A fire caused about $400,000 in damage to the Mililani Marketplace branch of L&L Drive In shortly after closing Sunday night.

A Honolulu Fire Department investigator determined the fire was set unintentionally set about 9:10 p.m. after workers left the grill on. Heat from the grill ignited grease along the back splash, said Capt. Terry Seelig, HFD spokesman.

Flames went up into the range hood and onto the roof of the building. An adjoining Safeway was evacuated for about 90 minutes due to smoke, Seelig said.