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Transitioning to low-GWP refrigerants doesn’t mean compromising on safety. The leading low-GWP candidates to replace R-410A are flammable, but they fall into the “lower flammability” classification designated as “2L.” Contractors must be aware of and properly trained in risk mitigation and safety procedures when using new lower-flammability rated refrigerants. In this article, we’ll distinguish A2Ls from A1s, provide technical information on “lower flammability,” and offer suggestions for contractors to handle A2Ls.

How are A2Ls and A1s the same?

  • The majority of the physical and chemical properties of these new Class A2L refrigerants are similar to traditional A1 refrigerants.
  • Both A2L and A1 refrigerants use similar oils. But just like with A1s, each A2L refrigerant will use a different, specific oil.
  • Installation of equipment that run A2L refrigerants will use the same general processes and types of tools as an installation of equipment running A1 refrigerants.

How are A2Ls different than A1s and B2Ls?

  • A2Ls are rated as “lower flammability,” while A1s are rated as having “no flame propagation.”
  • There is another classification, B2L, in the 2L class, which is rated as lower flammability and “higher toxicity.” B2Ls are generally not considered for use in human-comfort cooling systems.

What characterizes A2Ls as lower flammability?

  • A2Ls have slow flame speed and low heat of combustion.
Figure 3: Flammable Gases, Severity of Combustion Event.

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Chart originally appeard in this article.

  • A2L refrigerants are difficult to ignite for two reasons: their Minimum Ignition Energy (MIE)s are 100 to 1000 times higher than common fuels, and their LFLs are more than five times higher than common fuels.
Figure 4: Flammable Gases, Probability of Ignition Event.

Click the chart to enlarge

Chart originally appeard in this article.

Sources of Ignition

The following sources have potential to ignite A2Ls:

  • hot wire
  • safety match
  • lighter flame insertion
  • an open flame impinging on leaked refrigerant

A2Ls did NOT ignite when AHRTI tested the following sources, because each source’s energy is much lower than the A2L’s MIE. However, all contractors and technicians must ensure that all ignition sources are absent from the work area, and follow best practices for installation, service and maintenance:

  • cigarette insertion
  • barbeque lighter
  • plug & receptacle
  • light switch
  • hand mixer
  • cordless drill
  • friction spark
  • hair dryer
  • toaster
  • hot plate insertion
  • space heater insertion.

Ignition of an A2L refrigerant requires two precursors:

  1. A sizable refrigerant leak that mixes with air enough to exceed the lower flammability limit (LFL)
  2. Presence of a “competent” ignition source (exceeds minimum ignition energy) in the area that exceeds LFL; usually an open flame or very high energy ignition source

What do I need to do about it?

  • Contractors should never use A2L refrigerants in equipment designed for A1 refrigerants. A2Ls should only be used in equipment specifically designed for the given A2L refrigerant.
  • Follow best practices for working with refrigerants and get training from third-party organizations (AHRI, ACCA, ESCO Group) and OEMs, and follow all requirements within installation and operations manuals.


New Safety Standards

The goal of safety standards, such as UL 60335-2-40 and ASHRAE 15, is to mitigate the risk of those two events occurring.

The new safety standards, UL 60335-2-40 and ASHRAE 15, include several mitigations such as:

  • Refrigerant charge limits
  • Requirements for adequate room size to allow for dispersion or dilution
  • Removal of “competent” ignition sources within the equipment
  • Circulation or ventilation to reduce refrigerant concentration
  • Refrigerant detection devices (sensors)

Safety standards can help maintain a sufficient level of safety when using these refrigerants.

For more information on refrigerant classifications, check out AHRI’s explanation of what the classifications mean (PDF).

As of November 2021, more than 160 million HVAC units from over 40 manufacturers are using the class A2L refrigerant R-32 are already operating safely around the world in chillers, packaged rooftops, VRF, residential splits and window air conditioning units. Learn more at