Section

[Code of Federal Regulations]
[Title 29, Volume 8]
[Revised as of July 1, 2001]
From the U.S. Government Printing Office via GPO Access
[CITE: 29CFR1926.57]

[Page 45-71]

TITLE 29--LABOR

CHAPTER XVII--OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT
OF LABOR

PART 1926--SAFETY AND HEALTH REGULATIONS FOR CONSTRUCTION--Table of Contents

Subpart D--Occupational Health and Environmental Controls

Sec. 1926.57 Ventilation.

(a) General. Whenever hazardous substances such as dusts, fumes,
mists, vapors, or gases exist or are produced in the course of
construction work, their concentrations shall not exceed the limits
specified in Sec. 1926.55(a). When ventilation is used as an engineering
control method, the system shall be installed and operated according to
the requirements of this section.
(b) Local exhaust ventilation. Local exhaust ventilation when used
as described in (a) shall be designed to prevent dispersion into the air
of dusts, fumes, mists, vapors, and gases in concentrations causing
harmful exposure. Such exhaust systems shall be so designed that dusts,
fumes, mists, vapors, or gases are not drawn through the work area of
employees.
(c) Design and operation. Exhaust fans, jets, ducts, hoods,
separators, and all necessary appurtenances, including refuse
receptacles, shall be so designed, constructed, maintained and operated
as to ensure the required protection by maintaining a volume and
velocity of exhaust air sufficient to gather dusts, fumes, vapors, or
gases from said equipment or process, and to convey them to suitable
points of safe disposal, thereby preventing their dispersion in harmful
quantities into the atmosphere where employees work.
(d) Duration of operations. (1) The exhaust system shall be in
operation continually during all operations which it is designed to
serve. If the employee remains in the contaminated zone, the system
shall continue to operate after the cessation of said operations, the
length of time to depend upon the individual circumstances and
effectiveness of the general ventilation system.
(2) Since dust capable of causing disability is, according to the
best medical opinion, of microscopic size, tending to remain for hours
in suspension in still air, it is essential that the exhaust system be
continued in operation for a time after the work process or equipment
served by the same shall have ceased, in order to ensure the removal of
the harmful elements to the required extent. For the same reason,
employees wearing respiratory equipment should not remove same
immediately until the atmosphere seems clear.
(e) Disposal of exhaust materials. The air outlet from every dust
separator, and the dusts, fumes, mists, vapors, or gases collected by an
exhaust or ventilating system shall discharge to the outside atmosphere.
Collecting systems which return air to work area may be used if
concentrations which accumulate in the work area air do not result in
harmful exposure to employees. Dust and refuse discharged from an
exhaust system shall be disposed of in such a manner that it will not
result in harmful exposure to employees.
(f) 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.
(iv) Blast cleaning room. A complete enclosure in which blasting
operations are performed and where the operator

[[Page 46]]

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. 1926.55 or other pertinent sections
of this part.
(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), 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.
(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 particles 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 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

[[Page 47]]

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.
(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.
(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 NIOSH under 42 CFR part 84 for protecting
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. 1926.55 or other pertinent
sections of this part 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.
(iv) A respiratory protection program as defined and described in
Sec. 1926.103, shall be established wherever it is necessary to use
respiratory protective equipment.
(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.
(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. This equipment shall conform to the
requirements of Sec. 1926.102.
(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 applies to all operations where an
abrasive is

[[Page 48]]

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.
(g) 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 (50.8 cm) in diameter, and not
more than one-sixtieth of their diameter for those larger than 20 inches
(50.8 cm) 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.
(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.

[[Page 49]]

(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. 1926.55 or other pertinent 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 D-57.1
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 D-57.1 (following paragraph (g) of this
section).

Table D-57.1--Grinding and Abrasive Cutting-Off Wheels
------------------------------------------------------------------------
Minimum
Wheel exhaust
Wheel diameter, inches (cm) width, volume
inches (feet ³/
(cm) min.)
------------------------------------------------------------------------
To 9 (22.86).................................... 1\1/2\ 220
(3.81)
Over 9 to 16 (22.86 to 40.64)................... 2 (5.08) 390
Over 16 to 19 (40.64 to 48.26).................. 3 (7.62) 500
Over 19 to 24 (48.26 to 60.96).................. 4 (10.16) 610
Over 24 to 30 (60.96 to 76.2)................... 5 (12.7) 880
Over 30 to 36 (76.2 to 91.44)................... 6 (15.24) 1,200
------------------------------------------------------------------------

For any wheel wider than wheel diameters shown in Table D-57.1, increase
the exhaust volume by the ratio of the new width to the width shown.

Example: If wheel width = 4\1/2\ inches (11.43 cm),

then 4.54 x 610 = 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 D-
57.2.

Table D-57.2--Buffing and Polishing Wheels
------------------------------------------------------------------------
Minimum
Wheel exhaust
Wheel diameter, inches (cm) width, volume
inches cm) (feet ³/
min.)
------------------------------------------------------------------------
To 9 (22.86).................................... 2 (5.08) 300
Over 9 to 16 (22.86 to 40.64)................... 3 (7.62) 500
Over 16 to 19 (40.64 to 48.26).................. 4 (10.16) 610
Over 19 to 24 (48.26 to 60.96).................. 5 (12.7) 740
Over 24 to 30 (60.96 to 76.2)................... 6 (15.24) 1,040
Over 30 to 36 (76.2 to 91.44)................... 6 (15.24) 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 D-57.3.

