Author(s): Jesse Roman. Published on May 1, 2017.

Freezer Burn

A phase-out of environmentally damaging chemicals means that most refrigerators, freezers, and air conditioners may soon be using flammable refrigerants.


Like a suitor spurned over and over in love, the refrigeration and air conditioning industries can’t seem to find a good partner. While the mechanics of these indispensible technologies have been stable for decades, the substances that circulate through them absorbing heat and cooling the air—aptly named refrigerants—keep finding ways to foul things up.

A litany of refrigerants have been tried and left behind since commercial refrigeration began more than a century ago. Some were too toxic, others too flammable; some weren’t effective in certain climates, while some were environmentally ruinous. Each time a fatal flaw was revealed, the industry mobilized to find a replacement. Now that cycle is beginning again—this time with potentially serious implications for fire protection.

Last October, nearly 200 nations, including the United States, agreed to a relatively rapid phase down of a group of chemical compounds called hydrofluorocarbons, or HFCs, which, in addition to being the most widely used refrigerants in the world over the past two decades, are powerful greenhouse gases with thousands of times more global-warming potential than carbon dioxide. As a result, the Environmental Protection Agency (EPA), which is in charge of the phase out, has begun listing certain HFC refrigerants as unacceptable for use. The phase-out dates vary by chemical and application, but many common HFCs used in retail food refrigeration will be prohibited in new systems beginning January 1, 2021, and in air-conditioning systems by 2024.

As researchers look for suitable replacements, the prospects are complicated.

“The reality is there are only so many chemical compounds that actually work as refrigerants,” said Bill Walter, an engineering fellow at United Technologies and a member of the board of directors at the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), which publishes refrigerant safety codes. “Every time we cross one of these thresholds, we leave a bunch of chemicals behind and the ones that are left present new challenges.”

In February, researchers at the National Institute of Standards and Technology (NIST) completed a multiyear study to identify the best new refrigerant candidates to replace HFCs in air conditioning applications. All 27 fluids it tested with low climate impact are at least slightly flammable. “The takeaway is there is no perfect, easy replacement for current refrigerants,” NIST chemical engineer Mark McLinden said. “Going into the study, we thought surely there has to be something else. Turns out, not so much. So it was a bit surprising, a bit disappointing.”

Unless a unicorn-like chemical refrigerant with ideal properties—efficient, chemically stable, nontoxic, nonflammable, and environmentally friendly—is suddenly found, something will have to give, possibly certain restrictions on the use of flammable refrigerants.

Code-making panels from groups including ASHRAE and Underwriters Laboratories (UL), which both set safety standards for refrigerants and the equipment that use them, are considering increases to the amounts and types of flammable refrigerants that can be used in systems, opening the door to a future in which billions of appliances, from air-conditioning units to industrial HVAC systems to household refrigerators, will contain substances that burn.

“This is coming, and it’s coming quickly so it’s important to get this in front of the fire protection community,” said Walter. “We don’t want anyone to be surprised when the code change proposals come through.”


Promising, concerning alternatives

While the official global HFC phase-out effort is relatively new, the world is not starting from scratch. Phasing down HFCs has been under consideration for nearly a decade, and for much of that time the refrigeration industry has been working on developing refrigerants with lower global warming impact, Walter said. Europe has been aggressively replacing HFC refrigerants for years to curb its global warming impact, and the EPA, through its Significant New Alternatives Policy program, has been investigating and listing acceptable alternatives for a few years.

While the final refrigerant substitutes for most applications are still up for debate, two main groups—hydrocarbons such as propane, isobutane, and propylene, and a group of synthetic chemicals called hydrofluoroolefins, or HFOs—are the leading contenders. (Carbon Dioxide [CO2] is also being used in some instances but its effectiveness is limited in warm climates). The rub is, current model codes now severely restrict the use of both HFOs and hydrocarbons due to flammability concerns.

Propane, a highly flammable substance, is a very energy-efficient refrigerant with a low environmental impact. Some in the food industry see propane as a potential savior that “could effectively eliminate EPA compliance concerns for the foreseeable future,” according to Emerson Climate Technologies, a commercial HVAC consulting firm.

