Emergency responders are standing down after they evacuated a commercial waste processing plant at the site of a former uranium enrichment plant in Tennessee.

About 45 employees at Materials and Energy Corp. in Oak Ridge evacuated Monday morning after a plume of yellow smoke was released from a ventilation stack.

The U.S. Department of Energy says it was caused by a chemical reaction that is a normal part of the company’s work and there was no danger to the public.

Firefighters found there was no chemical contamination inside or outside. Workers in surrounding buildings were free to leave after being ordered to stay inside.

The former K-25 plant, where uranium for the first atomic bomb was processed, is being converted to an industrial park.