[Federal Register Volume 64, Number 243 (Monday, December 20, 1999)]
[Notices]
[Pages 71242-71261]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-32824]



[[Page 71241]]

_______________________________________________________________________

Part V





Department of Labor





_______________________________________________________________________



Occupational Safety and Health Administration



_______________________________________________________________________



Dixie Divers, Inc.; Grant of Permanent Variance; Notice

  Federal Register / Vol. 64, No. 243 / Monday, December 20, 1999 / 
Notices  

[[Page 71242]]



DEPARTMENT OF LABOR

Occupational Safety and Health Administration
[V-97-1]


Dixie Divers, Inc.; Grant of Permanent Variance

AGENCY: Occupational Safety and Health Administration, Department of 
Labor.

ACTION: Grant of permanent variance.

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SUMMARY: This notice announces the grant of a permanent variance to 
Dixie Divers, Inc. (Dixie). The permanent variance is from the 
Occupational Safety and Health Administration (OSHA) requirements for 
decompression chambers during mixed-gas diving operations, including 
paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph 
(b)(1) of 29 CFR 1910.426.
    The permanent variance covers recreational diving instructors and 
diving guides employed by Dixie. Using both classroom instruction and 
practice dives, recreational diving instructors train novice divers 
individually or in small groups in recreational diving knowledge and 
skills, including conventional diving procedures and the safe operation 
of diving equipment. Dixie's recreational diving instructors accompany 
students during practice dives, which vary in depth from a few feet of 
sea water (fsw) to 130 fsw, and last between 30 minutes and one hour. 
Diving guides (who may also serve as recreational diving instructors) 
lead small groups of trained sports divers to local undersea locations 
for recreational purposes; the guides select the diving locations and 
provide the sports divers with information regarding the dive site, 
including hazardous conditions and safe diving practices. While leading 
divers to a dive site, the guides dive to a maximum depth of 130 fsw 
for periods of 30 minutes to one hour.
    The permanent variance specifies the conditions under which Dixie's 
recreational diving instructors and diving guides may conduct their 
underwater training and guiding tasks using open-circuit, semi-closed-
circuit, or closed-circuit self-contained underwater breathing 
apparatus (SCUBA) supplied with a breathing gas consisting of a high 
percentage of oxygen (O2) mixed with nitrogen, and without a 
decompression chamber near the dive site. These conditions address: The 
requirements for SCUBA equipment, including carbon-dioxide canisters, 
counterlungs, moisture traps, moisture sensors, carbon-dioxide and 
O2 sensors, and information modules; depth limits for diving 
operations; use of nationally-recognized no-decompression limits and 
O2-exposure limits; the O2 and nitrogen 
composition of the breathing-gas mixture; procedures and equipment for 
producing and analyzing breathing-gas mixtures; emergency-egress 
procedures and systems; management of diving-related medical 
emergencies; procedures for maintaining diving logs; use of 
decompression tables and dive-decompression computers; and training 
requirements for recreational diving instructors and diving guides.

DATES: The effective date of the permanent variance is December 20, 
1999.

FOR FURTHER INFORMATION CONTACT: Office of Information and Consumer 
Affairs, Room N3647, U.S. Department of Labor, Occupational Safety and 
Health Administration, 200 Constitution Avenue, NW, Washington, DC 
20210, Telephone: (202) 693-1999.
    Additional information also is available from the following 
Regional and Area Offices:

Regional Office:

U.S. Department of Labor--OSHA, 61 Forsyth St., SW., Atlanta, GA 30303, 
Telephone: (404) 562-2300

Area Offices:

U.S. Department of Labor--OSHA, 5807 Breckenridge Parkway, Suite A, 
Tampa, FL 33610, Telephone: (813) 626-1177
U.S. Department of Labor--OSHA, 8040 Peters Road, Building H-100, 
Jacaranda Executive Court, Fort Lauderdale, FL 33324, Telephone: (954) 
424-0242
U.S. Department of Labor--OSHA, Ribault Building, suite 227, 1851 
Executive Center Drive, Jacksonville, FL 32207, Telephone: (904) 232-
2895

SUPPLEMENTARY INFORMATION:

I. Table of Contents

    The following Table of Contents identifies the major sections under 
``Supplementary Information.'' To understand fully the information 
presented in the following sections, we recommend reviewing the 40 
conditions of the permanent variance listed below under section VI.

I. Table of Contents
II. Background
III. Application for a Permanent Variance
IV. Comments to the Proposed Variance
    Part 1. Comments to proposed section I (Background).
    Part 2. Comments to proposed section II (Proposed Alternative).
    Part 3. Comments to proposed section III (Rationale for the 
Proposed Alternative).
    Part 4. Comments to proposed section VI (Issues).
    Part 5. General comments to the proposed variance.
    Part 6. Our revisions to the proposed variance.
V. Decision
VI. Order
VII. References
VIII. Authority and Signature

II. Background

    Dixie Divers, Inc. (Dixie) applied for a permanent variance from 
paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph 
(b)(1) of 29 CFR 1910.426 under Section 6(d) of the Occupational Safety 
and Health Act of 1970 (29 U.S.C. 655) and 29 CFR 1905.11. These 
paragraphs address the availability and use of decompression chambers 
during mixed-gas diving operations.
    Dixie operates six diving schools, either directly or as 
franchises. The schools employ 18 skilled and experienced recreational 
diving instructors to train novice divers in recreational diving 
knowledge and skills. The same 18 employees also serve as diving guides 
and lead groups of sport divers to local diving sites for recreational 
purposes. (We also refer to recreational diving instructors and diving 
guides jointly as ``employees'' or, more generally, as ``divers.'')
    As recreational diving instructors, the employees train 
recreational diving students in conventional diving procedures and the 
safe operation of diving equipment. The diving students may use an 
open-circuit, semi-closed-circuit, or closed-circuit self-contained 
underwater breathing apparatus (SCUBA) during these training dives. 
1 SCUBAs supply divers with compressed air or a breathing 
gas consisting of a high percentage of oxygen mixed with nitrogen or 
another inert gas. 2
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    \1\ The acronym for ``self-contained underwater breathing 
apparatus'' is ``SCUBA.'' The term ``SCUBA'' refers to open-circuit 
diving equipment alone, or to open-circuit, semi-closed-circuit, and 
closed-circuit diving equipment combined. The term ``rebreather'' 
refers to semi-closed-circuit or closed-circuit diving equipment 
alone or combined; this diving equipment recycles part or all of the 
exhaled breathing gas into the system that delivers the breathing 
gas to the diver.
    \2\ The abbreviation ``O2'' means ``oxygen,'' while 
the phrase ``nitrox breathing-gas mixture'' or the term ``nitrox'' 
refers to a breathing-gas mixture composed of nitrogen and 
O2 in varying proportions.
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    Dixie's training program for diving students involves both 
classroom instruction and practice dives in which the employees 
accompany diving students to maximum depths of 130 feet of sea water 
(fsw). These dives last between 30 minutes and one hour. During these 
dives, the recreational diving instructors provide underwater

[[Page 71243]]

instruction in, and allow the diving students to practice using, diving 
procedures and equipment. A recreational diving instructor may make as 
many as three to four training dives a day while training diving 
students either individually or in small groups.
    As diving guides, the employees lead small groups of trained sports 
divers to local undersea diving locations for recreational purposes. 
The diving guide selects the diving location prior to departure, and 
provides the sports divers with information regarding the dive site, 
including hazardous conditions and safe diving practices. The divers in 
the recreational diving groups use open-circuit, semi-closed-circuit, 
or closed-circuit SCUBAs that supply compressed air or a nitrox 
breathing-gas mixture during the dive. During these diving excursions, 
diving guides dive to a maximum depth of 130 fsw for periods of 30 
minutes to one hour. A diving guide may make as many as five 
recreational diving excursions a day.
    The places of employment affected by this permanent variance are:

Dixie Divers of Boca Raton, 8241 Glades Road, Boca Raton, FL 33434
Dixie Divers of Boynton Beach, 340 North Congress, Boynton Beach, FL 
33426
Dixie Divers of Deerfield, 1645 Southeast 3rd Court, Deerfield Beach, 
FL 33441
Dixie Divers of Key Largo, 103400 Overseas Highway, Key Largo, FL 33037
Dixie Divers of Palm Bay, 4651 Babcock Street, Northeast, Palm Bay, FL 
32905
Dixie Divers of Panama City, 109B West 23rd Street, Panama City, FL 
32405

III. Application for a Permanent Variance

    In its application for a permanent variance (referred to as 
``variance application,'' ``proposed variance,'' or ``proposal''), 
Dixie proposed an alternative to the decompression-chamber requirements 
of paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph 
(b)(1) of 29 CFR 1910.426. Paragraph (b)(2) of 29 CFR 1910.423 requires 
that ``[f]or any dive outside the no-decompression limits, deeper than 
100 fsw or using mixed gas as a breathing mixture, the employer shall 
instruct the diver to remain awake and in the vicinity of the 
decompression chamber which is at the dive location for at least one 
hour after the dive (including decompression or treatment as 
appropriate).'' Paragraph (c)(3)(iii) of 29 CFR 1910.423 requires that 
the decompression chamber be ``[l]ocated within 5 minutes of the dive 
location,'' while paragraph (b)(1) of 29 CFR 1910.426 permits mixed-gas 
diving only when a ``decompression chamber is ready for use at the dive 
location.'' The purpose of having a decompression chamber available and 
ready for use at the dive site is to treat two conditions: (1) 
Decompression sickness (DCS), which may occur from breathing air or 
mixed gases at diving depths and durations that require decompression; 
and (2) arterial-gas embolism (AGE), which may result from 
overpressurizing the lungs, usually while ascending rapidly to the 
surface during a dive.
    In the variance application, Dixie proposed to implement 
alternative procedures that meet or exceed the level of employee 
protection afforded by OSHA's decompression-chamber requirements. As an 
alternative to a decompression chamber, Dixie proposed to have its 
employees use open-circuit, semi-closed-circuit, or closed-circuit 
SCUBA supplied with breathing-gas mixtures that contain a fraction of 
O2 ranging from 22 to 40 percent (22-40%) by volume, with 
the remaining breathing-gas mixture consisting of nitrogen. In 
addition, the partial pressure of O2 in the nitrox 
breathing-gas mixture would never exceed 1.40 atmospheres absolute 
(ATA) 3 for any SCUBA. Dixie would use one of the following 
procedures to produce nitrox breathing-gas mixtures: Mixing pure 
nitrogen with pure O2; removing O2 from air for 
mixing with pure nitrogen; adding pure O2 to air; or de-
nitrogenating air (e.g., removing nitrogen from air using filter-
membrane systems 4). According to the proposal, Dixie would: 
Analyze the O2 fraction in the breathing-gas mixtures for 
accuracy; institute quality-assurance procedures for the analytic 
processes; and use breathing-gas mixing systems rated for O2 
service whenever the highest O2 fraction used in the mixing 
process exceeds 40 percent (40%). Dixie also proposed to restrict 
diving operations under the variance to depths of 130 fsw or less, and 
to use the nationally-recognized no-decompression limits and 
O2-exposure limits developed by the National Oceanic and 
Atmospheric Administration (NOAA) and Diving Science and Technology 
(DSAT).
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    \3\ ATA, as used here, is the partial pressure of a constituent 
gas in the total pressure of a breathing gas. If the percentage of 
the constituent gas in the breathing gas remains constant throughout 
a dive, its partial pressure or ATA, increases in proportion to 
increases in diving depth.
    \4\ Filter-membrane systems produce nitrox breathing-gas 
mixtures in two steps: First, they route air through filters to 
remove hydrocarbons and other contaminants, then they pass the 
decontaminated air through membranes that transfer O2 
across the membrane fibers at higher rates than nitrogen (hence, 
``de-nitrogenating air''). As the rate of air flow across the 
membrane fibers increases, the resulting ratio of O2 to 
nitrogen also increases. Under the permanent variance, a filter-
membrane system will reduce the hazards associated with producing 
high-O2 breathing-gas mixtures because the proportion of 
O2 in the system will never exceed 40 percent (40%).
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    By increasing the O2 partial pressure and decreasing the 
nitrogen partial pressure of the breathing-gas mixture compared to air, 
and by restricting dives to no-decompression limits and depths of 130 
fsw or less, Dixie asserted that both the rate and the severity of DCS 
would be no greater for its employees than for divers who operate 
according to paragraph (a)(2)(i) of 29 CFR 1910.401. In addition, Dixie 
contended that using nationally-recognized O2-exposure 
procedures would reduce the risk of O2 toxicity among its 
divers to the rate expected among divers who use hyperbaric air.
    Dixie proposed a number of other requirements to ensure that its 
employees remain within safe diving parameters, thereby avoiding DCS 
and AGE. These requirements included limiting the maximum carbon 
dioxide (CO2) level in the inhaled nitrox breathing-gas 
mixture to 0.01 ATA. Dixie would control excessive CO2 
levels as follows: By using pre-packed sorbent materials to absorb 
CO2 from the exhaled breathing gas prior to rebreathing; by 
installing sensors for detecting high CO2 levels or 
conditions that could result in high CO2 levels (such as 
moisture sensors to detect flooding in the breathing loop); and by 
using counterlungs to serve as low-breathing-resistance reservoirs for 
the breathing gas. In addition, Dixie proposed that its divers use an 
information module that provides them with critical dive information 
(e.g., gas pressures, water-temperature); the required information 
would vary with the type of SCUBA. For rebreathers, visual or auditory 
warning devices would alert the diver to significant equipment problems 
(e.g., solenoid failure, low battery levels) or deviations from 
established diving parameters (e.g., diverging from the planned 
O2 levels). Closed-circuit rebreathers would need to operate 
using a gas-controller package, a manually-operated gas-supply bypass 
valve, and separate O2 and diluent-gas cylinders.
    Dixie proposed a number of other conditions to safeguard its 
divers. For emergencies involving SCUBA malfunctions that could 
endanger diver health and safety (e.g., high CO2 levels), 
the proposed variance required that Dixie have a reliable ``bail-out 
system'' available. The bail-out system would need to provide a 
separate supply of

[[Page 71244]]

breathing gas to the second stage of the SCUBA regulator; when 
rebreathers are used, the bail-out system could deliver a diluent 
supply of breathing gas to the second stage of the regulator. Other 
protective conditions, which refined or emphasized existing 
requirements currently specified in OSHA's Commercial Diving Operations 
Standard (CDO Standard), included the following: Maintaining 
decompression tables and diving logs at the dive site; assuring the 
availability of personnel, facilities, and equipment to treat DCS and 
AGE; and providing quality control of diver training.
    In summary, Dixie stated that the occurrence and severity of DCS 
would be minimal when its divers breathe nitrox gas mixtures, while the 
risk of AGE would be negligible when they use the equipment and 
procedural safeguards specified in the variance application. 
Consequently, divers who use SCUBAs according to the proposed variance 
would experience a level of DCS and AGE that is equal to, or lower 
than, the level experienced by recreational diving instructors who dive 
under the conditions specified by the exemption to the CDO Standard at 
29 CFR 1910.401(a)(2)(i). These conditions allow for the use of 
compressed air supplied to open-circuit SCUBAs under no-decompression 
diving limits. Dixie asserted, therefore, that it should not have to 
maintain a decompression chamber at the dive location for its 
recreational diving instructors and diving guides when it complies with 
the conditions specified in the variance application.
    In a Federal Register notice published on October 31, 1997, we 
provided the public with a copy of Dixie's variance application (62 FR 
58995). This notice invited interested parties, including affected 
employers and employees, to submit written comments, data, views, and 
arguments regarding the variance application. In addition, the notice 
informed affected employers and employees of their right to request a 
hearing on the variance application. At the request of several parties, 
we extended the comment period for this notice until March 2, 1998 in a 
Federal Register announcement dated January 6, 1998 (63 FR 579).