Table D-57.3--Horizontal Single-Spindle Disc Grinder
------------------------------------------------------------------------
Exhaust
volume
Disc diameter, inches (cm) (ft. ³/
min.)
------------------------------------------------------------------------
Up to 12 (30.48)............................................ 220
Over 12 to 19 (30.48 to 48.26).............................. 390
Over 19 to 30 (48.26 to 76.2)............................... 610
Over 30 to 36 (76.2 to 91.44)............................... 880
------------------------------------------------------------------------

(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 D-57.4.

Table D-57.4--Horizontal Double-Spindle Disc Grinder
------------------------------------------------------------------------
Exhaust
volume
Disc diameter, inches (cm) (ft. ³/
min.)
------------------------------------------------------------------------
Up to 19 (48.26)............................................ 610
Over 19 to 25 (48.26 to 63.5)............................... 880
Over 25 to 30 (63.5 to 76.2)................................ 1,200
Over 30 to 53 (76.2 to 134.62).............................. 1,770
Over 53 to 72 (134.62 to 182.88)............................ 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

[[Page 50]]

more branch pipes having exhaust volumes as shown in Table D-57.5.

Table D-57.5--Vertical Spindle Disc Grinder
------------------------------------------------------------------------
One-half or more of Disc not covered
disc covered --------------------
---------------------
Disc diameter, inches (cm) Exhaust Exhaust
Number \1\ foot ³/ Number \1\ foot ³/
min. min.
------------------------------------------------------------------------
Up to 20 (50.8)............... 1 500 2 780
Over 20 to 30 (50.8 to 76.2).. 2 780 2 1,480
Over 30 to 53 (76.2 to 134.62) 2 1,770 4 3,530
Over 53 to 72 (134.62 to 2 3,140 5 6,010
182.88)......................
------------------------------------------------------------------------
\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 D-
57.6.

Table D-57.6--Grinding and Polishing Belts
------------------------------------------------------------------------
Exhaust
volume
Belts width, inches (cm) (ft. ³/
min.)
------------------------------------------------------------------------
Up to 3 (7.62).............................................. 220
Over 3 to 5 (7.62 to 12.7).................................. 300
Over 5 to 7 (12.7 to 17.78)................................. 390
Over 7 to 9 (17.78 to 22.86)................................ 500
Over 9 to 11 (22.86 to 27.94)............................... 610
Over 11 to 13 (27.94 to 33.02).............................. 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. D-57.3)
(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.
(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 D-57.2. The adjustable
tongue shown in the figure shall be kept in working order and shall be
adjusted within one-fourth inch (0.635 cm) of the wheel periphery at all
times.
(iii) Swing-frame grinders shall be provided with exhaust booths as
indicated in figure D-57.3.
(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 D-57.4 as the nature of
the work will permit.
(vi) Cradle grinding and polishing operations shall be performed
within a partial enclosure similar to figure D-57.5. 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

[[Page 51]]

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 D-57.6. 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 (2.54 cm) 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 D-57.7. 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 D-57.1.
(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 (2.54 cm) wide openings should be provided on either side.
Figure D-57.8 shows a typical hood for a belt operation.

[[Page 52]]

[GRAPHIC] [TIFF OMITTED] TC30OC91.000

Figure D-57.1--Vertical Spindle Disc Grinder Exhaust Hood and Branch
Pipe Connections

[[Page 53]]

--------------------------------------------------------------------------------------------------------------------------------------------------------
Dia. D inches (cm) Exhaust E Volume
------------------------------------------------------------------------------------------------ Exhausted at
4,500 ft/min Note
Min. Max. No Pipes Dia. ft³/min
--------------------------------------------------------------------------------------------------------------------------------------------------------
20 (50.8) 1 4\1/4\ 500 When one-half or more of the disc can
(10.795) be hooded, use exhaust ducts as shown
at the left.
Over 20 (50.8)................................. 30 (76.2) 2 4 (10.16) 780
Over 30 (76.2)................................. 72 (182.88) 2 6 (15.24) 1,770
Over 53 (134.62)............................... 72 (182.88) 2 8 (20.32) 3,140
--------------------------------------------------------------------------------------------------------------------------------------------------------
20 (50.8) 2 4 (10.16) 780 When no hood can be used over disc, use
exhaust ducts as shown at left.
Over 20 (50.8)................................. 20 (50.8) 2 4 (10.16) 780
Over 30 (76.2)................................. 30 (76.2) 2 5\1/2\ (13.97) 1,480
Over 53 (134.62)............................... 53 (134.62) 4 6 (15.24) 3,530
72 (182.88) 5 7 (17.78) 6,010
--------------------------------------------------------------------------------------------------------------------------------------------------------
Entry loss=1.0 slot velocity pressure + 0.5 branch velocity pressure.
Minimum slot velocity=2,000 ft/min--\1/2\-inch (1.27 cm) slot width.

[[Page 54]]

[GRAPHIC] [TIFF OMITTED] TC30OC91.001

Figure D-57.2--Standard Grinder Hood

----------------------------------------------------------------------------------------------------------------
Wheel dimension, inches (centimeters)
------------------------------------------------------------------------------------- Exhaust Volume of
Diameter outlet, inches air at
--------------------------------------------------------------------- Width, Max (centimeters) 4,500 ft/
Min= d Max= D E min
----------------------------------------------------------------------------------------------------------------
9 (22.86) 1\1/2\ (3.81) 3 220
Over 9 (22.86)...................................... 16 (40.64) 2 (5.08) 4 390
Over 16 (40.64)..................................... 19 (48.26) 3 (7.62) 4\1/2\ 500
Over 19 (48.26)..................................... 24 (60.96) 4 (10.16) 5 610
Over 24 (60.96)..................................... 30 (76.2) 5 (12.7) 6 880
Over 30 (76.2)...................................... 36 (91.44) 6 (15.24) 7 1,200
----------------------------------------------------------------------------------------------------------------
Entry loss = 0.45 velocity pressure for tapered takeoff 0.65 velocity pressure for straight takeoff.

