The Vallejo Fire Department is investigating whether a natural gas explosion that seriously injured two male maintenance employees at Vallejo High Schoolthis morning happened when the gas was turned back on for heating after repairs of damage from the Napa earthquake were completed, fire department spokesman Arthur Gonzales said.

“That was the initial report from the school. It’s speculation,” Gonzales said.

Gonzales said the school district said the classroom had not been used since the 6.0-magnitude Aug. 24 South Napa earthquake.