[Title 29 CFR 1910.94]
[Code of Federal Regulations (annual edition) - July 1, 2002 Edition]
[Title 29 - LABOR]
[Subtitle B - Regulations Relating to Labor (Continued)]
[Chapter Xvii - OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT]
[Part 1910 - OCCUPATIONAL SAFETY AND HEALTH STANDARDS]
[Subpart G - Occupational Health and Environmental Control]
[Sec. 1910.94 - Ventilation.]
[From the U.S. Government Printing Office]
29LABOR52002-07-012002-07-01falseVentilation.1910.94Sec. 1910.94LABORRegulations Relating to Labor (Continued)OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENTOCCUPATIONAL SAFETY AND HEALTH STANDARDSOccupational Health and Environmental Control
Sec. 1910.94 Ventilation.
(a) Abrasive blasting--(1) Definitions applicable to this paragraph-
-(i) Abrasive. A solid substance used in an abrasive blasting operation.
(ii) Abrasive-blasting respirator. A respirator constructed so that
it covers the wearer's head, neck, and shoulders to protect the wearer
from rebounding abrasive.
(iii) Blast cleaning barrel. A complete enclosure which rotates on
an axis, or which has an internal moving tread to tumble the parts, in
order to expose various surfaces of the parts to the action of an
automatic blast spray.
[[Page 196]]
(iv) Blast cleaning room. A complete enclosure in which blasting
operations are performed and where the operator works inside of the room
to operate the blasting nozzle and direct the flow of the abrasive
material.
(v) Blasting cabinet. An enclosure where the operator stands outside
and operates the blasting nozzle through an opening or openings in the
enclosure.
(vi) Clean air. Air of such purity that it will not cause harm or
discomfort to an individual if it is inhaled for extended periods of
time.
(vii) Dust collector. A device or combination of devices for
separating dust from the air handled by an exhaust ventilation system.
(viii) Exhaust ventilation system. A system for removing
contaminated air from a space, comprising two or more of the following
elements (a) enclosure or hood, (b) duct work, (c) dust collecting
equipment, (d) exhauster, and (e) discharge stack.
(ix) Particulate-filter respirator. An air purifying respirator,
commonly referred to as a dust or a fume respirator, which removes most
of the dust or fume from the air passing through the device.
(x) Respirable dust. Airborne dust in sizes capable of passing
through the upper respiratory system to reach the lower lung passages.
(xi) Rotary blast cleaning table. An enclosure where the pieces to
be cleaned are positioned on a rotating table and are passed
automatically through a series of blast sprays.
(xii) Abrasive blasting. The forcible application of an abrasive to
a surface by pneumatic pressure, hydraulic pressure, or centrifugal
force.
(2) Dust hazards from abrasive blasting. (i) Abrasives and the
surface coatings on the materials blasted are shattered and pulverized
during blasting operations and the dust formed will contain particles of
respirable size. The composition and toxicity of the dust from these
sources shall be considered in making an evaluation of the potential
health hazards.
(ii) The concentration of respirable dust or fume in the breathing
zone of the abrasive-blasting operator or any other worker shall be kept
below the levels specified in Sec. 1910.1000.
(iii) Organic abrasives which are combustible shall be used only in
automatic systems. Where flammable or explosive dust mixtures may be
present, the construction of the equipment, including the exhaust system
and all electric wiring, shall conform to the requirements of American
National Standard Installation of Blower and Exhaust Systems for Dust,
Stock, and Vapor Removal or Conveying, Z33.1-1961 (NFPA 91-1961), which
is incorporated by reference as specified in Sec. 1910.6, and subpart S
of this part. The blast nozzle shall be bonded and grounded to prevent
the build up of static charges. Where flammable or explosive dust
mixtures may be present, the abrasive blasting enclosure, the ducts, and
the dust collector shall be constructed with loose panels or explosion
venting areas, located on sides away from any occupied area, to provide
for pressure relief in case of explosion, following the principles set
forth in the National Fire Protection Association Explosion Venting
Guide, NFPA 68-1954, which is incorporated by reference as specified in
Sec. 1910.6.
(3) Blast-cleaning enclosures. (i) Blast-cleaning enclosures shall
be exhaust ventilated in such a way that a continuous inward flow of air
will be maintained at all openings in the enclosure during the blasting
operation.
(a) All air inlets and access openings shall be baffled or so
arranged that by the combination of inward air flow and baffling the
escape of abrasive or dust particules into an adjacent work area will be
minimized and visible spurts of dust will not be observed.
(b) The rate of exhaust shall be sufficient to provide prompt
clearance of the dust-laden air within the enclosure after the cessation
of blasting.
(c) Before the enclosure is opened, the blast shall be turned off
and the exhaust system shall be run for a sufficient period of time to
remove the dusty air within the enclosure.
(d) Safety glass protected by screening shall be used in observation
windows, where hard deep-cutting abrasives are used.
(e) Slit abrasive-resistant baffles shall be installed in multiple
sets at all small access openings where dust
[[Page 197]]
might escape, and shall be inspected regularly and replaced when needed.
(1) Doors shall be flanged and tight when closed.
(2) Doors on blast-cleaning rooms shall be operable from both inside
and outside, except that where there is a small operator access door,
the large work access door may be closed or opened from the outside
only.
(ii) [Reserved]
(4) Exhaust ventilation systems. (i) The construction, installation,
inspection, and maintenance of exhaust systems shall conform to the
principles and requirements set forth in American National Standard
Fundamentals Governing the Design and Operation of Local Exhaust
Systems, Z9.2-1960, and ANSI Z33.1-1961, which is incorporated by
reference as specified in Sec. 1910.6.