[[Page 55]]

[GRAPHIC] [TIFF OMITTED] TC30OC91.002

Figure D-57.3--A Method of Applying an Exhaust Enclosure to Swing-Frame
Grinders

[[Page 56]]

Note: Baffle to reduce front opening as much as possible
[GRAPHIC] [TIFF OMITTED] TC30OC91.003

Figure D-57.4

Standard Buffing and Polishing Hood
----------------------------------------------------------------------------------------------------------------
Wheel dimension, inches (centimeters)
------------------------------------------------------------------------------------- Exhaust Volume of
Diameter outlet, inches air at
--------------------------------------------------------------------- Width, Max E 4,500 ft/
Min= d Max= D min
----------------------------------------------------------------------------------------------------------------
9 (22.86) 2 (5.08) 3\1/2\ (3.81) 300
Over 9 (22.86)...................................... 16 (40.64) 3 (5.08) 4 500
Over 16 (40.64)..................................... 19 (48.26) 4 (11.43) 5 610
Over 19 (48.26)..................................... 24 (60.96) 5 (12.7) 5\1/2\ 740
Over 24 (60.96)..................................... 30 (76.2) 6 (15.24) 6\1/2\ 1.040
Over 30 (76.2)...................................... 36 (91.44) 6 (15.24) 7 1.200
----------------------------------------------------------------------------------------------------------------
Entry loss = 0.15 velocity pressure for tapered takeoff; 0.65 velocity pressure for straight takeoff.

[[Page 57]]

[GRAPHIC] [TIFF OMITTED] TC30OC91.004

Figure D-57.5--Cradle Polishing or Grinding Enclosure

[[Page 58]]

Entry loss = 0.45 velocity pressure for tapered takeoff
[GRAPHIC] [TIFF OMITTED] TC30OC91.005

Figure D-57.6--Horizontal Single-Spindle Disc Grinder Exhaust Hood and
Branch Pipe Connections

------------------------------------------------------------------------
Dia D, inches (centimeters) Volume
------------------------------------------------ Exhaust E, exhausted
dia. at 4,500 ft/
Min. Max. inches min ft ³/
(cm) min
------------------------------------------------------------------------
12 (30.48) 3 (7.6) 220
Over 12 (30.48)................ 19 (48.26) 4 (10.16) 390
Over 19 (48.26)................ 30 (76.2) 5 (12.7) 610
Over 30 (76.2)................. 36 (91.44) 6 (15.24) 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 59]]

[GRAPHIC] [TIFF OMITTED] TC30OC91.006

Figure D-57.7--Horizontal Double-Spindle Disc Grinder Exhaust Hood and
Branch Pipe Connections

----------------------------------------------------------------------------------------------------------------
Disc dia. inches (centimeters) Exhaust E Volume
---------------------------------------------------------------------------- exhaust at
4,500 ft/ Note
Min. Max. No Pipes Dia. min. ft³/
min
----------------------------------------------------------------------------------------------------------------
19 (48.26) 1 5 610
Over 19 (48.26)................ 25 (63.5) 1 6 880 When width ``W''
permits, exhaust ducts
should be as near
heaviest grinding as
possible.
Over 25 (63.5)................. 30 (76.2) 1 7 1,200
Over 30 (76.2)................. 53 (134.62) 2 6 1,770
Over 53 (134.62)............... 72 (182.88) 4 8 6,280
----------------------------------------------------------------------------------------------------------------
Entry loss = 0.45 velocity pressure for tapered takeoff.

[[Page 60]]

[GRAPHIC] [TIFF OMITTED] TC30OC91.007

Figure D-57.8.--A Typical Hood for a Belt Operation

Entry loss = 0.45 velocity pressure for tapered takeoff

------------------------------------------------------------------------
Exhaust
Belt width W. inches (centimeters) volume.
ft.\1\/min
------------------------------------------------------------------------
Up to 3 (7.62).............................................. 220
3 to 5 (7.62 to 12.7)....................................... 300
5 to 7 (12.7 to 17.78)...................................... 390
7 to 9 (17.78 to 22.86)..................................... 500
9 to 11 (22.86 to 27.94).................................... 610
11 to 13 (27.94 to 33.02)................................... 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 (g), 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.
(h) 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. 1926.66(a). (See sections 103, 104, and 105 of the Standard for
Spray Finishing Using Flammable and Combustible Materials, NFPA No. 33-
1969).
(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. 1926.66(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. 1926.66(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

[[Page 61]]

spray booth and supply or exhaust duct connected to it.
(ii) Unobstructed walkways shall not be less than 6\1/2\ feet (1.976
m) 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 (0.912 m) wide. In booths having multiple exits, such exits shall
not be less than 2 feet (0.608 m) wide, provided that the maximum
distance from the work location to the exit is 25 feet (7.6 m) 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. 1926.66(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. 1926.66(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 (h)(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. 1926.66(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 (h)(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.

