Flammable Refrigerants

Understanding Refrigerant Toxicity & Flammability

You may have noticed these while looking through Safety Data Sheets. You may have noticed them when looking at labels on refrigerant cylinders. I hope you noticed them while you were in the classroom. Either way, there are a lot of questions about how refrigerants and their safety group classifications and I’m going to do my best to answer them.

ASHRAE has come up with a classification of refrigerants that measures them by toxicity and by flammability. ASHRAE, or American Society of Heating and Air-Conditioning Engineers, has been around all the way back since 1894. They provide a collection of the technical and educational information in the heating, ventilating, refrigerating, and air-conditioning. Their official site can be found by clicking here. Through most circles they are seen as the standard bearer and the first most resource when it comes to refrigeration safety.


It should be noted that all substances can be toxic in sufficient amounts. Toxic effects have been observed in some of the most mundane substances such as water, salt, oxygen, and carbon dioxide but all of these were in extreme quantities. The key and the main difference between what is deemed as safe and what is viewed as toxic is the quantity or concentration needed to cause harm, and in some cases, the duration or repetition of exposure. Substances that pose a high risk with small quantity, even with short exposures, are regarded as highly toxic.

When it comes to refrigerants ASHRAE has divided them into two groups according to their toxicity:

  • Class A toxicity signifies refrigerants for which toxicity has not been identified at concentrations of less than or equal to four-hundred parts per million. Some example refrigerants that are rated as non toxic are R-22, R-134a, R-410A.
  • Class B toxicity signifies refrigerants for which there is evidence of toxicity at concentrations below four hundred parts per million. Some example refrigerants are Ammonia (R-717), and Opteon XP30 (R-514A).

As far as toxic refrigerants there are very few that are still on the market place today. Going back in time to the beginning of refrigeration toxicity was a problem with Ammonia but in today’s world there are very few toxic refrigerants that are still used.

That being said, there may be a resurfacing of toxic refrigerants with the new Hydrofluroolefin line of refrigerants that are being developed. As an example the new Opteon XP30 (R-514A) is rated as a class B toxicity level. This new refrigerant is designed to be a replacement for R-123 for centrifugal chillers. To be fair R-123 is also rated as a B classification so nothing has really changed here.


As I am sure most of you know flammability is a measurement of a substance’s ability to burn or ignite causing a fire or combustion. The two things that you look for when measuring flammability are what’s known as flash point and vapor pressure. The flash point is the absolute lowest temperature of a substance at which it can vaporize to form an ignitable mixture in the air. Vapor pressure indicates the evaporation rate. The higher the vapor pressure the lower the flash point and the higher flammability risk.

When it comes to refrigerants and their flammability ASHRAE has measured and classified them by three groupings:

  • Class 1 – No Flame Propagation.
    • This class indicates refrigerants that do not show flame propagation when tested in air at 21° Celsius (69.8° Fahrenheit) and 101 KPA. (14.6488 pounds of force per square inch.) In other words there is no risk here for flammability. Some example refrigerants are R-134a, R-410A, and R-22.
  • Class 2 – Lower Flammability
    • This class indicates refrigerants having a lower flammability limit of more than 0.10 kilograms per cubic meter or 0.0062 pounds per cubic foot at 21° Celsius (69.8° Fahrenheit) and 101 kPa (14.6488 pounds of force per square inch.) and a heat of combustion of less than 19 Kilojoule/Kilogram or 8.168 BTU/Pounds. Sorry for all of the conversions here but I wanted to cover my bases. I converted these using online tools but if you see something incorrect please reach out to me.
    • Some example refrigerants under this class two flammability category are: R-717 (Ammonia), R-141b, R-143a.
  • Class 2L – Lower Burning Velocity
    • Refrigerants in this sub-classification have a burning velocities less than or equal to 10 cm/s (3.9 in./s)
    • Now you may have noticed that at the beginning of this section that I said that there were three flammability classifications according to ASHRAE. Well, this was recently changed by adding this sub-classification. This was done to accommodate the new HFO refrigerant line, specifically the new HFO-1234yf automotive refrigerant.
  • Class 3 – Higher Flammability
    • Refrigerants in this classification indicate that they are highly flammable as defined by a lower flammability limit of less than or equal to 0.10 kilograms per cubic meter or 0.0062 pounds per cubic foot at 21° Celsius (69.8° Fahrenheit) and 101 kPa (14.6488 pounds of force per square inch.) or a heat of combustion greater than or equal to 19 Kilojoule/Kilogram or 8.168 BTU/Pounds.
    • Example refrigerants rated as a class three flammability are your Hydrocarbons. These include your R-170 (Ethane), R-290 (Propane), and R-600a (Isobutane).



Now when looking at the toxicity and flammability of a refrigerant you will notice that the toxicity and flammability classifications are combined into a letter and number combination. A few examples would be A1, B2, A3, A2. If you are ever unsure of what the classification is of the refrigerant that you are working on it is best to check the Safety Data Sheet that you have on file. If you cannot find it in your safety data sheet then I would recommend calling you supplier, calling the manufacturer, or even calling ASHRAE for assistance.


Thanks for reading and I hope that I was able to answer your questions.

Alec Johnson



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