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COMBUSTIBILITY OF HFC-134a
HFC-134a is nonflammable at ambient temperatures and
atmospheric pressure. However, tests have shown
HFC-134a to be combustible at pressures as low as 5.5
psig (139.3 kPa absolute) at 177°C (350°F) when mixed
with air at concentrations generally greater than 60%
volume air. At lower temperatures, higher pressures are
required for combustibility. (HCFC-22 is also combustible
at pressures above atmospheric in the presence of high
air concentrations). Test results and calculations have
shown:
• At ambient temperature, all concentrations of
HFC-134a in air are nonflammable at pressures
below 15 psig (205 kPa absolute).
• Combustible mixtures of air and HFC-134a will not
form when liquid HFC-134a is pumped into closed
vessel if initial air pressure in vessel is limited
to one atmosphere absolute and final pressure
is limited to 300 psig (2,170 kPa absolute). If initial
air pressure is greater than one atmosphere,
combustible mixtures may form as tank is filled.
Based on above information, the following operating
practices are recommended:
Leak Testing
• Equipment should NEVER be leak tested with a
pressurized mixture of HFC-134a and air. HFC-
134a may be safely pressured with dry nitrogen.
Bulk Delivery and Storage
• Tanks should normally be evacuated at start of filling,
and should never be filled while underpositive
air pressure.
• Tank pressure should never be allowed to exceed 300
psig (2,170 kPa) when filling with HFC-134a. Relief
devices on either tanks or HFC-134a supply system
usually prevent this.
• Tank pressures should be monitored routinely.
• Air lines should never be connected to storage tanks.
Filling and Charging Operations
• Before evacuating cylinders or refrigeration
equipment, any remaining refrigerant should
be removed by recovery system.
• Vacuum pump discharge lines should be free
of restrictions that could increase discharge
pressures above 15 psig (205 kPa) and result
in formation of combustible mixtures.
• Cylinders or refrigeration equipment should normally
be evacuated at start of filling,and should never be
filled while under positive air pressure.
• Final pressures should not exceed 300 psig
(2,170 kPa).
• Filled cylinders should periodically be analyzed for
air (nonabsorbable gas or NAG).
Refrigerant Recovery Systems
Efficient recovery of refrigerant from equipment or
containers requires evacuation at the end of the recovery
cycle. Suction lines to a recovery compressor should be
periodically checked for leaks to prevent compressing
air into the recovery cylinder during evacuation. In
addition, the recovery cylinder pressure should be
monitored, and evacuation stopped in the event of a rapid
pressure rise indicating the presence of noncondensable
air. The recovery cylinder contents should then be
analyzed for NAG, and the recovery system leak checked
if air is present. DO NOT continue to evacuate a
refrigeration system that has a major leak.
THERMAL DECOMPOSITION
HFC-134a vapors will decompose when exposed to high
temperatures from flames or electric resistance heaters.
Decomposition may produce toxic and irritating
compounds, such as hydrogen fluoride. The pungent
odors released will irritate the nose and throat and
generally force people to evacuate the area. Therefore,
it is important to prevent decomposition by avoiding
exposure to high temperatures.
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