[[Page 62]]

(A) If negative pressure exists within inlet ductwork, all seams and
joints 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) [Reserved]
(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 (2.736 to 3.648 m) of running length for ducts up to 12 inches
(0.304 m) 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.) 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 (45.72 cm) 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 D-57.7 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
D-57.7 when measured upstream or above the object being sprayed.

Table D-57.7--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:

[[Page 63]]

(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.
(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 (h)(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 D-57.8. 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 D-57.8, column 2, is 1.4 percent.
(2) Cubic feet of vapor per gallon from Table D-57.8, 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 D-57.8--Lower Explosive Limit of Some Commonly Used Solvents
------------------------------------------------------------------------
Lower
Cubic feet explosive
per gallon limit in
of vapor percent by
Solvent of liquid volume of
at 70 air at 70
deg.F deg.F
(21.11 (21.11
deg.C). deg.C)
------------------------------------------------------------------------
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--Stoddard 23.2 1.0
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 (100 deg.C).

(iii)(A) When an operator is in a booth downstream of the object
being sprayed, an air-supplied respirator or other type of respirator
approved by NIOSH under 42 CFR Part 84 for the material being sprayed
should be used by the operator.
(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

[[Page 64]]

booth or room is in use for spraying. The velocity of air through such
doors, dampers, or louvers shall not exceed 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 D-57.7.
(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. (12.77 deg.C.) 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. (18.33 deg.C.) 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. (18.33 deg.C.) 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 (h)(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 (h).
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.
(i) Open surface tanks--(1) General. (i) This paragraph applies to
all operations involving the immersion of materials in liquids, or in
the vapors of

[[Page 65]]

such liquids, for the purpose of cleaning or altering the surface or
adding to or imparting a finish thereto or changing the character of the
materials, and their subsequent removal from the liquid or vapor,
draining, and drying. These operations include washing, electroplating,
anodizing, pickling, quenching, dying, dipping, tanning, dressing,
bleaching, degreasing, alkaline cleaning, stripping, rinsing, digesting,
and other similar operations.
(ii) Except where specific construction specifications are
prescribed in this section, hoods, ducts, elbows, fans, blowers, and all
other exhaust system parts, components, and supports thereof shall be so
constructed as to meet conditions of service and to facilitate
maintenance and shall conform in construction to the specifications
contained in American National Standard Fundamentals Governing the
Design and Operation of Local Exhaust Systems, Z9.2-1960.
(2) Classification of open-surface tank operations. (i) Open-surface
tank operations shall be classified into 16 classes, numbered A-1 to D-
4, inclusive.
(ii) Determination of class. Class is determined by two factors,
hazard potential designated by a letter from A to D, inclusive, and rate
of gas, vapor, or mist evolution designated by a number from 1 to 4,
inclusive (for example, B.3).
(iii) Hazard potential is an index, on a scale of from A to D,
inclusive, of the severity of the hazard associated with the substance
contained in the tank because of the toxic, flammable, or explosive
nature of the vapor, gas, or mist produced therefrom. The toxic hazard
is determined from the concentration, measured in parts by volume of a
gas or vapor, per million parts by volume of contaminated air (p.p.m.),
or in milligrams of mist per cubic meter of air (mg./m. ³),
below which ill effects are unlikely to occur to the exposed worker. The
concentrations shall be those in Sec. 1926.55 or other pertinent
sections of this part.
(iv) The relative fire or explosion hazard is measured in degrees
Fahrenheit in terms of the closed-cup flash point of the substance in
the tank. Detailed information on the prevention of fire hazards in dip
tanks may be found in Dip Tanks Containing Flammable or Combustible
Liquids, NFPA No. 34-1966, National Fire Protection Association. Where
the tank contains a mixture of liquids, other than organic solvents,
whose effects are additive, the hygienic standard of the most toxic
component (for example, the one having the lowest p.p.m. or mg./m.
³) shall be used, except where such substance constitutes an
insignificantly small fraction of the mixture. For mixtures of organic
solvents, their combined effect, rather than that of either
individually, shall determine the hazard potential. In the absence of
information to the contrary, the effects shall be considered as
additive. If the sum of the ratios of the airborne concentration of each
contaminant to the toxic concentration of that contaminant exceeds
unity, the toxic concentration shall be considered to have been
exceeded. (See Note A to paragraph (i)(2)(v) of this section.)
(v) Hazard potential shall be determined from Table D-57.9, with the
value indicating greater hazard being used. When the hazardous material
may be either a vapor with a threshhold limit value (TLV) in p.p.m. or a
mist with a TLV in mg./m.3, the TLV indicating the greater
hazard shall be used (for example, A takes precedence over B or C; B
over C; C over D).

Note A:

(c1TLV1)+(c2TLV2)
+(c3TLV3)+; . .
.(cNTLVN)1

Where:

c = Concentration measured at the operation in p.p.m.

