A unmarked barrel full of an unknown liquid shut down the Spokane County Transfer Station in Spokane Valley Tuesday afternoon when it began spewing a “strong vaporous fume cloud.”

The Spokane Valley Fire Department and the Spokane Fire Department’s hazardous materials team responded to the transfer station at 3941 N. Sullivan Road just after 2:30 p.m. Workers said they noticed a smoking barrel mixed in with waste they were moving with a front end loader, said Valley Fire spokeswoman Melanie Rose.

Believing the 55-gallon barrel was on fire, the workers doused it with water, which created a large cloud of vapor.

More than a dozen employees and customers were evacuated from the area. Three employees were taken to a local hospital for an evaluation as a precaution, Rose said.

The hazardous materials team tested the liquid in the barrel and learned it was an acid with an oxidizer, Rose said. The barrel was turned over to Waste Connections of Spokane, which runs the transfer station, for safe disposal.