A powerful explosion demolished the Crystal City Towing service's office on Jefferson Davis Highway in Arlington last night. A man in the building at the time was critically injured.

According to one account the explosion was the second at Crystal City Towing in less than two years.

The victim was indentified as Mark Logan, an employe of another towing service who sometimes used the Crystal City office at 2827 Jefferson Davis Hwy. and had access to it. He reportedly entered the building about 9:15 p.m.

Logan flicked on a light switch and the one-story frame and cinder block building exploded.

"That building really blew up," said Thomas Murphy, proprietor of Murphy's Towing, a nearby business. The blast "really blew the hell out of [the] building," Murphy said.

Flames leaped from the building, and Logan, his clothing on fire, fought his way outside, where, in the words of a witness, he rolled on the ground, crying "help me, help me."

The witness, Marcus Johnson, a soldier stationed at Fort Myer, threw a coat over Logan, helping to extinguish the flames, and moved him away from the building.

Logan, suffered from second-and third-degree burns over 60 to 70 percent of his body, was taken first to Arlington Hospital, then transferred to the burn unit at Washington Hospital Center.

Logan's age was put at about 30. His address was not immediately available.

The cause of the blast could not be learned, but natural gas appeared to be ruled out. A spokesman for the Washington Gas Light Co. said the building was not listed on company records. According to the utility spokesman, the building's owner also said no natural gas was used there.

The blaze was reportedly brought under control by the first pieces of equipment dispatched by the Arlington fire department. No dollar estimate of the damage was available.