(a) When dust leaks are noted, repairs shall be made as soon as
possible.
(b) The static pressure drop at the exhaust ducts leading from the
equipment shall be checked when the installation is completed and
periodically thereafter to assure continued satisfactory operation.
Whenever an appreciable change in the pressure drop indicates a partial
blockage, the system shall be cleaned and returned to normal operating
condition.
(ii) In installations where the abrasive is recirculated, the
exhaust ventilation system for the blasting enclosure shall not be
relied upon for the removal of fines from the spent abrasive instead of
an abrasive separator. An abrasive separator shall be provided for the
purpose.
(iii) The air exhausted from blast-cleaning equipment shall be
discharged through dust collecting equipment. Dust collectors shall be
set up so that the accumulated dust can be emptied and removed without
contaminating other working areas.
(5) Personal protective equipment. (i) Employers must use only
respirators approved by the National Institute for Occupational Safety
and Health (NIOSH) under 42 CFR part 84 to protect employees from dusts
produced during abrasive-blasting operations.
(ii) Abrasive-blasting respirators shall be worn by all abrasive-
blasting operators:
(a) When working inside of blast-cleaning rooms, or
(b) When using silica sand in manual blasting operations where the
nozzle and blast are not physically separated from the operator in an
exhaust ventilated enclosure, or
(c) Where concentrations of toxic dust dispersed by the abrasive
blasting may exceed the limits set in Sec. 1910.1000 and the nozzle and
blast are not physically separated from the operator in an exhaust-
ventilated enclosure.
(iii) Properly fitted particulate-filter respirators, commonly
referred to as dust-filter respirators, may be used for short,
intermittent, or occasional dust exposures such as cleanup, dumping of
dust collectors, or unloading shipments of sand at a receiving point
when it is not feasible to control the dust by enclosure, exhaust
ventilation, or other means. The respirators used must be approved by
NIOSH under 42 CFR part 84 for protection against the specific type of
dust encountered.
(a) Dust-filter respirators may be used to protect the operator of
outside abrasive-blasting operations where nonsilica abrasives are used
on materials having low toxicities.
(b) Dust-filter respirators shall not be used for continuous
protection where silica sand is used as the blasting abrasive, or toxic
materials are blasted.
(iv) For employees who use respirators required by this section, the
employer must implement a respiratory protection program in accordance
with 29 CFR 1910.134.
(v) Operators shall be equipped with heavy canvas or leather gloves
and aprons or equivalent protection to protect them from the impact of
abrasives. Safety shoes shall be worn to protect against foot injury
where heavy pieces of work are handled.
(a) Safety shoes shall conform to the requirements of American
National Standard for Men's Safety-Toe Footwear, Z41.1-1967, which is
incorporated by reference as specified in Sec. 1910.6.
(b) Equipment for protection of the eyes and face shall be supplied
to the operator when the respirator design does not provide such
protection and to any other personnel working in the vicinity of
abrasive blasting operations.
[[Page 198]]
This equipment shall conform to the requirements of Sec. 1910.133.
(6) Air supply and air compressors. Air for abrasive-blasting
respirators must be free of harmful quantities of dusts, mists, or
noxious gases, and must meet the requirements for supplied-air quality
and use specified in 29 CFR 1910.134(i).
(7) Operational procedures and general safety. Dust shall not be
permitted to accumulate on the floor or on ledges outside of an
abrasive-blasting enclosure, and dust spills shall be cleaned up
promptly. Aisles and walkways shall be kept clear of steel shot or
similar abrasive which may create a slipping hazard.
(8) Scope. This paragraph (a) applies to all operations where an
abrasive is forcibly applied to a surface by pneumatic or hydraulic
pressure, or by centrifugal force. It does not apply to steam blasting,
or steam cleaning, or hydraulic cleaning methods where work is done
without the aid of abrasives.
(b) Grinding, polishing, and buffing operations--(1) Definitions
applicable to this paragraph--(i) Abrasive cutting-off wheels. Organic-
bonded wheels, the thickness of which is not more than one forty-eighth
of their diameter for those up to, and including, 20 inches in diameter,
and not more than one-sixtieth of their diameter for those larger than
20 inches in diameter, used for a multitude of operations variously
known as cutting, cutting off, grooving, slotting, coping, and jointing,
and the like. The wheels may be ``solid'' consisting of organic-bonded
abrasive material throughout, ``steel centered'' consisting of a steel
disc with a rim of organic-bonded material moulded around the periphery,
or of the ``inserted tooth'' type consisting of a steel disc with
organic-bonded abrasive teeth or inserts mechanically secured around the
periphery.
(ii) Belts. All power-driven, flexible, coated bands used for
grinding, polishing, or buffing purposes.
(iii) Branch pipe. The part of an exhaust system piping that is
connected directly to the hood or enclosure.
(iv) Cradle. A movable fixture, upon which the part to be ground or
polished is placed.
(v) Disc wheels. All power-driven rotatable discs faced with
abrasive materials, artificial or natural, and used for grinding or
polishing on the side of the assembled disc.
(vi) Entry loss. The loss in static pressure caused by air flowing
into a duct or hood. It is usually expressed in inches of water gauge.
(vii) Exhaust system. A system consisting of branch pipes connected
to hoods or enclosures, one or more header pipes, an exhaust fan, means
for separating solid contaminants from the air flowing in the system,
and a discharge stack to outside.
(viii) Grinding wheels. All power-driven rotatable grinding or
abrasive wheels, except disc wheels as defined in this standard,
consisting of abrasive particles held together by artificial or natural
bonds and used for peripheral grinding.
(ix) Header pipe (main pipe). A pipe into which one or more branch
pipes enter and which connects such branch pipes to the remainder of the
exhaust system.
