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R R e e f f r r i i g g e e r r a a t t i i o o n n S S y y s s t t e e m m
C C o o m m b b u u s s t t i i b b i i l l i i t t y y o o f f H H F F C C - - 1 1 3 3 4 4 a a
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.
B B a a s s e e d d o o n n a a b b o o v v e e i i n n f f o o r r m m a a t t i i o o n n , , t t h h e e f f o o l l l l o o w w i i n n g g
o o p p e e r r a a t t i i n n g g p p r r a a c c t t i i c c e e s s a a r r e e r r e e c c o o m m m m e e n n d d e e d d : :
L L e e a a k k T T e e s s t t i i n n g g
•
Equipment should NEVER be leak tested with
a pressurized mixture of HFC-134a and air.
HFC-134a may be safely pressured with dry
nitrogen.
B B u u l l k k D D e e l l i i v v e e r r y y a a n n d d S S t t o o r r a a g g e e
•
Tanks should normally be evacuated at start of
filling, and should never be filled while under
positive 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.
F F i i l l l l i i n n g g a a n n d d C C h h a a r r g g i i n n g g O O p p e e r r a a t t i i o o n n s s
•
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).
R R e e f f r r i i g g e e r r a a n n t t R R e e c c o o v v e e r r y y S S y y s s t t e e m m s s
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.
T T h h e e r r m m a a l l D D e e c c o o m m p p o o s s i i t t i i o o n n
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.
4-18
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