What to know about a chemical leak in Oklahoma

The chemical that leaked from a tanker truck in a city in Oklahoma is common but dangerous, and other leaks over the years have led to evacuations and deaths.

Hundreds of people were evacuated and dozens hospitalized because of the anhydrous ammonia leak from a tanker truck Wednesday night in Weatherford, about 70 miles (110 kilometers) west of Oklahoma City.

Here’s what to know about the leak and the chemical.

What happened in Oklahoma?

The tanker truck parked outside a Holiday Inn Express in Weatherford was spewing anhydrous ammonia. The driver had parked there to get a room for the night.

The cause seemed to be a mechanical failure on a valve or a faulty seal, the police chief said. Authorities have not said how much of the chemical was leaked.

Up to 600 people were staying in a shelter early Thursday, authorities said. Other nearby residents were told to shelter in place, although authorities lifted that order late Thursday morning. Residents were evacuated from several nursing homes and schools were closed for the day.

What is the chemical that’s leaking?

Anhydrous ammonia is used as a fertilizer to help provide nitrogen for corn and wheat plants. If a person touches it when it is in gas or liquid form, they could be burned.

More than 80% of the anhydrous ammonia produced in the U.S. is used for fertilizer, according to Airgas. The chemical is also used as a refrigerant.

What other accidents have occurred involving the chemical?

An explosion at a hydrogen and nitrogen product manufacturer in Mississippi last week caused an anhydrous ammonia leak and forced nearby residents to evacuate their homes.

Five people died of exposure to the chemical after a tanker truck crashed in Illinois in 2023, and about 500 people were evacuated for hours after the accident. An Ohio teenager told federal investigators that the truck was forced off the road when she drove past it in a minivan.

Other leaks involving anhydrous ammonia have occurred in recent years in Houston and Collins, Iowa.