Chemical refrigerants are assigned an R number which is determined systematically according to molecular structure. Common refrigerants are frequently referred to as Freon (a registered trademark of DuPont). The following is a list of refrigerants with their Type/Prefix, ASHRAE designated numbers, IUPAC chemical name, molecular formula, CAS registry number / Blend Name, Atmospheric Lifetime in years, Semi-Empirical Ozone depletion potential, net Global warming potential over a 100-year time horizon, Occupational exposure limit/Permissible exposure limit in parts per million (volume per volume) over a time-weighted average (TWA) concentration for a normal eight-hour work day and a 40-hour work week, ASHRAE 34 Safety Group in Toxicity & Flammability (in Air @ 60 °C & 101.3 kPa) classing, Ref