The state Department of Environmental Protection is investigating an accident Monday afternoon at the Allegheny Ludlum Steel Corp. in Washington County that resulted in the release of a yellow, toxic chemical cloud outside the plant.

The DEP said that an overhead crane malfunctioned and could not remove a stainless steel plate from a 10,000-gallon vat of hydrofluoric acid, causing a chemical reaction that resulted in the toxic cloud.

Local hazmat crews and the DEP advised about 100 residents living within a quarter-mile radius of the Canton plant to stay indoors as a precaution until the cloud dissipated.

Hydrofluoric acid is used in the steel industry as a corrosive to clean steel. In a concentrated, gaseous form it is a highly toxic chemical that can cause burns to the skin and eyes and may be fatal if inhaled or absorbed through the skin.

Dan Greenfield, an Allegheny Ludlum spokesman, said workers were evacuated from the area where the accident occurred and no employees were injured.