A2L – Mildly Flammable Refrigerants


01 September 2015

Jane Gartshore, from Cool Concerns, explores the challenges with A2L refrigerants.


There is no perfect refrigerant. To meet ever strengthening F Gas legislation we need refrigerants with a low global warming potential. But these refrigerants all have challenges – the high pressure and system differences associated with R744 or flammability.

There are a number of new HFC type refrigerants which have low flammability. For this type of refrigerant there is a trade-off between GWP and flammability – the refrigerants with the lowest GWP are flammable. The low GWP / low flammability HFCs include:

Refrigerant GWP Application
R32 675 ​Split AC, possibly VRV / VRF in future Performance similar to R410A
R1234ze 7 Trials in integrals and chillers Capacity lower than R134a so new compressors required
Solstice L20, L40, L41 <600 Honeywell replacements for R407C, R404A and R410A respectively, available for trials
DR3, DR7, DR5A <500 ​DuPont replacements for R407C, R404A and R410A respectively, available for trials

A: lower toxicity
1: non flammable
2L: lower flammability

B: higher toxicity
2: lower flammability
3: higher flammability
  • R404A and R744 are A1 refrigerants;
  • R717 is B2L;
  • Hydrocarbons such as R290 are A3 refrigerants;
  • The refrigerants listed in the table above (R32 etc.) are classified A2L.

Refrigerants are classified according to their toxicity and flammability

What does low flammability mean?

In accordance with ISO 817: 2014 Refrigerants -- Designation and safety classification ​

​The table below identifies the characteristics which determine the flammability classification.

No flame propagation when tested at 60C and 101.3 kPa

Safety classification Lower flammability level,% in air by volume Heat of combustion, J/kg Flame propagation
1 No flame propagation when tested at 60C and 101.3 kPa
2L, lower flammability > 3.5 <19,000 Exhibit flame propagation when tested at 60 degrees C and 101.3 kPa and have a maximum burning velocity of ≤ 10 cm/s when tested at 23 degrees C and 101.3 kPa
2, flammable > 3.5 <19,000 Exhibit flame propagation when tested at 60 degrees C and 101.3 kPa
3, higher flammability ≤3.5 ≤19,000 Exhibit flame propagation when tested at 60 degrees C and 101.3 kPa

In layman’s terms this means that, compared to propane, you need more of an A2L refrigerant to achieve a flammable mix, it is harder to ignite and when it is burning the flame travels more slowly.

  • When applying the refrigerant this means the maximum charge size is greater compared to HCs such as propane.
  • When handling the refrigerants this means you should take the same precautions as you would with a hydrocarbon.


Applying A2L refrigerants

EN378 is currently being revised and the revision will include A2L refrigerants. It provides data on lower flammability level and practical limits which then determine maximum charge sizes for different applications.

​As an illustration, the table below shows the maximum charge sizes for air conditioned room, using R290 (propane, an A3 refrigerant) and R32 (an A2L refrigerant). The calculations have been done for a wall mounted indoor unit.​

​Room size R290 max charge, kg R32 max charge, kg
3 m by 3 m 0.23 3.08
5 m by 9 m 0.51 6.89
​15.8 m by 15.8 m 1.19 16.24

The calculations are valid for split systems or VRV / VRF systems for comfort cooling or heating. Cooling using chillers would generally enable a larger maximum charge size.

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The different A2L refrigerants would have slightly different maximum charge sizes because they have different lower flammability levels, but the table shows that most splits will be able to use R32 with minimal problems, whereas for HC the charge limit is restrictive.

In addition, with A2L refrigerants if larger charge sizes are required, such as with VRV systems, it will be possible to use additional safety measures such as:

  • Refrigerant detection plus alarm;
  • Forced ventilation which can be permanent or turned on if refrigerant is detected;
  • Automatic valve shut down to limit the quantity of leaked refrigerant into the cooled room.


EN 378 Refrigerating systems and heat pumps — Safety and environmental requirements

Max charge from EN 378-1:2008 + A2:2012, C3.2 it.

Handling A2L refrigerants

As an industry we are already handling HC refrigerants – the handling of A2L refrigerant would follow the same procedure. In essence this includes:

  • Ensure the work area is well ventilated a free of sources of ignition;
  • Ensure the correct tools and equipment are used (e.g. R32 recovery machines are now available);
  • Prior to unbrazing, recover R32 from the system down to a vacuum and break the vacuum with dry nitrogen to avoid ignition;
  • Use appropriate leak detection.

Training for engineers on the safe use of A2L refrigerants is now available from suppliers and training providers (including Cool Concerns).


A2L refrigerants have a significant part to play if we are to reduce the GWP of the refrigerants we use. The low flammability poses some challenges. Appropriate training is required and for many systems additional safety measures are needed. These will increase costs but are not major barriers or show stoppers for most end users.

Further information can be provided by Cool Concerns Ltd, [email protected]

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