Natural gas that has been derived from hydraulic fracking is now the most commonly used fuel in gas fireplaces and kitchen ranges. It rose to that level over the past 15 years, with little examination of the health risks of the chemicals that are used in fracking and released when the gas is burned.

“Few if any people have actually tested for what else is in this gas,” says Nathan Phillips, a College of Arts & Sciences earth and environment professor, one of the country’s foremost experts on natural gas leaks and explosions in the United States. “It’s 90 to 95 percent methane, but what else?”

Phillips and a team of researchers from several universities and nonprofits are finding out, and they are concerned. Of the 108 volatile organic compounds, or substances that easily become vapors or gases, found in gas from four Massachusetts municipalities tested, 27 are chemicals that are considered hazardous by federal Clean Air Act standards, and 12 are suspected carcinogens.