IV. Comments on the Proposed Variance

    We received 123 comments in response to the two Federal Register 
notices. Of this total, two comments (Exs. 2-98 and 2-115) were 
duplications, and one comment (Ex. 2-112) consisted solely of a request 
to extend the comment period. (Exs. 6-1 to 6-17 also were requests to 
extend the comment period.) Two additional comments (Exs. 2-118 and 2-
119) requested a hearing on the proposal. We denied these hearing 
requests because neither of the two requestors employed recreational 
diving instructors, the subject of this variance application. OSHA 
received 103 comments that were general, non-specific endorsements of 
the variance application; the vast majority of these comments varied 
only slightly in content. The remaining 15 commenters submitted 
detailed comments regarding the conditions and issues specified in the 
variance application.
    We have organized our discussion of the substantive comments to the 
variance application into six parts. Comments concerning proposed 
section I (Background) are in Part 1, while Part 2 consists of comments 
made about the conditions specified in proposed section II (Proposed 
Alternative). Part 3 discusses comments made regarding proposed section 
III (Rationale for the Proposed Alternative), and Part 4 presents 
comments to the issues raised in proposed section VI (Issues). No 
commenters addressed sections IV and V of the variance application, 
titled ``References'' and ``Additional Information'' respectively. Part 
5 consists of general and miscellaneous comments. Throughout each of 
these five parts, we explain the actions we are taking with regard to 
individual comments or groups of comments. The last part, Part 6, 
describes refinements to the proposed variance that we have made in 
developing the permanent variance; these refinements are based upon our 
interpretation of the proposed conditions and our overall review of the 
record.
    We and other parties submitted additional exhibits (Exs. 4, 4A, 5, 
and 7 through 13) to the docket (see Table I). These exhibits, which 
contain scientific and technical information, provided additional 
information we used in replying to comments and discussing revisions to 
the proposal. The principal topics covered by the exhibits are: 
O2 toxicity; nitrogen narcosis; decompression procedures; 
the operation and use of SCUBAs; and treatment of diving-related 
medical emergencies. Table I below provides specific reference 
information on these exhibits.

   Table I.--Reference Information on Exhibits 4, 4A, and 5 Through 16
------------------------------------------------------------------------
 Ex.
 No.                         Reference information
------------------------------------------------------------------------
    4  D. J. Kenyon and R. W. Hamilton. ``Managing Oxygen Exposure when
        Preparing Decompression Tables.'' In: N. Bitterman and R.
        Lincoln (eds.), Proceedings of the XVth Meeting of the European
        Undersea Biomedical Society,  pages 72-77. European Undersea
        Biomedical Society, September 1989.
       R. W. Hamilton. ``IV. Oxygen Physiology, Toxicity, and
        Tolerance.'' In: R. W. Hamilton (author), Special Mix Diving:
        Part One, pages 25-38. Hamilton Research and Life Support
        Technologies, March 2, 1994.
   4A  R. W. Hamilton, R. E. Rogers, M. R. Powell, and R. D. Vann. The
        DSAT Recreational Dive Planner: Development and Validation of No-
        Stop Decompression Procedures for Recreational Diving. Diving
        Science and Technology, Inc., and Hamilton Research, Ltd.,
        February 28, 1994.
    5  D. Richardson (ed.-in-chief). Proceedings of Rebreather Forum
        2.0. Diving Science and Technology, Inc., 1996.
    7  R. W. Hamilton. ``Tolerating Exposure to High Oxygen Levels:
        Repex and Other Methods.'' Marine Technology Society Journal,
        volume 23, number 4, pages 19-25, December 1989.
    8  R. J. Kiessling and C. H. Maag. ``Performance Impairment as a
        Function of Nitrogen Narcosis.'' Journal of Applied Psychology,
        volume 46, number 2, pages 91-95, 1962.
    9  A. D. Baddeley. ``Influence of Depth on the Manual Dexterity of
        Free Divers: A Comparison Between Open Sea and Pressure Chamber
        Testing.'' Journal of Applied Psychology, volume 50, number 1,
        pages 81-85, 1966.
   10  A. D. Baddeley, J. W. De Figueredo, J. W. Hawkswell Curtis, and
        A. N. Williams. ``Nitrogen Narcosis and Performance Under
        Water.'' Ergonomics, volume 11, number 2, pages 157-164, 1968.
   11  W. B. Wright. ``Use of the University of Pennsylvania, Institute
        for Environmental Medicine Procedure for Calculation of
        Cumulative Pulmonary Oxygen Toxicity.'' U.S. Navy Experimental
        Diving Unit, Report 2-72, 1972.
   12  R. J. Biersner. ``Request for Your Recommendation Regarding
        Acceptable Delay in Recompression Treatment of Diving-Related
        Medical Emergencies.'' Memorandum to Dr. Edward D. Thalmann,
        August 28, 1998.

[[Page 71245]]

 
   13  E. D. Thalmann. Letter to R. J. Biersner Responding to the
        Memorandum in Ex. 12, October 5, 1998.
   14  J. R. Clarke. CO2 Canister Test Parameters and Procedure at NEDU.
        Attachment to U.S. Navy Experimental Diving Unit E-mail
        Memorandum, November 22, 1999.
   15  J. R. Clarke. ``Statistically Based CO2 Canister Duration Limits
        for Closed-Circuit Underwater Breathing Apparatus.'' U.S. Navy
        Experimental Diving Unit, Report 2-99, 1999.
   16  P. B. Bennett. ``Nitrox?'' Alert Diver, March/April, 1998.
------------------------------------------------------------------------

Part 1. Comments to proposed section I (Background).

    (a) The skills and experience of, and the diving operations 
performed by, the applicant's divers (62 FR 58996, second column) 
received two comments. Both comments were primarily concerned about 
Dixie's recreational diving instructors and diving guides engaging in 
diving activity beyond the scope of the proposed variance. The 
Association of Diving Contractors, Inc. (Ex. 2-99) contended that 
recreational diving instructors and diving guides ``[engage] in 
services of a commercial nature,'' and implied that the conditions of 
the variance application would allow them to extend their commercial 
diving activities beyond the scope of the proposed variance.
    The second commenter (Ex. 2-105) did not object to the proposed 
variance for no-decompression dives to depths of 130 fsw or less if 
they are ``of an instructional, training, or scientific nature and [do] 
not involve any form of salvage or underwater construction or related 
working tasks.'' This commenter stated that the recreational diving 
must ``not encompass working dives (i.e.[,] salvage, construction). 
This is a very [important] distinction as the commercial diving 
industry cannot bear the financial burden imposed by the insurance 
companies who would lump professional recreational instructors in with 
professional commercial divers.''
    In reply to these commenters, we note that the permanent variance 
will not cover recreational diving instructors and diving guides when 
they engage in activities that do not involve recreational diving 
instruction and diving guide activities. They must comply with our CDO 
Standard as appropriate, including the decompression-chamber 
requirements, while engaged in these other activities. To ensure that 
Dixie understands under what conditions the permanent variance applies, 
we are specifying in Condition (1) (see below at section VI, titled 
``Order'') that the permanent variance covers only recreational diving 
instructors and diving guides who are employees of Dixie Divers, Inc., 
and then only while they are performing as diving guides and 
recreational diving instructors.
    (b) The background information noted that the applicant's employees 
``may make as many as three or four training dives a day while training 
diving students'' and that ``[a] guide may make as many as five * * * 
excursions a day'' (62 FR 58996, second column). This background 
information elicited one comment. This commenter (Ex. 2-109) stated 
that ``[b]oth NAUI [National Association of Underwater Instructors] and 
PADI [Professional Association of Diving Instructors], the two largest 
certifying agencies in the U.S., limit instructors teaching entry-level 
classes to no more than two dives per day with a single class.'' The 
commenter also noted that ``Dixie could hire more instructors, which 
would lessen their time in the water, decreasing [their] nitrogen 
exposure, lessening their susceptibility to DCS, thus obviating the 
need for the variance.''
    The basis for the NAUI and PADI limitations is unclear (e.g., do 
these limits address diver safety or training effectiveness). 
Nevertheless, we believe that adopting the no-decompression procedures 
for repetitive diving published in the 1991 NOAA Diving Manual and by 
DSAT (Ex. 4A) as a condition of the permanent variance will protect 
Dixie's recreational diving instructors and diving guides at least as 
well as recreational diving instructors who use compressed air supplied 
to open-circuit SCUBAs under no-decompression diving limits specified 
in paragraph (a)(2)(i) of 29 CFR 1910.401.
    (c) The statement in this section that ``[e]mployees who use high-
oxygen breathing-gas mixtures will be able to make more or longer 
repetitive-training [or] excursion dives than they would using 
compressed-air open-circuit SCUBA'' (62 FR 58995, third column) 
received one comment. This commenter (Ex. 2-109) disagreed with this 
statement, claiming that nitrox breathing-gas mixtures may not reduce 
susceptibility to DCS and that ``[w]e know of no studies or evidence to 
show that diving to limits on the nitrox tables while breathing nitrox 
produces a lower incidence of DCS than diving to limits on air tables 
while breathing air.''
    We agree that the mathematical probability of DCS is similar for 
dives that result in equivalent levels of nitrogen saturation (e.g., 
dives made to a specific depth using air, and longer-duration dives 
made to the same depth using nitrox breathing-gas mixtures). 
Accordingly, for dives made using nitrox breathing-gas mixtures, the 
risk of DCS is lower only when these dives are at the same depths and 
for the same durations as the air dives. Note, however, that Condition 
J of the proposed variance limits the risk of DCS by requiring that 
divers remain within the no-decompression limits of NOAA's 
decompression tables, or other tables or formulas that Dixie 
demonstrates are equally effective in preventing DCS.
    (d) We stated in the ``Background'' section of the proposed 
variance that ``[a]s a result [of using nitrox breathing-gas mixtures], 
the mathematical probability of developing decompression sickness (DCS) 
is reduced compared to divers who use compressed air under the same 
diving conditions (i.e., depth, bottom time, and descent and ascent 
rates)'' (62 FR 58997, first column). This statement elicited two 
comments. The first commenter (Ex. 2-98) stated that high-O2 
nitrox breathing-gas mixtures will result in a reduced risk of DCS when 
used at the same depths and for the same durations as air, but only if 
the divers use the depth and duration limits specified for air 
decompression and do not extend the duration of the dive. The reduction 
in risk occurs because the nitrogen partial pressure in the nitrox 
breathing-gas mixture is less than the partial pressure of nitrogen in 
air at the specified depth. The second commenter (Ex. 2-109) asserted 
that Dixie has economic incentives to extend the duration of dives.
    We believe these commenters are correct that extending the duration 
of dives using high-O2 nitrox breathing-gas mixtures would 
increase the risk of DCS. However, we conclude that the

[[Page 71246]]

resulting risk would be comparable to using the equivalent partial 
pressure of nitrogen in air for that extended period. The basis for 
this conclusion is the equivalent-air-depth (EAD) formula published by 
NOAA, which is the nation's lead Federal agency for developing mixed-
gas decompression schedules used in scientific and technical diving 
operations. According to NOAA, EAD ``is the depth at which air will 
have the same nitrogen partial pressure as the [oxygen-]enriched mix 
has at the depth of the dive'' (1991 NOAA Diving Manual, page 15-7). 
NOAA applies its EAD formula in determining what equivalent air 
decompression limits to use with nitrox breathing-gas mixtures, and 
assumes that equivalent nitrogen partial pressures and dive durations 
will result in similar DCS risk. However, to provide Dixie's divers 
with an added margin of safety against DCS, the permanent variance 
requires that the partial pressure of nitrogen in the high-
O2 nitrox breathing-gas mixture used for a specific dive 
duration must never exceed the no-decompression limits for the 
equivalent partial pressure of nitrogen in air for that same duration 
published in the 1991 NOAA Diving Manual.

Part 2. Comments to proposed section II (Proposed Alternative).

    (a) Conditions A.1 and A.2 of the proposal, which specified 
requirements for CO2 scrubbers, CO2 sensors, 
moisture traps, moisture sensors, and over-pressure valves, received a 
number of comments. Several commenters (Exs. 2-98, 2-99, 2-105, and 2-
117) pointed out a typographical error in the stated CO2 
level in Condition A.1. The correct level is 0.01 ATA, not 0.1 ATA, and 
we have corrected it in the permanent variance.
    Condition A.1 in the proposed variance (Condition (4) in the 
permanent variance) stated that rebreathers must use commercially-
available, pre-packed, disposable scrubber cartridges or an equally 
effective alternative. Three commenters (Exs. 2-101, 2-105, and 2-114) 
took exception to the requirement that CO2 scrubbers must 
use sorbent cartridges that are commercially available, pre-packed, and 
disposable. They contended that such cartridges are not available for 
some rebreathers and, when available, are expensive. They also argued 
that rebreather manufacturers do not require pre-packed, disposable 
cartridges because many divers manually fill and pack most rebreather 
canisters. One commenter (Ex. 2-105) stated that ``no scientific 
evidence [shows that] a disposable[,] pre-packaged canister would 
perform safer or with greater efficiency than one packed by the user.'' 
Another commenter (Ex. 2-117), however, stated that ``[u]se [of 
disposable scrubber cartridges] in rebreathers reduces return to 
service time and reduces human error during servicing,'' and that 
[several manufacturers] have canisters that simplify replacement of 
sorbent material, while [at least one manufacturer] uses a disposable 
cartridge.''
    In reply to these commenters, we note that Condition A.1 in the 
proposed variance allowed Dixie to use an alternative to pre-packed 
CO2-sorbent materials, including manually-filled cartridges; 
Condition (4)(b) in the permanent variance will also permit this 
alternative, if it is acceptable to the rebreather manufacturer. 
However, Dixie bears the burden of demonstrating to us that its 
manually-filled cartridges are at least as effective as pre-packed 
sorbent materials in removing CO2 from the breathing loop; 
Dixie likely would get this information from the rebreather 
manufacturer.
    Proposed Condition A.2 required the use of CO2 sensors. 
One commenter (Ex. 2-25) endorsed this proposed requirement for closed-
circuit rebreathers, but claimed these sensors were unnecessary for 
semi-closed-circuit rebreathers because these rebreathers ``are 
regularly venting gas from the system which is replaced with high 
oxygen content gas * * * to prevent the buildup of carbon dioxide.'' We 
believe that CO2 sensors are necessary for semi-closed-
circuit rebreathers because divers can ``overbreathe'' these 
rebreathers. Overbreathing occurs when the diver's breathing rate is 
faster than the rate at which fresh breathing gas enters the inhalation 
bag; consequently, overbreathing causes the diver to rebreathe exhaled 
gas containing elevated levels of CO2. The information in 
Ex. 5 (pages P-19 through P-22) supports this conclusion. Therefore, 
CO2 sensors enable divers to detect increased CO2 
before it reaches hazardous levels.
    The commenter in Ex. 2-98 endorsed the use of CO2 
sensors, but claimed that this technology is ``currently unavailable 
even in the current U.S. Navy rebreathers.'' Two other commenters (Exs. 
2-105 and 2-114) also asserted that continuously-functioning 
CO2 sensors are not available commercially. However, another 
commenter (Ex. 2-117) contradicted these assertions; this commenter 
stated that CO2 sensors are available in several 
rebreathers.
    Four commenters (Exs. 2-99, 2-106, 2-113, and 2-114) claimed that 
few, if any, rebreathers on the market met proposed Conditions A.1 and 
A.2. One of these commenters (Ex. 2-106) stated, ``[M]any of the 
specifications for rebreathers represent the manufacturer-specific 
features of an intended unit that was never brought forward as a 
production model. We also manufacture diving rebreathers and protest 
any regulation that would arbitrarily bias compliance to one model.'' 
Four other commenters contended that the proposed variance favors or 
enhances the competitive position of one or more rebreather 
manufacturers (Exs. 2-99, 2-101, 2-105, and 2-114); no commenter, 
however, indicated which manufacturer(s) would benefit. One commenter 
(Ex. 2-114) stated that ``[implementing the proposed variance] would 
put every dive store and instructor who teaches rebreather diving in 
the U.S. out of business,'' and claimed that ``this [proposed] variance 
would in essence be a restraint of trade.''
    The information provided in Ex. 2-117 demonstrates that the 
required components are commercially available and used in several 
existing rebreathers. Other evidence in the record (Ex. 5, page 6-4) 
also shows that effective CO2 sensors are commercially 
available for closed-circuit rebreathers. We find that each proposed 
condition is necessary for diver safety, and that Dixie can either 
purchase rebreathers, or retrofit its existing rebreathers, to meet 
these conditions. In addition, we observe that no commenter found that 
any required component was unsafe.
    While the proposed variance did not require any CO2 
alarms, the commenter in Ex. 2-98 recommended that CO2 
sensors activate two alarms: The first alarm when the inhaled 
CO2 partial pressure is at 0.005 ATA (3.8 mmHg), to warn 
divers that they are approaching the upper CO2 limit; and 
the second alarm when inhaled CO2 reaches the partial 
pressure limit of 0.01 ATA (7.6 mmHg), to alert the diver to terminate 
the dive immediately. We agree with much of this comment, but we 
believe that once the alarm is activated at a CO2 partial 
pressure of 0.005 ATA, it must continue to provide a visual or auditory 
warning to the diver to take corrective action or terminate the dive 
before reaching the maximum CO2 limit of 0.01 ATA. The use 
of an activation level is similar to the action-level requirement found 
in many of OSHA's standards for toxic substances. Therefore, the 
permanent variance requires Dixie to

