Josh Lunsford had heard lightning strike close by before. But what he heard in the pre-dawn hours Monday was something different.

Instead of a pause between the flash of lightning and the crash of thunder, they came all at once, so loud it sounded like a gunshot next to his head. He knew immediately it had come awfully close.

Lunsford, pulling a substitute shift as a night security guard at the Loudoun County school system's bus garage, realized just how close when he darted out to his car from an awning, where he had been waiting for the rain to ease.

That's when he saw a tendril of smoke, the start of a fire, rising from the transportation operations center, a permanent trailer attached to the garage near Leesburg Executive Airport, south of town.

During the day, 25 people work in the building, drawing up bus routes and planning schedules. But at 5:30 a.m., the only workers there were Lunsford, a mechanic who arrived early to work and a dispatcher. None was in the building or hurt in the resulting blaze, which Loudoun fire and rescue officials estimated caused about $750,000 in damage.

After spotting the smoke, Lunsford said he told the dispatcher to call 911. Then he and the mechanic grabbed a fire extinguisher. They tried to get inside the building through an interior hallway that leads to the adjoining building, but the smoke was too heavy.

They went back outside, and Lunsford broke a window with his hand, cutting himself, though not seriously. The two men pointed the extinguisher inside, spraying until it ran out. But it did no good.

"It was just a natural reaction," Lunsford said. "At that point, we didn't realize how serious the fire was. All that was visible was a small fire. Later we were told the whole interior of the roof was engulfed in flames."

Fire and rescue personnel from Leesburg, Ashburn, Hamilton, Moorefield, Purcellville and Sterling responded to the scene.

By 3 p.m. Monday, the burned-out building still reeked of smoke. All that was visible through the soot-stained windows was a mess of tangled, burned wood and the collapsed ceiling.

Piled outside was the detritus of work life: melted computer monitors, burned seat cushions, a soggy and blackened copy of the Yellow Pages, a case of soda, each can burst open from the heat.

J. Michael Lunsford, director of transportation for the school system and Josh Lunsford's father, said employees were being set up in temporary offices in the Douglass support facility in Leesburg, a building recently vacated when the school system opened its new administrative offices in Ashburn. Lunsford said they could be there for the next year.

The fire came at one of the busiest times for Lunsford's employees, as they hurry to finish bus routes before students return to school. Lunsford said the staff was running a little ahead of schedule and still hopes to get the routes to parents by Monday.

The data necessary for the job were saved on mainframe computers and therefore unaffected by the blaze, but about 25 computers, as well as copiers and furniture, must be replaced, he said.