Three workers were injured Wednesday night in an explosion and fire at a Chesapeake Appalachia Powers gas drilling site in Avella, Washington County.

INDEPENDENCE — An explosion and fire at a gas well injured three workers Wednesday night, authorities said. The blast, at the Chesapeake Appalachia Powers site in Avella, was reported at about 6:20 p.m., Washington County emergency officials said.

Workers were transferring water used in a gas-extraction process called hydraulic fracturing, and several of the natural gas liquids storage tanks caught fire, said Katy Gresh, a spokeswoman for the Department of Environmental Protection’s southwest region. During hydraulic fracturing, also called fracking, water mixed with sand and chemicals, some of them toxic, is forced into the wells at high pressure, shattering the underground shale and releasing trapped gas. Residents in several communities where fracking occurs have voiced concerns about possible water contamination and other safety issues, but the gas companies say the procedure has been used safely for decades.

Two workers were flown to hospitals after Wednesday night’s explosion, and another was taken by ambulance, Gresh said. The extent of their injuries was not immediately known. The fire was reported extinguished at 9:30 p.m. Gresh said the three wells at the site appeared to be unaffected but that will be confirmed as an investigation begins today to determine the cause of the blast.

Company spokesman Stacey Brodak said emergency responders were keeping the natural gas liquid storage tanks cool. He said there was no danger to the public or environment.