Thick gray smoke visible for miles away billowed into the sky after the blaze broke out at 3:08 p.m. at the Paradise Mattress Co. at Bushwick and DeKalb Aves.
"There were flames shooting up on the back side," said Tony Ribot, who lives in the area. "They were shooting 15 feet in the air."
Fire Commissioner Nicholas Scoppetta said the blaze was the biggest of year because it was the first six-alarmer of 2004.
He said firefighters believe lightning from a storm caused the inferno because a witness reported seeing a bolt of lightning strike an air-conditioning unit on the rear of the roof.
"There was lightning in the area and it must have hit the roof," Ribot said. "We knew it hit something but we just didn't know what. Then we saw smoke and we knew where it hit."
Some 250 firefighters from 70 units battled the blaze, which went to six alarms at 5:40 p.m.
Because the company used polyurethane foam
