Flammable refrigerants


By Greg Scrivener

As some of you may be aware, there has been a lot of movement lately in the world of flammable refrigerants. A number of years ago, ASHRAE Standard 34 introduced a new flammability sub-classification called ‘2L’ and it looks like these ‘2L’ refrigerants are going to be a part of everyday life relatively soon.

Recall that the method used to give refrigerants a safety classification consists of a letter (A or B) followed by a number (1 through 3). The A or B denotes toxicity, with A being less toxic and B being more toxic. The numbers 1 through 3 represent a refrigerant’s flammability with 1 being least flammable and 3 being the most flammable. Most of the refrigerants we work with today have a safety group classification of A1; this means they have a low toxicity and a low flammability.

Without getting into too many details, the actual requirement for a refrigerant to receive a ‘1’ flammability rating is that it doesn’t show flame propagation in air at a temperature of 60°C. If the refrigerant meets the following requirements it is given a ‘2’ classification: (This information has been paraphrased and abbreviated from ASHRAE 34 – please refer to the standard for the exact wording and additional information regarding refrigerant blends.)

There is flame propagation shown at 60°C


The lower flammability limit (LFL) is greater than 0.1kg/m3. This LFL is the minimum concentration of the refrigerant in an air mixture required for the substance to be flammable.


The heat of combustion is less than 19,000kJ/kg

Finally, the refrigerant is classified with a ‘3’ flammability class if:
There is flame propagation shown at 60°C


The lower flammability limit (LFL) is less than 0.1kg/m3.


The heat of combustion is more than 19,000kJ/kg

So now you probably wonder what the problem might be. These definitions have been around for a long time and have worked fine up until now. So what does ‘2L’ mean and why is it needed?

Environmental driven

First the easy question – A 2L refrigerant is a refrigerant that meets all of the requirements of a ‘2’ classification but has a burning velocity of less than 10cm/second. Basically, the refrigerant is flammable but it doesn’t burn that fast. I am not sure of the exact reason that 10cm/second was chosen as the cut-off, but that is what we have to work with. Now the slightly more difficult question. Why do we even need it?

To understand why, take a look at Figure 1. In this chart, a number of popular refrigerants are shown with their corresponding global warming potential (GWP). In the “High” category you can see that R507 as a GWP of 3980. As you move down the list you see the GWP values decreasing. R134 has a GWP of 1430, R32 is 675, R1234yf is 4, etc.

Also indicated beside the GWP values is the refrigerant’s toxicity and flammability classification. I’m pretty sure you picked up on the trend: In order to achieve lower GWP values it appears as if we are going to have to tolerate some flammability. Intuitively at a basic and much simplified level this makes some sense. The less stable (i.e. the more flammable) a molecule is the quicker it will break down in the atmosphere.

Figure : The GWP of a number of refrigerants shown with their corresponding safety classification

Figure : The GWP of a number of refrigerants shown with their corresponding safety classification

Notice also the only low GWP refrigerant in common use that achieves an A1 safety classification is CO2. As we have discussed before, CO2 makes a very good refrigerant in some applications but it is not always suitable.

New classification created

In order to provide the safety codes (ASHRAE 15, CSA B52) with a framework to create new safety rules that would allow the use of flammable refrigerants in places where it is not currently allowed, the 2L classification was born.

What has happened since then? On the surface, not much in North America. But there has and continues to be an enormous amount of work going on behind the scenes to try to generate acceptable rules for these refrigerants with the goal of allowing them in as many applications as is safe.

At I write this, there is an ASHRAE 15 addendum out for public review that will allow 2L refrigerants to be used in most air conditioning applications for human comfort. This addendum will likely be followed by additional addenda that will continue to expand the applications for 2L refrigerants.

At the same time, UL is well into including 2L refrigerants into equipment that they are listing. A listing by a recognized laboratory is one of the key methods that is used to ensure some sort of safety and quality control in manufactured products. It will take some time for these changes to percolate through into the building, fire and mechanical codes, but it truly looks like “slightly” flammable refrigerants will be on your wholesaler’s shelves in the not too distant future.

Significant research underway

Another significant step in this progress is the recent funding announcement by ASHRAE, AHRI and the U.S. Department of Energy to spend $5.2 million dollars researching scenarios based around the flammability of the 2L refrigerants. If you ask me, this research should have been started years ago, but better late than never I suppose.

As a point of interest, the automotive industry started dealing with this first and you have been able to buy vehicles in North America that have 2L refrigerants as their factory AC charge for a number of years already.

There are some fairly substantial code and safety implications for Canada when the final form of these changes works its way into CSA standards, assuming of course that they do. Most of the issues arise out of compliance and enforcement. There are some pretty serious loopholes in our legislation and in our safety standards that should be addressed before this equipment becomes prevalent in the marketplace.

And let’s be honest, even if the loopholes are closed, there is next to no enforcement of CSA B52 in air conditioning applications. Even in large refrigeration plants, the vast majority of the standard is not enforced or inspected in most jurisdictions. There will continue to be changes, some faster than others, over the next few years in regards to our appetite for these refrigerants and what role they end up taking, but at the moment it sure looks like we will be seeing a lot of them.


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