidity levels on
the 7E7, its proposed long-range, high-altitude aircraft. Airbus will also
offer an improved air ventilation system on its new large aircraft, the
A380. Because of the competitive nature of the aircraft manufacturing
industry, few details are available on the 7E7 and A380 ventilation
systems. Boeing and Airbus
39The House of Lords, Select Committee on Science and Technology, Air
Travel and Health, 5th Report HL.
officials noted that if current research and surveillance efforts indicate
problems with any aspects of the ventilation systems in their aircraft,
they would work toward developing the necessary technologies to deal with
these problems.
Conclusions The combined research efforts of FAA and ASHRAE on cabin air
quality will provide a foundation of knowledge, according to some members
of the committee that produced the 2001 Council report on cabin air
quality. However, as currently designed and funded, these efforts may not
answer many long-standing questions about the effect of air quality on
cabin occupants' health and comfort. FAA is attempting to balance the need
to conduct additional research on the healthfulness of cabin air quality
with other research priorities, such as improving passenger safety. Our
prior work on airliner cabin safety and health has underscored the
importance of setting risk-based research priorities, in part by
establishing cost and effectiveness estimates to allow direct comparisons
among competing research priorities. In commenting on this prior work, FAA
cautioned that if too much emphasis is placed on cost/benefit analyses,
potentially valuable research may not be undertaken. We concur in that
caution. However, information on the nature and extent of health effects
from cabin air is needed in order to identify potential health threats so
that it can be determined if action is warranted to improve cabin air
quality and to target research and development accordingly. Moreover,
committee members recommended more study of these issues, and others in
the industry have concerns about FAA's surveillance and research program
as currently conceived. Committee members were particularly concerned
about FAA's decision to delay action on ensuring that air quality
regulations are adequate or being met on all flights. In addition, the
agency's current plan to monitor cabin air quality on only two aircraft
types during part I of its program will not provide FAA with information
that is generalizable to the U.S. commercial airliner fleet. Thus, key
questions that the agency's research and surveillance program were
designed to address will remain unanswered if part II of FAA's program is
not properly designed and adequately funded. Such information is also
needed to guide the development of new technologies. Given the importance
of this research and surveillance effort, the program needs to be well
designed, properly funded, coordinated with international cabin air
quality research efforts such as those ongoing in Europe and Australia,
and conducted in accordance with accepted standards for independence and
oversight. The Council in its 2001 report recommended that Congress
designate a federal agency to conduct or direct the cabin air quality
research program and
recent legislation assigned FAA as the lead federal agency for this
effort. FAA has begun a surveillance and research program on its own.
Furthermore, FAA has not taken steps to ensure that HEPA filters, which
are a proven technology for eliminating some contaminants such as viruses
and bacteria from recirculated cabin air, are used as widely as possible
on commercial aircraft. FAA does not currently require the use of filters
on recirculated air. Nevertheless, we found that a number of aircraft
manufacturers and airlines voluntarily install them and that the vast
majority of larger commercial aircraft are equipped with HEPA filters.
However, we also found that only a few smaller regional jets that
recirculate cabin air have HEPA or any other type of filters. FAA has
decided to delay addressing the 2001 Council report recommendation calling
for the agency to investigate the need for air cleaning equipment on
aircraft ventilation systems until it completes its cabin air quality
surveillance and research program in 2006 or 2007. FAA needs to determine
the costs and benefits of requiring HEPA filters on commercial aircraft
that recirculate air.
Finally, although FAA has made some progress in implementing the Council's
recommendation regarding the need to increase the availability of
information on health issues related to air travel, more needs to be done.
Creating links on the FAA Web site to pertinent information on the CDC and
WHO Web sites is a good start, but navigating the FAA's Web site to reach
these links is difficult. In addition to improving the user friendliness
of the FAA Web site links, some commenting committee members suggested
that FAA should consider other methods for disseminating information on
the health risks of flying, such as providing brochures for physicians to
use when discussing these issues with patients.
