Refrigerant Safety Classes: ASHRAE 34 A1, A2L, A2, A3, B2L Explained

How to read a safety group

The safety group is set by ANSI/ASHRAE Standard 34. Per Addendum g to 34-2016, it has two or three characters: the capital letter is toxicity and the number, with or without a suffix letter, is flammability. That gives eight groups: A1, A2L, A2, A3, B1, B2L, B2 and B3.

The codes use these groups to decide charge limits, machinery room rules and listing requirements, so the class on the nameplate decides how the system may be installed. It is not a judgment about how dangerous a cylinder is to handle; every class is under pressure and every class can displace oxygen in a closed space.

Toxicity: A or B

A (lower toxicity): occupational exposure limit (OEL) of 400 ppm or more.
B (higher toxicity): OEL below 400 ppm.

Most fluorocarbons in AC and refrigeration are A. R-123 (B1) and ammonia (R-717, B2L) are the B refrigerants a field tech is most likely to meet. Table 1103.1 in the ICC 2024 A2L changes lists an OEL of 50 ppm for R-123 against 1,000 ppm for R-22 and R-410A.

Flammability: 1, 2L, 2 and 3

Flammability is tested to ASTM E681 with a spark ignition source. The criteria below are from Addendum g; values in parentheses are SI.

Class	Name	Criteria for a single-compound refrigerant
1	No flame propagation	No flame propagation when tested at 140°F (60°C) and 14.7 psia (101.3 kPa)
2L	Lower flammability	Flame propagates at 140°F and 14.7 psia, LFL above 0.0062 lb/ft³ (0.10 kg/m³), heat of combustion below 8,169 Btu/lb (19,000 kJ/kg), and maximum burning velocity of 3.9 in/s (10 cm/s) or less
2	Flammable	Flame propagates at 140°F and 14.7 psia, LFL above 0.0062 lb/ft³ (0.10 kg/m³), heat of combustion below 8,169 Btu/lb (19,000 kJ/kg), without the 2L burning velocity limit
3	Higher flammability	Flame propagates, and LFL of 0.0062 lb/ft³ (0.10 kg/m³) or less, or heat of combustion of 8,169 Btu/lb (19,000 kJ/kg) or more

The 10 cm/s burning velocity is what separates 2L from 2. The ICC fire code changes use the same line: a Category 1B flammable gas includes one with a fundamental burning velocity below 3.9 in/s (10 cm/s), and several explosion-control requirements do not apply to Category 1B gases at or under that velocity.

How 2L became its own class

The foreword to Addendum g says it “makes several changes with the intent to make 2L a separate classification of refrigerants.” Before that, refrigerants were assigned to three classes (1, 2, 3) with 2L as an optional subclass of Class 2. Addendum g changed this to four classes (1, 2L, 2, 3).

That is why older references and some code tables show R-32 or R-1234yf as “A2” with a note. Table 1103.1 in the ICC 2024 change document shows these refrigerants moved from A2 to A2L.

Blends: WCF and WCFF

A blend’s composition can drift within its manufacturing tolerance, and it fractionates during a leak because the components boil off at different rates. ASHRAE 34 handles this with two cases:

WCF (worst case formulation): the worst case of the blend as formulated, before any leak.
WCFF (worst case of fractionation for flammability): the worst case composition reached as the blend fractionates, determined from a fractionation analysis (Normative Appendix B, Section B2 of the standard).

Addendum g classifies blends on both their WCF and WCFF, and each must meet the class criteria. A fractionation analysis is not required if all components are in the same class. Blends whose flammability or toxicity can change as they fractionate get a safety group based on the worst case of fractionation.

This is why R-454B (R-32 plus R-1234yf, both 2L) is 2L. It is also why some A1 blends contain a flammable component such as R-32 or a hydrocarbon and still rate A1: their worst cases do not propagate flame. On the job, fractionation is the reason zeotropic blends are charged as liquid; see the temperature glide calculator.

Common refrigerants by safety group

Classes are from IMC Table 1103.1 as printed in the ICC 2024 A2L change document, except R-717, which is from ASHRAE 34 as recorded in our refrigerant data (EPA SNAP pages still print B2 for ammonia).

Group	Refrigerants
A1	R-22, R-134a, R-410A, R-404A, R-407C, R-448A, R-449A, R-513A, R-744 (CO2), R-1233zd(E)
A2L	R-32, R-454B, R-454A, R-454C, R-455A, R-452B, R-1234yf, R-1234ze(E)
A2	R-152a
A3	R-290 (propane), R-600a (isobutane)
B1	R-123
B2L	R-717 (ammonia)

Why the class matters in the field

The class drives the rules a tech meets on the job:

Equipment listing. In the ICC required changes to the 2021 IRC, A2L systems must be listed to UL/CSA 60335-2-40 (M1411.2), while A1 systems may be listed to UL/CSA 60335-2-40 or UL 1995.
Comfort cooling. IMC 1104.3.1 (ICC 2024 changes) says high-probability systems used for human comfort must use Group A1 or A2L refrigerant, with listed exceptions.
Charge limits and room area. UL 60335-2-40 limits charge against room area for flammable refrigerants. In an ASHRAE Journal roundtable, UL’s Brian Rodgers described the m1 limit as the charge limit when only room area is used (m1 ≤ 6 × LFL), with mitigation required above it. See refrigerant detection systems.
Cylinder marking. AHRI Guideline N-2017 defines flammable refrigerants as those rated 2, 2L or 3 in ASHRAE 34 and calls for a red band on the container shoulder or top. See refrigerant cylinder colors.

Editions to know

ASHRAE 34-2016, Addendum g: made 2L a separate class (the addendum document is dated June 2018).
ASHRAE 34-2022: the edition referenced by the 2024 I-Codes, per the ICC IRC change document’s referenced-standards list.
ASHRAE 34-2024: the current edition. The UNEP/ASHRAE factsheet summarizes designations and classes under 34-2024 with addenda.

Classifications for new blends are added by addenda, so check the current factsheet when a nameplate shows a refrigerant you have not seen before.

Refrigerant flammability and safety classes

Key facts