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OM-166 941 Page 2
atmosphere or where the radiant energy can penetrate
to atmospheres containing even minute amounts of
trichloroethylene or perchloroethylene.
C. Fire and Explosion Prevention
Causes of fire and explosion are: combustibles reached
by the arc, flame, flying sparks, hot slag or heated mate-
rial; misuse of compressed gases and cylinders; and
short circuits.
BE AWARE THAT flying sparks or falling slag can pass
through cracks, along pipes, through windows or doors,
and through wall or floor openings, out of sight of the
goggled operator. Sparks and slag can fly 35 feet.
To prevent fires and explosion:
Keep equipment clean and operable, free of oil, grease,
and (in electrical parts) of metallic particles that can
cause short circuits.
If combustibles are in area, do NOT weld or cut. Move
the work if practicable, to an area free of combustibles.
Avoid paint spray rooms, dip tanks, storage areas, ven-
tilators. If the work cannot be moved, move comb-
ustibles at least 35 feet away out of reach of sparks and
heat; or protect against ignition with suitable and snug-
fitting, fire-resistant covers or shields.
Walls touching combustibles on opposite sides should
not be welded on (or cut). Walls, ceilings, and floor near
work should be protected by heat-resistant covers or
shields.
Fire watcher must be standing by with suitable fire extin-
guishing equipment during and for some time after weld-
ing or cutting if:
a. appreciable combustibles (including building
construction) are within 35 feet
b. appreciable combustibles are further than 35
feet but can be ignited by sparks
c. openings (concealed or visible) in floors or walls
within 35 feet may expose combustibles to
sparks
d. combustibles adjacent to walls, ceilings, roofs,
or metal partitions can be ignited by radiant or
conducted heat.
Hot work permit should be obtained before operation to
ensure supervisor’s approval that adequate precau-
tions have been taken.
After work is done, check that area is free of sparks,
glowing embers, and flames.
An empty container that held combustibles, or that can
produce flammable or toxic vapors when heated, must
never be welded on or cut, unless container has first
been cleaned as described in AWS Standard A6.0,
listed 7 in Standards Index.
This includes: a thorough steam or caustic cleaning (or
a solvent or water washing, depending on the combusti-
ble’s solubility) followed by purging and inerting with ni-
trogen or carbon dioxide, and using protective equip-
ment as recommended in A6.0. Waterfilling just below
working level may substitute for inerting.
A container with unknown contents should be cleaned
(see preceding paragraph). Do NOT depend on sense
of smell or sight to determine if it is safe to weld or cut.
Hollow castings or containers must be vented before
welding or cutting. They can explode.
Explosive atmospheres. Never weld or cut where the air
may contain flammable dust, gas, or liquid vapors (such
as gasoline).
D. Compressed Gas Equipment
Standard precautions. Comply with precautions in this
manual, and those detailed in CGA Standard P-1, SAFE
HANDLING OF COMPRESSED GASES IN CYLIN-
DERS, listed 11 in Standards Index.
1. Pressure Regulators
Regulator relief valve is designed to protect only the
regulator from overpressure; it is not intended to protect
any downstream equipment. Provide such protection
with one or more relief devices.
Never connect a regulator to a cylinder containing gas
other than that for which the regulator was designed.
Remove faulty regulator from service immediately for
repair (first close cylinder valve). The following symp-
toms indicate a faulty regulator:
Leaks-if gas leaks externally.
Excessive Creep-if delivery pressure continues to rise
with downstream valve closed.
Faulty Gauge-if gauge pointer does not move off stop
pin when pressurized, nor returns to stop pin after pres-
sure release.
Repair. Do NOT attempt to repair. Send faulty regula-
tors for repair to manufacturer’s designated repair cen-
ter, where special techniques and tools are used by
trained personnel.
2. Cylinders
Cylinders must be handled carefully to prevent leaks
and damage to their walls, valves, or safety devices:
Avoid electrical circuit contact with cylinders including
third rails, electrical wires, or welding circuits. They can
produce short circuit arcs that may lead to a serious ac-
cident. (See 1-3C.)
ICC or DOT marking must be on each cylinder. It is an
assurance of safety when the cylinder is properly han-
dled.
Identifying gas content. Use only cylinders with name of
gas marked on them; do not rely on color to identify gas
content. Notify supplier if unmarked. NEVER DEFACE
or alter name, number, or other markings on a cylinder. It
is illegal and hazardous.
Empties: Keep valves closed, replace caps securely;
mark MT; keep them separate from FULLS and return
promptly.
Prohibited use. Never use a cylinder or its contents for
other than its intended use, NEVER as a support or
roller.