Recommendations for Executive Action
To help ensure that FAA's research and surveillance efforts on airliner
cabin air quality answer critical outstanding questions about the nature
and extent of potential health effects of cabin air quality on passengers
and flight attendants, GAO recommends that the Secretary of Transportation
direct the FAA Administrator to
o develop a detailed plan for the research and surveillance efforts,
including key milestones and funding estimates, in accordance with
generally accepted practices for oversight and independence;
o appoint a committee of acknowledged experts in the fields of aircraft
ventilation and public health, including representatives of EPA and NIOSH,
to assist in planning and overseeing the research and surveillance efforts
recommended by the National Research Council in 2001;
o leverage the findings of international research on airliner cabin air
quality to inform FAA's surveillance and research efforts; and
o report to Congress annually on the progress and findings of the
research and surveillance efforts and funding needs.
In order to help improve the healthfulness of cabin air for commercial
aircraft passengers and cabin crews, the FAA Administrator should assess
the costs and benefits of requiring the use of HEPA filters on commercial
aircraft with ventilation systems that recirculate cabin air. If FAA
chooses to require the use of HEPA filters, it should also ensure that the
regulation covers the maintenance requirements for these filters.
In addition, to increase access to information on the health risks related
to air travel, the FAA Administrator should direct the staff responsible
for the FAA Web site to improve the links to other Web sites containing
this information. The Administrator should also consult with medical
associations and health organizations, such as CDC, on other ways to
increase the dissemination of this information.
Agency Comments We provided copies of a draft of this report to the
Department of Transportation for review and comment. FAA generally agreed
with the report's contents and its recommendations. The agency provided us
with oral comments, primarily technical clarifications, which we have
incorporated as appropriate.
As agreed with your office, unless you publicly announce the contents of
this report earlier, we plan no further distribution until 30 days from
the report date. At that time, we will send copies of this report to
interested congressional committees, the Secretary of Transportation, and
the Administrator, FAA. We will also make copies available to others upon
request. In addition, the report will be available at no charge on the GAO
Web site at http://www.gao.gov.
Please call me at (202) 512-2834 if you or your staff have any questions
concerning this report. Major contributors to this report are listed in
appendix VI.
Sincerely yours,
Gerald L. Dillingham Director, Civil Aviation Issues
Appendix I
Objectives, Scope, and Methodology
The Ranking Democratic Member of the Subcommittee on Aviation, House
Committee on Transportation and Infrastructure, asked us to provide
information on steps that the aviation community is taking to address
concerns about cabin air quality. Specifically, our research focused on
the following questions: (1) What is known about the major potential
health effects of air quality in commercial airliner cabins on passengers
and flight attendants? (2) What actions has the National Research Council
recommended to improve cabin air quality, and what is the status of those
actions? (3) What technologies are available today to improve the air
quality in commercial airliner cabins, and which, if any, should be
required?
To answer the first question, we reviewed the December 2001 National
Research Council report on aircraft cabin air quality, which was the most
current and comprehensive examination of the existing literature on this
issue and made recommendations for potential approaches for improving
cabin air quality. We also independently reviewed many of the studies on
issues related to cabin air quality, paying particular attention to those
issued after the publication of the 2001 Council report.1 We also gathered
information from the governments of Australia, Canada, and the United
Kingdom and airlines. We also interviewed officials representing the
Federal Aviation Administration (FAA), the World Health Organization
(WHO), the Centers for Disease Control and Prevention (CDC), the National
Institute for Occupational Safety and Health (NIOSH), the Aerospace
Medical Association (AsMA), the Air Transport Association (ATA), the
Association of Flight Attendants (AFA), the International Airline
Passengers Association (IAPA), aircraft and air filter manufacturers, as
well as experts on cabin air quality issues, including members of the
committee that produced the 2001 Council report on cabin air quality.