[[Page 71247]]

integrate the CO2 sensors with an alarm (either visual or 
auditory) that operates continuously at and above a CO2 
partial pressure of 0.005 ATA.
    The proposed variance did not specify calibration requirements for 
CO2 sensors. Nevertheless, the commenter in Ex. 2-98 stated 
that any CO2 sensor adopted for use in rebreathers must be 
``tested both in the laboratory and in manned diving trials,'' and that 
the ``[d]ata from these trials must support [the] accuracy, reliability 
and ruggedness'' of CO2 sensors. While this commenter did 
not specify a protocol or criteria for testing these factors, we agree 
that, at a minimum, Dixie must determine the accuracy of CO2 
sensors before its divers use them. Such a determination is necessary 
to enable Dixie to eliminate sensors that are unreliable or that cannot 
function under rugged diving conditions. Therefore, in developing 
provisions for calibrating and maintaining the accuracy of 
CO2 sensors (see Condition (9) in the permanent variance), 
we have adopted the requirements that Dixie specified for O2 
sensors in Condition A.4 of the variance application, with one major 
revision: Instead of using an accuracy of 1 percent (1%) by volume, 
Condition (9)(c) of the permanent variance requires that CO2 
sensors be accurate ``to within 10 percent (10%) of a CO2 
concentration of 0.005 ATA or less,'' based on the comments in Ex. 2-
98. Using a test or standard gas containing a CO2 
concentration of 0.005 ATA or less will ensure that the sensors can 
accurately detect CO2 levels that can be harmful to Dixie's 
divers. Additionally, in view of the harmful effects that can result 
from high levels of CO2, we consider a maximum error rate of 
no more than 10 percent (10%) of a CO2 partial pressure of 
0.005 ATA to be within acceptable limits.
    The commenter in Ex. 2-98 also argued that, as an alternative to 
CO2 sensors, ``the breathing apparatus manufacturer [must] 
produce data from manned trials that substantiate [the] operational 
CO2 canister-duration limits over the entire depth, water 
temperature, and exercise range for which the breathing apparatus is 
designed. Furthermore, the manufacturer must clearly state what these 
limits are.'' While the proposed variance did not mention such an 
alternative, we agree with the general approach recommended by this 
commenter. However, we believe that valid and reliable data for 
determining CO2-sorbent replacement schedules can be 
obtained from carefully controlled and executed testing protocols that 
use breathing machines instead of divers to evaluate the canisters. 
Therefore, Condition (10)(a)(i) of the permanent variance permits Dixie 
to use a schedule for replacing the CO2-sorbent material in 
canisters if the rebreather manufacturer developed the replacement 
schedule using the canister-testing protocol specified in Appendix A of 
this notice. We adapted this protocol from the canister-testing 
parameters and procedure provided by the U.S. Navy Experimental Diving 
Unit (NEDU) (Ex. 14); NEDU is the lead federal agency for testing 
CO2-sorbent replacement schedules, and the diving industry 
recognizes the NEDU canister-testing protocol as the industry standard. 
Additionally, the employer can use a CO2-sorbent replacement 
schedule developed by a rebreather manufacturer only if the 
manufacturer analyzed the protocol results using the statistical 
procedures specified by NEDU (Ex. 14 and 15).
    The canister-testing protocol developed by NEDU addresses the three 
factors recommended by the commenter in Ex. 2-98: Depth, exercise level 
(ventilation rate), and water temperature. Depth is the maximum depth 
at which a diver would use the CO2-sorbent material, which 
for the permanent variance is 130 fsw. We selected three combinations 
of ventilation rates and CO2-injection rates from the NEDU 
protocol to simulate three diverse levels of exercise (light, moderate, 
and heavy). The four water temperatures used in the NEDU protocol are 
40, 50, 70, and 90 degrees F (4.4, 10.0, 21.1, and 32.2 degrees C, 
respectively); these temperatures represent the wide range of water 
temperatures that Dixie's recreational diving instructors are likely to 
encounter. We revised the NEDU protocol slightly by: Limiting the 
maximum depth to 130 fsw; requiring an O2 fraction of 0.28 
in a nitrox breathing gas (this fraction being the maximum 
O2 concentration permitted at this depth by the permanent 
variance); providing tolerance limits for water temperatures; and 
defining canister duration as the time taken to reach 0.005 ATA of 
CO2 (the CO2 level specified in the permanent 
variance at which divers are to eliminate excessive CO2 in 
the breathing gas or terminate the dive). In addition, our protocol 
uses only mandatory language, and expressly prohibits the use of 
replacement schedules based on extrapolation of the protocol results. 
OSHA prohibits extrapolation of the protocol results because the 
statistical-analysis procedures developed by NEDU (Ex. 15) do not 
provide a method for estimating the duration of CO2-sorbent 
materials beyond the results obtained during the canister-testing 
trials. OSHA believes this approach significantly improves the validity 
and reliability of the replacement schedules derived from these 
results. After thoroughly reviewing the NEDU canister-testing protocol 
and adapting it the conditions of the permanent variance, we believe 
that CO2-sorbent replacement schedules based on the 
requirements of Appendix A of the permanent variance will enable Dixie 
to replace CO2-sorbent materials in a timely manner, thereby 
ensuring the health and safety of its divers.
    While we are confident that CO2-sorbent replacement 
schedules developed according to Condition (10) of the permanent 
variance will protect divers under ordinary diving conditions, we 
believe that these schedules do not address a condition that can 
seriously compromise canister effectiveness: Moisture in the canister, 
which usually results from canister flooding. Based on our review of 
the record, we find that moisture traps and moisture sensors can 
effectively control this condition. In this regard, proposed Condition 
A.2 required the use of moisture traps and moisture sensors. Several 
commenters (Exs. 2-101, 2-105, and 2-117) claimed that existing 
rebreathers already use moisture traps. The commenter in Ex. 2-101 
stated, without explanation, that ``making them a requirement would be 
restrictive.'' This commenter also asserted that moisture sensors are 
unnecessary because CO2 sensors perform the same function. 
(The commenter did not specify the term ``function,'' but we assume 
that it refers to the capability to indicate canister flooding.) A 
second commenter (Ex. 2-105) noted that moisture sensors would be an 
important safety feature, but asserted that they were not available 
commercially. However, another commenter (Ex. 2-117) claimed that 
moisture sensors are available from several companies. One commenter 
(Ex. 2-105) noted that excessive moisture can impair electrical systems 
in rebreathers, and asked us to specify where to place the moisture 
sensors to prevent these problems.
    Moisture traps are necessary to keep water out of the canisters 
because water leakage into canisters can substantially reduce the 
CO2-absorbing properties of the sorbent material. Moisture 
sensors, in turn, detect excessive water or flooding inside the 
canister that can compromise the CO2-sorbent material. 
Moisture sensors, therefore, warn the diver of hazardous water leakage 
into the canister. The commenters in Exs. 2-101, 2-105, and 2-117 noted 
that

[[Page 71248]]

moisture traps are available commercially and that existing rebreathers 
routinely use them. The information in Ex. 2-117 also indicates that 
moisture sensors are commercially available. While we believe that 
rebreather manufacturers should place moisture sensors on the 
inhalation side of the breathing loop, we leave the design and location 
of moisture sensors and moisture traps to their technical expertise. 
Dixie must ensure that its divers use these components consistent with 
the rebreather manufacturer's instructions, and that the moisture 
sensors alert the diver of moisture in the breathing loop in sufficient 
time to terminate the dive and return safely to the surface. We have 
incorporated these conditions into the permanent variance.
    In the proposed variance, Condition A.2 specified that rebreathers 
contain over-pressure valves. Regarding over-pressure valves, one 
commenter (Ex. 2-101) asked us to define the term ``over-pressure 
valve,'' while two commenters (Exs. 2-105 and 2-117) asserted that 
existing rebreathers already have over-pressure valves. One of these 
commenters (Ex. 2-105) noted that over-pressure valves are ``important 
protection to reduce the risk of [AGE] and associated pressure[-
]induced injuries and [rebreather] damage.''
    An over-pressure valve is a valve on the counterlung that releases 
breathing gas from the counterlung when the pressure reaches a set 
level; we have incorporated this meaning into the permanent variance. 
Rebreathers routinely are designed with over-pressure valves. These 
valves perform a critical safety function by helping to regulate 
breathing-gas volume and pressure.
    Condition A.2 of the proposed variance also specified that Dixie 
use redundant (i.e., at least two) CO2 sensors and redundant 
moisture sensors; it also required that these sensors function 
continuously. One commenter (Ex. 2-101) agreed with the proposed 
requirement for a continuously-functioning CO2 sensor, but 
did not believe that additional CO2 sensors were necessary. 
This commenter noted that both CO2 and moisture sensors will 
alert the diver whenever the breathing loop, most likely the 
CO2-sorbent material, is no longer capable of removing 
exhaled CO2. We agree with this commenter that 
CO2 and moisture sensors serve much the same purpose--to 
inform the diver of conditions (for example, reduced efficiency of the 
CO2-sorbent material) that may cause CO2 to 
accumulate in the breathing loop. By measuring the amount of 
CO2 in the inhaled breathing gas (after the gas passes 
through the sorbent material in the canister to remove CO2) 
CO2 sensors can detect an elevated CO2 level that 
may indicate depletion of the CO2-sorbent material because 
of canister flooding. An elevated CO2 level, in turn, warns 
the diver to take corrective action, including terminating the 
dive.5 As noted previously, moisture sensors detect 
excessive water or flooding inside the canister that can reduce the 
sorbent material's capacity to remove CO2 from the inhaled 
breathing gas. The independent functions performed by these sensors 
(i.e., a CO2 sensor measures CO2 in the breathing 
gas, while a moisture sensor detects excessive moisture in the 
canister) indicates that a malfunction in one sensor is unlikely to 
result in a malfunction in the other sensor.
---------------------------------------------------------------------------

    \5\ In addition, a CO2 sensor alerts the diver to 
increased CO2 levels in the inhaled breathing gas that 
may result from other conditions, including depleted sorbent 
material (saturated with CO2) and channeling or 
overbreathing (exhaled air bypassing the sorbent material).
---------------------------------------------------------------------------

    Several other conditions make sensor redundancy unnecessary. First, 
the symptoms of excessive CO2 do not develop as rapidly as 
the symptoms of O2 toxicity; 6 consequently, a 
properly trained and experienced diver will be able to recognize a 
number of effects associated with excessive CO2 and take 
appropriate action, including terminating the dive. These effects 
include: Reduced buoyancy (from the increased weight caused by canister 
flooding); shortness of breath (from CO2 displacing 
O2 in the diver's lungs); an increase in breathing 
resistance during inhalation (caused by difficulty moving the breathing 
gas through wet CO2-sorbent material); and a large number of 
bubbles vented through the rebreather's exhaust valve (venting related 
to the increased exhaust pressure caused by exhaling against wet 
CO2-sorbent material). Secondly, the permanent variance 
(Conditions (7) and (8)) requires that both the moisture sensor and 
CO2 sensor function continuously, ensuring early detection 
of a CO2-related problem by the diver. Lastly, Condition 
(30) of the permanent variance requires that the divers use an open-
circuit emergency-egress system (a ``bail-out'' system); this system 
will provide the divers with the capability to shift to a known, safe, 
and immediately-available breathing gas, and to terminate the dive 
safely whenever a CO2-related problem occurs.
---------------------------------------------------------------------------

    \6\ The rapid onset of symptoms resulting from O2 
toxicity provides a major rationale for requiring redundant 
O2 sensors.
---------------------------------------------------------------------------

    Based on this record, we find that: Carbon-dioxide sensors and 
moisture sensors provide independent means of detecting a 
CO2-related problem; symptoms related to excessive levels of 
CO2 develop more slowly than the symptoms of excessive 
O2; a properly trained and experienced diver will recognize 
the effects of excessive CO2 in sufficient time to take 
correct action; the requirement that CO2 sensors and 
moisture sensors be continuously functioning assures real-time 
detection of CO2-related problems; and the required bail-out 
system provides the diver with a safe means to terminate a dive 
following detection of a CO2-related problem. This record 
demonstrates that the proposed requirements for redundant 
CO2 sensors and redundant moisture sensors are unnecessary; 
we believe that the only basis for requiring redundant sensors is if 
the rebreather manufacturer includes them in the equipment design or 
specifications. Therefore, we have revised the conditions accordingly 
in the permanent variance.
    (b) Proposed Condition A.3, which required the use of flexible 
breathing bags (also known as ``counterlungs'') with rebreathers, 
elicited the following comment (Ex. 2-105):

    Not all rebreathers use breathing bags. However, they all employ 
some type of counter lung providing a compliant volume. Certain 
types of rebreathers utilize a large diaphragm or bellows assembly. 
There would be no purpose in mandating a particular counterlung 
configuration. The only regulation that could be mandated might be a 
minimum volumetric displacement.

