Wednesday, July 10, 2019

Refrigerant Flammability Safety Rating

This is a re-post of an article I posted earlier. Flammable refrigerants are now really a fact of life, and so it is important that technicians understand the different classifications regarding refrigerant flammability. In particular, it is helpful to understand the difference between class 3 highly flammable refrigerants and class 2L, lower flammability refrigerants. 

I confess that I have always thought of flammability as an either or question: it either burns or it doesn’t. So the concept of different levels of flammability was a hard one for me to grasp. I wondered: what is the difference between 3,2, and 2L refrigerant designations? What follows is a somewhat lengthy discussion of what I learned.

First off, found that it is not all that simple. There are several flammability characteristics that can be compared: lower flammability limit, upper flammability limit, auto ignition temperature, minimum ignition energy, heat of combustion, and flame velocity. The table at the bottom of the article shows these different specifications for a small selection of flammable refrigerants. Note that pressure and temperature also play a part. For the ASHRAE safety tests, a temperature of 140°F at atmospheric pressure is specified. You get different results when applying higher pressures and temperatures.

The original three classifications (1,2,3) were determined by the lower flammability limit and the heat of combustion. Later, ASHRAE added a 2L category for refrigerants with burning velocities less than 10 centimeters per second. The table below summarizes the different flammability classifications.
Lower Flammability Limit % by volume
Heat of Combustion
Burning Velocity
Does not support combustion at atmospheric pressure
Greater than 3.5%
Less than 19 kj/g
10 cm/s or less
Greater than 3.5%
Less than 19 kj/g
Greater than 10 cm/s
3.5% or less
19 kj/g or more

Lower flammability limit (LFL) is the minimum percentage required in air to be combustible. For example propane (R290) has an LFL of 2.1% by volume while ammonia (R717) has an LFL of 15%. Notice that propane only requires 2.1% while ammonia requires 15%. So that is one difference – the amount that must build up before it can burn.

The upper flammability limit (UFL) describes the maximum concentration which will still burn. If the concentration of flammable vapors exceeds the UFL, it will not ignite. It is more difficult to draw a straight line comparison using the UFL. However, you can say that refrigerants whose LFL and UFL are closer together are generally a bit safer simply because the conditions for a flammable mixture are less likely to occur.

The auto ignition temperature is the temperature which the flammable mixture will ignite. With the exception of 1234yf, the lower flammability refrigerants have higher auto ignition temperatures than the more flammable refrigerants.

The minimum ignition energy is a bit different than the auto ignition temperature. It is the amount of energy that must be used to ignite a flammable mixture, measured in megajoules. Note that in this case R1234yf stands out because the minimum ignition energy is so high compared to the other refrigerants. Also note that the class 2L refrigerants all have minimum ignition energy ratings in the hundreds of megajoules or higher while propane’s minimum ignition energy is a very small 0.25 megajoules. Basically, this means it takes a lot more energy to ignite the 2L refrigerants than a highly flammable refrigerant such as propane. Again, this means that the chance of having the right condition for combustion is much lower for class 2L refrigerants.

The heat of combustion is a measure of the amount of heat created when the refrigerant burns. Note that the class 2L and class 2 refrigerants have a heat of combustion in the single digits per gram while propane jumps to 46 kilojoules per gram. This means that the heat produced by combustion of a class 2L or class 2 refrigerant is far less than a class 3 refrigerant. Indeed, it would be possible for a class 2L refrigerant to burn and not ignite other nearby flammable materials.

Burning velocity is the characteristic which distinguishes 2 and 2L refrigerants. It is the speed with which the flame advances. Note that the 2L class refrigerants have a burning velocity in the single digits while 152a, a class 2 refrigerant, has a burning velocity of 23 cm/sec. Propane’s burning velocity is twice that of 152a. The take home point here is that the flames from higher flammability refrigerants spread faster.

So wrapping it up, my general impression is that lower flammability refrigerants are less likely to burn in the first place and when they do burn, the flames are not as hot and do not spread as quickly as a high flammability refrigerant such as propane.