(x) Hoods and enclosures. The partial or complete enclosure around
the wheel or disc through which air enters an exhaust system during
operation.
(xi) Horizontal double-spindle disc grinder. A grinding machine
carrying two power-driven, rotatable, coaxial, horizontal spindles upon
the inside ends of which are mounted abrasive disc wheels used for
grinding two surfaces simultaneously.
(xii) Horizontal single-spindle disc grinder. A grinding machine
carrying an abrasive disc wheel upon one or both ends of a power-driven,
rotatable single horizontal spindle.
(xiii) Polishing and buffing wheels. All power-driven rotatable
wheels composed all or in part of textile fabrics, wood, felt, leather,
paper, and may be coated with abrasives on the periphery of the wheel
for purposes of polishing, buffing, and light grinding.
(xiv) Portable grinder. Any power-driven rotatable grinding,
polishing, or buffing wheel mounted in such manner that it may be
manually manipulated.
(xv) Scratch brush wheels. All power-driven rotatable wheels made
from wire or bristles, and used for scratch cleaning and brushing
purposes.
[[Page 199]]
(xvi) Swing-frame grinder. Any power-driven rotatable grinding,
polishing, or buffing wheel mounted in such a manner that the wheel with
its supporting framework can be manipulated over stationary objects.
(xvii) Velocity pressure (vp). The kinetic pressure in the direction
of flow necessary to cause a fluid at rest to flow at a given velocity.
It is usually expressed in inches of water gauge.
(xviii) Vertical spindle disc grinder. A grinding machine having a
vertical, rotatable power-driven spindle carrying a horizontal abrasive
disc wheel.
(2) Application. Wherever dry grinding, dry polishing or buffing is
performed, and employee exposure, without regard to the use of
respirators, exceeds the permissible exposure limits prescribed in
Sec. 1910.1000 or other sections of this part, a local exhaust
ventilation system shall be provided and used to maintain employee
exposures within the prescribed limits.
(3) Hood and branch pipe requirements. (i) Hoods connected to
exhaust systems shall be used, and such hoods shall be designed,
located, and placed so that the dust or dirt particles shall fall or be
projected into the hoods in the direction of the air flow. No wheels,
discs, straps, or belts shall be operated in such manner and in such
direction as to cause the dust and dirt particles to be thrown into the
operator's breathing zone.
(ii) Grinding wheels on floor stands, pedestals, benches, and
special-purpose grinding machines and abrasive cutting-off wheels shall
have not less than the minimum exhaust volumes shown in Table G-4 with a
recommended minimum duct velocity of 4,500 feet per minute in the branch
and 3,500 feet per minute in the main. The entry losses from all hoods
except the vertical-spindle disc grinder hood, shall equal 0.65 velocity
pressure for a straight takeoff and 0.45 velocity pressure for a tapered
takeoff. The entry loss for the vertical-spindle disc grinder hood is
shown in figure G-1 (following Sec. 1910.94(b)).
Table G-4--Grinding and Abrasive Cutting-Off Wheels
------------------------------------------------------------------------
Minimum
Wheel exhaust
Wheel diameter (inches) width volume
(inches) (feet\3\/
min.)
------------------------------------------------------------------------
To 9............................................ 1\1/2\ 220
Over 9 to 16.................................... 2 390
Over 16 to 19................................... 3 500
Over 19 to 24................................... 4 610
Over 24 to 30................................... 5 880
Over 30 to 36................................... 6 1,200
------------------------------------------------------------------------
For any wheel wider than wheel diameters shown in Table G-4, increase
the exhaust volume by the ratio of the new width to the width shown.
Example: If wheel width=4\1/2\ inches, then
4.5/4x610 = 686 (rounded to 690).
(iii) Scratch-brush wheels and all buffing and polishing wheels
mounted on floor stands, pedestals, benches, or special-purpose machines
shall have not less than the minimum exhaust volume shown in Table G-5.
Table G-5--Buffing and Polishing Wheels
------------------------------------------------------------------------
Minimum
Wheel exhaust
Wheel diameter (inches) width volume
(inches) (feet\3\/
min.)
------------------------------------------------------------------------
To 9............................................ 2 300
Over 9 to 16.................................... 3 500
Over 16 to 19................................... 4 610
Over 19 to 24................................... 5 740
Over 24 to 30................................... 6 1,040
Over 30 to 36................................... 6 1,200
------------------------------------------------------------------------
(iv) Grinding wheels or discs for horizontal single-spindle disc
grinders shall be hooded to collect the dust or dirt generated by the
grinding operation and the hoods shall be connected to branch pipes
having exhaust volumes as shown in Table G-6.
Table G-6--Horizontal Single-Spindle Disc Grinder
------------------------------------------------------------------------
Exhaust
volume
Disc diameter (inches) (ft.\3\/
min.)
------------------------------------------------------------------------
Up to 12.................................................... 220
Over 12 to 19............................................... 390
Over 19 to 30............................................... 610
Over 30 to 36............................................... 880
------------------------------------------------------------------------
[[Page 200]]
(v) Grinding wheels or discs for horizontal double-spindle disc
grinders shall have a hood enclosing the grinding chamber and the hood
shall be connected to one or more branch pipes having exhaust volumes as
shown in Table G-7.
Table G-7--Horizontal Double-Spindle Disc Grinder
------------------------------------------------------------------------
Exhaust
volume
Disc diameter (inches) (ft.\3\/
min.)