    We consider breathing bags to be a type of counterlung. Even though 
the proposed variance used the terms ``breathing bags'' and 
``counterlungs'' interchangeably, we agree with the commenter that the 
permanent variance should not specify a particular counterlung 
configuration. We have revised the condition accordingly in the 
permanent variance. In addition, while we agree with the need to 
specify a minimum volumetric displacement, we believe that the 
rebreather manufacturer should determine this value. In this regard, 
Dixie must ensure that its divers use the counterlung according to the 
rebreather manufacturer's instructions, and the counterlung must 
displace enough volume to sustain the diver's respiration rate during 
any diving condition. We have incorporated these conditions into the 
permanent variance.
    (c) Proposed Condition A.4 addressed ``bail-out systems,'' which 
are supplemental breathing-gas systems used by divers for emergency 
ascent to the surface if the SCUBA malfunctions. The proposed condition 
specified that bail-out systems must integrate the

[[Page 71249]]

second stage of the SCUBA regulator with either a separate supply of 
emergency breathing gas or, for semi-closed-circuit and closed-circuit 
rebreathers, a diluent supply of emergency breathing gas. Two 
commenters (Exs. 2-100 and 2-105) responded to the proposed condition. 
The first commenter (Ex. 2-100) recommended that the system contain at 
least 35 cubic feet of emergency breathing gas. This volume was based 
on maximum consumption rates related to a number of variables, 
including water temperature, diver's thermal protection, speed of 
current, lung volume, and psychological stress. The second commenter 
(Ex. 2-105) stated that ``[a] bail-out system is a necessity for all 
rebreather use.''
    We agree that the bail-out system must enable the diver to 
terminate the dive safely under ``worst-case'' conditions. We believe, 
however, that the rebreather manufacturer is in the best position to 
determine what capacity of breathing gas is needed for safe operation 
of the bail-out system. In this regard, Dixie must ensure that its 
divers use the bail-out system according to the rebreather 
manufacturer's instructions. Dixie must also ensure that the bail-out 
system supplies sufficient emergency breathing gas to enable a diver to 
terminate the dive and return safely to the surface; the rebreather 
manufacturer can make this determination after Dixie provides the 
critical diving parameters (e.g., depth of dive and breathing rate). We 
have revised this condition accordingly in the permanent variance.
    (d) Proposed Condition A.5 specified requirements for information 
modules, which provide divers with information about the dive, 
including gas pressures, dive times, and descent and ascent rates. One 
commenter (Ex. 2-114) stated that the information module is a dive 
computer, that no rebreathers are available commercially that integrate 
dive computers with breathing systems, and that no dive computer 
``includes displays that directly warn of rebreather solenoid failure 
and excessive descent rates.'' In response, although we believe that it 
would be advantageous if dive computers included such information and 
warning displays, neither the proposed nor the permanent variance 
require it. The permanent variance requires Dixie to equip its divers 
with sensor and display systems that provide information on time, 
depth, ascent, and descent to divers who use closed-circuit 
rebreathers, and time, ascent, and descent information to divers who 
use semi-closed-circuit rebreathers. Both types of rebreathers must 
also have alarms or visual displays that warn the diver about excessive 
ascent and descent rates, as well as depth levels that are shallower 
than the ceiling-stop depth. The permanent variance does not require 
that a dive computer provide this capability.
    (e) Proposed Condition B required that closed-circuit rebreathers 
must use the following sensors: (1) Sensors that measure supply 
pressures for O2 and diluent gas; (2) depth sensors; (3) 
continuously-functioning and redundant temperature-compensated 
O2 sensors; and (4) continuously-functioning gas-loop and 
ambient water-temperature sensors. One commenter (Ex. 2-114) asserted 
that no existing rebreathers have continuously-functioning sensors for 
assessing gas-loop and ambient water temperatures. A second commenter 
(Ex. 2-117) contradicted this assertion, claiming that ``transducers 
and thermocouples are readily available from numerous companies'' for 
sensing pressure, depth, and ambient water temperature.
    We believe that temperature sensors are necessary for diver safety. 
Water-temperature sensors alert divers to the possibility of 
hypothermia. In addition, gas-loop temperature sensors and water-
temperature sensors allow divers to estimate the duration of their 
CO2-sorbent material. Efficiency of the CO2-
sorbent material deteriorates with decreasing temperatures (1991 NOAA 
Diving Manual, page 16-9). Thus, if divers are able to estimate the 
duration of their CO2-sorbent material, they can judge how 
long they can dive even if their CO2 sensors malfunction. 
Even if no existing rebreather incorporates temperature sensors as 
stated by the commenter in Ex. 2-114, Dixie's proposal to use such 
sensors will provide its divers with additional protection from 
temperature-related diving hazards; therefore, we have included this 
condition in the permanent variance.
    (f) For open-circuit SCUBA, proposed Condition C specified that the 
concentration of O2 must not exceed 40 percent (40%) of the 
breathing gas by volume, or, for any SCUBA, an O2 partial 
pressure of 1.40 ATA. Three commenters (Exs. 2-104, 2-106, and 2-113) 
recommended that we increase the partial pressure of O2 in 
the breathing-gas mixture from 1.4 to 1.6 ATA; these commenters 
asserted that recreational divers use the 1.6 ATA level regularly and 
safely, and that this use conforms to prevailing rebreather practices.
    In reply to these commenters, we believe that the research data 
cited in the proposed variance support our conclusion that a maximum 
O2 level of 1.40 ATA prevents O2 toxicity. The 
commenters provided no data or studies to support a maximum 
O2 exposure of 1.6 ATA, nor could we find any relevant data 
or study to support this recommendation for SCUBA diving. Evidence in 
the record (see Exs. 4, 4A, 5 (pages 3-5 through 3-15, P-15, and P-37 
through P-43), and 7) also demonstrates that breathing 1.6 ATA of 
O2 for extended periods increases the risk of O2 
toxicity compared to breathing 1.4 ATA of O2. The increased 
risk of O2 toxicity means that little tolerance exists for 
errors in O2 control and delivery equipment (e.g., 
O2 sensors, solenoids) and in calculating O2 
exposures.
    One commenter (Ex. 2-106) noted that we should consider both 
partial pressure and the duration of a dive when determining 
O2 exposure limits. Another commenter (Ex. 2-109) maintained 
that when they use high-oxygen breathing-gas mixtures, Dixie's 
recreational diving instructors and diving guides can dive for longer 
periods than when they use air as the breathing gas. Long dive 
durations extend a diver's exposure to elevated levels of oxygen, 
thereby increasing the diver's risk of developing O2 
toxicity, as well as DCS. Regarding the first comment (Ex. 2-106), we 
note that the O2 exposure limits specified in the proposed 
variance address both duration and level of O2 exposure. 
Similarly, in response to the second commenter (Ex. 2-109) we believe 
that Conditions C and E in the proposed variance address the concern 
about O2 toxicity expressed in Ex. 2-109; these proposed 
conditions cited research studies attesting to the safety of breathing 
O2 at a partial pressure of 1.40 ATA.
    (g) Condition D in the proposal limited the diving depth to ``no 
deeper than 130 fsw, or to a maximum oxygen partial pressure delivered 
to the diver of 1.40 ATA, whichever is most restrictive.'' The proposed 
condition elicited two comments. The first commenter (Ex. 2-99) stated 
that the Association of Diving Contractors, a trade association for the 
commercial-diving industry, requires decompression chambers at the dive 
site for dives deeper than 80 fsw or for dives outside the no-
decompression limits because ``there is still a possibility of a rapid 
ascent to the surface and hence, a [risk of AGE] brought on by 
eliminated or accelerated decompression [during] the ascent.'' The 
second commenter (Ex. 2-113) considered a maximum diving depth of 160 
or 170 fsw to be safe.
    The proposal reduced the risk of DCS resulting from ``eliminated or 
accelerated decompression'' to minimal

[[Page 71250]]

levels by requiring Dixie to ensure that its divers use nationally-
recognized no-decompression diving limits. The proposal lowered the 
risk of AGE by including a number of procedural and equipment 
requirements (e.g., specified O2 levels in the breathing-gas 
mixture and installation of O2 and CO2 sensors) 
that would minimize the need to make rapid (emergency) ascents to the 
surface during a dive; such ascents can cause AGE by overpressurizing 
the lungs. We believe that these proposed requirements would protect 
recreational diving instructors from the risks associated with DCS and 
AGE as well as, or better than, the provisions of 29 CFR 
1910.401(a)(2)(i) (the exemption in OSHA's CDO Standard for 
recreational diving instructors who use open-circuit, air-supplied 
SCUBA).
    We are not extending the depth limit to 160 or 170 fsw because we 
believe that doing so would place the diver at increased risk of 
nitrogen narcosis (as well as DCS). This increased risk would occur 
because the partial pressure of nitrogen in the breathing gas would be 
higher at 160-170 fsw than at 130 fsw. Previous research (Exs. 8, 9, 
and 10) demonstrates that hyperbaric air has significant narcotic 
effects even at 100 fsw or about 4.00 ATA (which is equivalent to a 
nitrogen partial pressure of 3.16 ATA). Using 28 percent (28%) 
O2 at 130 fsw (equivalent to about 1.40 ATA O2), 
the partial pressure of nitrogen would be 3.56 ATA, which is only 
slightly above the narcotic threshold specified by the previous 
research.
    (h) Proposed Condition E established O2-exposure limits 
for the breathing-gas mixtures, requiring that divers ``not exceed the 
24-hour single-exposure time limits specified by the 1991 NOAA Diving 
Manual or other oxygen-exposure limits, such as the Diving Science and 
Technology (DSAT) Oxygen Exposure Table, that provide a level of 
oxygen-toxicity protection at least equivalent to the level of 
protection afforded by the 1991 NOAA Diving Manual.'' The proposed 
condition received two comments. One commenter (Ex. 2-98) agreed with 
using the NOAA O2-exposure limits and a maximum 
O2 partial pressure of 1.4 ATA, stating that these limits 
``should not make the probability of oxygen toxicity * * * 
significantly different than when breathing air.'' At O2 
partial pressures above 1.3 ATA, this commenter recommended using the 
exposure durations specified in Table 15-1 of NOAA's 1991 Diving 
Manual. According to this commenter, using the NOAA table ``would make 
the probability of CNS O2 toxicity [extremely low].'' The 
second commenter (Ex. 2-100) asserted that a commercial subsidiary of 
the Professional Association of Diving Instructors developed the DSAT 
O2-exposure limits. The commenter contended that this 
subsidiary is not a recognized research authority and is ``motivated by 
profit and not necessarily the public benefit.'' According to this 
commenter:

    NOAA is a highly regarded and recognized source of diving 
research and operational protocol. If oxygen exposure limits are not 
to exceed the 24-hour single exposure time limits specified in the 
1991 NOAA Diving Manual[,] then citing additional sources of oxygen 
exposure limits[] that[,] by default, can only be the same or more 
conservative, is unnecessary and likely confusing.

    The comments in Ex. 2-98 support the maximum O2-exposure 
limit of 1.40 ATA specified in proposed Condition E. We agree with the 
commenter that CNS toxicity is the principal basis for specifying 
O2 exposure limits; accordingly, we discussed the need to 
prevent O2-induced CNS toxicity in detail in the proposed 
variance (62 FR 58999-59000).
    Regarding the comments in Ex. 2-100, we find that the 
O2-toxicity protection afforded to divers by the DSAT tables 
under the diving conditions specified in the variance application is at 
least equivalent to the level of safety that they get from the 
O2-exposure limits specified in the 1991 NOAA Diving Manual. 
The rationale provided in the proposed variance, as well as additional 
evidence submitted to the record (Exs. 4 and 7), support this 
conclusion.
    We have deleted the proposed general language that would have 
allowed Dixie to use non-NOAA O2-exposure limits (other than 
DSAT's) when these limits ``provide a level of oxygen-toxicity 
protection at least equivalent to the level of protection afforded by 
the 1991 NOAA Diving Manual.'' We believe this provision would 
introduce unnecessary uncertainty into the permanent variance when two 
adequate sources of O2 limits are already available for 
Dixie's use. Accordingly, we have revised this provision so that only 
the O2-exposure limits identified in the proposal are 
acceptable for the permanent variance; these limits are from the 1991 
NOAA Diving Manual, and the Enriched Air Operations and Resources Guide 
published in 1995 by the Professional Association of Diving Instructors 
(commonly referred to as the ``1995 DSAT Oxygen Exposure Table''). If 
other O2-exposure limits become available in the future, 
Dixie may request us to amend the permanent variance if it provides 
evidence that demonstrates their safety.
    (i) Proposed Condition F, which required that ``[n]itrogen shall be 
the only inert gas used to obtain the breathing-gas mixture,'' elicited 
two comments. One commenter (Ex. 2-103) asserted that recreational 
diving instructors and diving guides ``use gas blends to increase 
safety,'' implying that we should allow divers to use additional inert 
gases in the breathing-gas mixture. The second commenter (Ex. 2-113) 
also noted that tri-mix breathing gases (usually consisting of 
O2, N2, and He) have been used safely by many 
divers.
    Dixie proposed to use nitrogen as the only inert gas in the 
breathing-gas mixture under the specified conditions encountered by its 
divers (i.e., no-decompression dives to depths that do not exceed 130 
fsw). We need not consider the use of other inert gases as part of 
Dixie's permanent variance because Dixie did not seek our approval for 
the use of these gases. In any case, we believe that other inert gases 
(e.g., helium) have limited, if any, application under the conditions 
of this variance.
    (j) Proposed Conditions G, H, and I specified, respectively, the 
requirements for: Mixing and analyzing nitrox breathing-gas mixtures; 
compressors used to produce the nitrox breathing-gas mixtures; and 
SCUBAs exposed to high-pressure (pressures exceeding 300 psi) nitrox 
breathing-gas mixtures. These proposed conditions received four 
comments. The first commenter (Ex. 2-99) contended that the proposal 
did not provide specifications for O2-clean systems and 
measurement accuracy, and did not require the delivery of pre-mixed 
breathing gas ``from a reliable and competent source with high 
standards of documented quality control in place.''
    The second commenter (Ex. 2-105) asked: What is the basis for the 
O2-cleaning and O2-service requirements and the 
300 psi limit; at what minimum O2 level would these 
requirements apply; and how does OSHA define ``O2 
compatible.'' The commenter agreed with the use of oil-free compressors 
for mixing nitrox breathing-gas mixtures. The commenter noted, however, 
that employees who use these compressors need proper training and that 
``[s]pecial consideration must be given * * * to material use, material 
compatibility, system design, cleaning[,] and maintenance.'' The 
commenter described several hazards associated with mixing nitrox 
breathing gases, including: Partial-pressure blending into cylinders 
not prepared properly for O2 service; inducing 
O2-enriched breathing-