717 Ammonia
290 Propane
Safety Group
Lower Flammability LImit
Upper Flammability Limit
Auto Ignition Temperature
Minimum Ignition Energy
5,000 – 10,000 mJ
30 – 100 mJ
100 – 300 mJ
0.38 mJ
0.25 mJ
Heat of Combustion
9.5 kJ/g
9 kJ/g
22.5 kJ/g
6.3 kJ/g
46.3 kj/g
Burning Velocity
1.5 cm/sec
6.7 cm/sec
7.2 cm/sec
23 cm/sec
46 cm/sec

Friday, June 28, 2019

Appliances with Flammable Refrigerant Are In Stores Now

The EPA has approved limited use of flammable refrigerants in appliances. Specifically, R32, R290, R600a, and R441a. They are only approved for appliances with a limited charge, and the appliances must have warning labels to tell anyone working on the equipment that the refrigerant is flammable. However, the manufacturers have not gone out of their way to make sure the end consumer is aware that the refrigerant inside the appliance is flammable. R32 is an HFC with an ASHRAE Safety rating of A2L, which means it is low in toxicity but moderately flammable. You already use it without knowing it. 

R32 is used in many newer HFC zeotropic blends, including R-410A. These blends are generally rated A1 (low toxicity and non-flammable) because the mixture will not burn with the concentrations of R32 in them. R32 can be found at your local big-box store in window units and portable air conditioners. You have to look pretty hard to find it, but somewhere in the information they will tell you what refrigerant is in the unit. 

The other flammables are all hydrocarbons. They are all rated A3 – low toxicity but highly flammable. R290 is propane, R600a is isobutane, and R441a is a hydrocarbon blend. I have seen freezers and refrigerator-freezers at big box stores with R600a (isobutane) for refrigerant. 

Appliances using these highly flammable refrigerants have the required flammable refrigerant warning labels, but they are usually on the back of the appliance where the service access is. If you want to know if that shiny new refrigerator has explosive refrigerant in it you need to look at the back. I noticed that one refrigerator with R600a refrigerant also had a paper stating that using the appliance meant you agreed to binding arbitration as your sole legal remedy for any problems with the appliance. I don’t know if that manufacturer now makes this same disclaimer on all of their appliances, but it is worth asking about before purchasing. 

R290 (propane) is used on many small and medium sized commercial refrigeration refrigerators and freezers. R441a is used in some vending machines and smaller commercial refrigeration machines. I will talk some more in subsequent posts about flammable refrigerants, safe use, and safe service practices.

Tuesday, November 6, 2018

Tripped Rollout Switch

Anytime you have to reset a rollout switch on a furnace, warning alarms should go off in your head. The switch is not the problem, it is a symptom of a very serious problem. Just resetting the switch and going on is like turning off a fire alarm and leaving the fire burning. You need to find out why the rollout tripped. Rollout switches trip because flames are burning back where they are not supposed to be. Possible causes include a stopped up vent, a stopped up heat exchanger, low gas pressure, or a cracked heat exchanger. All of these conditions are very serious and have the potential to do great harm. Figure 1 shows a common rollout switch.
Figure 1 Rollout Switch
In the case of the plugged vent or heat exchanger. The flue gas cannot exit quickly enough, builds up and pushes the flames out of the heat exchanger into the area where normally there is only secondary combustion air. Although 80% gas furnace heat exchangers seldom become restricted, the condensing, secondary heat exchangers on 90% furnaces often become restricted. Either way, you must have a clear heat exchanger and vent to operate the furnace safely.