Table D-57.9--Determination of Hazard Potential
------------------------------------------------------------------------
Toxicity group
--------------------------------------
Hazard potential Gas or
vapor Mist (mg./ Flash point in
(p.p.m.) m³) degrees F. (C.)
------------------------------------------------------------------------
A................................ 0-10 0-0.1 ...............
B................................ 11-100 0.11-1.0 Under 100
(37.77)
C................................ 101-500 1.1-10 100 200 (37.77-
93.33)
D................................ Over 500 Over 10 Over 200
(93.33)
------------------------------------------------------------------------

(vi) Rate of gas, vapor, or mist evolution is a numerical index, on
a scale of from 1 to 4, inclusive, both of the relative capacity of the
tank to produce gas, vapor, or mist and of the

[[Page 66]]

relative energy with which it is projected or carried upwards from the
tank. Rate is evaluated in terms of
(A) The temperature of the liquid in the tank in degrees Fahrenheit;
(B) The number of degrees Fahrenheit that this temperature is below
the boiling point of the liquid in degrees Fahrenheit;
(C) The relative evaporation of the liquid in still air at room
temperature in an arbitrary scale--fast, medium, slow, or nil; and
(D) The extent that the tank gases or produces mist in an arbitrary
scale--high, medium, low, and nil. (See Table D-57.10, Note 2.) Gassing
depends upon electrochemical or mechanical processes, the effects of
which have to be individually evaluated for each installation (see Table
D-57.10, Note 3).
(vii) Rate of evolution shall be determined from Table D-57.10. When
evaporation and gassing yield different rates, the lowest numerical
value shall be used.

Table D-57.10--Determination of Rate of Gas, Vapor, or Mist Evolution \1\
----------------------------------------------------------------------------------------------------------------
Liquid
Rate temperature, Degrees below Relative Gassing \3\
deg.F. (C.) boiling point evaporation \2\
----------------------------------------------------------------------------------------------------------------
1............................... Over 200 (93.33) 0-20 Fast.............. High.
2............................... 150-200 (65.55- 21-50 Medium............ Medium.
93.33)
3............................... 94-149 (34.44-65) 51-100 Slow.............. Low.
4............................... Under 94 (34.44) Over 100 Nil............... Nil.
----------------------------------------------------------------------------------------------------------------
\1\ In certain classes of equipment, specifically vapor degreasers, an internal condenser or vapor level
thermostat is used to prevent the vapor from leaving the tank during normal operation. In such cases, rate of
vapor evolution from the tank into the workroom is not dependent upon the factors listed in the table, but
rather upon abnormalities of operating procedure, such as carryout of vapors from excessively fast action,
dragout of liquid by entrainment in parts, contamination of solvent by water and other materials, or improper
heat balance. When operating procedure is excellent, effective rate of evolution may be taken as 4. When
operating procedure is average, the effective rate of evolution may be taken as 3. When operation is poor, a
rate of 2 or 1 is indicated, depending upon observed conditions.
\2\ Relative evaporation rate is determined according to the methods described by A. K. Doolittle in Industrial
and Engineering Chemistry, vol. 27, p. 1169, (3) where time for 100-percent evaporation is as follows: Fast: 0-
3 hours; Medium: 3-12 hours; Slow: 12-50 hours; Nil: more than 50 hours.
\3\ Gassing means the formation by chemical or electrochemical action of minute bubbles of gas under the surface
of the liquid in the tank and is generally limited to aqueous solutions.

(3) Ventilation. Where ventilation is used to control potential
exposures to workers as defined in paragraph (i)(2)(iii) of this
section, it shall be adequate to reduce the concentration of the air
contaminant to the degree that a hazard to the worker does not exist.
Methods of ventilation are discussed in American National Standard
Fundamentals Governing the Design and Operation of Local Exhaust
Systems, Z9.2-1960.
(4) Control requirements. (i) Control velocities shall conform to
Table D-57.11 in all cases where the flow of air past the breathing or
working zone of the operator and into the hoods is undisturbed by local
environmental conditions, such as open windows, wall fans, unit heaters,
or moving machinery.
(ii) All tanks exhausted by means of hoods which
(A) Project over the entire tank;
(B) Are fixed in position in such a location that the head of the
workman, in all his normal operating positions while working at the
tank, is in front of all hood openings; and
(C) Are completely enclosed on at least two sides, shall be
considered to be exhausted through an enclosing hood.
(D) The quantity of air in cubic feet per minute necessary to be
exhausted through an enclosing hood shall be not less than the product
of the control velocity times the net area of all openings in the
enclosure through which air can flow into the hood.

[[Page 67]]

Table D-57.11--Control Velocities in Feet Per Minute (f.p.m.) for Undisturbed Locations
----------------------------------------------------------------------------------------------------------------
Enclosing hood Canopy hood \2\
------------------------ Lateral -----------------------
Class One open Two open exhaust \1\ Three open Four open
side sides sides sides
----------------------------------------------------------------------------------------------------------------
B-1 and A-2........................................ 100 150 150 Do not use Do not use
A-3 \2\, B-1, B-2, and C-1......................... 75 100 100 125 175
A-3, C-2, and D-1 \3\.............................. 65 90 75 100 150
B-4 \2\, C-3, and D-2 \3\.......................... 50 75 50 75 125
A-4, C-4, D-3 \3\, and D-4 \4\..................... .......... .......... ........... .......... ..........
----------------------------------------------------------------------------------------------------------------
\1\ See Table D-57.12 for computation of ventilation rate.
\2\ Do not use canopy hood for Hazard Potential A processes.
\3\ Where complete control of hot water is desired, design as next highest class.
\4\ General room ventilation required.

(iii) All tanks exhausted by means of hoods which do not project
over the entire tank, and in which the direction of air movement into
the hood or hoods is substantially horizontal, shall be considered to be
laterally exhausted. The quantity of air in cubic feet per minute
necessary to be laterally exhausted per square foot of tank area in
order to maintain the required control velocity shall be determined from
Table D-57.12 for all variations in ratio of tank width (W) to tank
length (L). The total quantity of air in cubic feet per minute required
to be exhausted per tank shall be not less than the product of the area
of tank surface times the cubic feet per minute per square foot of tank
area, determined from Table D-57.12.
(A) For lateral exhaust hoods over 42 inches (1.06 m) wide, or where
it is desirable to reduce the amount of air removed from the workroom,
air supply slots or orifices shall be provided along the side or the
center of the tank opposite from the exhaust slots. The design of such
systems shall meet the following criteria:
(1) The supply air volume plus the entrained air shall not exceed 50
percent of the exhaust volume.
(2) The velocity of the supply airstream as it reaches the effective
control area of the exhaust slot shall be less than the effective
velocity over the exhaust slot area.