HFOs, meanwhile, are slightly flammable and very efficient synthetic refrigerants with much lower global warming potential than HFCs. HFOs could be used in a variety of refrigerant applications, from chillers, commercial and household refrigeration, a variety of air-conditioning units, and more.

Apartment building with multiple air-conditioning units in windows.

Ripple Effect New requirements for refrigerants will also affect a variety of heating, ventilation, and air-conditioning applications. Photograph: iStockPhoto

In terms of flammability, propane and HFOs differ significantly. Although some HFOs are flammable, “they have a very high lower flammable limit, so it takes a lot to leak before they ignite—and when they do burn they don’t give off a lot of heat and tend to burn very slowly,” Walter said. “These are all desirable qualities if you have to use a flammable chemical.” The properties are so unique that ASHRAE created a relatively new flammability classification called 2L to accommodate them.

ASHRAE’s refrigerant safety rating system is based on toxicity and flammability—nontoxic refrigerants are class A, and toxic refrigerants are class B; the numbers 1, 2, and 3 following the class indicate levels of flammability, from nonflammable (1), lower flammability (2), to higher flammability (3). The new 2L classification is reserved for chemicals like HFOs that are mildly flammable, but have much lower flame propagation speeds than regular class 2 refrigerants.

Model codes have not yet been updated to recognize the new 2L class, so HFOs are still considered A2 refrigerants by regulators, Walter said. Propane, a hydrocarbon also used in gas grills, is listed as A3, the highest flammability rating. Current codes severely limit the charge size—the amount of refrigerant used in a system—for both A2 and A3 refrigerants, effectively banning them for most large-scale applications. For instance, UL 471, Commercial Refrigerators and Freezers, limits the charge size for A3 refrigerants such as propane to 150 grams, or about half a cup of liquid. That is enough to run a small beverage cooler at a supermarket checkout line, but not nearly enough for the large glass-door refrigeration cases in the dairy or frozen-food aisles.

Industries that rely on refrigeration are eager to see charge limits for these more environmentally friendly yet flammable refrigerants increased. Some are frustrated that, while environmental regulation is mandating change, safety regulation is limiting their ability to take steps to comply. Some are forging ahead anyway as best they can.

In January 2016, U.S. retailer Target announced that it would begin to transition to lower global warming potential refrigerants in new and replacement stand-alone refrigeration equipment in its stores. The company identified propane as the ideal choice both because it meets future environmental standards, and Target’s internal testing has shown that propane is over 50 percent more efficient as a refrigerant than HFCs, Paul Anderson, the director of engineering at Target, said in an interview. The transition has started with small propane self-contained refrigerant coolers with charge sizes up to 150 grams, the maximum amount currently allowed by the EPA.

“There is not a silver-bullet-solution refrigerant that exists for retailers, but we need propane as one of the tools in our toolbox,” Anderson said. “We want to get there sooner rather than later, because you can imagine the costs of switching refrigerants every few years. We need to get to an end game that is best for our employees, customers, and the environment.”

Although there are now 600 Target stores with small propane refrigerant coolers, there would be many more—including some smaller stores using propane refrigerants exclusively—if not for code restrictions on charge sizes for A2 and A3 refrigerants, Anderson said. For stores to use propane refrigerants exclusively, A3 charge-size limits would need to be increased to 1 kilogram to accommodate larger refrigeration cases, he said. European standards now allow charge sizes up to 1.5 kilograms for flammable refrigerants in some scenarios.

Despite the charge-limit restrictions, larger-scale use of propane refrigerants is starting to be tested in the U.S. Last year, a 49,000 square foot Whole Foods in California received permission from the EPA and local authorities to test market what’s called a “cascade” refrigeration system that uses a combination of propane and carbon dioxide. Seven chiller units on the building’s roof contain a total of about 265 pounds of propane, which never leaves the roof. Instead it’s used to chill and condense the CO2, which then travels throughout the building below chilling the supermarket coolers. It’s a design that is already in use throughout Europe. Ammonia, another efficient natural refrigerant, has also been used in roof chillers on a trial basis in these cascade systems.

These moves by Target and Whole Foods and others indicate how eager the supermarket industry is to move toward the refrigerant future, said Keilly Witman, a supermarket refrigeration consultant who for years ran an EPA program aimed at helping grocers reduce refrigerant leakage.

