Authorities are still trying to determine what caused a large fire aboard a ship docked at San Diego Naval Base on Sunday. In all, 21 people were hospitalized in the three-alarm fire on the USS Bonhomme Richard—17 sailors and four civilians, reports the AP. None of the injuries are believed to be life-threatening, with smoke inhalation and heat exhaustion blamed for most of the hospitalizations. For now, the Navy thinks the fire began in a lower cargo hold where vehicles and equipment are stored, reports the San Diego Union-Tribune. About 160 sailors were aboard the 23-year-old vessel when the fire was reported Sunday morning, and all were evacuated.
“The heat of a fire of this nature can warp the steel, and that can be a major problem for any ship,” a maritime professor at Fordham University tells the AP. "On an older ship, it's even more of a problem.” Witnesses reported hearing an explosion before the fire broke out, and Rear Adm. Philip Sobeck tells the San Diego newspaper the blast may have been caused by a change in air pressure. The fire was still burning Monday morning, and it could burn for days, San Diego's fire chief tells CNN. The ship has no ordnance aboard, and while it has about a million gallons of fuel, authorities say it is stored "well below" the fire. (Read more Navy stories.)