SAN FRANCISCO — A massive blaze that erupted at a lumber warehouse near Interstate 880 in Oakland late last month started in an area of the building that housed a range of heavy machinery and charging equipment, officials said Tuesday. The fire broke out May 26 around 8 p.m. at Economy Lumber Co. on the 700 block of High Street, spewing pillars of smoke and slowing traffic on the nearby highway. …While fire investigators could not pinpoint the exact item that started the fire, they determined that the flames originated near several power outlets, battery chargers, large saws and lithium battery-powered forklifts, Oakland Fire Department spokesperson Michael Hunt said. Investigators could not determine the cause due to “significant destruction” on the ground floor area of the two-story warehouse and the “lack of certainty about which material or equipment involved was the original ignition point,” he said.