[[Page 71251]]

gas mixtures into the intake of compressors not designed for this 
purpose; and contamination of mixtures with hydrocarbons or oil. The 
commenter also recommended that we permit the use of O2 
analyzers that involve processes or mechanisms other than fuel-cells 
(e.g., gas chromatography, thermal conductivity), stating that such 
analyzers are accurate and ``have been in use worldwide for many 
years.''
    A third commenter (Ex. 2-116) made a number of recommendations to 
improve the safety of mixing nitrox breathing gases, including: 
Prohibit the use of oil-lubricated air compressors for mixing nitrox 
breathing gases containing 22-40 percent (22-40%) O2; 
require compressor and filter-system manufacturers to certify that 
their equipment is safe for the gases used in the breathing mixtures; 
require filter-system manufacturers to certify that the equipment used 
to clean air (for mixing with pure O2) produces 
O2-compatible breathing gases (i.e., breathing gases with 
low hydrocarbon levels); and require Dixie to monitor hydrocarbon 
contamination continuously. The commenter also submitted suggested 
revisions to the proposed text based on these recommendations.
    In reply to the commenters who requested information on which 
standards we would use to ensure accurate mixing and decontamination 
(especially hydrocarbon removal) of nitrox breathing gases, we note 
that Dixie must comply with 29 CFR 1910.101 (Compressed Gases (General 
Requirements)) and 29 CFR 1910.169 (Air Receivers), and applicable 
provisions of 29 CFR 1910.134 (Respiratory Protection). We agree with 
the comment in Ex. 2-105 that Dixie must use only properly trained 
personnel to mix breathing gases, and we have revised the permanent 
variance accordingly.
    To reduce the risk of O2 explosions, proposed Condition 
I required that SCUBA using high-O2 breathing-gas mixtures 
or pure O2 at pressures exceeding 300 psi be designed for 
O2 service. We derived the 300 psi limit by interpolating 
between the pressure limit (125 psi) for pure O2 and the 
pressure limit (500 psi) for compressed air specified in paragraph 
(i)(3) of 29 CFR 1910.430. We note, however, that Sec. 1910.430(i)(1) 
requires that equipment using O2 mixtures exceeding 40 
percent (40%) O2 by volume be designed for O2 
service; this requirement is based on the serious explosion risk 
associated with these O2 mixtures. Therefore, to reduce the 
risk of an O2 explosion, we have revised the permanent 
variance to require that SCUBA using breathing-gas mixtures that exceed 
40 percent (40%) O2 by volume at pressures over 125 psi be 
designed for O2 service.
    The proposed variance explained that an O2 analyzer that 
uses a fuel-cell process would be acceptable. However, O2 
analyzers based on other processes are also acceptable if they meet the 
requirements specified in Conditions 22 and 24(a) of the permanent 
variance.
    We agree with the commenter in Ex. 2-116 that Dixie must only use 
compressors and filters that manufacturers have certified will produce 
O2-compatible breathing-gas mixtures and will withstand the 
pressures involved. We believe these requirements substantially reduce 
the risk of O2-related explosions that can occur while 
mixing nitrox breathing gases under high pressure. Accordingly, we have 
incorporated these requirements into the permanent variance. Consistent 
with existing requirements in our CDO Standard, the permanent variance 
also requires an O2-service rating for compressors used for 
mixing high-pressure O2 whenever O2 fractions 
could exceed 40 percent (40%) by volume, as specified in paragraphs 
(i)(1) and (i)(2) of 29 CFR 1910.430.
    A fourth commenter (Ex. 2-117) stated that O2 analyzers, 
oil-less compressors, and filter-membrane systems are available 
commercially, and identified several companies that manufacture this 
equipment. These comments demonstrate that Dixie can readily meet the 
requirements in the permanent variance to use O2 analyzers, 
oil-less compressors, and filter-membrane systems when mixing nitrox 
breathing gases for rebreathers.
    (k) Proposed Condition J, which identified the no-decompression 
limits that Dixie must use, elicited three comments. One commenter (Ex. 
2-98) asserted that using high-O2 breathing-gas mixtures and 
diving in accordance with the no-decompression limits for air diving 
specified in the 1991 NOAA Diving Manual would reduce the risk of 
developing DCS. This commenter also recommended comparing other, 
``equivalent,'' no-decompression limits to the NOAA limits using a 
method that ``give[s] acceptable prediction of DCS probability when 
applied to data bases * * * where the dive profile is accurately known 
and the outcome (DCS or no DCS) is known.'' The commenter added that 
``the employer must show through adequate records that the DCS 
incidence using these other procedures [is] acceptably low,'' and 
asserted that ``an ongoing evaluation of safety through record keeping 
is essential.''
    Another commenter (Ex. 2-109) stated that the ``DSAT [no-
decompression air] tables, [which] are based on a shorter tissue half-
time, predict more rapid out-gassing and therefore allow much longer 
repetitive dives than the Navy [no-decompression air] tables would 
following similar bottom times and surface intervals.'' This commenter 
concluded, however, that the DSAT and U.S. Navy no-decompression limits 
provide similar levels of diver protection.
    The third commenter (Ex. 2-99) noted that the proposal did not 
consider ``omitted decompression'' that may occur while instructing and 
supervising novice divers. This commenter asserted that novice divers 
are ``prone to panic and thus more susceptible to an occurrence that 
[may require] * * * a decompression chamber on site.''
    Based on these comments, we conclude that the permanent variance 
needs to contain specific recommendations for no-decompression limits. 
Therefore, we have decided to remove the provision for ``equivalent'' 
no-decompression limits from the permanent variance. In doing so, we 
have carefully reviewed the findings and recommendations of Dr. R. W. 
Hamilton et al. in Ex. 4A (``DSAT Recreational Dive Planner: 
Development and Validation of No-Stop Decompression Procedures for 
Recreational Diving'' or ``the Planner''). Based on evidence cited in 
the Planner, we find that the scientific community accepts the DSAT no-
decompression tables; in addition, the program of extensive laboratory 
and field testing described in the Planner has demonstrated that the 
DSAT no-decompression tables are reliable and valid. Accordingly, the 
permanent variance allows Dixie to use the DSAT no-decompression tables 
and the no-decompression limits in the 1991 NOAA Diving Manual. Should 
other no-decompression limits become available in the future, Dixie may 
request us to amend the permanent variance. The application would need 
to demonstrate that the alternative no-decompression limits are at 
least as protective as the limits specified in the permanent variance.
    In an earlier response to the commenter in Ex. 2-109 in paragraph 
(d) of Part 1, we stated that NOAA's EAD formula can accurately 
estimate the DCS risk associated with nitrox breathing-gas mixtures 
based on equivalent nitrogen partial pressures and dive durations used 
in air diving. In addition, we disagree with this commenter's 
recommendation to adopt the U.S. Navy's no-decompression

[[Page 71252]]

limits. If we were to adopt these limits, we would unnecessarily 
restrict a major application of rebreathers (i.e., to use high levels 
of O2 in the breathing-gas mixture to extend the diving 
duration at a specific depth beyond the duration limit specified for 
air).
    As previously noted, the commenter in Ex. 2-99 expressed concern 
about diving-related incidents among novice divers, and implied that 
recreational diving instructors could be placed at risk of DCS or AGE 
under these conditions. We find that the risk of DCS is negligible 
under these conditions because the recreational diving instructors and 
novice divers will be using the NOAA or DSAT no-decompression tables 
and, therefore, will have no need to decompress. If a novice diver 
panics and makes a rapid ascent to the surface, the recreational diving 
instructor has been trained and has the necessary experience to follow 
the novice diver to the surface in an orderly fashion, thereby avoiding 
AGE.
    (l) Proposed Condition K.3, which specified the entries that divers 
must make in the diving log, received only one comment (Ex. 2-109). 
This commenter asked who would make the entries, stating that 
``frequently, other than the paying passengers * * * there is only the 
boat captain and the instructor [or] guide.'' Dixie Divers consists of 
several small commercial diving businesses that may have difficulty 
finding an employee to make entries in the diving log. After we 
published the proposed variance, Dixie asked us to revise the proposed 
condition to permit non-employees to make entries in the log. In 
addition, Dixie asked for a similar revision to proposed Condition L, 
which required the employer to verify the availability of treatment 
resources for medical emergencies, and to enter the verification in the 
diving log. Recognizing that any properly-qualified individual can make 
such entries, we have revised these provisions to permit Dixie to use 
non-employees to perform these tasks, but only after verifying their 
qualifications to do so. As the employer, Dixie will be responsible for 
assuring that the entries are made, regardless of who makes them.
    (m) Proposed Condition L required that Dixie confirm, on a daily 
basis before commencing diving operations, the availability of 
resources to treat a diving-related medical emergency, including 
``transportation * * * capable of delivering [an injured diver] to the 
decompression chamber within two hours of the injury.'' A commenter 
(Ex. 2-109) asked, ``Does this imply that if they are told a chamber is 
down or the Coast Guard can't confirm readiness, that they'll cancel 
the diving for that day?'' This commenter cautioned that ``if an 
accident happens after a significant amount of time has passed since 
the call, [a decompression chamber] may not be available at that time 
[because it's in use or undergoing maintenance].'' Based on these 
comments, we have clarified the requirement in the permanent variance 
by specifying that Dixie must confirm that the required treatment 
resources are ``available during each day's diving operations.''
    This commenter (Ex. 2-109) also argued that a decompression chamber 
should be within one hour from the dive site, instead of two hours, 
because of the ``relatively short distance off-shore that most Florida 
diving is done,'' and any ``[t]ime delay in getting an injured diver to 
a chamber can severely lessen the chances of full recovery from DCS.'' 
In reviewing this recommendation, we asked the Divers Alert Network 
(DAN) for assistance. DAN is the nation's leading private-sector 
organization providing DCS treatment recommendations to recreational 
divers and diving guides.
    With DAN's assistance, we identified 13 locations in Florida where 
suitable decompression chambers (6.0 ATA pressure capability, dual-
lock, multiplace) are available to the public for treating diving-
related medical emergencies. These chambers are in Pensacola, Panama 
City, Tallahassee, Gainesville, Jacksonville, Inverness, Orlando, 
Tampa, Fort Myers, Miami, Tavernier, Marathon, and Key West. These 13 
decompression-facility sites are within two hours transit time of any 
diving location in Florida, including off-shore, state-controlled 
waters. This transit time assumes the use of surface vehicle 
transportation traveling at the maximum legal speed limit, and includes 
30 minutes to make land when diving off-shore. In response to the 
commenter's statement that increases in treatment delay will ``severely 
lessen the chances of full recovery from DCS,'' we sought evidence with 
respect to one-hour or two-hour treatment delays from Dr. Edward D. 
Thalmann (Ex. 12). Dr. Thalmann is a world-renowned expert in treating 
diving-related medical emergencies among recreational divers; he is 
also the author of a number of scientific publications that address the 
causes and treatment of diving-related medical emergencies, especially 
DCS.
    In his reply (Ex. 13), Dr. Thalmann compared the risk of AGE and 
DCS among recreational divers who breathe air as opposed to nitrox. He 
then estimated the maximum delay in decompression treatment that would 
not worsen the treatment outcome. Dr. Thalmann noted that AGE is the 
most life-threatening diving-related medical emergency that can occur 
and that, to treat the most serious cases, a decompression chamber 
should be available at the dive site. He recognized that this 
recommendation went far beyond our existing requirements for some types 
of recreational diving (e.g., recreational diving instruction covered 
by paragraph (a)(2)(i) of 29 CFR 1910.401). In this regard, Dr. 
Thalmann stated that AGE ``is a rare occurrence and can be avoided with 
proper training and experience.'' Dr. Thalmann concluded that AGE ``is 
essentially independent of the time at depth'' and that ``there is no 
evidence * * * [to] suggest that the occurrence and outcome of [AGE] 
would be any different breathing a [n]itrox mixture [other] than air.''
    Regarding DCS, Dr. Thalmann asserted that research data show that 
the EAD approach (see the discussion above under paragraph (d) of Part 
1) is valid for computing no-decompression limits for O2 
partial pressures as high as 1.5 ATA. Based on this research and his 
field experience, Dr. Thalmann stated that DCS associated with 
breathing a nitrox gas mixture ``should not be substantially different 
in incidence and severity compared to diving on air[,] provided the 
[n]itrox no-decompression times are computed from accepted air no-
decompression limits using the [NOAA's] EAD [formula].'' Dr. Thalmann 
concluded that, within these constraints, ``there is no rationale for 
having different requirements for recompression chamber availability 
for air and [n]itrox no-decompression diving.''
    In addressing treatment delay, Dr. Thalmann reviewed available 
research studies, as well as data from DAN. According to Dr. Thalmann, 
the DAN data ``apply to recreational diving only where the vast 
majority of diving is within no-decompression limits.'' The results 
show that, for both pain-only DCS and DCS with severe neurological 
symptoms, a treatment delay of four hours can occur without diminishing 
treatment success (i.e., complete relief of symptoms). In conclusion, 
Dr. Thalmann stated, ``There is no significant body of evidence to 
suggest that, so long as one is diving within accepted no-decompression 
limits breathing air or [n]itrox, having access to a recompression 
facility within 4 hours is inadequate.''
    Dr. Thalmann's reply demonstrates several points: (1) The risk of 
AGE and DCS while breathing air or a nitrox gas

[[Page 71253]]

mixture should not differ when the dive conforms to accepted no-
decompression limits computed using the EAD approach; (2) maintaining a 
decompression chamber at the dive site to treat AGE is unnecessary and 
impractical because AGE is a rare occurrence that proper training and 
diving experience can prevent; and (3) as much as a four-hour delay in 
treating DCS does not diminish treatment outcomes. Based on this 
evidence, as well as a complete review of the existing record, we have 
decided to keep the provision permitting a two-hour timeframe for 
treating DCS, as proposed by Dixie.
    As part of his reply, Dr. Thalmann also recommended that we revise 
the phrase ``within two hours of the injury'' in proposed Condition L.1 
to read ``[2] hours after it is recognized that symptoms of [a 
decompression incident] are present.'' We acknowledge that the proposed 
language was unclear, but we also believe that the recommended wording 
may be confusing as well. Therefore, we have adopted new language in 
the permanent variance that expresses the requirement in terms of the 
maximum delay permitted in transporting the injured diver to a suitable 
decompression chamber; the revised language reads, ``* * * within two 
(2) hours travel time from the dive site.''
    (n) Proposed Condition N specified that Dixie was responsible for 
initial treatment of diving-related medical emergencies, and that it 
had to ensure that ``two personnel, one of whom shall be a diver 
employed by [Dixie] and both of whom are qualified in first-aid and the 
administration of treatment oxygen'' were available at the dive site 
for this purpose. Two commenters responded to this provision. The first 
commenter (Ex. 2-100) stated that the provision appears to be ``an 
attempt by Dixie Divers * * * to use the process to gain an unfair 
advantage in the recreational diving market by requiring all diving 
operations to contract with a `diver employed by the applicant.' '' The 
second commenter (Ex. 2-109) asserted that this requirement would be 
difficult to satisfy because the ``typical crew on a Florida boat is 
[a] captain and instructor.'' Dixie, as a small business with few 
employees, supported the second commenter's assertion, and requested 
that it be permitted to use qualified non-employees to meet this 
requirement.
    In reply to these comments, we note that Dixie and all other 
employers engaged in commercial diving operations must already provide, 
as appropriate, on-site support personnel to perform a variety of tasks 
(see, e.g., the requirements in paragraph (c) of 29 CFR 1910.410 and 
paragraph (c)(2) of 29 CFR 1910.426). These personnel can also perform 
duties as specified in proposed Condition N. We recognize, however, 
that the main purpose of this provision is to ensure that properly-
qualified personnel are available, regardless of their employment 
status. Therefore, we have revised this provision to permit Dixie to 
use non-employees for first-aid and O2 treatment. However, 
Dixie may do so only if it verifies their qualifications to perform 
these tasks before it starts the day's diving operations.
    (o) Proposed Condition O specified the training requirements for 
Dixie's recreational diving instructors and diving guides, including 
the requirement that an industry-recognized training agency certify 
that the divers are capable of using the diving equipment and 
breathing-gas mixtures needed for their recreational diving operations. 
The National Association of Underwater Instructors (NAUI) (Ex. 2-100) 
noted its affiliates offer ``a full range of training programs from 
Skin Diver through Instructor Course Director, including certification 
in oxygen enriched air, semi-closed circuit and closed circuit 
rebreather diver.'' Nonetheless, NAUI found the proposed condition 
ambiguous because it ``does not provide a definition of the diving 
industry or outline any process or criteria to evaluate and recognize a 
training agency that would establish the legitimacy of its training.''
    We agree with NAUI's comment that this provision in the proposed 
variance was confusing. Additionally, we believe that an employer is in 
the best position to determine if the training that its divers obtain 
is adequate to perform their jobs safely and effectively. Therefore, we 
have revised the proposed provision and have made the training 
requirement in the permanent variance performance-based; that is, Dixie 
must ensure that its employees receive training that enables them to 
perform safely and effectively while using open-circuit SCUBAs or 
rebreathers supplied with nitrox breathing-gas mixtures. However, we 
specified several critical tasks that the recreational diving 
instructors and diving guides employed by Dixie must be trained to 
perform safely and effectively, including: Recognizing the effects 
associated with breathing excessive CO2 and O2; 
taking appropriate action after detecting the effects of breathing 
excessive CO2 and O2; and properly evaluating, 
operating, and maintaining their open-circuit SCUBAs and rebreathers. 
We addressed the importance of recognizing and responding properly to 
the effects of excessive CO2 and O2 in our 
earlier discussions of Conditions A.2 and E of the proposed variance. 
Based on our review of Ex. 5 (especially pages 11-1 through 11-15), we 
believe that divers must also know how to evaluate, operate, and 
maintain their rebreathers under the diving conditions that they 
encounter as recreational diving instructors and diving guides. We have 
specified these revisions in Condition 38 of the permanent variance.

