Three workers were overcome by heat Wednesday during an emergency drill at the U.S. Army's Newport Chemical Depot, where the deadly Cold War nerve agent VX is being destroyed, officials said.

The workers, one of whom was treated at a local hospital and released, wore rubber protective suits in temperatures that reached 82 degrees by 1 p.m., when the exercise was stopped.

The full-scale, annual exercise, which also involves local emergency workers, is held to ensure the depot and community could handle a VX emergency.

More than 250,000 gallons of the chemical -- so deadly a pin drop can kill an adult in minutes -- are being destroyed at the depot, the only place VX ever was made. Destruction began last month and could take three years.