------------------------------------------------------------------------
Up to 19.................................................... 610
Over 19 to 25............................................... 880
Over 25 to 30............................................... 1,200
Over 30 to 53............................................... 1,770
Over 53 to 72............................................... 6,280
------------------------------------------------------------------------
(vi) Grinding wheels or discs for vertical single-spindle disc
grinders shall be encircled with hoods to remove the dust generated in
the operation. The hoods shall be connected to one or more branch pipes
having exhaust volumes as shown in Table G-8.
Table G-8--Vertical Spindle Disc Grinder
------------------------------------------------------------------------
One-half or more of Disc not covered
disc covered ---------------------
----------------------
Disc diameter (inches) Exhaust Exhaust
Number \1\ foot\3\/ Number \1\ foot\3\/
min.) min.
------------------------------------------------------------------------
Up to 20.................... 1 500 2 780
Over 20 to 30............... 2 780 2 1,480
Over 30 to 53............... 2 1,770 4 3,530
Over 53 to 72............... 2 3,140 5 6,010
------------------------------------------------------------------------
\1\ Number of exhaust outlets around periphery of hood, or equal
distribution provided by other means.
(vii) Grinding and polishing belts shall be provided with hoods to
remove dust and dirt generated in the operations and the hoods shall be
connected to branch pipes having exhaust volumes as shown in Table G-9.
Table G-9--Grinding and Polishing Belts
------------------------------------------------------------------------
Exhaust
volume
Belts width (inches) (ft.\3\/
min.)
------------------------------------------------------------------------
Up to 3..................................................... 220
Over 3 to 5................................................. 300
Over 5 to 7................................................. 390
Over 7 to 9................................................. 500
Over 9 to 11................................................ 610
Over 11 to 13............................................... 740
------------------------------------------------------------------------
(viii) Cradles and swing-frame grinders. Where cradles are used for
handling the parts to be ground, polished, or buffed, requiring large
partial enclosures to house the complete operation, a minimum average
air velocity of 150 feet per minute shall be maintained over the entire
opening of the enclosure. Swing-frame grinders shall also be exhausted
in the same manner as provided for cradles. (See fig. G-3)
(ix) Where the work is outside the hood, air volumes must be
increased as shown in American Standard Fundamentals Governing the
Design and Operation of Local Exhaust Systems, Z9.2-1960 (section 4,
exhaust hoods).
(4) Exhaust systems. (i) Exhaust systems for grinding, polishing,
and buffing operations should be designed in accordance with American
Standard Fundamentals Governing the Design and Operation of Local
Exhaust Systems, Z9.2-1960.
(ii) Exhaust systems for grinding, polishing, and buffing operations
shall be tested in the manner described in American Standard
Fundamentals Governing the Design and Operation of Local Exhaust
Systems, Z9.2-1960.
(iii) All exhaust systems shall be provided with suitable dust
collectors.
(5) Hood and enclosure design. (i)(a) It is the dual function of
grinding and abrasive cutting-off wheel hoods to protect the operator
from the hazards of bursting wheels as well as to provide a means for
the removal of dust and dirt generated. All hoods shall be not less in
structural strength than specified in the American National Standard
Safety Code for the Use, Care, and Protection of Abrasive Wheels, B7.1-
1970, which is incorporated by reference as specified in Sec. 1910.6.
(b) Due to the variety of work and types of grinding machines
employed, it is necessary to develop hoods adaptable to the particular
machine in question, and such hoods shall be located as close as
possible to the operation.
(ii) Exhaust hoods for floor stands, pedestals, and bench grinders
shall be designed in accordance with figure G-2. The adjustable tongue
shown in the figure shall be kept in working order and shall be adjusted
within one-fourth inch of the wheel periphery at all times.
(iii) Swing-frame grinders shall be provided with exhaust booths as
indicated in figure G-3.
[[Page 201]]
(iv) Portable grinding operations, whenever the nature of the work
permits, shall be conducted within a partial enclosure. The opening in
the enclosure shall be no larger than is actually required in the
operation and an average face air velocity of not less than 200 feet per
minute shall be maintained.
(v) Hoods for polishing and buffing and scratch-brush wheels shall
be constructed to conform as closely to figure G-4 as the nature of the
work will permit.
(vi) Cradle grinding and polishing operations shall be performed
within a partial enclosure similar to figure G-5. The operator shall be
positioned outside the working face of the opening of the enclosure. The
face opening of the enclosure should not be any greater in area than
that actually required for the performance of the operation and the
average air velocity into the working face of the enclosure shall not be
less than 150 feet per minute.
(vii) Hoods for horizontal single-spindle disc grinders shall be
constructed to conform as closely as possible to the hood shown in
figure G-6. It is essential that there be a space between the back of
the wheel and the hood, and a space around the periphery of the wheel of
at least 1 inch in order to permit the suction to act around the wheel
periphery. The opening on the side of the disc shall be no larger than
is required for the grinding operation, but must never be less than
twice the area of the branch outlet.
(viii) Horizontal double-spindle disc grinders shall have a hood
encircling the wheels and grinding chamber similar to that illustrated
in figure G-7. The openings for passing the work into the grinding
chamber should be kept as small as possible, but must never be less than
twice the area of the branch outlets.
(ix) Vertical-spindle disc grinders shall be encircled with a hood
so constructed that the heavy dust is drawn off a surface of the disc
and the lighter dust exhausted through a continuous slot at the top of
the hood as shown in figure G-1.
(x) Grinding and polishing belt hoods shall be constructed as close
to the operation as possible. The hood should extend almost to the belt,
and 1-inch wide openings should be provided on either side. Figure G-8
shows a typical hood for a belt operation.
