ASHRAE Standard 34: Refrigerant Safety Classifications

Document Summary

ASHRAE Standard 34 (Designation and Safety Classification of Refrigerants) is the canonical industry reference for assigning refrigerants to safety groups based on toxicity and flammability. The classification combines toxicity letters (A = lower toxicity, B = higher) with flammability digits (1 = no flame propagation, 2L = lower flammability, 2 = flammability, 3 = higher flammability). Class A3 is the highest flammability tier for non-toxic refrigerants. Propane (R-290) and isobutane (R-600a) are both A3. HCR 4141 is treated as an A3-equivalent blend per EPA SNAP submissions.