Two people are dead and one is in critical condition after a “chemical release” at a West Virginia manufacturing facility, officials said Wednesday.

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The incident occurred at 9:46 a.m. at Catalyst Refiners, Inc. Institute in Kanawha County, authorities said in a news release.

Twenty-one people sought medical care or evaluation at the plant, which manufactures silver catalyst, according to the release. Five employees from the county’s emergency ambulance authority were being evaluated for possible exposure, the officials said.

The facility was in the process of shutting down its operations and cleaning the facility after a chemical reaction created hydrogen sulfide, a toxic, flammable gas, according to the release.

The local school district instituted a shelter-in-place order at several schools out of what the officials described as an abundance of caution. That order was later lifted.

Additional information about the victims wasn’t immediately available, nor was it clear what prompted the reaction.