[[Page 202]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.015
----------------------------------------------------------------------------------------------------------------
Dia D. inches Exhaust E Volume
-------------------------------------------------------------------- Exhausted
at 4,500 Note
Min. Max. No Dia. ft/min
Pipes ft\3\/min
----------------------------------------------------------------------------------------------------------------
20 1 4\1/4\ 500 When one-half or more of the
disc can be hooded, use
exhaust ducts as shown at the
left.
Over 20................................. 30 2 4 780
Over 30................................. 72 2 6 1,770
Over 53................................. 72 2 8 3,140
----------------------------------------------------------------------------------------------------------------
20 2 4 780 When no hood can be used over
disc, use exhaust ducts as
shown at left.
Over 20................................. 20 2 4 780
Over 30................................. 30 2 5\1/2\ 1,480
Over 53................................. 53 4 6 3,530
72 5 7 6,010
----------------------------------------------------------------------------------------------------------------
Entry loss=1.0 slot velocity pressure + 0.5 branch velocity pressure.
Minimum slot velocity=2,000 ft/min--\1/2\-inch slot width.
[[Page 203]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.016
----------------------------------------------------------------------------------------------------------------
Wheel dimension, inches
----------------------------------------------------------------------------------------- Exhaust Volume of
Diameter outlet, air at
----------------------------------------------------------------------------- Width, Max inches E 4,500 ft/
Min=d Max=D min
----------------------------------------------------------------------------------------------------------------
9 1\1/2\ 3 220
Over 9.......................................................... 16 2 4 390
Over 16......................................................... 19 3 4\1/2\ 500
Over 19......................................................... 24 4 5 610
Over 24......................................................... 30 5 6 880
Over 30......................................................... 36 6 7 1,200
----------------------------------------------------------------------------------------------------------------
Entry loss = 0.45 velocity pressure for tapered takeoff 0.65 velocity pressure for straight takeoff.
[[Page 204]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.017
[[Page 205]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.018
Standard Buffing and Polishing Hood
----------------------------------------------------------------------------------------------------------------
Wheel dimension, inches
----------------------------------------------------------------------------------------- Exhaust Volume of
Diameter outlet, air at
----------------------------------------------------------------------------- Width, Max inches E 4,500 ft/
Min=d Max=D min
----------------------------------------------------------------------------------------------------------------
9 2 3\1/2\ 300
Over 9.......................................................... 16 3 4 500
Over 16......................................................... 19 4 5 610
Over 19......................................................... 24 5 5\1/2\ 740
Over 24......................................................... 30 6 6\1/2\ 1.040
Over 30......................................................... 36 6 7 1.200
----------------------------------------------------------------------------------------------------------------
Entry loss = 0.15 velocity pressure for tapered takeoff; 0.65 velocity pressure for straight takeoff.
[[Page 206]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.019
[[Page 207]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.020
------------------------------------------------------------------------
Dia D, inches Volume
------------------------------------------------ Exhaust E, exhausted
dia. at 4,500 ft/
Min. Max. inches min ft\3\/
min
------------------------------------------------------------------------
12 3 220
Over 12............................ 19 4 390
Over 19............................ 30 5 610
Over 30............................ 36 6 880
------------------------------------------------------------------------
Note: If grinding wheels are used for disc grinding purposes, hoods must
conform to structural strength and materials as described in 9.1.
Entry loss = 0.45 velocity pressure for tapered takeoff.
[[Page 208]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.021
----------------------------------------------------------------------------------------------------------------
Disc dia. inches Exhaust E Volume
------------------------------------------------------------------------ exhaust at
4,500 ft/ Note
Min. Max. No Pipes Dia. min. ft\3\/
min
----------------------------------------------------------------------------------------------------------------
19 1 5 610
Over 19............................ 25 1 6 880 When width ``W'' permits,
exhaust ducts should be as
near heaviest grinding as
possible.
Over 25............................ 30 1 7 1,200
Over 30............................ 53 2 6 1,770
Over 53............................ 72 4 8 6,280
----------------------------------------------------------------------------------------------------------------
Entry loss = 0.45 velocity pressure for tapered takeoff.
[[Page 209]]
[GRAPHIC] [TIFF OMITTED] TC27OC91.022
------------------------------------------------------------------------
Exhaust
Belt width W. Inches volume.
ft.\1\/min
------------------------------------------------------------------------
Up to 3..................................................... 220
3 to 5...................................................... 300
5 to 7...................................................... 390
7 to 9...................................................... 500
9 to 11..................................................... 610
11 to 13.................................................... 740
------------------------------------------------------------------------
Minimum duct velocity = 4,500 ft/min branch, 3,500 ft/min main.
Entry loss = 0.45 velocity pressure for tapered takeoff; 0.65 velocity
pressure for straight takeoff.
(6) Scope. This paragraph (b), prescribes the use of exhaust hood
enclosures and systems in removing dust, dirt, fumes, and gases
generated through the grinding, polishing, or buffing of ferrous and
nonferrous metals.
(c) Spray finishing operations--(1) Definitions applicable to this
paragraph--(i) Spray-finishing operations. Spray-finishing operations
are employment of methods wherein organic or inorganic materials are
utilized in dispersed form for deposit on surfaces to be coated,
treated, or cleaned. Such methods of deposit may involve either
automatic, manual, or electrostatic deposition but do not include metal
spraying or metallizing, dipping, flow coating, roller coating,
tumbling, centrifuging, or spray washing and degreasing as conducted in
self-contained washing and degreasing machines or systems.
(ii) Spray booth. Spray booths are defined and described in
Sec. 1910.107(a). (See sections 103, 104, and 105 of the Standard for
Spray Finishing Using Flammable and Combustible Materials, NFPA No. 33-
1969, which is incorporated by reference as specified in Sec. 1910.6).
(iii) Spray room. A spray room is a room in which spray-finishing
operations not conducted in a spray booth are performed separately from
other areas.
