Understanding Refrigerant Safety Classification Tech Note

Understanding Refrigerant Safety Classification

In Tech / Application Notesby Bacharach

Refrigerants can pose numerous hazards, including as it relates to toxicity, flammability, asphyxiation and / or physical hazards. The American Society of Heating, Refrigerating and Air-Conditioning Engineering (ASHRAE) Standard 34 classifies refrigerants by hazard based on toxicity and flammability.

The safety group classification for each refrigerant has two or three alphanumeric characters (e.g., B1 or A2L). The first character shows the toxicity and the numeral, with or without a suffix letter, indicates the flammability.

The following table provides an overview of ASHRAE’s Standard 34 refrigerant safety group classification.

Refrigerant Safety Group Classification
Lower Toxicity Higher Toxicity
Higher Flammability A3 R-290 (Propane), R-600a (Isobutane) B3
Lower Flammability A2


A2L* R-32, R-1234yf, R-1234ze(E) B2L* R-717 (Ammonia / NH3)
No Flame Propagation A1 R-22, R-124a, R-410A, R-1233zd(E), R-404A, R-407C, R-507A, R-744 (Carbon Dioxide / CO2) B1 R-123

Refrigerant Toxicity

There are two classes for toxicity: lower toxicity (Class A) and higher toxicity (Class B).

Class A refrigerants are refrigerants for which toxicity has not been identified at concentrations less than or equal to 400 parts per million (PPM) by volume, based on data used to determine threshold limit values (TLV)-time weighted average (TWA) or consistent indices.

Class B refrigerants are refrigerants for which there is evidence of toxicity at concentrations below 400 ppm by volume, based on data used to determine TLV-TWA or consistent indices.

Refrigerant Flammability

There are four classes of flammability: 1, 2L, 2 or 3.

Class 1 is for refrigerants that, when tested, show no flame propagation at 140°F (60°C) and 14.7 psia (101.3 kPa). Class 2 is for refrigerants that, when tested, exhibit flame propagation at 140°F (60°C) and 14.7 psia (101.3 kPa), have a heat of combustion less than 19,000 kJ/kg (8,174 British thermal units BTU/lb), and have a lower flammability limit (LFL) greater than 0.10 kg/m3.

Now, Class 2 is divided up into a subcategory of low versus high. In fact, refrigerants are designated in the 2L subclass if they have a maximum burning velocity of 3.9 in./s (10 cm/s) or lower when tested at 73.4°F (23.0°C) and 14.7 psia (101.3 kPa). The purpose of the 2L subclass is to reflect the lower flammability properties of the new low-GWP refrigerant options on the rise, such as hydrofluoro-Olefins (HFOs), like R-1234yf and R-1234ze.

Moreover, Class 3 is for refrigerants that, when tested, exhibit flame propagation at 140°F (60°C) and 14.7 psia (101.3 kPa) and that either have a heat of combustion of 19,000 kJ/kg (8,174 BTU/lb) or greater or a LFL of 0.10 kg/m3 or lower.

In sum, refrigerants in class “3” are highly flammable; refrigerants in class “2” are considered less flammable; and those in class “2L” are mildly flammable.

These classifications are used in the guidelines for determining how much refrigerant can be used in an occupied space. For example, in the case of ammonia, which is both toxic and flammable at the right concentration, the allowed concentration in an occupied space for ammonia is 320 ppm per ASHRAE Standard 34. (By contrast, R-32 is 36,000 ppm; R-32 has a low toxicity but it is flammable.)

Standards (e.g., ASHRAE 15 & EN 378) and guidelines use this number to determine what size charge can be permitted in a particular facility such that, if one were to leak all that charge into an occupied space, you would not exceed this concentration limit.

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