Part 3. Comments to Proposed Section III (Rationale for the Proposed 
Alternative)

    (a) In discussing Conditions A and B in the proposed variance, we 
noted that the existing exemption for recreational diving instructors 
in paragraph (a)(2)(i) of 29 CFR 1910.401 in our CDO Standard does not 
refer to rebreathers. We explained that ``such equipment was not 
available or in common use by recreational diving instructors when 
OSHA's [CDO] Standard was promulgated in 1977'' (62 FR 58999, first 
column). A commenter (Ex. 2-109) noted that this statement gave the 
false impression that rebreather equipment ``is readily used by the 
recreational diving community.'' Regarding the experience of the 
recreational diving community with rebreathers, this commenter asserted 
that ``while the argument can be made that [rebreathers have] been used 
safely within the scientific and commercial diving industries, it can 
also be argued that those divers are more highly trained and the 
operations more closely monitored than is the norm in the recreational 
diving industry.''
    Our discussion of the rationale for Conditions A and B as proposed 
noted that ``data related to the reliability and safety of [rebreather 
equipment] are difficult to obtain because its use by recreational 
divers is still uncommon''; however, we now believe that data are 
available showing that recreational diving instructors and diving 
guides can use rebreathers safely and reliably. We revised our opinion 
after reviewing Ex. 5 (especially pages 2-2, 7-1, and 7-2), which shows 
that various military organizations have a 50-year history of using 
rebreathers safely, scientific and technical divers have been doing so 
for over 20 years, and, currently, recreational diving instructors and 
diving students safely perform rebreather diving. We believe, 
therefore, that we have sufficient knowledge about rebreather 
technology and diving procedures to determine that the conditions 
specified in the permanent

[[Page 71254]]

variance will protect Dixie's recreational diving instructors and 
diving guides at least as well as having an on-site decompression 
chamber.
    (b) The rationale for proposed Conditions C through E justified the 
use of DSAT's Oxygen Exposure Table (62 FR 58999, second and third 
columns). This rationale elicited one comment (Ex. 2-109). This 
commenter stated that specifying time limits in the DSAT Oxygen 
Exposure Table in terms of total dive time ``is * * * a very common 
industry practice and not some great concession on Dixie's part, as the 
wording of the sentence would perhaps lead you to believe.'' In this 
case, we agree that the use of a common industry practice will enable 
Dixie to comply with the permanent variance without additional effort, 
while providing adequate diver protection.
    (c) Proposed Condition K provided a rationale for using dive-
decompression computers, noting that no-decompression limits for 
repetitive dives can involve ``tedious and time-consuming calculations 
* * * made by hand.'' It concluded that dive-decompression computers 
would ``assist divers in decreasing their exposure to excessive ascent 
rates, oxygen toxicity, and DCS that could result from errors in 
calculating repetitive no-decompression diving schedules manually.'' 
(62 FR 59000, third column.) The single commenter (Ex. 2-109) on this 
point claimed that manual calculations ``[can be] taught in the first 
or second lecture of most entry-level [SCUBA] classes'' and performed 
in a couple of minutes. This commenter also asserted that manual 
calculations may provide an additional margin of safety from DCS 
because they typically determine decompression using the deepest depth 
attained during a dive. By contrast, dive-decompression computers may 
reduce decompression (and therefore increase the risk of DCS) by 
``measur[ing the] exact depth every few seconds and recalculat[ing 
decompression] based on actual depth.''
    In reply, we note that Condition K as proposed allowed Dixie the 
flexibility to use either manual calculations or dive-decompression 
computers. Nevertheless, manual calculation is subject to human error, 
and computer use can reduce such error. The permanent variance will 
reduce problems associated with using dive-decompression computers to 
avoid decompression by restricting the no-decompression limits to the 
most recent decompression tables and formulas published by NOAA and 
DSAT.
    (d) The rationale for proposed Conditions O and P addressed the 
requirements for diver certification, noting that ``Condition O 
provides general uniformity to the diver qualification and training 
process, as well as quality control over the certifying agencies.'' (62 
FR 59001, third column.) A commenter (Ex. 2-109) stated that the 
certification requirement imposed no burden on Dixie because it was 
consistent with existing industry practice; in addition, the 
requirement was unlikely to bring uniformity to diver qualifications 
because ``different dive stores, certifying under the same national 
standards, can still turn out divers [and] instructors of varying 
proficiency levels.'' In reply, we note that we do expect these 
requirements to make training programs more uniform (than is presently 
the case) in the way that they train recreational diving instructors 
and diving guides, and this uniformity should substantially reduce much 
of the variability in diver proficiency.

Part 4. Comments to Proposed Section VI (Issues)

    In the proposal, we invited the public to submit information and 
specific comments and rationale on nine other issues. Only one 
commenter (Ex. 2-109) did so. This commenter addressed the first issue, 
which requested commenters to differentiate the underwater tasks and 
types of diving performed by recreational diving instructors and diving 
guides, and to relate these differences to the probability of 
experiencing diving-related medical problems. The commenter stated 
that, during training dives, recreational diving instructors ``will 
probably do multiple ascents * * * but may be exposed to less time in 
the water than a dive guide since students generally are excited and 
[consume more air] than experienced divers.'' The commenter stated 
that, during the ascent-training phase, recreational diving instructors 
must ``make multiple, generally rapid, ascents with each of the 
students, increasing the chances of a DCS hit.'' The commenter added 
that recreational diving instructors are ``at a slightly greater risk 
[than diving guides] of AGE from the ascents and perhaps a slightly 
elevated chance of DCS due to rapid ascents,'' although ``[t]he 
likelihood of the instructor getting DCS or AGE * * * is probably 
extremely small.''
    Regarding diving guides, the commenter asserted that it escorts 
experienced divers who, typically, are less excitable than novice 
divers; based on this assumption, the commenter asserted that 
experienced divers would consume breathing gases at slower rates than 
novice divers. The commenter concluded that slow rates of gas 
consumption would extend dive durations which, combined with the deeper 
dives made by diving guides compared to recreational diving 
instructors, would increase the diving guides' risk of DCS. In response 
to this commenter, we refer to our earlier discussion of this issue in 
Part I. In this discussion, we agreed that ``using high-O2 
nitrox breathing-gas mixtures would increase the risk of DCS,'' but 
concluded that ``the resulting risk would be comparable to using the 
equivalent partial pressure of nitrogen in air for that extended 
period.''

Part 5. General Comments to the Proposed Variance

    One commenter (Ex. 2-105) indicated that a number of topics needed 
clarification or were ``so controversial or comprehensive in nature 
that this level of detail in a policy document may not be 
appropriate.'' These areas are: Validating dive-decompression 
computers, including the programmable safety factors used in these 
computers; updating decompression data; identifying programmable gas-
percentage options; using failure mode and effects analysis of critical 
components and assemblies to develop consensus regarding the general 
safety and accuracy of dive-decompression computers; determining the 
relevance of, and necessity for, monitoring environmental temperatures 
and the breathing-loop gases in closed-circuit rebreathers; and 
recognizing standards developed by the equipment manufacturers. The 
commenter stated that ``[t]o expand on just a few of [these areas] 
would make this document much [too long].'' Nevertheless, the commenter 
asserted, without explanation, that ``from a standpoint of technical 
diving facts [the proposed variance] is grossly inaccurate and in many 
cases written with twisted facts,'' and that the ``[proposed] variance 
as written has the potential to expose employees (i.e.[,] dive shop 
technicians, instructors) to dangerous situations.''
    In large part, these areas of concern address the safety and 
standardization of dive-decompression computers. Under the permanent 
variance, use of dive-decompression computers is optional; however, if 
Dixie uses these computers, it must also provide its divers with 
specific decompression information. Regardless of computer use or 
availability, Dixie must have hard-copy decompression tables at the 
dive site. Thus, the permanent variance specifies the conditions that 
Dixie must meet to ensure that its employees' diving activities conform 
to accepted

[[Page 71255]]

no-decompression practices, whether or not Dixie uses dive-
decompression computers.
    Another commenter (Ex. 2-109) stated that ``[t]o retailers * * * 
nitrox is marketed as a new profit center. In an industry with flat 
growth over the past few years, and where profit margins are small to 
begin with, nitrox * * * can be sold to the diving consumer as a 
`safer' alternative to air, thus generating more profits * * * through 
the sale of classes and equipment specific to nitrox.'' Regarding 
diving safety, this commenter asserted that the high level of diving 
skills acquired by commercial divers made them safer than recreational 
diving instructors and diving guides, and referred to statistics from 
the Divers Alert Network (DAN) to support this assertion:

[T]he statistics [for 1996] show that 0.2% of the reported accidents 
involved commercial divers, but 17.1% of the accidents involved 
Instructors or Divemasters (dive guides). The latter are the same two 
categories * * * who make up Dixie Diver's employees who would be 
exempt under the variance. In 1995, the numbers were 0.5% for 
commercial divers versus 15.9% for instructors[-] divemasters. In 1994, 
the numbers were 0.0% for commercial divers and 21.5% for instructors[-
]divemasters.

    The statistics cited by this commenter do not address the principal 
conditions specified in the permanent variance (i.e., recreational 
diving instructors and diving guides who make no-decompression dives 
using nitrox breathing-gas mixtures). In a recent editorial in Alert 
Diver (Ex. 16, page 2), DAN's director (Dr. Peter B. Bennett) addressed 
the safety of nitrox dives made by recreational divers (which includes 
sports divers, as well as recreational diving instructors and diving 
guides). Dr. Bennett stated that ``[b]etween 1990 and 1993 DAN 
collected data on 21 cases of mixed-gas diving injuries. In 1994 there 
were 10, and in 1996, 16 injuries occurred. The 1996 data [are] based 
on 23 nitrox or mixed-gas injuries requiring recompression treatment. * 
* * The International Association of Nitrox and Technical Divers * * * 
certified 17,780 U.S. nitrox divers from 1985 to 1996.'' Based on this 
information, an average of less than 0.001 per cent of recreational 
divers who use nitrox breathing-gas mixtures are injured each year. 
Additionally, both Dr. Bennett (Ex. 16, pages 2 and 6) and other DAN 
representatives (Ex. 4A, page 60) admit that valid comparisons cannot 
be made between different categories of divers because adequate 
baseline data (e.g., the number and types of dives made by all divers 
in a category) are not available. In conclusion, we believe that the 
protections afforded by the conditions specified in the permanent 
variance will reduce the prevalence of diving-related injuries among 
Dixie's recreational diving instructors (who also have substantial 
experience in using nitrox breathing-gas mixtures) below the already 
low injury rates cited in Dr. Bennett's editorial.

Part 6. Our Revisions to the Proposed Variance

    (a) When divers use rebreathers, proposed Condition A.4 provided 
for a supplemental supply of breathable gas during emergency egress 
(referred to as the ``bail-out system''); this supply would consist of 
a diluent breathing gas connected to the second stage of the regulator. 
We have added a phrase to the permanent variance to address alternative 
means of emergency egress when open-circuit SCUBA provides the nitrox 
breathing-gas mixture. It allows Dixie to use the reserve breathing-gas 
supplies specified in paragraph (c)(4) of 29 CFR 1910.424 for this 
purpose. This alternative, specified in Condition (30)(b)(i) in the 
permanent variance, is an existing requirement for open-circuit SCUBA.
    When the bail-out system consists of a separate supply of emergency 
breathing gas, Condition A.1 of the proposed variance permitted Dixie 
to use air as the emergency breathing gas. The permanent variance 
retains this provision.
    (b) Conditions A.5.a and A.5.b in the proposed variance specified 
the use of an information module that provides time, depth, ascent, and 
descent data to divers who use closed-circuit rebreathers, and time, 
ascent, and descent information to divers who use semi-closed-circuit 
rebreathers. Proposed Condition A.5.c required both types of 
rebreathers to have alarms or visual displays that warn the diver about 
excessive ascent and descent rates, as well as depth levels that are 
shallower than the ceiling-stop depth. While Dixie's recreational 
diving instructors and diving guides could use dive-decompression 
computers for this purpose, we believe that such computers are 
unnecessary because the divers will be diving within no-decompression 
limits, and the technical capability of dive-decompression computers 
exceeds the requirements of no-decompression dives. An information 
module that provides the divers with the specified dive information 
will permit them to remain within no-decompression limits and to 
descend and ascend the water column at the rates specified by the 
diving tables. We believe, therefore, that the information module will 
ensure that Dixie's divers remain as safe as they would if they used 
dive-decompression computers.
    (c) Proposed Condition A.5.c also requires that, for both semi-
closed-circuit and closed-circuit rebreathers, the information module 
must warn the diver of low battery voltage. As noted in Ex. 5 (page P-
59), a partial or total electronic failure interferes with sensor and 
control systems and may have serious safety consequences for the diver. 
We believe that the diver's safety depends on properly-operating 
electrical power supplies and electrical and electronic circuits. 
Accordingly, we have revised the proposal by requiring that Dixie 
perform the following procedure: ``Before each day's diving operations, 
and more often when necessary, * * * ensure that the electrical power 
supplies and electrical and electronic circuits in each rebreather are 
operating as required by the rebreather manufacturer's instructions.'' 
Condition (12) of the permanent variance contains this revision.
    (d) Proposed Conditions B.1 and G.1.c addressed O2 
sensor and control requirements for closed-circuit rebreathers. 
Conditions (13) through (17) in the permanent variance consolidate 
these requirements in a single location.
    (e) For closed-circuit rebreathers, proposed Condition G.1.c 
specifies the use of O2 sensors to assess the O2 
fraction in the breathing loop, while proposed Condition G.1.d requires 
Dixie to determine (i.e., calibrate) sensor accuracy according to the 
rebreather manufacturer's instructions. As noted in the proposal, 
maintaining accurate O2 partial pressures in the breathing 
loop is critical to diver health and safety. To assure safe operation 
of O2 sensors, we believe that the permanent variance must 
specify the frequency for assessing the accuracy of O2 
sensors. Such an approach is consistent with the rebreather community's 
use of regular diving-equipment assessments (see Ex.5, pages 4-1 
through 4-13, and 14-2). Condition (15) of the permanent variance, 
therefore, requires that ``[b]efore each day's diving operations, and 
more often when necessary, [Dixie] must calibrate O2 sensors 
as required by the sensor manufacturer's instructions[.]'' Removing 
inaccurate O2 sensors from service and replacing them with 
correctly-calibrated sensors is a logical and expected consequence of 
the calibration process; we are specifying this requirement in 
Conditions (15)(d) and (15)(e) of the permanent variance.

