Three workers were injured, two seriously, during an explosion at an oil company site 16 miles south of Charlotte, the Atascosa County sheriff said Monday.

The men were in a trailer using a water well-type perforating gun when it exploded, said Atascosa County Sheriff David Soward. He wasn't sure if the gun was being loaded when the blast happened.

A third person working nearby suffered minor injuries.

The two men, ages 29 and 30, were taken by ambulance to the sheriff's department, then flown by helicopter to San Antonio Military Medical Center. Their injuries were described as severe.