Table D-57.12--Minimum Ventilation Rate in Cubic Feet of Air Per Minute Per Square Foot of Tank Area for Lateral
Exhaust
----------------------------------------------------------------------------------------------------------------
C.f.m. per sq. ft. to maintain required minimum velocities
at following ratios (tank width (W)/tank length (L)).\1\,
Required minimum control velocity, f.p.m. (from \2\
Table D-57.11) -----------------------------------------------------------
0.0-0.09 0.1-0.24 0.25-0.49 0.5-0.99 1.0-2.0
----------------------------------------------------------------------------------------------------------------
Hood along one side or two parallel sides of tank when one hood is against a wall or baffle.\2\
Also for a manifold along tank centerline.\3\

----------------------------------------------------------------------------------------------------------------
Hood along one side or two parallel sides of free standing tank not against wall or baffle.

----------------------------------------------------------------------------------------------------------------
50.................................................. 75 90 100 110 125
75.................................................. 110 130 150 170 190
100................................................. 150 175 200 225 250
150................................................. 225 260 300 340 375
----------------------------------------------------------------------------------------------------------------
\1\ It is not practicable to ventilate across the long dimension of a tank whose ratio W/L exceeds 2.0.
It is undesirable to do so when W/L exceeds 1.0. For circular tanks with lateral exhaust along up to 1/2 the
circumference, use W/L=1.0; for over one-half the circumference use W/L=0.5.
\2\ Baffle is a vertical plate the same length as the tank, and with the top of the plate as high as the tank is
wide. If the exhaust hood is on the side of a tank against a building wall or close to it, it is perfectly
baffled.
\3\ Use W/2 as tank width in computing when manifold is along centerline, or when hoods are used on two parallel
sides of a tank.
Tank Width (W) means the effective width over which the hood must pull air to operate (for example, where the
hood face is set back from the edge of the tank, this set back must be added in measuring tank width). The
surface area of tanks can frequently be reduced and better control obtained (particularly on conveyorized
systems) by using covers extending from the upper edges of the slots toward the center of the tank.

[[Page 68]]

(3) The vertical height of the receiving exhaust hood, including any
baffle, shall not be less than one-quarter the width of the tank.
(4) The supply airstream shall not be allowed to impinge on
obstructions between it and the exhaust slot in such a manner as to
significantly interfere with the performance of the exhaust hood.
(5) Since most failure of push-pull systems result from excessive
supply air volumes and pressures, methods of measuring and adjusting the
supply air shall be provided. When satisfactory control has been
achieved, the adjustable features of the hood shall be fixed so that
they will not be altered.
(iv) All tanks exhausted by means of hoods which project over the
entire tank, and which do not conform to the definition of enclosing
hoods, shall be considered to be overhead canopy hoods. The quantity of
air in cubic feet per minute necessary to be exhausted through a canopy
hood shall be not less than the product of the control velocity times
the net area of all openings between the bottom edges of the hood and
the top edges of the tank.
(v) The rate of vapor evolution (including steam or products of
combustion) from the process shall be estimated. If the rate of vapor
evolution is equal to or greater than 10 percent of the calculated
exhaust volume required, the exhaust volume shall be increased in equal
amount.
(5) Spray cleaning and degreasing. Wherever spraying or other
mechanical means are used to disperse a liquid above an open-surface
tank, control must be provided for the airborne spray. Such operations
shall be enclosed as completely as possible. The inward air velocity
into the enclosure shall be sufficient to prevent the discharge of spray
into the workroom. Mechanical baffles may be used to help prevent the
discharge of spray. Spray painting operations are covered by paragraph
(h) of this section.
(6) Control means other than ventilation. Tank covers, foams, beads,
chips, or other materials floating on the tank surface so as to confine
gases, mists, or vapors to the area under the cover or to the foam,
bead, or chip layer; or surface tension depressive agents added to the
liquid in the tank to minimize mist formation, or any combination
thereof, may all be used as gas, mist, or vapor control means for open-
surface tank operations, provided that they effectively reduce the
concentrations of hazardous materials in the vicinity of the worker
below the limits set in accordance with paragraph (i)(2) of this
section.
(7) System design. (i) The equipment for exhausting air shall have
sufficient capacity to produce the flow of air required in each of the
hoods and openings of the system.
(ii) The capacity required in paragraph (i)(7)(i) of this section
shall be obtained when the airflow producing equipment is operating
against the following pressure losses, the sum of which is the static
pressure:
(A) Entrance losses into the hood.
(B) Resistance to airflow in branch pipe including bends and
transformations.
(C) Entrance loss into the main pipe.
(D) Resistance to airflow in main pipe including bends and
transformations.
(E) Resistance of mechanical equipment; that is, filters, washers,
condensers, absorbers, etc., plus their entrance and exit losses.
(F) Resistance in outlet duct and discharge stack.
(iii) Two or more operations shall not be connected to the same
exhaust system where either one or the combination of the substances
removed may constitute a fire, explosion, or chemical reaction hazard in
the duct system. Traps or other devices shall be provided to insure that
condensate in ducts does not drain back into any tank.
(iv) The exhaust system, consisting of hoods, ducts, air mover, and
discharge outlet, shall be designed in accordance with American National
Standard Fundamentals Governing the Design and Operation of Local
Exhaust Systems, Z9.2-1960, or the manual, Industrial Ventilation,
published by the American Conference of Governmental Industrial
Hygienists 1970. Airflow and pressure loss data provided by the
manufacturer of any air cleaning device shall be included in the design
calculations.