To address the second question, we interviewed Council committee members
about their views on how FAA was addressing the recommendations they made
in their report. Before conducting the interviews, we provided the
committee members with information from FAA on its plans for addressing
the Council's recommendation. We then asked them for their views on the
approach for addressing each of the recommendations. We conducted
interviews with 11 of the 13 committee
1See the Selected Bibliography at the end of this report and, in
particular, Hocking, Martin B., "Trends in Cabin Air Quality on Commercial
Aircraft: Industry and Passenger Perspectives," Reviews on Environmental
Health 17, 1 (2002): 1-49; and Rayman, Russell B., "Cabin Air Quality,"
Aviation, Space and Environmental Medicine 73 (2002): 211-215.
Appendix I
Objectives, Scope, and Methodology
members; we were unable to contact 2 members. Of the 11 members we
interviewed, 8 agreed to provide their views on at least some of the
recommendations. Three members declined to address any of the
recommendations, saying that they were outside their fields of expertise
and that they had not followed the progress of FAA's implementation of the
recommendations.
To address the third question, we interviewed representatives of aircraft
manufacturers, filter manufacturers, FAA officials, and experts on
aircraft ventilation systems, including members of the committee. To
determine HEPA filter usage, we first identified the 28 airlines that
account for 99.94 percent of the revenue passenger miles (RPM) flown by
U.S. airlines as reported in Aviation Daily for May 2003.2 Fourteen of
these airlines had aircraft that recirculate cabin air. The other 14 only
had smaller regional aircraft or larger aircraft that did not recirculate
cabin air. After selecting the 28 airlines, we obtained information from
Air Transport World (Airclaims 2002 data, July 2003 edition) on the number
of aircraft they operate by model type. We then obtained information from
the aircraft manufacturers that allowed us to categorize the 5,354
aircraft in the 28 airlines by whether or not they recycle air (see table
3).
Table 3: Number of Large and Regional Aircraft of Top 28 Airlines That Do
or Do Not Recycle Cabin Air
Cabin air not
Aircraft size Cabin air recycled recycled Total
Larger aircraft 3,422 348 3,770
Regional aircraft 1,087 497 1,584
Total 4,509 845 5,354
Source: GAO.
Larger aircraft included the commercial aircraft manufactured by Airbus,
Boeing, and McDonnell Douglas. Regional aircraft included Avions de
Transport Regional (ATR), British Aerospace (BAe), Bombardier, Dornier,
Embraer, Fokker, Jetstream, and Saab models.
2A revenue passenger mile is a standard unit of passenger demand for air
transport, defined as one fare-paying passenger transported one mile.
Appendix I
Objectives, Scope, and Methodology
Our primary focus with the larger aircraft was to determine the HEPA
filter usage for the 3,422 larger aircraft that recycled cabin air. To
obtain this information, we surveyed the 14 airlines that had aircraft in
this category and obtained responses from 12 (covering 3,038 of the 3,422
aircraft in this category). Our survey form, which we administered by
e-mail, asked the airlines to provide the following information: the
number of active aircraft by model type as of June 30, 2003; the number of
active aircraft with HEPA filters; the number of active aircraft without
HEPA filters; the reasons why HEPA filters are not used; and, if
applicable, the types of filters used if other than HEPA filters.
Our primary focus with the regional aircraft was to determine what
percentage of these aircraft recycled air, and, for those aircraft that
did recycle air, what percentage would require major modifications to be
retrofitted with a HEPA filter. We were able to make this determination on
the basis of information provided by the manufacturers. Because only a
small portion of the regional aircraft that recycle air are capable of
being fitted with HEPA filters, we did not survey the 13 airlines that had
only regional aircraft. In the cases where returned surveys also included
information on regional aircraft that could use HEPA filters with little
or no retrofitting, we found that only a small portion were doing so.