[[Page 71256]]

    (f) Proposed Condition G.1.c accepted O2 sensors only if 
they were electromechanical. Evidence in the record (Ex. 5, page 5-11) 
indicates that O2-sensor technology is undergoing continued 
development and refinement. We believe, therefore, that specifying 
``electromechanical'' O2 sensors is too limiting, and we 
have revised this provision to specify that Dixie must use 
O2 sensors approved by the rebreather manufacturer (see 
Condition (14)(b) in the permanent variance).
    (g) Condition G.1.d in the proposed variance required Dixie to 
maintain the accuracy of the equipment used to analyze O2 in 
the breathing-gas mixture ``in accordance with the manufacturer's 
instructions.'' We intended this requirement to apply to the analytic 
equipment used both to calibrate O2 sensors and to determine 
the O2 fraction in nitrox breathing-gas mixtures. To clarify 
this intention, we have included the requirement separately in 
Conditions (15)(b) and (22)(b) in the permanent variance.
    (h) We have clarified the provision in proposed Condition G.2.a 
that addressed the analysis of O2 in nitrox breathing-gas 
mixtures obtained from commercial suppliers. This revision requires 
Dixie to ensure that the supplier of the mixture analyzes the 
O2 fraction in the mixture in the charged tank after 
disconnecting the tank from the charging apparatus. This clarification 
prevents the supplier from using the O2 sensor on the 
charging apparatus for this purpose, a procedure that could result in 
an incorrect determination. The revised provision is in Condition 
(23)(b) of the permanent variance.
    (i) Proposed Conditions K.3 and K.4 required that Dixie maintain a 
diving log and decompression tables at the dive site. The diving log 
documents the critical dive parameters. Divers who do not use dive-
decompression computers must use the decompression tables; the tables 
also serve as a back-up resource to divers with dive-decompression 
computers. We have revised the proposed conditions to ensure that Dixie 
maintains a diving log and decompression tables at the dive sites for 
all diving operations covered by the permanent variance, whether or not 
its divers use a dive-decompression computer. The revised provision 
also clarifies that the decompression tables must be hard copies and 
conform to the no-decompression limits specified in Condition (28) of 
the permanent variance. Condition (37) of the permanent variance 
contains the revised requirements.
    (j) Regarding the term ``portable oxygen,'' proposed Condition M 
specified that ``the oxygen shall be available for administration to 
the diver during the entire period the diver is being transported to a 
decompression chamber.'' The O2 supplied for this purpose 
must be pure O2, and the injured diver must receive the 
O2 continuously from the time Dixie detects the diving-
related medical emergency until the diver begins treatment in a 
decompression chamber. We have revised the proposal to clarify these 
requirements. Therefore, Condition (33) in the permanent variance 
requires Dixie to ensure that the portable O2 equipment 
supplies pure O2 to the injured diver's transparent mask, 
and that sufficient O2 is available to treat injured divers 
until they reach a decompression chamber.
    (k) In the proposed variance, one provision (Condition G.1.d) 
required Dixie to maintain the accuracy of the equipment used to 
analyze the O2 fraction of the breathing gas ``in accordance 
with the manufacturer's instructions.'' To clarify which manufacturer 
is being addressed in this provision, we revised the relevant 
conditions of the permanent variance (Conditions (15)(b) and (22)(b)) 
to refer specifically to the manufacturer of the O2 analyzer 
(who seems to us to be in the best position to specify how its 
O2 analyzer should be calibrated). We have made similar 
revisions to other provisions of the permanent variance, including 
Condition (9) (which specifies calibration requirements for 
CO2 sensors) and to Condition (15) (which specifies the 
calibration requirement for O2 sensors).
    The permanent variance contains a general requirement (Condition 
(3)) to use rebreathers according to the manufacturer's instructions. 
We repeat this requirement in several other important conditions of the 
permanent variance. We have added this provision because SCUBA 
manufacturers select and develop the characteristics and parameters of 
SCUBA equipment, design and integrate the equipment accordingly, 
procure or manufacture the equipment components, and then assemble and 
test the final products. There is a wide range of SCUBA designs and 
capabilities, and there are no uniform standards for the design, 
function, and use of SCUBA. We believe, therefore, that the SCUBA 
manufacturer is in the best position to specify the components, 
configuration, and operation of its product. In addition, the 
rebreather conference held recently in Redondo Beach, California, 
recommended that ``[m]anufacturers must provide written procedures, pre 
and post dive checklists, and a schedule for required maintenance.'' 
The SCUBA manufacturers who attended the conference endorsed this 
recommendation (see Ex. 5, page 14-2).

V. Decision

    Dixie Divers, Inc. seeks a permanent variance from the 
decompression-chamber requirements of paragraphs (b)(2) and (c)(3)(iii) 
of 29 CFR 1910.423 and paragraph (b)(1) of 29 CFR 1910.426. These 
provisions require an employer to have a decompression chamber 
available and ready for use at the dive site to treat two diving-
related medical emergencies that employees may experience--
decompression sickness (DCS) and arterial-gas embolism (AGE). Divers 
may develop DCS after decompressing inadequately during dives in which 
they breathe a mixed gas (e.g., nitrox). AGE results from 
overpressurizing the lungs, usually during a rapid ascent to the 
surface; overpressurization causes the air sacs in the lungs to rupture 
and disperse bubbles into the pulmonary veins.
    These decompression-chamber provisions require employers to ensure 
that: Employees remain awake and in the vicinity of a decompression 
chamber for at least one hour after the dive whenever they make no-
decompression dives, dive to depths deeper than 100 feet of sea water, 
or use a mixed-gas breathing mixture (paragraph (b)(2) of 29 CFR 
1910.423); and a decompression chamber is located within five minutes 
from the dive site and is ready for use (paragraph (c)(3)(iii) of 29 
CFR 1910.423 and paragraph (b)(1) of 29 CFR 1910.426).
    In its variance application, Dixie stated that nitrox breathing-gas 
mixtures reduce the occurrence and severity of DCS, while the equipment 
and procedural safeguards specified in the variance application lower 
the risk of AGE. (See section II, ``Application for a Permanent 
Variance,'' of this notice for a thorough review of Dixie's variance 
application.) Dixie asserted that the risk of DCS and AGE for divers 
who use the SCUBA equipment and diving procedures proposed in the 
variance application would be equal to, or less than, that experienced 
by divers exempted from our CDO Standard. This exemption, specified in 
paragraph (a)(2)(i) of 29 CFR 1910.401, applies to recreational diving 
instructors who use compressed air supplied to open-circuit SCUBAs 
under no-decompression diving limits. Dixie concluded, therefore, that 
we should not require it to maintain a decompression chamber at the 
dive site if it complies with the

[[Page 71257]]

conditions proposed in the variance application.
    After reviewing the variance application, comments made to the 
record about the application, and other technical and scientific 
information submitted to the record, we have revised the proposed 
variance to require Dixie to use specific procedures and equipment 
safeguards for its divers when they engage in recreational diving 
instruction and perform services as diving guides. Therefore, under 
Sec. 6(d) of the OSH Act, and based on the record discussed above, we 
find that when Dixie complies with the conditions of the following 
order, its divers will be exposed to working conditions that are at 
least as safe and healthful as they would be if Dixie complied with 
paragraphs (b)(2) and (c)(3)(iii) of 29 CFR 1910.423 and paragraph 
(b)(1) of 29 CFR 1910.426.

VI. Order

    We issue this order authorizing Dixie Divers, Inc. to comply with 
the following conditions instead of complying with paragraphs (b)(2) 
and (c)(3)(iii) of 29 CFR 1910.423 and paragraph (b)(1) of 29 CFR 
1910.426:

Application of the Permanent Variance

    (1) This permanent variance applies only to the recreational diving 
instructors and diving guides (``divers'') employed by Dixie Divers, 
Inc. (designated as ``you'' or ``your'') when your:
    (a) Recreational diving instructors train diving students in the 
use of recreational diving procedures and the safe operation of diving 
equipment, including open-circuit, semi-closed-circuit, or closed-
circuit self-contained underwater breathing apparatus (SCUBA) during 
these training dives;
    (b) Diving guides lead small groups of trained sports divers who 
use open-circuit, semi-closed-circuit, or closed-circuit SCUBAs to 
local undersea diving locations for recreational purposes; and
    (c) Divers use a nitrox breathing-gas mixture consisting of a high 
percentage of oxygen (O2) (i.e., over 22 percent (22%) by 
volume) mixed with nitrogen and supplied by an open-circuit, semi-
closed-circuit, or closed-circuit SCUBA.
    (2) This permanent variance does not apply when your divers engage 
in diving activities other than recreational diving instruction or 
diving guide duties.

Equipment Requirements for Rebreathers

    (3) You must ensure that your divers use rebreathers (i.e., semi-
closed-circuit and closed-circuit SCUBAs) in accordance with the 
rebreather manufacturer's instructions.
    (4) Regarding CO2-sorbent materials in canisters:
    (a) You must ensure that each rebreather uses a manufactured (i.e., 
commercially pre-packed), disposable scrubber cartridge containing a 
CO2-sorbent material that:
    (i) Is approved by the rebreather manufacturer;
    (ii) Removes CO2 from your divers' exhaled gas; and
    (iii) Maintains the CO2 level in the breathable gas 
(i.e., the gas that your divers are inhaling directly from the 
regulator) below a partial pressure of 0.01 atmospheres absolute (ATA); 
or
    (b) You may use an alternative scrubber method if:
    (i) The rebreather manufacturer permits such use;
    (ii) You use the alternative method according to the rebreather 
manufacturer's instructions; and
    (iii) You demonstrate that the alternative method meets the 
requirements specified above in Condition (4)(a) of this order.
    (5) You must ensure that each rebreather has a counterlung that 
supplies a volume of breathing gas to your divers that is sufficient to 
sustain their respiration rate and contains an over-pressure valve.
    (6) You must ensure that each rebreather uses a moisture trap in 
the breathing loop, and that the moisture trap and its location in the 
breathing loop are approved by the rebreather manufacturer.
    (7) You must ensure that each rebreather has a continuously-
functioning moisture sensor that connects to a visual (e.g., digital, 
graphic, or analog) or auditory (e.g., voice, pure tone) alarm that 
warns your divers of moisture in the breathing loop in sufficient time 
to terminate the dive and return safely to the surface.
    (8) You must ensure that each rebreather contains a continuously-
functioning CO2 sensor in the breathing loop, and that the 
CO2 sensor and its location in the breathing loop are 
approved by the rebreather manufacturer. You must also integrate the 
CO2 sensor used in a rebreather with an alarm that:
    (a) Operates in a visual (e.g., digital, graphic, or analog) or 
auditory (e.g., voice, pure tone) mode;
    (b) Is readily detectable by your divers under the diving 
conditions in which they operate; and
    (c) Remains continuously activated when the inhaled 
CO2 level reaches and exceeds 0.005 ATA.
    (9) Before each day's diving operations, and more often when 
necessary, you must calibrate the CO2 sensor according to 
the sensor manufacturer's instructions. In doing so, you must:
    (a) Ensure that the equipment and procedures used to perform this 
calibration are accurate to within 10 percent (10%) of a CO2 
concentration of 0.005 ATA or less;
    (b) Maintain this accuracy as required by the sensor manufacturer's 
instructions;
    (c) Ensure that the calibration of the CO2 sensor 
demonstrates an accuracy to within 10 percent (10%) of a CO2 
concentration of 0.005 ATA or less;
    (d) Replace the CO2 sensor when it fails to meet the 
accuracy requirements specified above in Condition (9)(c) of this 
order; and
    (e) Ensure that the replacement CO2 sensor meets the 
accuracy requirements specified above in Condition (9)(c) of this order 
before you place a rebreather in operation.
    (10) As an alternative to using a continuously-functioning 
CO2 sensor, you may use schedules for replacing 
CO2-sorbent material provided by the rebreather 
manufacturer. You may use these CO2-sorbent replacement 
schedules only if:
    (a) The rebreather manufacturer has:
    (i) Developed the replacement schedules according to the canister-
testing protocol provided below in Appendix A of this order;
    (ii) Analyzed the canister-testing results using the statistical 
procedures described in U.S. Navy Experimental Diving Unit Report 2-99 
(see section VII (``References'') below); and
    (iii) Specified the replacement schedule in terms of the lower 
prediction line (or limit) of the 95% prediction interval. In this 
regard, the rebreather manufacturer may derive replacement schedules by 
interpolating among, but not by extrapolating beyond, the depth, water 
temperatures, and exercise levels used during canister testing; and
    (b) You replace the CO2-sorbent material in the canister 
as required by Condition (4) of this order.
    (11) You must ensure that each rebreather has an information module 
that provides:
    (a) Visual (e.g., digital, graphic, or analog) or auditory (e.g., 
voice, pure tone) displays that will effectively warn your divers of 
solenoid failure (when the rebreather uses solenoids) and other 
electrical weaknesses or failures (e.g., low battery voltage);
    (b) For semi-closed circuit rebreathers, visual displays for the 
partial pressure of CO2, or deviations

[[Page 71258]]

above and below a preset CO2 partial pressure of 0.005 ATA; 
and
    (c) For closed-circuit rebreathers:
    (i) Visual displays for the partial pressures of O2 and 
CO2, or deviations above and below a preset CO2 
partial pressure of 0.005 ATA and a preset O2 partial 
pressure of 1.40 ATA; and
    (ii) A visual display for the gas temperature in the breathing 
loop.
    (12) Before each day's diving operations, and more often when 
necessary, you must ensure that the electrical power supplies and 
electrical and electronic circuits in each rebreather are operating as 
required by the rebreather manufacturer's instructions.

Special Requirements for Closed-Circuit Rebreathers

    (13) You must ensure that closed-circuit rebreathers use supply-
pressure sensors for the O2 and diluent (i.e., air or 
nitrogen) gases and continuously-functioning sensors for detecting 
temperature in the inhalation side of the gas-loop and the ambient 
water.
    (14) You must ensure that:
    (a) At least two O2 sensors are located in the 
inhalation side of the breathing loop;
    (b) The O2 sensors are continuously-functioning, 
temperature-compensated, and approved by the rebreather manufacturer.
    (15) Before each day's diving operations, and more often when 
necessary, you must calibrate O2 sensors as required by the 
sensor manufacturer's instructions. In doing so, you must:
    (a) Ensure that the equipment and procedures used to perform the 
calibration are accurate to within 1 percent (1%) of the O2 
fraction by volume;
    (b) Maintain this accuracy as required by the manufacturer of the 
calibration equipment;
    (c) Ensure that the sensors are accurate to within 1 percent (1%) 
of the O2 fraction by volume;
    (d) Replace O2 sensors when they fail to meet the 
accuracy requirements specified above in Condition (15)(c) of this 
order; and
    (e) Ensure that the replacement CO2 sensors meet the 
accuracy requirements specified above in Condition (15)(c) of this 
order before you place a rebreather in operation.
    (16) You must ensure that closed-circuit rebreathers have:
    (a) A gas-controller package with electrically-operated solenoid 
O2-supply valves;
    (b) A pressure-activated regulator with a second-stage diluent-gas 
addition valve;
    (c) A manually-operated gas-supply bypass valve to add 
O2 or diluent gas to the breathing loop; and
    (d) Separate O2 and diluent-gas cylinders to supply the 
breathing-gas mixture.

O2 Concentration in the Breathing Gas

    (17) You must ensure that the fraction of O2 in the 
nitrox breathing-gas mixture:
    (a) Is greater than the fraction of O2 in compressed air 
(i.e., exceeds 22 percent (22%) O2 by volume);
    (b) For open-circuit SCUBA, never exceeds a maximum fraction of 
breathable O2 of 40 percent (40%) by volume or a maximum 
O2 partial pressure of 1.40 ATA, whichever exposes your 
divers to less O2; and
    (c) For rebreathers, never exceeds a maximum O2 partial 
pressure of 1.40 ATA.

Depth and O2 Partial Pressure Limits

    (18) Regardless of the diving equipment your divers use, you must 
ensure that they dive no deeper than 130 feet of sea water (fsw) or to 
a maximum O2 partial pressure of 1.40 ATA, whichever exposes 
them to less O2.
    (19) Regarding O2 exposure, you must:
    (a) Ensure that the exposure of your divers to partial pressures of 
O2 between 0.60 and 1.40 ATA does not exceed the 24-hour 
single-exposure time limits specified either by the 1991 National 
Oceanic and Atmospheric Administration Diving Manual (the ``1991 NOAA 
Diving Manual'') or by the report entitled Enriched Air Operations and 
Resources Guide, published in 1995 by the Professional Association of 
Diving Instructors (known commonly as the ``1995 DSAT Oxygen Exposure 
Table'') (see section VII (``References'') below); and
    (b) Determine your diver's O2-exposure duration using 
the diver's maximum O2 exposure (partial pressure of 
O2) during the dive and the total dive time (i.e., from the 
time the diver leaves the surface until the diver returns to the 
surface).

