11
FLASHBACK
is the return of flame through the blowpipe into the hoses and even the regulators. Depending on its severity, it
may also reach the acetylene cylinder, causing heating and decomposition of the contents.
If any of these events occurs, especially flashback, immediately close the oxygen blowpipe valve followed by the fuel gas
blowpipe valve. Close cylinder valves and if cylinders heat up, cool as described below.
Check operating conditions and equipment faults before restarting. Discard any gas hose when flashback into the hose has
occurred.
Gas leaks
Leaking gas is a potential hazard wherever it occurs and whichever the gas. Fuel gases present the greatest hazard since all
commonly used fuels can ignite even when in low concentrations in air and require minimum energy to do so, i.e. any spark or
source of high temperature is sufficient to start a fire or an explosion.
Oxygen makes all materials more readily combustible and will increase the intensity and severity of any fire.
Inert gases displace oxygen and can cause unnoticed loss of alertness and then asphyxiation.
The sources of gas leaks include:
a)
Cylinder fittings (valves, safety devices) damaged or in poor condition
b)
Valves not closed off when equipment is not in use.
c)
Breakable connections improperly made up or in poor condition (scored or dirty nipples, conical seatings, O-rings).
The typical oxygen-fuel gas plant has many connections points in the cylinder valves, regulators, hoses, blowpipe and
tips and nozzles. Each of these is a potential leak point if not in good condition.
d)
Hoses in poor condition.
Whenever a gas leak is suspected or detected, operations should cease, the leak rectified immediately if possible, heat sources
removed or switched off and the area cleared until gas has dispersed.
Ignition of Oxygen Regulators, Hoses and other High Pressure Equipment
Although accidents of this type are rare, when they do occur the results may include serious injury, a major fire or even fatality.
Care in use and maintenance of oxygen regulators and other equipment is therefore extremely important.
Ignition may occur due to:
a)
Spontaneous ignition of oil, grease or hydrocarbon liquids in high pressure oxygen. Keep oil and grease away from
regulators and other equipment, do not use oil or grease as a lubricant for tight threads etc and do not use oily rags,
tools or operate with oily hands.
b)
Use of equipment (e.g. pressure regulators, manifolds, high pressure leads) not clearly designated as suitable for high
pressure oxygen and rated for the same pressure as the cylinders in use. Use only equipment clearly marked for
oxygen, of a suitable pressure rating, clean and in good operating condition.
c)
Particles entrained in high-velocity gas streams (e.g. piping, valve connections) causing ignition in cylinder valve or
regulator seats and seals. Cleanliness and generally good housekeeping practice are required. Always "crack" the
cylinder valve before fitting equipment.
d)
Rapid opening of the oxygen cylinder valve causing a high temperature at the regulator seat and seals.
The cylinder valve
MUST BE OPENED SLOWLY.
Cylinders in fires
The most common incidents are those involving ignitions of fuel leakages from regulator and hose connections near the
cylinder. If this occurs, as appropriate, either the cylinder valve should be closed or the pressure regulator adjusting screw
released, using a gloved hand, and the fire extinguished as soon as possible. Otherwise, use of a dry powder or CO2 fire
extinguisher should be followed by closing of the cylinder valve to prevent re-ignition.
If it is not possible to extinguish quickly fires of any type with a fire extinguisher, further attempts should not be made and:
a)
The area should be evacuated (100 metres minimum).
b)
The fire brigade should be called.
c)
If attempts are made to fight the fire, they should be done only from a protected position and using copious
quantities of water.
d)
Cylinders not involved in the fire and which have not become heated should be moved away as quickly as possible,
provided this can be done without risk. Cylinder valves should be closed. Cylinders which have been heated can
explode even after the fire has been extinguished, particularly acetylene cylinders.
e)
When the fire brigade arrives, they should be notified of the location and number of cylinders involved in the fire, and
the name of the gases they contain.
f)
Inform the gas supplier as soon as possible
g)
If the cylinder contents are unknown, the actions taken should be those for acetylene cylinders
INSTRUCTION MANUAL FOR UNI-FLAME
GAS WELDING, FLAME CUTTING AND GOUGING KIT