Appendix II
Biographical Information on the National Research Council Committee
Dr. Morton Lippman
Professor of environmental medicine and director of the Center for
Particulate Matter Health Effects Research and of the Human Exposure and
Health Effects Research Program at New York University School of Medicine.
Dr. Harriet A. Burge
Associate professor of environmental microbiology at the Harvard School of
Public Health. Dr. Burge's current area of research is on the role of
environmental exposures in the development of asthma and evaluating
exposure to fungi, dust mite, cockroach, and cat allergens in three
separate epidemiology studies assessing risk factors for the development
of asthma.
Dr. Byron Jones
Associate dean for Research and Graduate Programs and director of the
Engineering Experiment Station at the College of Engineering, Kansas State
University. Dr. Jones's research interests are in heat and mass transfer,
human thermal systems simulation, and thermal measurements and
instrumentation.
Dr. Janet M. Macher
Air pollution research specialist with the Division of Environmental and
Occupational Disease Control of the California Department of Health
Services. Her research has focused on the evaluation of methods to collect
and identify airborne biological material and on engineering measures to
control airborne infectious and hypersensitivity diseases.
Dr. Michael S. Morgan
Professor in the Department of Environmental Health, Industrial Hygiene
and Safety Program of the University of Washington and director of the
Northwest Center for Occupational Health and Safety. His research is
focused on human response to inhalation of air contaminants, including the
products of combustion and volatile solvents, and has encompassed both
ambient air contaminants and occupational environmental health hazards.
Dr. William W. Nazaroff
Professor of environmental engineering in the Department of Civil and
Environmental Engineering of the University of California, Berkeley. His
main research interest is indoor air quality, with emphasis on
pollutantsurface interactions, transport/mixing phenomena, aerosols,
environmental tobacco smoke, source characterization, exposure assessment,
and control techniques.
Appendix II
Biographical Information on the National
Research Council Committee
Dr. Russell B. Rayman
Executive director of the Aerospace Medical Association in Alexandria,
Virginia, retired from the U.S. Air Force in 1989 with the rank of colonel
after a military medical career.
Dr. John D. Spengler
The Akira Yamaguchi Professor of Environmental Health and Human Habitation
and director of the Environmental Science and Engineering Program at the
Harvard School of Public Health. Dr. Spengler's research is focused on
assessment of population exposures to environmental contaminants that
occur in homes, offices, schools, and during transit, as well as in the
outdoor environment.
Dr. Ira B. Tager
Professor of epidemiology in the Division of Public Health, Biology, and
Epidemiology at the University of California, Berkeley, and is codirector
and principal investigator for the Center for Family and Community Health.
Dr. Tager's research includes the development of exposure assessment
instruments for studies of health effects of chronic ambient ozone
exposure in childhood and adolescence, the effects of ozone exposure on
pulmonary function, and the effects of oxidant and particulate air
pollution on cardio-respiratory morbidity and mortality and morbidity from
asthma in children.
Dr. Christiaan Van Netten
Associate professor in the Department of Health Care and Epidemiology at
the University of British Columbia and head of the Division of
Occupational and Environmental Health. Dr. Van Netten's research interests
include environmental toxicology and the use of electrodiagnostics to
monitor worker exposure to agents that affect the peripheral nervous
system.
Dr. Bernard Weiss
Professor of environmental medicine and pediatrics at the University of
Rochester School of Medicine and Dentistry. His special interest and
publications lie primarily in areas that involve chemical influences on
behavior, including the neurobehavioral toxicology of metals such as lead,
mercury, and manganese.
Appendix II
Biographical Information on the National
Research Council Committee
Dr. Charles J. Weschler
Adjunct professor in the Department of Environmental and Community
Medicine at the University of Medicine and Dentistry of New Jersey, Robert
Wood Johnson Medical School/Rutgers. His research interests, among others,
include chemical interactions among indoor pollutants and the chemistry of
the outdoor environment as it impacts the indoor environment.