Mixing and Analyzing the Breathing Gas

    (20) You must ensure that only properly trained personnel mix 
nitrox breathing gases, and that nitrogen is the only inert gas used in 
the breathing-gas mixture.
    (21) When mixing nitrox breathing gases, you must mix the 
appropriate breathing gas before you deliver the mixture to the 
breathing-gas cylinders, using the continuous-flow or partial-pressure 
mixing techniques specified in the 1991 NOAA Diving Manual, or using a 
filter-membrane system.
    (22) Before the start of each day's diving operations, you must 
determine the O2 fraction of the breathing-gas mixture using 
an O2 analyzer. In doing so, you must:
    (a) Ensure that the O2 analyzer is accurate to within 1 
percent (1%) of the O2 fraction by volume; and
    (b) Maintain this accuracy as required by the manufacturer of the 
analyzer.
    (23) When the breathing gas is a commercially-supplied nitrox 
breathing-gas mixture, you must ensure that the supplier:
    (a) Determines the O2 fraction in the breathing-gas 
mixture using an analytic method that is accurate to within 1 percent 
(1%) of the O2 fraction by volume;
    (b) Makes this determination when the mixture is in the charged 
tank and after disconnecting the charged tank from the charging 
apparatus;
    (c) Documents the O2 fraction in the mixture; and
    (d) Provides you with a written certification of the O2 
analysis.
    (24) For commercially-supplied nitrox breathing-gas mixtures, you 
must ensure that the O2 is Grade A (also known as 
``aviator's oxygen'') or Grade B (referred to as ``industrial-medical 
oxygen''), and meets the specifications, including the purity 
requirements, found in the 1991 NOAA Diving Manual. In doing so, you 
must:
    (a) Ensure that the analytic method used to make this determination 
is accurate to within 1 percent (1%) of the O2 fraction by 
volume; and
    (b) Obtain a written certificate to this effect from the supplier.
    (25) Before producing nitrox breathing-gas mixtures using a 
compressor in which the gas pressure in any system component exceeds 
125 pounds per square inch (psi), you must:
    (a) Have the compressor manufacturer certify in writing that the 
compressor is suitable for mixing high-pressure air with the highest 
O2 fraction used in the nitrox breathing-gas mixture;
    (b) Ensure that the compressor is oil-less or oil-free and rated 
for O2 service unless you comply with the requirements of 
Condition (26) of this order; and
    (c) Ensure that the compressor meets the requirements specified in 
paragraphs (i)(1) and (i)(2) of 29 CFR 1910.430 whenever the highest 
O2 fraction used in the mixing process exceeds 40 percent 
(40%).
    (26) Before producing nitrox breathing-gas mixtures using an oil-
lubricated compressor to mix high-pressure air with O2, 
regardless of the

[[Page 71259]]

gas pressure in any system component you must:
    (a) Have the compressor manufacturer certify in writing that the 
compressor is suitable for mixing the high-pressure air with the 
highest O2 fraction used in the nitrox breathing-gas 
mixture;
    (b) Filter the high-pressure air to produce O2-
compatible air;
    (c) Have the filter-system manufacturer certify in writing that the 
filter system used for this purpose is suitable for producing 
O2-compatible air;
    (d) Continuously monitor the air downstream from the filter for 
hydrocarbon contamination; and
    (e) Use only uncontaminated air (i.e., air containing no 
hydrocarbon particulates) for the nitrox breathing-gas mixture.
    (27) You must ensure that diving equipment using nitrox breathing-
gas mixtures or pure O2 under high pressure (i.e., exceeding 
125 psi) conforms to the O2-service requirements specified 
in paragraphs (i)(1) and (i)(2) of 29 CFR 1910.430.

Use No-Decompression Limits

    (28) For diving conducted while using nitrox breathing-gas 
mixtures, you must ensure that each of your divers remains within the 
no-decompression limits specified for single and repetitive air diving 
and published in the 1991 NOAA Diving Manual or the report entitled 
Development and Validation of No-Stop Decompression Procedures for 
Recreational Diving: The DSAT Recreational Dive Planner, published in 
1994 by Hamilton Research Ltd. (known commonly as the ``1994 DSAT No-
Decompression Tables'') (see section VII (``References'') below).
    (29) You may permit your divers to use a dive-decompression 
computer designed to regulate decompression if the dive-decompression 
computer uses the no-decompression limits specified above in Condition 
(28) of this order and provides output that reliably represents those 
limits.

Emergency Egress

    (30) Regardless of the diving equipment your divers use (i.e., 
open-circuit SCUBA or rebreathers), you must ensure that the diving 
equipment consists of:
    (a) An open-circuit emergency-egress system (a ``bail-out'' system) 
in which:
    (i) The second stage of the regulator connects to a separate supply 
of emergency breathing gas; and
    (ii) The emergency breathing gas consists of air or the same nitrox 
breathing-gas mixture used during the dive; or
    (b) One of the following alternative bail-out systems:
    (i) For open-circuit SCUBAs, the emergency-egress systems specified 
in paragraph (c)(4) of 29 CFR 1910.424; or
    (ii) For semi-closed-circuit and closed-circuit rebreathers, a 
system configured so that the second stage of the regulator connects to 
a diluent supply of emergency breathing gas.
    (31) You must ensure that the bail-out system performs reliably and 
provides sufficient emergency breathing gas to enable your diver to 
terminate the dive and return safely to the surface.

Diving-Related Medical Emergencies

    (32) Before each day's diving operations, you must ensure that:
    (a) A hospital, qualified health-care professionals, and the 
nearest Coast Guard Coordination Center (or an equivalent rescue 
service operated by a state, county, or municipal agency) are available 
for diving-related medical emergencies;
    (b) These treatment resources are available when you notify them of 
the diving-related medical emergency;
    (c) A list of telephone or call numbers for these health-care 
professionals and facilities is readily available at the dive site; and
    (d) Transportation to a suitable decompression chamber is readily 
available when no decompression chamber is at the dive site, and that 
this transportation can deliver your injured diver to the decompression 
chamber within two (2) hours travel time from the dive site.
    (33) You must ensure that portable O2 equipment is 
available at the dive site to treat your injured divers. In doing so, 
you must ensure that:
    (a) This equipment delivers pure O2 to a transparent 
mask that covers the injured diver's nose and mouth; and
    (b) Sufficient O2 is available for administration to the 
injured diver from the time you recognize the symptoms of a diving-
related medical emergency until the injured diver reaches a 
decompression chamber for treatment.
    (34) Before each day's diving operations, you must:
    (a) Ensure that at least two individuals, either employees or non-
employees, qualified in first-aid and administering O2 
treatment are available at the dive site to treat diving-related 
medical emergencies; and
    (b) Verify their qualifications for this task.

Diving Logs and Decompression Tables

    (35) You must maintain a diving log at the dive site and ensure 
that:
    (a) Before starting each day's diving operations, the individual 
who verifies the availability of the treatment resources required above 
under Condition (32) of this order makes a signed entry to this effect 
in the diving log; and
    (b) The diving log contains the following information for each 
dive:
    (i) The time when the diver left the surface, left the bottom, and 
returned to the surface;
    (ii) The maximum depth of the dive; and
    (iii) If a diver uses a dive-decompression computer, the name of 
the manufacturer and the model and serial numbers.
    (36) Before starting each day's diving operations, you must:
    (a) Designate an employee or a non-employee to make the entries in 
the diving log; and
    (b) Verify that the designee understands the:
    (i) Diving and medical terminology required to make proper entries; 
and
    (ii) Procedures for making entries in the diving log.
    (37) You must ensure that a hard-copy of the decompression tables 
used for the dives (as specified above in Condition (28) of this order) 
is readily available at the dive site, whether or not your divers use 
dive-decompression computers.

Diver Training

    (38) You must ensure that your divers receive training that enables 
them to perform their work safely and effectively while using open-
circuit SCUBAs or rebreathers supplied with nitrox breathing-gas 
mixtures. Accordingly, your divers must be able to perform critical 
tasks safely and effectively, including, but not limited to:
    (a) Recognizing the effects of breathing excessive CO2 
and O2;
    (b) Taking appropriate action after detecting the effects of 
breathing excessive CO2 and O2; and
    (c) Properly evaluating, operating, and maintaining their diving 
equipment under the diving conditions they encounter.

The Order: Notification and Duration

    (39) You must notify the divers affected by this order using the 
same means that you used to inform them of the variance application.
    (40) This order remains effective until modified or revoked under 
section 6(d) of the Occupational Safety and Health Act of 1970.

Appendix A (Mandatory).--Testing Protocol for Determining the 
CO2 Limits of Rebreather Canisters

    If the employer replaces CO2-sorbent material using a 
schedule provided by

[[Page 71260]]

the rebreather manufacturer (hereafter, manufacturer), then the 
employer must ensure that the manufacturer developed the schedule 
according to the protocol specified below in this appendix. The 
employer must also: Use only the CO2-sorbent material 
specified by the manufacturer (and that is consistent with the 
requirements of Condition 10(b)(ii) of this order); ensure that the 
manufacturer analyzes the canister-duration results using the 
statistical analysis specified in U.S. Navy Experimental Diving Unit 
(NEDU) Report 2-99 (see Section VII (``References'') of the permanent 
variance); and ensure that the manufacturer specifies the replacement 
schedule in terms of the lower prediction line (or limit) of the 95% 
prediction interval.
    1. The manufacturer must use the following procedures to ensure 
that the CO2-sorbent material meets the specifications of 
the material's manufacturer: NATO CO2 absorbent-activity 
test; RoTap shaker and nested sieves to determine granule-size 
distribution; NEDU-derived Schlegel test to assess friability; and 
NEDU's MeshFit software to evaluate mesh size conformance to 
specifications.
    These procedures involve a quality-control assessment of the 
CO2-sorbent material. Canister durations are suspect if 
these procedures indicate that the CO2-sorbent material used 
in canister testing either exceeds or falls below the specifications 
provided by the material's manufacturer. Therefore, for the purposes of 
this canister-testing protocol, rebreather manufacturers must use only 
CO2-sorbent materials that meet the specifications provided 
by the material's manufacturer.
    2. While operating the rebreather at a maximum depth of 130 feet of 
sea water (fsw), the manufacturer must use a breathing machine to 
continuously ventilate the rebreather with breathing gas that is at 
100% humidity and warmed to a temperature of 98.6 degrees F (37 degrees 
C) in the heating-humidification chamber. The breathing gas must be a 
nitrox mixture, with the oxygen (O2) fraction maintained at 
0.28 (equivalent to 1.4 ATA of O2 at 130 fsw, the maximum 
O2 concentration permitted at this depth by the permanent 
variance); the manufacturer must measure the O2 
concentration of the inhalation breathing gas delivered to the 
mouthpiece.
    3. The manufacturer must test canisters using the following three 
ventilation rates (with required breathing-machine tidal volumes and 
frequencies, and CO2-injection rates, provided for each 
ventilation rate):

------------------------------------------------------------------------
                                          Breathing
Ventilation rates  Breathing-machine       machine        CO2-injection
  (liters/min.,      tidal volumes       frequencies     rates (liters/
    ATPS \1\)           (liters)        (breaths per     min., STPD \2\)
                                            min.)
------------------------------------------------------------------------
22.5               l.5                15                0.90
40.0               2.0                20                1.35
62.5               2.5                25                2.25
------------------------------------------------------------------------
\1\ ATPS means ambient temperature and pressure, saturated with water.
\2\ STPD means standard temperature and pressure, dry; the standard
  temperature is 0 degrees C.

The manufacturer must perform the CO2 injection at a 
constant (steady) and continuous rate during each testing trial. An 
employer cannot use a rebreather at a work rate higher than the work 
rates simulated in this testing protocol unless the manufacturer adds 
the appropriate combinations of ventilation-CO2-injection 
rates to the protocol.
    4. The manufacturer must determine canister duration using a 
minimum of four (4) water temperatures, including 40, 50, 70, and 90 
degrees F (4.4, 10.0, 21.1, and 32.2 degrees C, respectively). An 
employer cannot use a rebreather at a water temperature that is lower 
than the minimum, or higher than the maximum, water temperature used in 
this testing protocol unless the manufacturer adds a lower or higher 
temperature to the protocol.
    5. The manufacturer must monitor the breathing-gas temperature at 
the rebreather mouthpiece (at the ``chrome T'' connector) and ensure 
that this temperature conforms to the temperature of a diver's exhaled 
breath at the water temperature and ventilation rate used during the 
testing trial. (NEDU can provide the manufacturer with information on 
the temperature of a diver's exhaled breath at various water 
temperatures and ventilation rates, as well as techniques and 
procedures used to maintain these temperatures during the testing 
trials.)
    6. Testing must consist of at least eight (8) testing trials for 
each combination of temperature and ventilation-CO2-
injection rates. (For example, eight testing trials at 40 degrees F 
using a ventilation rate of 22.5 lpm at a CO2-injection rate 
of 0.90 liters/min.) While water temperature may vary slightly 
( 2.0 degrees F or 1.0 degree C) between each of the eight 
testing trials, the manufacturer must maintain strict control of water 
temperature ( 1.0 degree F or 0.5 degree C) within each 
testing trial. The rebreather manufacturer must use the average 
temperature for each set of eight testing trials in the statistical 
analysis of the resulting data.
    7. The testing-trial result is the time taken for the inhaled 
breathing gas to reach 0.005 ATA of CO2. Using the canister-
duration results from these testing trials, the rebreather manufacturer 
must: Analyze the canister-duration results using the repeated-measures 
statistics described in NEDU Report 2-99 (see Section VII 
(``References'') of the permanent variance); and specify the 
replacement schedule for CO2-sorbent materials in terms of 
the lower prediction line (or limit) of the 95% confidence interval.

VII. References

    This order cites the following references:

    (1) National Oceanic and Atmospheric Administration (1991). NOAA 
Diving Manual: Diving for Science and Technology. U.S. Government 
Printing Office, Washington, D.C.
    (2) Diving Science and Technology (1995). Analysis of Proposed 
Oxygen Exposure Limits for DSAT Oxygen Exposure Table Against 
Existing Database of Manned Oxygen Test Dives. Enriched Air 
Operations and Resource Guide. International PADI, Inc., Rancho 
Santa Margarita, California.
    (3) R. W. Hamilton, R. E. Rogers, M. R. Powell, and R. D. Vann 
(1994). Development and Validation of No-Stop Decompression 
Procedures for Recreational Diving: The DSAT Recreational Dive 
Planner. Hamilton Research, Ltd., Tarrytown, New York.
    (4) J. R. Clarke. ``Statistically Based CO2 Canister 
Duration Limits for Closed-Circuit

[[Page 71261]]

Underwater Breathing Apparatus.'' U.S. Navy Experimental Diving 
Unit, Report 2-99, 1999.
    Copies of these references are available from the Docket Office, 
Room N-2625, Occupational Safety and Health Administration, U.S. 
Department of Labor, 200 Constitution Avenue, NW, Washington, DC 
20210; telephone (202) 693-2350 or fax (202) 693-1648.

VIII. Authority and Signature

    The authority for this order is section 6(d) of the Occupational 
Safety and Health Act of 1970 (29 USC 655), Secretary of Labor's Order 
No. 6-96 (62 FR 111), and 29 CFR part 1905.

    Signed at Washington, DC, this 9th day of December 1999.
Charles N. Jeffress,
Assistant Secretary of Labor.
[FR Doc. 99-32824 Filed 12-17-99; 8:45 am]
BILLING CODE 4510-26-P