HC-12a
Bruce G Bostwick
being flammable ... If I get in a wreck bad enough to release the
refrigerant from my A/C, I'm going to be *much* more worried about the 20
gallons of *much* more flammable and/or _EXPLOSIVE_ gasoline under me
than I am about a few liters of propane/butane mix.
Besides, don't R-12 and R-134a both turn into *seriously* toxic stuff when
they get hot? I'd almost rather the refrigerant catch fire ...
<BGB> li...@ccwf.cc.utexas.edu
Thomas V. Myers
It's almost trivial to puncture the condensor in a relatively minor
collision. It's hanging out there barely behind your bumper. It's even more
fun when somebody with no brakelights stops in front of you at night. You
hit their rear end, rupturing your condensor AND shattering one or both
headlights leaving hot filaments hanging in the breeze blowing out of the
condensor. Propane + hot filament = torch. Pressure drops, flame flashes
back inside the condensor, BOOM.
Gasoline generally doesn't explode within the tank. If the fuel lines are
broken or the tank is ruptured, it goes all over and burns VERY hot, but so
does propane/butane. Exploding gas tanks are stuff for movies and NBC.
Cheers, Tom
--
Tom Myers : tvm...@icdc.delcoelect.com
JWISNIA
tvm...@koicds01.icdc.delcoelect.com (Thomas V. Myers) writes:
>>>>>Propane + hot filament = torch. Pressure drops, flame flashes
back inside the condensor, BOOM.<<<<<
Do you really think the condensor would create much shrapnel which could
find its way back to the passenger compartment? Seems to me that there's
not much volume inside a condensor, I bet it would just split a seam or
two. Any DATA on this available?
Reminds me of the time I had a beautiful '72 Buick Electra convertible
(What a LOCOMOTIVE that one was) which had a bit of RUBBER fuel line
feeding the carb. Anyway that line developed a crack or pinhole leak and
started spraying gas into the engine compartment. I started smelling fuel
and pulled to a stop just as something touched it off with a WHOOM that
popped the hood open. I bailed out and cried while I watched the car burn
'till the fireboys got there. What a sad day that was....
George Goble
>Bruce G Bostwick (ll...@utxdp.dp.utexas.edu) wrote:
>> I always have to laugh when I hear the oft-repeated concerns about HC-12a
>> being flammable ... If I get in a wreck bad enough to release the
>> refrigerant from my A/C, I'm going to be *much* more worried about the 20
>> gallons of *much* more flammable and/or _EXPLOSIVE_ gasoline under me
>> than I am about a few liters of propane/butane mix.
>
>> Besides, don't R-12 and R-134a both turn into *seriously* toxic stuff when
>> they get hot? I'd almost rather the refrigerant catch fire ...
>
>It's almost trivial to puncture the condensor in a relatively minor
>collision. It's hanging out there barely behind your bumper. It's even more
>fun when somebody with no brakelights stops in front of you at night. You
>hit their rear end, rupturing your condensor AND shattering one or both
>headlights leaving hot filaments hanging in the breeze blowing out of the
>condensor. Propane + hot filament = torch. Pressure drops, flame flashes
>back inside the condensor, BOOM.
Gasoline, methane, ethane, propane, butane, pentane, hexane, heptane,
octane, nonane .. asphaltane.. are all hydrocarbons, and all have
roughly the same upper and lower limits of flammability in air..
Roughly 2-8% in air by volume, or they will not even burn.
It is the vapor which "burns".. Gasoline == (pentane thru nonane
blend of hydrocarbons + detergents + octane boosters, etc)
Heavier hydrocarbons have more heat of combustion once they are
ignited.
The biggest danger from ANY hydrocarbons (propane or gasoline), is to
let a bunch of it out and have it NOT ignite.. until a big cloud
of fumes form.. and then ignite it.. you will get an explosion.
Gasoline will pool under the car after a wreck, and set there
giving off fumes. Propane/butane refrigerant (only 1.5lb in
the total A/C).. will flash off to gas immediately, and dissapate.
One also has engine oil, brake fluid, dripping on hot manifolds,
forming explosive vapor.. Approx 4-5 Qt of oil @ ~5lb/gal so
there is more than refrigerant..