[[Page 69]]

(8) Operation. (i) The required airflow shall be maintained at all
times during which gas, mist, or vapor is emitted from the tank, and at
all times the tank, the draining, or the drying area is in operation or
use. When the system is first installed, the airflow from each hood
shall be measured by means of a pitot traverse in the exhaust duct and
corrective action taken if the flow is less than that required. When the
proper flow is obtained, the hood static pressure shall be measured and
recorded. At intervals of not more than 3 months operation, or after a
prolonged shutdown period, the hoods and duct system shall be inspected
for evidence of corrosion or damage. In any case where the airflow is
found to be less than required, it shall be increased to the required
value. (Information on airflow and static pressure measurement and
calculations may be found in American National Standard Fundamental
Governing the Design and Operation of Local Exhaust Systems, Z9.2-1960,
or in the manual, Industrial Ventilation, published by the American
Conference of Governmental Industrial Hygienists.)
(ii) The exhaust system shall discharge to the outer air in such a
manner that the possibility of its effluent entering any building is at
a minimum. Recirculation shall only be through a device for contaminant
removal which will prevent the creation of a health hazard in the room
or area to which the air is recirculated.
(iii) A volume of outside air in the range of 90 percent to 110
percent of the exhaust volume shall be provided to each room having
exhaust hoods. The outside air supply shall enter the workroom in such a
manner as not to be detrimental to any exhaust hood. The airflow of the
makeup air system shall be measured on installation. Corrective action
shall be taken when the airflow is below that required. The makeup air
shall be uncontaminated.
(9) Personal protection. (i) All employees working in and around
open-surface tank operations must be instructed as to the hazards of
their respective jobs, and in the personal protection and first aid
procedures applicable to these hazards.
(ii) All persons required to work in such a manner that their feet
may become wet shall be provided with rubber or other impervious boots
or shoes, rubbers, or wooden-soled shoes sufficient to keep feet dry.
(iii) All persons required to handle work wet with a liquid other
than water shall be provided with gloves impervious to such a liquid and
of a length sufficient to prevent entrance of liquid into the tops of
the gloves. The interior of gloves shall be kept free from corrosive or
irritating contaminants.
(iv) All persons required to work in such a manner that their
clothing may become wet shall be provided with such aprons, coats,
jackets, sleeves, or other garments made of rubber, or of other
materials impervious to liquids other than water, as are required to
keep their clothing dry. Aprons shall extend well below the top of boots
to prevent liquid splashing into the boots. Provision of dry, clean,
cotton clothing along with rubber shoes or short boots and an apron
impervious to liquids other than water shall be considered a
satisfactory substitute where small parts are cleaned, plated, or acid
dipped in open tanks and rapid work is required.
(v) Whenever there is a danger of splashing, for example, when
additions are made manually to the tanks, or when acids and chemicals
are removed from the tanks, the employees so engaged shall be required
to wear either tight-fitting chemical goggles or an effective face
shield. See Sec. 1926.102.
(vi) When, during the emergencies specified in paragraph (i)(11)(v)
of this section, employees must be in areas where concentrations of air
contaminants are greater than the limits set by paragraph (i)(2)(iii) of
this section or oxygen concentrations are less than 19.5 percent, they
must use respirators that reduce their exposure to a level below these
limits or that provide adequate oxygen. Such respirators must also be
provided in marked, quickly-accessible storage compartments built for
this purpose when the possibility exists of accidental release of
hazardous concentrations of air contaminants. Respirators must be
approved by NIOSH under 42 CFR part 84, selected

[[Page 70]]

