This is a case of Big Corporations (DuPont/Honeywell) buying influence. I don't understand why the EPA would mandate this extremely deadly and toxic HFO 1234yf, other than Dupont/Honeywell buying the EPA off. R134a is way safer and less toxic to the environment. DuPont claims it is hard to ignite but Mercedes showed that the substance ignited when researchers sprayed it and A/C compressor oil onto a car's hot engine. A senior Daimler engineer who ran the tests, stated "We were frozen in shock, I am not going to deny it. We needed a day to comprehend what we had just seen." Combustion occurred in more than two thirds of their simulated head-on collisions. The engineers also noticed etching on the windshield caused by the corrosive gases.[26] On September 25, 2012, Daimler issued a press release[9] and proposed a recall of cars using the refrigerant. The German automakers argued for continued use of carbon dioxide refrigerants, which they argued to be safer. These whacked out environmentalist obsession with carbon dioxide, all based on a theory. In the atmosphere, HFO-1234yf degrades to trifluoracetic acid which is a mildly phytotoxic strong organic acid with no known biodegradation mechanism in water. In case of fire it releases highly corrosive and toxic hydrogen fluoride and the highly toxic gas carbonyl fluoride. But hey at least it is not an evil carbon dioxide. You know CO2 its what we exhale, in every soda, plants need it to grow and it is the basis of all life on earth.