Say, you still manage to ignite the propane leaking out of the
condensor, the fire will stay 1-2 feet away from the leak..
as the propane which is closer is moving faster than the flame
propagation speed and even if the flame did reach the condenser,
it will not "blow up".. since it would have to contain 92-98%
air (2-8% propane/butane) to burn back inside the condenser
and explode (same goes for lighting off hair spray, etc)
>
R-12 systems contain about 8-12oz of "mineral" oil, which is not
all that flammable.. but when mixed with R-12, and a "blowout"
happens (in a wreck).. the R-12 blows out oil, and the R-12
flashes to vapor immed.. leaving an oil aerosol or fog. This
fog is very flammable. We have made 10 foot diameter "fireballs"
with just a couple of oz of R-12/oil mixtures
>Gasoline generally doesn't explode within the tank. If the fuel lines are
>broken or the tank is ruptured, it goes all over and burns VERY hot, but so
>does propane/butane. Exploding gas tanks are stuff for movies and NBC.
This is true.
There is much much more gasoline than refrigerant in a car. Exploding
air conditioners are for generating "fear" in the public to achieve
some other end.. such as deciding to buy a new car instead (with R-134a)..
There is SOME risk with hydrocarbon refrigerants, just like R-12/oil..
50,000 things had hydrocarbon refrigerants last year.. and there were
no reported "safety" incidents from all that.. Hydrocarbons are a MUCH
GREATER RISK to the pocketbooks of the automakers, and the chemical
companies.. since they are so cheap, there is no money to be made on them.
By keeping old cars running (with A/C).. Billions of $$$ of premature
new car sales are prevented...you go figure...
>
> Cheers, Tom
>--
>Tom Myers : tvm...@icdc.delcoelect.com
--ghg
George Goble
>In article <Ctzt2...@icdc.delcoelect.com>,
>tvm...@koicds01.icdc.delcoelect.com (Thomas V. Myers) writes:
>
>>>>>>Propane + hot filament = torch. Pressure drops, flame flashes
>back inside the condensor, BOOM.<<<<<
>
>Do you really think the condensor would create much shrapnel which could
>find its way back to the passenger compartment? Seems to me that there's
>not much volume inside a condensor, I bet it would just split a seam or
>two. Any DATA on this available?
There is no air in the condenser.. combustion needs fuel + oxidizer..
Explosion needs fuel + oxizider intimately mixed beforehand..
If you really want to worry, look at those "tire inflator/sealer" kits..
Many of them contain propane/butane for the propellant/fill gas..
Now you have air in the tire, mixed with fuel, under pressure..
this is a BOMB by defination. There have been reports of service
stations nearly leveled when the attendant let the air/propane out,
and lit a cigarette.. those tires can have the explosive power of
a grenade or more... Nobody talks much about those..
Tire inflators are not a major economic threat to anyone..
But a recent Popular Mechanics ran an article titled "50,000
Grenades on Wheels".. They weren't referring to tire inflators
either..(hint: OZ-12 refrigerant).. Now go count all the ADvertizing
from the car companies in the magazine... and go figure out
what happens if said advertizing disapeared for a couple of years..
--ghg
John De Armond
>headlights leaving hot filaments hanging in the breeze blowing out of the
>condensor. Propane + hot filament = torch. Pressure drops, flame flashes
>back inside the condensor, BOOM.
As with most phobias, this one is based in fiction. Until one can propose
a viable method whereby the interior of the condensor is somehow
optimally oxygenated in the instant between the end of discharge and
the extinguishment of the flame, this scenario remains the product of a
vivid imagination. And if you've ever attempted to make a pipe bomb
from copper pipe filled with propane and oxygen (NOT air), you'll realize
that what WOULD happen were there to be sufficient oxygen inside the
condenser would be a "pop" as the condenser failed in one place, probably
at the leak and let the combustion gases escape.
>Gasoline generally doesn't explode within the tank. If the fuel lines are
>broken or the tank is ruptured, it goes all over and burns VERY hot, but so
>does propane/butane. Exploding gas tanks are stuff for movies and NBC.
As are exploding condensers. Guess this is the "unintended acceleration"
albatross of the air conditioning world.
John
--
John De Armond, WD4OQC, Marietta, GA j...@dixie.com
Performance Engineering Mag. Unsolicited email published at my sole discretion
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