(iv) Minimum maintained velocity. Minimum maintained velocity is the
velocity of air movement which must be maintained in order to meet
minimum specified requirements for health and safety.
(2) Location and application. Spray booths or spray rooms are to be
used to enclose or confine all operations. Spray-finishing operations
shall be located as provided in sections 201 through 206 of the Standard
for Spray Finishing Using Flammable and Combustible Materials, NFPA No.
33-1969.
(3) Design and construction of spray booths. (i) Spray booths shall
be designed and constructed in accordance with Sec. 1910.107(b) (1)
through (4) and (6) through (10) (see sections 301-304 and 306-310 of
the Standard for Spray Finishing Using Flammable and Combustible
Materials, NFPA No. 33-1969), for general construction specifications.
For a more detailed discussion of fundamentals relating to this subject,
see ANSI Z9.2-1960
(a) Lights, motors, electrical equipment, and other sources of
ignition shall conform to the requirements of Sec. 1910.107 (b)(10) and
(c). (See section 310 and chapter 4 of the Standard for Spray Finishing
Using Flammable and Combustible Materials NFPA No. 33-1969.)
(b) In no case shall combustible material be used in the
construction of a spray booth and supply or exhaust duct connected to
it.
[[Page 210]]
(ii) Unobstructed walkways shall not be less than 6\1/2\ feet high
and shall be maintained clear of obstruction from any work location in
the booth to a booth exit or open booth front. In booths where the open
front is the only exit, such exits shall be not less than 3 feet wide.
In booths having multiple exits, such exits shall not be less than 2
feet wide, provided that the maximum distance from the work location to
the exit is 25 feet or less. Where booth exits are provided with doors,
such doors shall open outward from the booth.
(iii) Baffles, distribution plates, and dry-type overspray
collectors shall conform to the requirements of Sec. 1910.107(b) (4) and
(5). (See sections 304 and 305 of the Standard for Spray Finishing Using
Flammable and Combustible Materials, NFPA No. 33-1969.)
(a) Overspray filters shall be installed and maintained in
accordance with the requirements of Sec. 1910.107 (b)(5), (see section
305 of the Standard for Spray Finishing Using Flammable and Combustible
Materials, NFPA No. 33-1969), and shall only be in a location easily
accessible for inspection, cleaning, or replacement.
(b) Where effective means, independent of the overspray filters, are
installed which will result in design air distribution across the booth
cross section, it is permissible to operate the booth without the
filters in place.
(iv) (a) For wet or water-wash spray booths, the water-chamber
enclosure, within which intimate contact of contaminated air and
cleaning water or other cleaning medium is maintained, if made of steel,
shall be 18 gage or heavier and adequately protected against corrosion.
(b) Chambers may include scrubber spray nozzles, headers, troughs,
or other devices. Chambers shall be provided with adequate means for
creating and maintaining scrubbing action for removal of particulate
matter from the exhaust air stream.
(v) Collecting tanks shall be of welded steel construction or other
suitable non-combustible material. If pits are used as collecting tanks,
they shall be concrete, masonry, or other material having similar
properties.
(a) Tanks shall be provided with weirs, skimmer plates, or screens
to prevent sludge and floating paint from entering the pump suction box.
Means for automatically maintaining the proper water level shall also be
provided. Fresh water inlets shall not be submerged. They shall
terminate at least one pipe diameter above the safety overflow level of
the tank.
(b) Tanks shall be so constructed as to discourage accumulation of
hazardous deposits.
(vi) Pump manifolds, risers, and headers shall be adequately sized
to insure sufficient water flow to provide efficient operation of the
water chamber.
(4) Design and construction of spray rooms. (i) Spray rooms,
including floors, shall be constructed of masonry, concrete, or other
noncombustible material.
(ii) Spray rooms shall have noncombustible fire doors and shutters.
(iii) Spray rooms shall be adequately ventilated so that the
atmosphere in the breathing zone of the operator shall be maintained in
accordance with the requirements of paragraph (c)(6)(ii) of this
section.
(iv) Spray rooms used for production spray-finishing operations
shall conform to the requirements for spray booths.
(5) Ventilation. (i) Ventilation shall be provided in accordance
with provisions of Sec. 1910.107(d) (see chapter 5 of the Standard for
Spray Finishing Using Flammable or Combustible Materials, NFPA No. 33-
1969), and in accordance with the following:
(a) Where a fan plenum is used to equalize or control the
distribution of exhaust air movement through the booth, it shall be of
sufficient strength or rigidity to withstand the differential air
pressure or other superficially imposed loads for which the equipment is
designed and also to facilitate cleaning. Construction specifications
shall be at least equivalent to those of paragraph (c)(5)(iii) of this
section.
(b) [Reserved]
(ii) Inlet or supply ductwork used to transport makeup air to spray
booths or surrounding areas shall be constructed of noncombustible
materials.
(a) If negative pressure exists within inlet ductwork, all seams and
joints
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shall be sealed if there is a possibility of infiltration of harmful
quantities of noxious gases, fumes, or mists from areas through which
ductwork passes.
(b) Inlet ductwork shall be sized in accordance with volume flow
requirements and provide design air requirements at the spray booth.
(c) Inlet ductwork shall be adequately supported throughout its
length to sustain at least its own weight plus any negative pressure
which is exerted upon it under normal operating conditions.
(iii)(a) Exhaust ductwork shall be adequately supported throughout
its length to sustain its weight plus any normal accumulation in
interior during normal operating conditions and any negative pressure
exerted upon it.
