Explosion damages high-rise

NFPA Journal, Nov/Dec 1997 by Tremblay, Kenneth J

NEW YORK

An explosion in a restaurant's cooking exhaust system damaged a high-rise office building. Fortunately, the resulting fire burned itself out before it spread beyond the area of origin.

The 33-story building of fireresistive constuction was part of a complex of similar buildings, containing stores, restaurants, and offices. Sprinklers protected the building, but the fire was extinguished before they could operate. The building also contained smoke detectors, but they didn't operate because there were none in the room of fire origin.

Several of the building's occupants called the fire department at 7:10 p.m. to report an explosion and fire, and responding firefighters, aware of the potential life hazard and the serious nature of the reports, braced themselves for a serious incident. First-in companies discovered the fire in a second-floor restaurant kitchen and noted heavy smoke coming from the roof. They advanced a 2 1/2-inch hose line into the restaurant, supplied the fire department sprinkler connection, and began to treat injured occupants. When the firefighters reached the area of fire origin, they found that the blaze had burned itself out and that they only had to check for fire extension.

The blaze started when heat from a gas-fired restaurant stove ignited grease that had built up in an overhead cooking exhaust system. The restaurant's dry chemical extinguishing system failed to operate, and the blaze burned uncontrolled. Investigators believe that heat from the burning grease vaporized more grease ahead of the flame front, so that when the flame caught up with the grease vapor, it caused a small vapor explosion that damaged ductwork all the way to the 33rd floor. Flames flashed back past the point of origin, injuring several employees who were trying to control the blaze with portable fire extinguishers.

The explosion forced concrete block walls out of plumb, damaged nearby HVAC ducts, and blew open access panels to the grease duct in several areas. A hazardous materials team gathered fabricated asbestos particles from the damaged grease ducts on the 33rd floor.

Nine civilians suffered second-degree burns and other minor injuries, and none of the firefighters were injured. Dollar loss wasn't reported.