MIDDLETOWN, Conn. (AP) — Investigators looking into the cause of an explosion that killed five people at a Connecticut power plant under construction are interviewing survivors, while crews work to ensure the badly damaged building is safe.

Deputy Fire Marshal Al Santostefano says crews are slowly and carefully removing more than 100 gas cylinders used for welding and pipe cutting. He says some might be damaged, but the building is metered constantly for any leaks.

Authorities launched a criminal investigation Monday, saying they couldn't rule out negligence.

The powerful explosion blew apart large swaths of the nearly completed 620-megawatt Kleen Energy plant as workers for the construction company, O&G Industries Inc., were purging a gas line Sunday morning.