(b) Exhaust ductwork shall be sized in accordance with good design
practice which shall include consideration of fan capacity, length of
duct, number of turns and elbows, variation in size, volume, and
character of materials being exhausted. See American National Standard
Z9.2-1960 for further details and explanation concerning elements of
design.
(c) Longitudinal joints in sheet steel ductwork shall be either
lock-seamed, riveted, or welded. For other than steel construction,
equivalent securing of joints shall be provided.
(d) Circumferential joints in ductwork shall be substantially
fastened together and lapped in the direction of airflow. At least every
fourth joint shall be provided with connecting flanges, bolted together,
or of equivalent fastening security.
(e) Inspection or clean-out doors shall be provided for every 9 to
12 feet of running length for ducts up to 12 inches in diameter, but the
distance between cleanout doors may be greater for larger pipes. (See
8.3.21 of American National Standard Z9.1-1951, which is incorporated by
reference as specified in Sec. 1910.6.) A clean-out door or doors shall
be provided for servicing the fan, and where necessary, a drain shall be
provided.
(f) Where ductwork passes through a combustible roof or wall, the
roof or wall shall be protected at the point of penetration by open
space or fire-resistive material between the duct and the roof or wall.
When ducts pass through firewalls, they shall be provided with automatic
fire dampers on both sides of the wall, except that three-eighth-inch
steel plates may be used in lieu of automatic fire dampers for ducts not
exceeding 18 inches in diameter.
(g) Ductwork used for ventilating any process covered in this
standard shall not be connected to ducts ventilating any other process
or any chimney or flue used for conveying any products of combustion.
(6) Velocity and air flow requirements. (i) Except where a spray
booth has an adequate air replacement system, the velocity of air into
all openings of a spray booth shall be not less than that specified in
Table G-10 for the operating conditions specified. An adequate air
replacement system is one which introduces replacement air upstream or
above the object being sprayed and is so designed that the velocity of
air in the booth cross section is not less than that specified in Table
G-10 when measured upstream or above the object being sprayed.
Table G-10--Minimum Maintained Velocities Into Spray Booths
----------------------------------------------------------------------------------------------------------------
Airflow velocities, f.p.m.
Operating conditions for objects Crossdraft, f.p.m. ----------------------------------------
completely inside booth Design Range
----------------------------------------------------------------------------------------------------------------
Electrostatic and automatic airless Negligible................. 50 large booth............. 50-75
operation contained in booth without
operator.
100 small booth............ 75-125
Air-operated guns, manual or automatic.... Up to 50................... 100 large booth............ 75-125
----------------------------------------------------------------------------------------------------------------
150 small booth............ 125-175
Air-operated guns, manual or automatic.... Up to 100.................. 150 large booth............ 125-175
----------------------------------------------------------------------------------------------------------------
200 small booth............ 150-250
----------------------------------------------------------------------------------------------------------------
Notes:
(1) Attention is invited to the fact that the effectiveness of the spray booth is dependent upon the
relationship of the depth of the booth to its height and width.
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(2) Crossdrafts can be eliminated through proper design and such design should be sought. Crossdrafts in
excess of 100fpm (feet per minute) should not be permitted.
(3) Excessive air pressures result in loss of both efficiency and material waste in addition to creating a
backlash that may carry overspray and fumes into adjacent work areas.
(4) Booths should be designed with velocities shown in the column headed ``Design.'' However, booths operating
with velocities shown in the column headed ``Range'' are in compliance with this standard.
(ii) In addition to the requirements in paragraph (c)(6)(i) of this
section the total air volume exhausted through a spray booth shall be
such as to dilute solvent vapor to at least 25 percent of the lower
explosive limit of the solvent being sprayed. An example of the method
of calculating this volume is given below.
Example: To determine the lower explosive limits of the most common
solvents used in spray finishing, see Table G-11. Column 1 gives the
number of cubic feet of vapor per gallon of solvent and column 2 gives
the lower explosive limit (LEL) in percentage by volume of air. Note
that the quantity of solvent will be diminished by the quantity of
solids and nonflammables contained in the finish.
To determine the volume of air in cubic feet necessary to dilute the
vapor from 1 gallon of solvent to 25 percent of the lower explosive
limit, apply the following formula:
Dilution volume required per gallon of solvent = 4 (100-LEL) (cubic feet
of vapor per gallon)/ LEL
Using toluene as the solvent.
(1) LEL of toluene from Table G-11, column 2, is 1.4 percent.
(2) Cubic feet of vapor per gallon from Table G-11, column 1, is
30.4 cubic feet per gallon.
(3) Dilution volume required=
4 (100-1.4) 30.4/ 1.4 = 8,564 cubic feet.
(4) To convert to cubic feet per minute of required ventilation,
multiply the dilution volume required per gallon of solvent by the
number of gallons of solvent evaporated per minute.
Table G-11--Lower Explosive Limit of Some Commonly Used Solvents
------------------------------------------------------------------------
Lower
Cubic feet explosive
per gallon limit in
Solvent of vapor percent by
of liquid volume of
at 70 air at 70
deg.F. deg.F
------------------------------------------------------------------------
Column 1 Column 2
Acetone......................................... 44.0 2.6
Amyl Acetate (iso).............................. 21.6 \1\ 1.0
Amyl Alcohol (n)................................ 29.6 1.2
Amyl Alcohol (iso).............................. 29.6 1.2
Benzene......................................... 36.8 \1\ 1.4
Butyl Acetate (n)............................... 24.8 1.7
Butyl Alcohol (n)............................... 35.2 1.4
Butyl Cellosolve................................ 24.8 1.1
Cellosolve...................................... 33.6 1.8
Cellosolve Acetate.............................. 23.2 1.7
Cyclohexanone................................... 31.2 \1\ 1.1
1,1 Dichloroethylene............................ 42.4 5.9
1,2 Dichloroethylene............................ 42.4 9.7
Ethyl Acetate................................... 32.8 2.5
Ethyl Alcohol................................... 55.2 4.3
Ethyl Lactate................................... 28.0 \1\ 1.5
Methyl Acetate.................................. 40.0 3.1
Methyl Alcohol.................................. 80.8 7.3
Methyl Cellosolve............................... 40.8 2.5
Methyl Ethyl Ketone............................. 36.0 1.8
Methyl n-Propyl Ketone.......................... 30.4 1.5
Naphtha (VM&P) (76 deg. Naphtha)................ 22.4 0.9
Naphtha (100 deg.Flash) Safety Solvent-- 23.2 1.0
Stoddard Solvent...............................