Dr. Hanspeter Witschi
Professor of toxicology and associate director of the Institute for
Toxicology and Environmental Health at the University of California,
Davis. Dr. Witschi's research interests include experimental toxicology,
biochemical pathology, and the interaction of drugs and toxic agents with
organ function at the cellular level.
Source: National Research Council.
Appendix III
Transmission of Severe Acute Respiratory Syndrome (SARS) on Board Aircraft
Is Rare and Associated with Proximity
Aboard aircraft, cabin occupants are confined in close quarters for
extended periods and can be exposed to infectious diseases carried by
other occupants. Because air travel is rapid, people can complete their
journeys before the symptoms of a disease begin. Consequently, there has
been much concern regarding the in-flight transmission of contagious
diseases, particularly tuberculosis and, more recently, severe acute
respiratory syndrome (SARS). As part of our review of airliner cabin air
quality, we tracked the status of SARS and air travel.
SARS is a serious respiratory illness that has affected persons in Asia,
North America, and Europe. According to the World Health Organization
(WHO), as of September 26, 2003, there were an estimated 8,098 probable
cases reported in 27 countries, including 29 cases in the United States.
There have been 774 deaths worldwide, none of which have occurred in the
United States. The Centers for Disease Control and Prevention (CDC)
believes SARS is caused by a previously unrecognized coronavirus.1 The
symptoms of SARS can include a fever, chills, headache, other body aches,
and a dry cough.
SARS appears to be transmitted by close personal contact, which includes
touching the eyes, nose, or mouth after touching the skin of infected
individuals or objects that have been contaminated with infectious
droplets released by an infected individual while coughing or sneezing.
People with SARS pose the highest risk of transmission to household
members and health care personnel in close contact. Most cases of SARS
involved people who cared for or lived with someone with SARS or had
direct contact with objects contaminated with infectious droplets.
Information to date suggests that people are most likely to be infectious
when they have symptoms such as fever or cough. However, it is not known
how long before or after their symptoms begin that people with SARS might
be able to transmit the disease to others. Most of the U.S. cases of SARS
have occurred among travelers returning to the United States from other
parts of the world affected by SARS, such as China. According to WHO, as
of September 26, 2003, the latest probable case of SARS reported in the
United States was on July 13, 2003. However, there is no evidence that
SARS is spreading in the United States. WHO has reported that although
1A coronavirus is so named because it looks like a corona or halo when
viewed under an electron microscope. Two human coronaviruses cause about
30 percent of common colds. Coronavirses have been found to infect cattle,
pigs, horses, turkeys, chickens, cats, dogs, rats, and mice.
Appendix III
Transmission of Severe Acute Respiratory
Syndrome (SARS) on Board Aircraft Is Rare
and Associated with Proximity
the global outbreak of SARS has been contained, considerable uncertainty
surrounds the question of whether SARS might recur, perhaps according to a
seasonal pattern. Several respiratory illnesses occur much less frequently
when temperature and humidity are high and then return when the weather
turns cooler. WHO has also requested all countries to remain vigilant for
the recurrence of SARS and to maintain their capacity to detect and
respond to the reemergence of SARS, should it occur. The CDC has conducted
broadcasts over the Internet for healthcare providers on preparing for the
return of SARS.
WHO has reported that as of May 23, 2003, there have been 29 probable
cases of in-flight SARS transmissions on four flights worldwide. Out of
the 29 cases, 24 were on one flight, and 4 of the 29 cases were flight
attendants. WHO has stated that since then there have been no reported
cases of inflight SARS transmissions. The WHO Director of Communicable
Diseases stated there is a very low risk of catching SARS on an airplane
through the airplane's ventilation system. He noted that nearly all of the
in-flight transmissions occurred between passengers who were sitting near
each other. This official also stated that airport screening procedures
have been effective in keeping individuals displaying SARS symptoms from
boarding aircraft. In October 2003, WHO issued a report in which it did
not find evidence that SARS is an airborne disease. This report further
stated that at all outbreak sites the main route of transmission was
direct contact, via the eyes, nose, and mouth, with infectious respiratory
droplets.
