Yes, as stated originally, different refrigerants are OK'd by EPA for different purposes. Even hazardous ammonia is OK for a stationary food refrigeration plant. (Not many of these collide at 65 mph, so the hazards are different.)
Also as stated earlier, the manufacturer is not the preferred source of info, and may misdirect you to different info. For example, Autoignition temperature, the temp where a material will self ignite WITHOUT THE PRESENCE OF AN EXTERNAL IGNITION SOURCE (such as underhood wiring, coils, etc) is a different consideration than flash point or upper and lower explosive limits. Consulting the Manufacturers Material Safety Data Sheets provides REAL data.
For example, the autoignition temp for propane is 871 F, but the propane flash point is -156F, and the LEL/UEL (lower and upper explosive concentration levels) are 2.1 to 9.5%. Gasoline has an autoignition temp of 495F, a flash point of -50 (less hazardous than the propane), and a more narrow range of explosive levels 1.4-7.6% LEL/UEL. R134a has no flammability, autoignition temp, or flash point. It is NOT flammable, whereas propane and gasoline are both listed as Highly Flammable. The "much higher autoignition temp than r134a" exists because the non-flammable r134a quenches the autoignition temp of the propane, and ANY temperature is 'much higher' than no temperature.
While r134a can decompose at extremely high temperatures to create acids, and has lethal asphyxiation capabilities and medical side effects at very high concentraions, Propane is an anasthetic gas at moderately high concentrations, and is also an asphyxiant at high concentrations. It will kill you just as dead as the 134a.
The NFPA lists r134a as a 2 out of 4 (4 being worst) for health effects, 0 for flammability, 0 for reactivity. Propane is listed as a 1/4/0 - less of a health effect, maximum flammability, no reactivity.
Since Freeze 12 is apparently a mixture of 80% r134a and 20% propane, I fail to see any health advantage (in fact, there is now a sum of the health hazards). Also, a flammable component has been added to the 'mix'.
This is not a pitch for people to use r134a, or a defense of the EPA as the ultimate authority for everything, or a claim that cars are going to burst into flame from using Freeze 12. It sounds as if a proper legal conversion may be a good choice for a refrigerant, and it is on the EPA authorized list. The possible extra cooling from adding 20% propane to r134 may offset the minimal increase in flammable material accident potential. The issues of proper conversion, compressor warantee, proper labelling, oil compatibility, etc. are also worth considering.
To deny, minimize, or obfuscate that there is a hazard, even a very small one, is irresponsible. To claim 'Drop In' status is illegal. The only manufacturer document that is certified to not be an advertising pitch or redirect of your question is a Material Safety Data Sheet. If you don't have the experience to use the MSDS, then go with the EPA determination over a manufacturers advertising, FAQs, or 'facts' quoted out of context or for systems not remotely similar in application to your proposed use. Then research the issues EPA doesn't cover, such as compressor life span.
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Last edited by JCE; 04-16-2002 at 11:41 PM.