Hot and Cold – Ongoing Phase-Out of HFCs May Lead to the Use of Flammable Refrigerants
It’s been nearly a year since the U.S. and more than 100 other nations around the world pledged to phase out the use of chemical compounds called hydrofluorocarbons (HFCs) in refrigerators and air conditioners. This amendment to the 1987 Montreal Protocol on protecting the ozone layer means many common HFCs will be banned from use in all new commercial refrigeration systems by 2021, and in air-conditioning systems by 2024. That’s great news for the environment, but what does it have to do with fire protection? Unfortunately, many of the more environmentally-friendly chemicals being considered for refrigerant replacements pose minor to severe flammability risks.
“For the FPE community, much needs to be done to keep up,” said University of Maryland Fire Protection Engineering Professor Peter Sunderland. “This is a new hazard that has not been considered much yet.”
Earlier this summer, the NFPA published a report (available here) that outlines some of the potential replacements and their flammability risks. There’s a lot of technical information, so we’ve highlighted the key facts for you.
Non-toxic refrigerants are categorized by flammability:
A1: No flame propagation
A2L: Lower burning velocity, much lower flame propagation speeds than regular class 2 (recently created by ASHRAE to accommodate chemicals with these unique properties)
A2: Lower flammability
A3: Higher flammability
The top two groups in the running for most probable replacement are hydrocarbons (like propane, isobutane and propylene), and the synthetic chemicals known as hydrofluoroolefins, or HFOs—both of which have been restricted due to their levels of flammability.
Propane, a hydrocarbon commonly used in gas grills, is categorized as an A3 refrigerant. So, while it may be revered by the food industry for being energy-efficient with minimal impact on the environment, its high flammability is a concern to the fire protection industry. Current American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) codes restrict the charge limit of A3 refrigerants like propane to 150 grams (or about a half-cup of liquid)—not nearly enough to run the giant refrigeration cases needed in food retail. Charge limits for A3 refrigerants would need to be increased to 1 kilogram to accommodate those larger cases—a risk that makes those in the safety industry nervous.
HFOs have considerably lower global warming potential (GWP) than the HFCs currently in use, and have the potential to be used as a refrigerant across the board (commercial and household refrigerators, air-conditioning units, chillers, etc.). As an A2L refrigerant, they’re mildly flammable with a higher low flammability limit (LFL), which means ignition would require a higher concentration of the gas to be dispersed in the presence of an ignition source; in other words, it would likely require a significant leak to create a significant risk. Furthermore, when HFOs do burn, they tend to burn slowly without giving off much heat, which is a desirable characteristic if you must use a flammable refrigerant. Codes don’t yet reflect the recent addition of the A2L class, though, so until model codes are updated, HFOs are still considered A2 refrigerants.
In May of this year, ASHRAE published a report called Flammability and New Refrigerant Options (that you can read in its entirety here). According to the article, refrigerant flammability can be defined by considering and controlling the following three factors:
- Likelihood of a fire or combustion event resulting from a refrigerant leak that reaches the lower flammability limit (LFL), or the lower end of the concentration range over which a flammable mixture of gas in the air can be ignited at a given temperature.
- Presence of an ignition source that has sufficient energy needed to initiate combustion of the refrigerant.
- Impact of the severity a potential event, which includes the probability of combustion, the anticipated pressure rise, the potential to cause injury to personnel, and the likelihood to cause a secondary fire.
There’s only so much time before the phase-out of HFCs must be complete, and several agencies are doing their due diligence in the meantime: ASHRAE, the Air-Conditioning, Heating and Refrigeration Technology Institute (AHRTI), and the U.S. Department of Energy (DOE) have teamed up to research refrigerant flammability. Here’s what they’re working on:
- AHRTI is investigating how refrigerant charge size, release height, leak rate, humidity, room size and temperature affect the severity of events.
- In collaboration with Oak Ridge National Laboratory, the DOE is studying the methodology of today’s charge limits for all flammable refrigerants and whether or not they can be increased.
The report predicts that “trade-offs between GWP, flammability, and efficiency will need to be made” when selecting the next generation of refrigerants. The risk of increasing flammability in commercial refrigerants is very real and should certainly not be overlooked by the industry.
For more information on the topic, check out the following reports: