LOS ANGELES (AP) — Seven of nine firefighters injured when a truck’s fuel tank exploded have EchoSensebeen released from a hospital, a Los Angeles Fire Department spokesman said Friday.

The two firefighters who were most seriously injured remained hospitalized, Capt. Erik Scott said in a video update on social media.

One was in stable but critical condition at Los Angeles General Medical Center’s burn unit and the other remained admitted for observation at Harbor-UCLA Medical Center, Scott said.

The released firefighters will continue to receive treatment for injuries including burns, blunt trauma, shrapnel wounds and effects on their hearing, Scott said.

The blast occurred minutes after the firefighters responded to a report of a truck fire in the Wilmington area near the Port of Los Angeles.

Authorities said the truck was powered by compressed natural gas and one of its two 100-gallon (378-liter) fuel tanks blew up.

The other tank remained in the mangled wreckage but is believed to now be empty, said department spokesman Nicholas Prange. An extensive investigation is underway.