ATLANTA >> As the U.S. tries to phase out a polluting refrigerant that is used in millions of air conditioners across the country, unapproved coolant is popping up on the market — with potentially dangerous consequences.

The FBI is warning people to be on alert for refrigerant substitutes that have not been approved by the Environmental Protection Agency. Some contain propane, which is flammable and can explode or catch fire if, for example, a technician servicing an air conditioner gets too close to the coolant while soldering. So far, the explosions have been rare.

The problem has cropped up as the U.S. phases out R-22, a chemical used for decades as a refrigerant in air conditioners and refrigerators. Because R-22 destroys the ozone layer, it is being banned globally under an international treaty. The EPA is guiding the switch over to ozone-friendlier refrigerants, and has listed approved ones on its website.

The phaseout caused prices of R-22 to skyrocket, increasing the demand for cheaper, unapproved replacements, many of which are made in China and sold on the black market. Products like “Super Freeze 22a” have been selling mostly online or over the telephone to home owners and “do-it-yourselfers,” circumventing stores and regulators, the FBI said on its website. The FBI has launched an investigation into the sale of unapproved refrigerants but declined to answer questions from The Associated Press.

It is unclear how many people may have fallen victim to a refrigerant scam. Reports of fires or explosions seem rare. The EPA, without citing specific examples, said it knows of cases in the U.S. and abroad where people have been injured after using unapproved refrigerants in air conditioners. Additionally, the agency took action against at least one U.S. company in 2013 for selling an unapproved refrigerant that had the potential to explode.

There have been scattered reports of deaths overseas. A New Zealand firefighter was killed and seven others were seriously injured in a 2008 explosion blamed on a propane-based gas being used to cool a refrigeration warehouse, according to local media reports at the time. More recently, dock workers in Vietnam and Brazil were killed after giant shipping containers exploded when suspected counterfeit refrigerant was placed in their cooling units, according to shipping reports obtained by the U.N. Environment Programme.

The Air-Conditioning, Heating and Refrigeration Institute, an Arlington, Virginia-based trade association, has yet to hear about an accident occurring domestically, said Karim Amrane, vice president of regulatory policy and research with the group.

Allison Bailes, founder of Energy Vanguard, an energy efficiency consulting and design firm in Decatur, Georgia, said consumers should choose only contractors who are licensed, preferably those who have North American Technical Excellence certification.

“Tell them you want the type of refrigerant — if it needs refrigerant — that it is manufactured for. If it’s supposed to be R-22, then put R-22 in it,” Bailes said. Companies that skirt the law are “creating the potential for greater cost to their customers and causing injury or death to techs who work on those systems later.”

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Environmental Protection Agency:

http://www.epa.gov/ozone/snap/r22a.html

http://www.epa.gov/ozone/enforce/blackmkt.html#cases

http://www.epa.gov/ozone/snap/refrigerants/lists/homeac.html