SAE International, after a new round of tests, said a controversial refrigerant favored by most automakers is safe for use in mobile air conditioning units.
The automotive engineering group conducted additional tests with 11 automakers after Daimler AG raised concerns last year about HFO-1234yf. The German automaker and parent of Mercedes-Benz voiced concerns that the refrigerant, jointly developed by Honeywell and DuPont Co., could ignite on the hot surface of an engine if mixed with air conditioning compressor oil, releasing dangerous hydrogen fluoride gas.
Daimler's concerns prompted SAE -- formerly known as the Society of Automotive Engineers -- to review tests and data, and retest the refrigerant after Daimler found problems with it during simulated crash tests in August.
SAE now calls those simulated crash tests "unrealistic."
"Their testing created extreme conditions that favored ignition while ignoring many mitigating factors that would be present in an actual real-world collision," SAE said in a report.
According to the report, the risk of a fire caused by the refrigerant is low compared with other potential causes of ignition and "well below risks that are commonly viewed as acceptable by the general public."
SAE said a person was 20,000 times more likely to die in a plane crash than be exposed to a vehicle fire caused by a leak and ignition of HFO-1234yf.
A DuPont spokeswoman said the company was pleased with the report, and endorses the methodology SAE used to conduct tests on the refrigerant.
"We believe this kind of transparent approach is necessary if the results of an evaluation are to have meaning for industry members and regulators around the world," the spokeswoman said.
The 11 automakers that worked with SAE on the latest test and review include Chrysler Group, Fiat, Ford Motor Co., General Motors, Honda Motor Co., Hyundai Motor Co., Jaguar Land Rover, Mazda, PSA Peugeot Citroen, Renault and Toyota Motor Corp.
Daimler did not participate in the latest tests, but it took part in initial testing in December, according to Reuters.
A Daimler spokesman wrote in an e-mail that the company stopped participating in the tests because it believes SAE's methodology "dilutes the results." He denounced claims that Daimler's testing is unrealistic.
"Our reproducible test procedure models refrigerant leakage in the engine compartment -- for example due to a severe head-on collision after engine load -- in real driving situations," the spokesman wrote. "The setup of our test is based -- among others -- on findings from our in-house accident research department and is considered by many experts as a realistic scenario."
SAE says that the recent tests addressed Daimler's concerns.
"The conclusions from SAE's latest expanded evaluation, combined with years of extensive testing in the U.S., Europe and elsewhere, again leaves no doubt that HFO-1234yf is safe for automotive applications," Ken Gayer, general manager for Honeywell Fluorine Products, said in a statement. "The fact that all 11 global automakers participating in the project agreed with the SAE [test] conclusions is further proof that this product can be used safely."
Daimler and Volkswagen backed off plans to use the chemical refrigerant this year while GM began adopting it across much of its vehicle lineup.
GM officials have publicly backed the refrigerant for months, noting said their tests did not reproduce the same results claimed by Daimler. In April, Opel, a GM subsidiary and a rival of Daimler and VW, said it would continue to use the refrigerant, according to Reuters. Ford also said that month that it found no problems with the product.
SAE's latest tests included an analysis of recent testing by automakers and vehicle crash data, on-vehicle simulations, laboratory simulations, bench tests and more than 100 releases of refrigerant in the engine compartment.
The refrigerant underwent an initial round of testing from 2007 to 2009 and was approved for use.