An explosion Monday at U.S. Steel’s Clairton Coke Works near Pittsburgh killed two workers and injured at least 10 others, five critically.

The blast occurred between two batteries at the nation’s largest coke manufacturing plant, prompting air quality monitoring and precautionary shelter-in-place advice for nearby residents, though no harmful pollution levels were detected.

The cause is under investigation, and company and union officials pledged support for affected workers and a thorough review of the incident, NBC News has reported.

Written by B.C. Begley