by a competent industrial hygienist or other technically-qualified
source, and used in accordance with 29 CFR 1926.103.
(vii) Near each tank containing a liquid which may burn, irritate,
or otherwise be harmful to the skin if splashed upon the worker's body,
there shall be a supply of clean cold water. The water pipe (carrying a
pressure not exceeding 25 pounds (11.325 kg)) shall be provided with a
quick opening valve and at least 48 inches (1.216 m) of hose not smaller
than three-fourths inch, so that no time may be lost in washing off
liquids from the skin or clothing. Alternatively, deluge showers and eye
flushes shall be provided in cases where harmful chemicals may be
splashed on parts of the body.
(viii) Operators with sores, burns, or other skin lesions requiring
medical treatment shall not be allowed to work at their regular
operations until so authorized by a physician. Any small skin abrasions,
cuts, rash, or open sores which are found or reported shall be treated
by a properly designated person so that chances of exposures to the
chemicals are removed. Workers exposed to chromic acids shall have a
periodic examination made of the nostrils and other parts of the body,
to detect incipient ulceration.
(ix) Sufficient washing facilities, including soap, individual
towels, and hot water, shall be provided for all persons required to use
or handle any liquids which may burn, irritate, or otherwise be harmful
to the skin, on the basis of at least one basin (or its equivalent) with
a hot water faucet for every 10 employees. See Sec. 1926.51(f).
(x) Locker space or equivalent clothing storage facilities shall be
provided to prevent contamination of street clothing.
(xi) First aid facilities specific to the hazards of the operations
conducted shall be readily available.
(10) Special precautions for cyanide. Dikes or other arrangements
shall be provided to prevent the possibility of intermixing of cyanide
and acid in the event of tank rupture.
(11) Inspection, maintenance, and installation. (i) Floors and
platforms around tanks shall be prevented from becoming slippery both by
original type of construction and by frequent flushing. They shall be
firm, sound, and of the design and construction to minimize the
possibility of tripping.
(ii) Before cleaning the interior of any tank, the contents shall be
drained off, and the cleanout doors shall be opened where provided. All
pockets in tanks or pits, where it is possible for hazardous vapors to
collect, shall be ventilated and cleared of such vapors.
(iii) Tanks which have been drained to permit employees to enter for
the purposes of cleaning, inspection, or maintenance may contain
atmospheres which are hazardous to life or health, through the presence
of flammable or toxic air contaminants, or through the absence of
sufficient oxygen. Before employees shall be permitted to enter any such
tank, appropriate tests of the atmosphere shall be made to determine if
the limits set by paragraph (i)(2)(iii) of this section are exceeded, or
if the oxygen concentration is less than 19.5 percent.
(iv) If the tests made in accordance with paragraph (i)(11)(iii) of
this section indicate that the atmosphere in the tank is unsafe, before
any employee is permitted to enter the tank, the tank shall be
ventilated until the hazardous atmosphere is removed, and ventilation
shall be continued so as to prevent the occurrence of a hazardous
atmosphere as long as an employee is in the tank.
(v) If, in emergencies, such as rescue work, it is necessary to
enter a tank which may contain a hazardous atmosphere, suitable
respirators, such as self-contained breathing apparatus; hose mask with
blower, if there is a possibility of oxygen deficiency; or a gas mask,
selected and operated in accordance with paragraph (i)(9)(vi) of this
section, shall be used. If a contaminant in the tank can cause
dermatitis, or be absorbed through the skin, the employee entering the
tank shall also wear protective clothing. At least one trained standby
employee, with suitable respirator, shall be present in the nearest
uncontaminated area. The standby employee must be able to communicate
with the employee in the tank and be able to haul him out of the tank
with a lifeline if necessary.

[[Page 71]]

(vi) Maintenance work requiring welding or open flame, where toxic
metal fumes such as cadmium, chromium, or lead may be evolved, shall be
done only with sufficient local exhaust ventilation to prevent the
creation of a health hazard, or be done with respirators selected and
used in accordance with paragraph (i)(9)(vi) of this section. Welding,
or the use of open flames near any solvent cleaning equipment shall be
permitted only after such equipment has first been thoroughly cleared of
solvents and vapors.
(12) Vapor degreasing tanks. (i) In any vapor degreasing tank
equipped with a condenser or vapor level thermostat, the condenser or
thermostat shall keep the level of vapors below the top edge of the tank
by a distance at least equal to one-half the tank width, or at least 36
inches (0.912 m), whichever is shorter.
(ii) Where gas is used as a fuel for heating vapor degreasing tanks,
the combustion chamber shall be of tight construction, except for such
openings as the exhaust flue, and those that are necessary for supplying
air for combustion. Flues shall be of corrosion-resistant construction
and shall extend to the outer air. If mechanical exhaust is used on this
flue, a draft diverter shall be used. Special precautions must be taken
to prevent solvent fumes from entering the combustion air of this or any
other heater when chlorinated or fluorinated hydrocarbon solvents (for
example, trichloroethylene, Freon) are used.
(iii) Heating elements shall be so designed and maintained that
their surface temperature will not cause the solvent or mixture to
decompose, break down, or be converted into an excessive quantity of
vapor.
(iv) Tanks or machines of more than 4 square feet (0.368 m\2\) of
vapor area, used for solvent cleaning or vapor degreasing, shall be
equipped with suitable cleanout or sludge doors located near the bottom
of each tank or still. These doors shall be so designed and gasketed
that there will be no leakage of solvent when they are closed.
(13) Scope. (i) This paragraph (i) applies to all operations
involving the immersion of materials in liquids, or in the vapors of
such liquids, for the purpose of cleaning or altering their surfaces, or
adding or imparting a finish thereto, or changing the character of the
materials, and their subsequent removal from the liquids or vapors,
draining, and drying. Such operations include washing, electroplating,
anodizing, pickling, quenching, dyeing, dipping, tanning, dressing,
bleaching, degreasing, alkaline cleaning, stripping, rinsing, digesting,
and other similar operations, but do not include molten materials
handling operations, or surface coating operations.
(ii) Molten materials handling operations means all operations,
other than welding, burning, and soldering operations, involving the
use, melting, smelting, or pouring of metals, alloys, salts, or other
similar substances in the molten state. Such operations also include
heat treating baths, descaling baths, die casting stereotyping,
galvanizing, tinning, and similar operations.
(iii) Surface coating operations means all operations involving the
application of protective, decorative, adhesive, or strengthening
coating or impregnation to one or more surfaces, or into the interstices
of any object or material, by means of spraying, spreading, flowing,
brushing, roll coating, pouring, cementing, or similar means; and any
subsequent draining or drying operations, excluding open-tank
operations.

[44 FR 8577, Feb. 9, 1979; 44 FR 20940, Apr. 6, 1979, as amended at 58
FR 35099, June 30, 1993; 61 FR 9250, Mar. 3, 1996; 63 FR 1295, Jan. 8,
1998]