In December 2003, the New England Journal of Medicine published the
results of a study on the transmission of SARS on three flights that
transported at least one person who had SARS.2 The study found that on one
flight carrying four people with SARS symptoms, one other person at most
developed the disease, and no illness was documented on another flight
transporting a person with presymptomatic SARS. However, on a third flight
carrying a symptomatic person, 22 probable cases of SARS3 occurred among
the other 119 passengers. According to the study, for the
2Olsen, Sonja J. et al., "Transmission of the Severe Acute Respiratory
Syndrome on Aircraft," The New England Journal of Medicine 349; 25 (2003):
2416-2422.
3According to the study, laboratory confirmed SARS developed in 16
persons, 2 others were given diagnosis of probable SARS and four were
reported to have SARS but could not be interviewed by the study team. WHO
reported that as of May 23, 2003, 24 probable SARS transmissions occurred
on this flight. The study does not indicate the reason for the
discrepancy.
Appendix III
Transmission of Severe Acute Respiratory
Syndrome (SARS) on Board Aircraft Is Rare
and Associated with Proximity
22 people with illness, the mean time from the flight to the onset of
symptoms was four days, and there were no recognized exposures to persons
with SARS before or after the flight. The study found that illness in
passengers was related to the physical proximity to the person with SARS
on the flight. Illness was reported in 8 of the 23 passengers seated in
the three rows in front of the person with SARS, as compared to 10 of the
88 passengers seated elsewhere on the aircraft. The study noted however,
that 90 percent of the passengers who became ill on the flight were seated
more than 36 inches from the person with SARS, which had been the cutoff
used to define the spread of SARS droplets in other investigations. The
study authors speculated that "airborne, small particle, or other remote
transmission may be more straightforward explanations for the observed
distribution of cases." The study concluded that SARS transmissions may
occur on flights carrying people in the symptomatic stages of the disease
and that measures to reduce the risk of transmission are warranted.
In November of 2003, more than 50 leading SARS researchers from 15
countries concluded that a safe and effective vaccine would be an
important complement to existing SARS control strategies. Most of the
experts agreed, however, that a SARS vaccine will not be available in
time, should an epidemic reoccur in the near future. A WHO official stated
that the licensing and commercialization of a SARS vaccine could probably
not be realized in 2004.
According to the International Air Transport Association (IATA),
passengers are not at risk from being infected with the SARS virus from
the cabin crew, who must be medically fit, without SARS symptoms, and
physically capable to fly and fulfill their duties. CDC has stated that
there is currently no evidence that a person can be infected with SARS
from handling baggage or goods, because the primary means of infection is
close personal contact. CDC has also stated the transmission of SARS has
been associated with close contact with people with SARS symptoms, such as
passengers on an aircraft.
The CDC has issued travel alerts and advisories for travel to areas
affected by SARS. A travel advisory recommends that nonessential travel be
deferred; in contrast, a travel alert informs travelers of the health
concern and provides advice about specific precautions. The CDC recommends
that if SARS is suspected in an outpatient setting, healthcare providers
should provide and place a surgical mask over the person's nose and mouth.
The CDC further recommends that if this is not feasible, the person with
SARS should be asked to cover his/her mouth with a disposable tissue when
Appendix III
Transmission of Severe Acute Respiratory
Syndrome (SARS) on Board Aircraft Is Rare
and Associated with Proximity
coughing, sneezing, or talking. WHO has urged airport officials in
countries affected with SARS outbreaks to take precautionary screening
measures, such as asking passengers if they have had contact with anyone
who has had the disease. U.S. airlines that fly to Asia report that they
are following CDC and WHO guidelines. FAA has links to the CDC and WHO
guidelines on its Web site. U.S. airlines that do not fly internationally
are not modifying their procedures because they see no SARS risk to cabin
occupants. According to ATA officials, U.S. airlines that do not fly
internationally were not advised by CDC to modify procedures because there
was no evidence of community transmission of SARS in the United States.
