INSTITUTE, W.Va. (AP) — A chemical leak at a West Virginia silver recovery business killed two people and sent 19 others to the hospital, authorities said.

The leak occurred at the Catalyst Refiners plant in Institute as workers were preparing to shut down at least part of the facility, Kanawha County Commission Emergency Management Director C.W. Sigman said.

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A chemical gas reaction occurred at the plant involving nitric acid and another substance, Sigman said, speaking at a news briefing. He added that there was "a violent reaction of the chemicals and it instantaneously overreacted."

"Starting or ending a chemical reaction are the most dangerous times," Sigman said.

Among the injured were seven ambulance workers responding to the leak, officials said.

Other people were taken to the hospitals in private cars or even in one case a garbage truck, Sigman said.

A shelter in place order was issued for the surrounding area and lifted more than five hours later. Officials said all the deaths and injuries occurred on the plant site.

"You had to get really close to the facility to smell it," Sigman said.

The leak required a large scale decontamination operation in which people had to remove all their clothes and be sprayed down, authorities said.

Catalyst Refiners works to remove silver from what remains of chemical processes and can find thousands of dollars of the precious metal just by vaccuming the floors in a plant's offices, Sigmon said.

Ames Goldsmith Corp., the owner of Catalyst Refiners, said it is saddened by the deaths and its thoughts were with all those impacted and their families.

"This is an unfathomably difficult time," said the company statement released at the news briefing. "Our thoughts and prayers are with our colleagues and their families."

Ames Goldsmith promised to work with local, state and federal officials as they investigate what happened.

The plant is located near Institute, a community about 10 miles west of Charleston, the state capital.

Jeffrey Collins contributed to this report from Columbia, South Carolina.