Flames that leapt high above the roof drew a crowd who watched the fire destroy an apartment house in less than an hour Saturday. "We have no idea what started it at this point," said District Chief R.W. Hawkins as firefighters dowsed the charred building. He said the building, at 441 Sixth St. N, apparently was occupied when the fire started, but everyone managed to get out safely. The two-alarm blaze started about 3:45 p.m. in the two-story, four-unit building. At 4:30, the fire had been extinguished and firefighters were responding to hot spots that threatened to reignite the wood structure. Spectators in this neighborhood of multifamily dwellings filled a parking lot across the street and lined bordering streets. Hawkins said Saturday afternoon that he had no estimate of the value of property that was destroyed.