However, all ATA-member airlines cooperated fully with CDC in instances
where there was a possible person with SARS who might have transferred
from an international to a domestic flight.
Appendix IV
European CabinAir Study: Scope and Methodology
In 2001, Building Research Establishment, Ltd. (BRE)1 initiated a study on
cabin air quality that was estimated to cost $8 million. The following
link provides the official description of the effort as posted on BRE's
Internet site:
http://projects.bre.co.uk/envdiv/cabinair/work_programme.html
To further the industry's understanding of what is known about air quality
issues by assessing the current level of air quality found in aircraft
cabins, BRE will monitor four generic aircraft types in flight and assess
cabin air quality and ventilation system performance, including the
effects of passenger density and flight duration. A total of 50 such
flights are planned. The findings will identify current best practice and
will be used to improve understanding of (1) what constitutes good cabin
air; (2) the impact on the safety, health, and comfort of passengers and
cabin crew; and (3) the effects on operating costs, fuel energy use, and
the external environment.
To identify the technology (i.e., environmental control systems including
filtration and air distribution) that is available to improve cabin air
quality, BRE will develop new designs to address various air quality
issues, including the control of carbon dioxide, humidification, outside
air supply, and the recirculation and filtration of air. Operating costs
and energy consumption will be analyzed in relation to environmental
impacts. New designs must be suitable for retrofitting to existing
aircraft, either as complete environmental control systems or as
subsystems within existing units. The overall intention is to make
environmental control systems flexible and easy to operate. For example,
improved systems might enable the crew to match the system to the
passenger load factor, reduce bleed air, or provide additional comfort in
different areas of the cabin.
BRE will seek to improve the performance of filtration systems and then
develop new technologies and systems. It will assess existing filtration
systems and consider how the installation process and activities such as
maintenance, lifting, and cleaning affect performance. A technology
demonstrator rig will be developed to test new filtration systems. New and
enhanced features will be developed to mitigate such problems as the
recirculation of pollutants, bacteria, and viruses. Other major factors
1Building Research Establishment, Ltd. (BRE) is a high-level
research-based consultancy organization, owned by a not-for-profit entity
headquartered in the United Kingdom. BRE provides the aviation industry
with expert advice on cabin environment issues and particularly on air
quality in passenger aircraft.
Appendix IV
European CabinAir Study: Scope and
Methodology
include the compatibility of the filtration systems with the overall
environmental control system, operational costs, and energy consumption.
The effectiveness of current air distribution systems will be gauged
through in-flight monitoring. New design strategies and technologies, such
as personal controls, will be developed with the goal of maximizing the
effectiveness of cabin ventilation. The study will also look at ways of
making the distribution system more easily integrated with aircraft
design.
To assess and determine potential improvements to existing standards and
performance specifications for the cabin environment, BRE will assess
existing standards. Potential improvements to existing standards and
specifications will be determined. Checks will be carried out to ensure
the feasibility of the performance specifications and costs and to
identify any environmental implications. New performance indexes and
comfort criteria will also be defined, and BRE will develop a model to be
tested.
Appendix V
Surveillance and Research Programs
Key recommendations of the Council report were to establish surveillance
and research programs to determine effects of cabin air quality on
aircraft occupants' health and comfort.
Surveillance Program The following is a detailed description of these
programs as stated in the Council report.
Surveillance program objectives
o To determine aircraft compliance with existing Federal Aviation
Regulations (FARS) for air quality.
o To characterize accurately air quality and establish temporal trends of
air-quality characteristics in a broad sample of representative aircraft.
o To estimate the frequency of nonroutine operations in which serious
degradation of cabin air quality occurs.
o To systematically document health effects or complaints of passengers
and crew related to routine conditions of flight or air-quality incidents;
to be effective, this effort must be conducted and coordinated in
conjunction with air-quality monitoring.