A cracked heat exchanger  can also lead to tripped rollout switches. A cracked heat exchanger can allow positive pressure air from the blower into the heat exchanger and reduce the draft. If the hole is big enough, the pressure in that cell of the heat exchanger can become positive, and push the flames out of the heat exchanger into the area where normally there is only secondary combustion air. Figure 2 shows an example of this. Look carefully at the burner on the left. See that there is no bright inner cone. That is because the flames are coming back out of the tube. The burner to the right of it looks normal.
Figure 2 Flames rolling out (left burner)
Low gas pressure can cause the flame to retreat from the burner port, back into the burner body, often all the way to the orifice. Figure 3 shows an example of flames burning back at the orifice due to low gas pressure.
Figure 3 Flames burning back at orifice

Whenever you find a furnace with a tripped rollout switch, you need to determine why the rollout switch has tripped. I know no professional would ever jump out a safety device, such as a rollout switch. But just to make certain – NEVER “fix” a furnace by jumping out a rollout switch. The switch is not the problem – it may be the reason nobody died.

Friday, October 26, 2018

EPA Proposes NEW Rules Change

I am a little late getting this out. On October 1, 2018, the EPA proposed a rules change that would effectively wipe out all regulations on non-ozone depleting refrigerants.
Really, the only ozone depleting refrigerant that is widely in service now is R-22, which will be pretty much extinct in a few years. For all of today’s refrigerants, such as HFCs and HFOs, this rule change would mean anyone could purchase refrigerant, no certification would be required to handle refrigerant, no refrigerant recovery would be required, no mandatory leak checks, pretty much no regulations. This would put technicians following best industry practices at an economic disadvantage compared to folks who don’t both purchasing things like recovery machines. It would open up the path for Home Depot and Lowes to sell systems to the public, since purchasers would no longer be required to be certified. I believe it would lead to more mangled equipment, as well as mangled DIY folks who watched a You-Tube video on how to change their own compressor. I urge you to write in to the EPA and tell them that you want to keep the current regulations, passed on November 18, 2016. All comments must be received by November 15, 2018.
Here is a link to the full text of the proposed rule changes

Here are the instructions for submitting a comment
Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2017-0629, at You will need to copy and paste the Docket ID 

Friday, August 17, 2018

Bristol Compressors Closing

It is sad whenever a company in HVACR cannot make a go of it. Bristol Compressors has announced that they are closing after more than 40 years in business. They developed some innovative products, such as the Inertia Compressors with suction valves built into pistons that separated allowing suction gas to travel through the piston head, or the Twin-Single compressors that had a unique crankshaft which moved both pistons up and down in one direction and only one piston in the other direction.  More details on the closing here 

Wednesday, August 1, 2018

Chemours (Dupont) Buys ICOR International

I just got an email info blast from ICOR in which it states that ICOR is now a wholly owned subsidiary of Chemours. Tht surpised me, so I looked a littel further into it and found an article on :Cooling Post" dated April 8, 2018 which confrms that Chemours bought ICOR. Here is the link to the Cooling Post artcle
Here is the link to the info blast that ICOR sent me.

Basically it is warning against cheap refrigerant from unknown sources. As always, if you stick with legitimate supply houses you are pretty safe. If you get it off the back of someone's truck at midnight in the parking lot behind the bar, well you might not be getting what you think you are getting. Even ordering over the internet is risky if you are are buying it from someone outside of the normal distribution chain. There is now counterfeit refrigerant out there, so just because the jog says Honeywell or Chemours does not mean that it really is from that manufacturer. Some of the counterfeit stuff has hydrocarbons in it and could be quite dangerous in a system that is not designed for explosive refrigerant.

Thursday, July 26, 2018

New Low GWP Non-Flammable R410A Replacement

This will be a short post because I don't know a lot of details yet. Honeywell is developing a new three part zeotropic refrigerant that can replace R410A. It has a relatively low GWP of 733 compared to 2088 for 410A, and most significantly, is non-flammable. Honeywell's trade name for it is Solstice N41, the ASHRAE number is R466A. It reportedly contains the same two chemicals as in R410A (R32 and R125). A third is added - trifluoroiodomethane (CF3I). This third component is currently used a a fire retardant. It also helps reduce the GWP of the mixture. The new refrigerant is not claimed to be a "drop-in" for R410A, but required design modifications are said to be minimal. The refrigerant is currently undergoing ASHRAE testing, but has received a preliminary A1 rating.  I have now told you all I know, and it did not take very long. Here are links to two articles about this new refrigerant.