The Tennessee Occupational Safety and Health Administration (TOSHA) is investigating last week’s explosion at an Eastman Chemical in Kingsport, Tennessee that released potentially toxic chemicals into the air.

The incident occurred on Wednesday morning with a process upset in the coal gasification area of the manufacturing site. The upset created a loud noise and a visible plume. No one was injured. Employees were sheltered in place and residents near the plant were asked to do the same.

Most operations at the plant that were idled after the incident have resumed.

The company said in a press release that hydrogen and carbon monoxide were emitted as a result of the explosions.

WJHL news reported that the Tennessee Department of Environment and Conservation said that the emissions “were in excess of the limits set by TDEC and that such excess emissions were atypical from a normally operating process at Eastman.”

Eastman Chemical says there was no impact to human health or the environment as a result of this event.

“We realize an event such as this causes concern to our employees, their families and our community neighbors and we truly appreciate everyone’s cooperation as we work to determine exactly what happened and the cause” said the company in a statement.

TOSHA’s investigation is expected to take up to ten weeks to complete.