Gina McCarthy, President Obama’s nominee to head the Environmental Protection Agency, faces some tough questions Thursday morning at her confirmation hearing before the Senate Committee on Environment and Public Works. One of those is why she championed an “ozone-friendly” refrigerant that has proved to be less than friendly to both the environment and humans.

In 2011, McCarthy, then assistant administrator for EPA’s Office of Air and Radiation, approved the use of HFO-1234yf, hailing it as a life-saving and environmentally sound chemical for use in cars’ air conditioning systems. The EPA also offered incentives for automakers using the refrigerant, which was developed by Honeywell and DuPont.

“This new chemical helps fight climate change and ozone depletion,” said McCarthy at the time. “It is homegrown innovative solutions like this that save lives and strengthen our economy.”

But tests by Mercedes-Benz engineers last year found that when HFO-1234yf came in contact with a car’s hot engine, it burst into flames. As it burned, it emitted hydrogen fluoride, “a chemical far more deadly to humans than hydrogen cyanide, emitted in such amounts that it turned the windshield white as it began to eat into the glass,” according to Americans for Limited Government.

When vented into the air the substance also degrades to trifluoroacetic acid, which can be harmful to plants.

Mercedes-Benz subsequently banned the refrigerant and recalled the cars that already had it installed. BMW followed, And in March, Volkswagen also said it will stop using it, according to AutoBlog Green.

Not only is the refrigerant flammable and toxic when burned, it doesn’t strengthen the U.S. economy, ALG said. The compound is produced in China and Japan, and U.S. plants that produce the current industry standard refrigerant can’t be retrofitted to make it.

Honeywell CEO Dave Cote lobbied Congress on hydrofluorocarbons for two years, according to ALG, until the EPA approved his company’s refrigerant. He has also been an outspoken supporter of President Obama and his 2009 stimulus package.

As Obama’s nominee for EPA administrator, McCarthy’s role in approving an apparently unsafe and unprofitable refrigerant deserves a closer look.