"To the best of my knowledge, brine is not flammable," he said. Accidents involving brine are typically spills, he said, "so that, I don't understand."
Brine is 99.5 percent water and sand, and drillers typically do not add potentially flammable chemicals, DeMarco said. What flows back up from a well is mostly salty water, and any chemicals are diluted.
"Contrary to what some people like to say," he said, "we don't use diesel fuel or any of those kinds of additives that would be flammable."
But David McMahon of the West Virginia Surface Owners' Rights Organization said the fracking fluid often contains volatile organic compounds, "so brine tanks can have vapors of these that are surely explosive."
Many people who live near well pads are worried about those compounds being vented into the atmosphere and harming air quality, he said.
Though the development of the Marcellus shale field underlying West Virginia has been booming, the DEP says there have been only five fatal accidents since 2008. Three have involved well sites, while two involved access road activities.
EQT is one of the largest exploration and production companies in the Appalachian shale gas fields, with drilling rights to more than 3.5 million acres in West Virginia, Pennsylvania, Kentucky and Virginia.
EQT's website says it has proven reserves of more than 32 trillion cubic feet equivalent, and it's grown those reserves by more than 120 percent over the past five years.
EQT says it plans to spend $1 billion in well development this year.
Associated Press writer John Raby contributed from Charleston.