HFO-1234yf has properties similar to HFC-134a, but is mildly flammable. Flammability was thoroughly considered in the multiple rigorous evaluations by industry stakeholders and by independent globally recognized third-party laboratories.
According to an SAE International presentation,(1) “Flammability testing at Hughes, Ineris, and Exponent labs have demonstrated the difficulty in igniting the HFO-1234yf refrigerant under the most severe testing conditions.” The presentation also states that “Risk assessment indicates a very low probability that an accidental release of refrigerant creates a sufficient concentration at the same time and location as a sufficient ignition source.” The risk assessments concluded that HFO-1234yf can be safely used in mobile air-conditioning. Safety standards have been published and address safe use guidelines.
Automobiles have in the engine compartment a number of materials that are significantly more flammable than HFO-1234yf, including brake and transmission fluids, coolant, lubricants, and gasoline. Automakers developed ways to enable them to safely use these materials, just as they have established recommendations to enable the safe use of HFO-1234yf.