LETHAL R-134a concentrations from evaporator failure

ghg at worldserver.com ghg at worldserver.com
Mon Nov 3 07:41:07 EST 1997


LETHAL R-134a CONCENTRATIONS IN PASSENGER COMPARTMENTS MAY OCCUR
FROM EVAPORATOR FAILURE

In August 1997, a study was done at the Armstrong laboratory, Wright
Patterson Air Force Base, Dayton, OH. The report, "Human Inhalation of
Halon 1301, HFC-134a and HFC-227ea for Collection of Pharmacokinetic
Data" was authored by A. Vinegar, R. Cook, J McCafferty, M. Caracci, and
G. Jepson.

The concentration of R-134a being used was extremely low and (then
thought) that nothing bad was going to happen. To quote from the bottom
of page 10 (page 11 if abstract prepended), "Subject #3 was the first
volunteer exposed to

HFC-134a.  The exposure concentration was 4000 ppm (0.4% v/v) and was
scheduled to last for 30 minutes with a 5 minute postexposure evaluation
period as was accomplished in the Halon 1301 portion of the study. 
Approximately 4.5 minutes into the exposure, the subject lost
consciousness and both pulse and blood pressure dropped to zero."

The test was aborted and medical personnel intervened and revived the
subject.
Suppose it wasnt a test in a medical lab, that person would be "dead".

The industry, has in general, tried to "coverup" this "problem", often
reporting "Human Subject Faints During Botched Air Force R-134a
Inhalation test".  They then go on to theorize that the nurse wiggled the
blood drawing needle and that made the subject "faint".  See (on the web)
www.autofrost.com/humanhal2.pdf to download your own copy or call Monroe
Air Tech at 1-800-424-3836 for a copy. Be your own judge.  Using "0.4%"
(4000 ppm) parts per million of R-134a vapor in air as the "lethal"
amount, the following calculations were performed on several late model
cars.  They assume a bad evaporator leak or rupture, allowing the factory
listed charge amount

to escape into the passenger compartment.  R-134a is heavier than air, so
if the air is not "stirred" by a fan, heavier concentrations will be
found in low spots and lower in high spots.  For these purposes, we will
assume the air is stirred and the concentration is uniform.

The specific Volume of R-134a vapor at "normal" pressure (from the NIST
Standard Reference Database 23 "NIST THERMODYNAMIC PROPERTIES OF
REFRIGERANTS AND REFRIGERANT MIXTURES") is 3.69 cubic feet per pound
(cf/lb).  If you blow off a 1 lb can of R-134a into am empty garbage bag
(sealed), it will occupy 3.69 cubic feet.

	     SPECVOL134a CF   R-134a CHG lb         1        1,000,000 parts
conc. (ppm) = -----------   X -------------  X   --------  X
----------------
		  lb                            Int.Vol CF   per million

1998 CAR		Interior(CF)	lb R134a  pass.conc ppm  Times
lethal
Ford Escort		87		1.75	  74,224	  18.6
GEO Prism		84		1.7	  74,679	  18.7
Chevy Cavalier		92		1.5	  60,163	  15.0
Ford Taurus		101		2.13	  77,819	  19.5
Ford F150*		80		2.38	  109,778	  27.4
Toyota Camry		96.8		1.88	  71,665	  17.9
Ford Mustang		83		2.13	  94,695	  23.7
Chevy Malibu		98.6		1.75	  65,492	  16.4
Honda Accord		90.4		1.43	  58,371	  14.6
Chevy S-10*		80		2	  92,250	  23.1
Chevy MonteCarlo	96.1		2	  76,795	  19.2
Olds Cutlass Supreme	95		1.75	  67,974	  17.0
Buick Skylark		87		2.25	  95,431	  23.9
BMW 5 Series		93.5		3.27	  129,051	  32.3
* Estimated, since interior volume was not available

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