Air Force officials said an electrical “arc flash” led to the injuries of two workers at Offutt Air Force Base near Omaha, Neb., last week. 

The two men were doing routine maintenance on an electrical circuit near the U.S. Strategic Command headquarters last Wednesday when the arc flash caused a flash fire, pressure blast and sound blast, according to a report from the Omaha World-Herald.

Officials with Offutt said one person injured was a member of the 55th Wing Civil Engineering Squadron and the other was an Omaha Public Power District employee. Both patients were transported off the base to area hospitals. The extent of their injuries is not yet known. They were both conscience and alert at the time of transport, WOWT News out of Nebraska reported.

The arc flash briefly disrupted power in the StratCom building, but a back-up generator quickly kicked in.

The 55th Wing safety office has opened an investigation into what caused the incident, said Drew Nystrom, a 55th Wing spokesman.