Executive Summary

From 2006 to 2009 SAE International administered a cooperative research project (CRP1234) 

which evaluated R-1234yf, a new low global warming potential (GWP) automotive refrigerant. 

Using fault tree analysis (FTA) the results of the CRP1234 assessment showed that the risk 

associated with the use of R-1234yf in automotive vehicles is well below those commonly 

considered acceptable by the general public and regulatory agencies. The risk assessment was 

submitted to the U.S. Environmental Protection Agency (US EPA) as part of the Significant New 

Alternatives Policy (SNAP) approval process, and the US EPA subsequently approved R-1234yf 

for use in US vehicles. 

In the EU, manufacturers are required to comply with the Mobile Air Conditioning (MAC) 

Directive (2006/40/EC) for new vehicle types effective 1 January 2011 with enforcement deferred 

to vehicles built on or after 1 January 2013. The EU commission has supported the introduction 

of R-1234yf as this meets the requirements of the MAC Directive. Manufacturers who have 

certified new vehicle types to this directive are obliged to build vehicles from 1 January 2013 

with a low global warming potential (GWP) refrigerant. 

On September 25, 2012 the German automotive manufacturer Daimler issued a press release 

suggesting that new testing conducted by the company had shown R-1234yf to pose a greater risk 

of vehicle fire than was estimated by the CRP1234 analysis. To address the Daimler claims, a 

new CRP (CRP1234-4) was organized in October of 2012. All OEMs were invited to attend. 

After extensive testing and analysis, the new CRP concluded that the refrigerant release testing 

completed by Daimler was unrealistic. Their testing created extreme conditions that favored 

ignition while ignoring many mitigating factors that would be present in an actual real-world 

collision. 

With this in mind, the new CRP, with input from Daimler, initiated two new fault tree scenarios 

to realistically address these claims. The new CRP also reviewed and analyzed extensive new 

OEM test data which was used to complete the new FTA. The two new fault tree scenarios 

consider the possibility of an individual being unable to exit the vehicle due to a collision or a 
non-collision event that involves a refrigerant/oil release, the refrigerant/oil being ignited and the 

fire propagating. The FTA examined average risks across the entire global fleet and used a 

number of conservative assumptions to ensure that the final risk estimate would be more likely to 

overestimate rather than underestimate actual risks. 

Based on the updated analysis, the estimated overall risk of vehicle fire exposure attributed to use 

of R-1234yf is conservatively estimated at 3 x 10-12 events per vehicle operating hour. This is 

nearly six orders of magnitude less than the current risk of vehicle fires due to all causes 

(approximately 1 x 10-6 per vehicle operating hour) and also well below other risks accepted by 

the general public. The table below shows the current overall risk of occupant exposure to 

adverse events based on R-1234yf usage is on the same order of magnitude as that estimated in 

the prior work of CRP1234. Therefore, the conclusions of the former CRP risk assessment are 

still valid: risks are still very small compared to the risks of a vehicle fire from all causes and well 

below risks that are commonly viewed as acceptable by the general public. All OEMs in the new 

CRP have indicated agreement with these conclusions. The members* are European, North 

American and Asian OEMs: Chrysler/Fiat, Ford, General Motors, Honda, Hyundai, Jaguar Land 

Rover, Mazda, PSA, Renault and Toyota. 

Probability of Various Adverse Events Compared to Estimated Probability of Events 

Associated with Vehicle Operation-Related Leaks of R-1234yf 

Event Probability per 

vehicle per 

operating hour 

Citation 

Probability of being in a police reported vehicle collision 4 x 10-5 NHTSA, 2013 

Probability of automotive vehicle fire (any cause) 1 x 10-6 Ahrens, 2013; FHA, 

2009 

Probability of vehicle collision due to vehicle brake failure 3 x 10-7 New York State DMV, 

2008 

Probability of dying in a regularly scheduled plane trip in a developed 

nation 7 x 10-8 Barnett, 2011 

Estimated probability of vehicle occupant/former occupant 

experiencing HF exposure above health based limits associated with 

an R-1234yf ignition event 

5 x 10-12 CRP1234, 2009 

Estimated probability of vehicle occupant being exposed to a 

vehicle fire due to R-1234yf ignition (due to leak and ignition in 

engine compartment) 

3 x 10-12 Current analysis 

Estimated probability of vehicle occupant being exposed to an open 

flame due to R-1234yf ignition (primarily due to leak and ignition in 

cabin) 

9 x 10-14 CRP1234, 2009 

*Daimler, BMW and Audi initially participated in the new CRP but eventually chose to withdraw.