“You have to realize how frustrating it is for these companies, which have no choice but to use refrigerants, to constantly have to pay to transition from one bad one to another,” Witman said. “For the very first time in the history of the food industry, we might have refrigerants that we can use that would finally eliminate this environmental problem. That has never been the case.”

Research and testing

With pressure from the EPA, industry, and safety officials to find a safe and viable solution, activity is moving quickly on many fronts as the cutoff date for HFCs approaches.

Target is a lead sponsor of a Fire Protection Research Foundation (FPRF) project that is analyzing the fire hazard of propane refrigerants in commercial retail and kitchen settings. The project, currently underway, includes a literature review of past research, as well as computer simulations and full-scale testing of propane refrigerants under various circumstances. Results could be published as early as July. The entire project from funding to testing has an accelerated timeline, reflecting both the interest and importance of the issue.

“We did zero fundraising, which is very unusual—usually we have to go out and solicit money for projects,” said Casey Grant, the FPRF’s executive director. “But Target rallied others. We’ve been on a rocket sled trying to keep up with this thing.”

Various additional projects are also now underway to test the potential hazards of replacement refrigerants in different scenarios, as well as to improve refrigeration equipment to “engineer out” some of the potential dangers, Walter said.

ASHRAE, the U.S. Department of Energy, the Air-Conditioning, Heating & Refrigeration Institute, and the California Air Resource Board have jointly put up $5.6 million to fund seven “high-priority” research programs to be completed this year. The projects will look at many angles of the problem, including potential ignition sources on equipment or in the vicinity; where flammable refrigerant may concentrate in event of a leak; sensors to detect leaks before concentration reaches the lower flammability level; risk assessments in various scenarios in the event a refrigerant does ignite; guidelines for flammable refrigerant handling and equipment servicing and installing; and evaluation of the proper basis for setting limits on how much and what types of flammable refrigerants can be used for certain applications and equipment. Simultaneously, manufacturers are working to improve equipment efficiency and to reduce the overall charge sizes required, which would in effect reduce the potential hazard.

All of that work will ultimately inform ASHRAE 15, Safety Standard for Refrigeration Systems, which is what most model codes reference, as well as the relevant UL product standards. Those code and standard changes could begin happening as early as late 2017 or early 2018.

Big changes to NFPA documents to address the refrigerant change likely won’t be necessary, said Guy Colonna, a division director at NFPA.

Air conditioning stat

“We don’t address refrigerants as separately categorized materials like ASHRAE does, so our codes and standards are less impacted by this change in process to a different substance,” he said. “The primary focus of our hazardous chemicals documents are for storage, handling, and use in the context of fire protection.”

In other words, relevant NFPA codes already address general fire safety and protection for these potential replacement refrigerants. Specifically addressing fire protection for these substances used for refrigeration applications isn’t in the purview of NFPA codes and standards.

Relevant NFPA codes—NFPA 55, Compressed Gases and Cryogenic Fluids; NFPA 58, Liquefied Petroleum Gas; and NFPA 30, Flammable and Combustible Liquids—may come into play indirectly, however. For instance, if HVAC companies start storing large quantities of flammable gases or liquids, NFPA codes and standards may compel them to take additional or different fire protection measures, Colonna said.

While nobody can say yet exactly what will happen as the process for phasing out HFCs continues, it’s almost certain that code changes allowing more flammable refrigerants are coming, and likely soon.

“I think it’s safe to say that the charge size for 2L refrigerant will likely increase to a certain extent,” Walter said. “A nonflammable refrigerant would be preferable obviously, but the next step is to go to one of these 2L refrigerants and apply appropriate safety requirements to the equipment. We are comfortable that we can use 2L safely and we are working hard on standards to make it happen.”

Walter, like others in the safety industry, is much more cautious and unsure about increasing charge limits on class 3 refrigerants like propane. If that happens—a big if—it will probably be a small increase, he said.

Retailers like Target understand that caution. They are also eager to find out what will be allowed.

“The safety of guests and employees are first and foremost on our mind, so we want to go in cautiously, make sure there is testing, and understand all of the hazards related,” Anderson of Target said. “That’s the whole reason we started this joint venture with the Research Foundation and NFPA.”

JESSE ROMAN is associate editor for NFPA Journal. Top Photograph: Getty Images