Propyl Acetate (n).............................. 27.2 2.8
Propyl Acetate (iso)............................ 28.0 1.1
Propyl Alcohol (n).............................. 44.8 2.1
Propyl Alcohol (iso)............................ 44.0 2.0
Toluene......................................... 30.4 1.4
Turpentine...................................... 20.8 0.8
Xylene (o)...................................... 26.4 1.0
------------------------------------------------------------------------
\1\ At 212 deg.F.
(iii)(a) When an operator is in a booth downstream from the object
being sprayed, an air-supplied respirator or other type of respirator
must be used by employees that has been approved by NIOSH under 42 CFR
part 84 for the material being sprayed.
(b) Where downdraft booths are provided with doors, such doors shall
be closed when spray painting.
(7) Make-up air. (i) Clean fresh air, free of contamination from
adjacent industrial exhaust systems, chimneys, stacks, or vents, shall
be supplied to a spray booth or room in quantities equal to the volume
of air exhausted through the spray booth.
(ii) Where a spray booth or room receives make-up air through self-
closing doors, dampers, or louvers, they shall be fully open at all
times when the booth or room is in use for spraying. The velocity of air
through such doors, dampers, or louvers shall not exceed
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200 feet per minute. If the fan characteristics are such that the
required air flow through the booth will be provided, higher velocities
through the doors, dampers, or louvers may be used.
(iii)(a) Where the air supply to a spray booth or room is filtered,
the fan static pressure shall be calculated on the assumption that the
filters are dirty to the extent that they require cleaning or
replacement.
(b) The rating of filters shall be governed by test data supplied by
the manufacturer of the filter. A pressure gage shall be installed to
show the pressure drop across the filters. This gage shall be marked to
show the pressure drop at which the filters require cleaning or
replacement. Filters shall be replaced or cleaned whenever the pressure
drop across them becomes excessive or whenever the air flow through the
face of the booth falls below that specified in Table G-10.
(iv)(a) Means for heating make-up air to any spray booth or room,
before or at the time spraying is normally performed, shall be provided
in all places where the outdoor temperature may be expected to remain
below 55 deg.F. for appreciable periods of time during the operation of
the booth except where adequate and safe means of radiant heating for
all operating personnel affected is provided. The replacement air during
the heating seasons shall be maintained at not less than 65 deg.F. at
the point of entry into the spray booth or spray room. When otherwise
unheated make-up air would be at a temperature of more than 10 deg.F.
below room temperature, its temperature shall be regulated as provided
in section 3.6.3 of ANSI Z9.2-1960.
(b) As an alternative to an air replacement system complying with
the preceding section, general heating of the building in which the
spray room or booth is located may be employed provided that all
occupied parts of the building are maintained at not less than 65
deg.F. when the exhaust system is in operation or the general heating
system supplemented by other sources of heat may be employed to meet
this requirement.
(c) No means of heating make-up air shall be located in a spray
booth.
(d) Where make-up air is heated by coal or oil, the products of
combustion shall not be allowed to mix with the make-up air, and the
products of combustion shall be conducted outside the building through a
flue terminating at a point remote from all points where make-up air
enters the building.
(e) Where make-up air is heated by gas, and the products of
combustion are not mixed with the make-up air but are conducted through
an independent flue to a point outside the building remote from all
points where make-up air enters the building, it is not necessary to
comply with paragraph (c)(7)(iv)(f) of this section.
(f) Where make-up air to any manually operated spray booth or room
is heated by gas and the products of combustion are allowed to mix with
the supply air, the following precautions must be taken:
(1) The gas must have a distinctive and strong enough odor to warn
workmen in a spray booth or room of its presence if in an unburned state
in the make-up air.
(2) The maximum rate of gas supply to the make-up air heater burners
must not exceed that which would yield in excess of 200 p.p.m. (parts
per million) of carbon monoxide or 2,000 p.p.m. of total combustible
gases in the mixture if the unburned gas upon the occurrence of flame
failure were mixed with all of the make-up air supplied.
(3) A fan must be provided to deliver the mixture of heated air and
products of combustion from the plenum chamber housing the gas burners
to the spray booth or room.
(8) Scope. Spray booths or spray rooms are to be used to enclose or
confine all spray finishing operations covered by this paragraph (c).
This paragraph does not apply to the spraying of the exteriors of
buildings, fixed tanks, or similar structures, nor to small portable
spraying apparatus not used repeatedly in the same location.
[39 FR 23502, June 27, 1974, as amended at 40 FR 23073, May 28, 1975; 40
FR 24522, June 9, 1975; 43 FR 49746, Oct. 24, 1978; 49 FR 5322, Feb. 10,
1984; 55 FR 32015, Aug. 6, 1990; 58 FR 35308, June 30, 1993; 61 FR 9236,
Mar. 7, 1996; 63 FR 1269, Jan. 8, 1998; 64 FR 13909, Mar. 23, 1999]
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