Surveillance program approach
o Continuously monitor and record ozone, carbon monoxide, and carbon
dioxide, fine particles, cabin pressure, temperature, and relative
humidity.
o Sample a representative number of flights over a period of 1 to 2
years.
o Continue to monitor flights to ensure accurate characterization of air
quality as new aircraft come online and aircraft equipment ages or is
upgraded.
Appendix V
Surveillance and Research Programs
o Conduct a program for the systematic collection, analysis, and
reporting of health data with the cabin crew as the primary study group.1
Research Program The following is a detailed description of the research
program, including long-standing questions regarding air quality,
objectives, and program approach.
Outstanding air qualityrelated questions to be addressed by the research
program
o How is the ozone concentration in the cabin environment affected by
various factors (e.g., ambient concentrations, reaction with surfaces, the
presence and effectiveness of catalytic converters) and what is the
relationship between cabin ozone concentrations and health effects on
cabin occupants?
o What is the effect of cabin pressure altitude on susceptible cabin
occupants, including infants, pregnant women, and people with
cardiovascular disease?
o Does the environmental control system (ECS) provide sufficient quantity
and distribution of outside air to meet the FAA regulatory requirements,
and to what extent is cabin ventilation associated with complaints from
passengers and cabin crew? Can it be verified that infectious disease
agents are transmitted primarily between people who are in close contact?
Does recirculating cabin air increase cabin occupants' risk of exposure?
o What is the toxicity of the constituents or degradation products of
engine lubricating oils, hydraulic fluids, and de-icing fluids, and is
there a relationship between exposures to them and reported health effects
on cabin crew? How are these oils, fluids, and degradation products
distributed from the engines into the ECS and throughout the cabin
environment?
1On March 4, 2003, FAA announced the creation of a voluntary program for
air carriers, called the Aviation Safety and Health Partnership Program.
Through this program, the agency intends to enter into partnership
agreements with participating air carriers, which will, at a minimum, make
data on their employees' injuries and illnesses available to FAA for
collection and analysis.
Appendix V
Surveillance and Research Programs
o What are the magnitudes of exposures to pesticides in aircraft cabins,
and what is the relationship between the exposures and reported symptoms?
o What is the contribution of low relative humidity to the perception of
dryness, and do other factors cause or contribute to the irritation
associated with the dry cabin environment during flight?
Research program objectives
o To investigate possible association between specific air quality
characteristics and health effects or complaints.
o To evaluate the physical and chemical factors affecting specific air
quality characteristics in aircraft cabins.
o To determine whether FARS for air quality are adequate to protect
health and ensure the comfort of passengers and crew.
o To determine exposure to selected contaminants (e.g., constituents of
engine oils and hydraulic fluids, their degradation products, and
pesticides) and establish their potential toxicity more fully.
Research program approach o Use continuous monitoring data from
surveillance program when possible.
o Monitor additional air quality characteristics on selected flights as
necessary (e.g., integrated particulate-matter sampling to assess exposure
to selected contaminants).
o Identify and monitor "problem" aircraft and review maintenance and
repair records to evaluate issues associated with air quality incidents.
o Collect selected health data (e.g., pulse-oximetry data to assess
arterial oxygen saturation of passengers and crew).
o Conduct laboratory and other ground-based studies to characterize air
distribution and circulation and contaminant generation, transport, and
degradation in the cabin and the ECS.
Appendix VI
GAO Contacts and Staff Acknowledgments
GAO Contacts Gerald L. Dillingham, (202) 512-2834 Beverly L. Norwood,
(202) 512-2834
Staff In addition to the individuals named above, Kevin Bailey, Jim
Geibel, David Ireland, Bert Japikse, Stanley Kostyla, Edward Laughlin,
Donna Leiss, and
Acknowledgments Maria Romero made key contributions to this report.
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