A Computer to Outguess a Raging Fire
Published: March 7, 2000
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The model has also explained a number of flukes in the behavior of fire alarms and sprinklers. For example, in fire tests in a basement with exposed ceiling beams, the sprinkler farthest from the fire consistently ignited before those directly over the flames. A computer simulation revealed that the beams were acting as a conduit and were channeling heat from the fire to the distant sprinkler so fast that the sensor on the nearest sprinkler never became warm enough to activate it.
The model showed that in sprinkler skip, water from one sprinkler cools the heat sensor on its neighbor so that the second sprinkler is not activated, thus increasing the possibility that the fire will spread. Adjusting the sensitivity or placement of the sprinklers solves the problem.
A similar computer model developed in the late 1990's demonstrated that under specific sea and wind conditions, burning the oil spilled from a tanker caused less environmental damage, despite the smoke and air pollution, than removing it after it has washed ashore. Experiments confirmed the model, and since then spilled oil has been burned at sea off Alaska in 1998 and after an oil tanker, the New Carissa, foundered off Coos Bay, Ore., in 1999.
Simulations now play an equally crucial role in developing, designing and testing new kinds of fire codes, based not on requirements for number and placement of exits, sprinklers, extinguishers and the like but rather on fire safety goals.
These performance-based codes set specific goals for fire safety, including the amount of time needed to warn and evacuate the building's occupants, and the efficiency of the smoke detection and sprinkler systems, but leave up to the design team the how to meet those goals.
Mr. Bukowski estimated that these codes, being developed in Japan, Australia, New Zealand and parts of Europe, can cut the cost of fire protection in a new building -- now set at 15 or 20 percent of the construction cost -- -- by a third, while improving safety. The fire research laboratory is working on a model performance-based code of its own.
Still, the Fire Dynamic Simulator cannot yet predict when flashover will occur because of the sheer complexity of calculating the interactions of hot and cold air, radiant temperatures and the ignition points of multiple materials over a long period.
''Fire modeling is like predicting the weather,'' Dr. McGrattan said. ''We're pretty good in the short term, but not in the longer term. We can predict the first couple of minutes of a fire successfully, but after that, things become more dicey.'' Nonetheless, he said he expected in the next five years to be able to ''confidently predict for any given room what the flash point will be.''
Despite the progress made in bringing their models to fire engineers, the researchers admit that firefighters are reluctant to embrace the technology, preferring in most cases to rely on their experience and traditional methods. Still Dr. McGrattan expects computer simulations to be widely used in training, because they can provide a clearer view of fire than video cameras or eyes blinded by smoke.
Scientists at the Building and Fire Research Laboratory also hope within four years to have built a control panel that has embedded in it a ''zone'' model for tracking the progress of a fire in a building in real time. Sensors monitoring temperature, occupancy, smoke alarms, sprinklers, ventilation and other systems, would relay information back to the program, which would also have an inventory of material in the building.
Constantly updating its data, the computer would determine the location and intensity of a fire, as well as movement, and feed that information directly to firefighters, in all likelihood saving lives and reducing injuries.
Photos: A computer program analyzes different types of fires, including the plume, far right, and one involving stacks of boxes, above. (Courtesy of the National Institute of Standards and Technology); Dr. Kevin McGrattan helped to design the computer program that simulates the burning of an oil spill, middle image, off the coast of Alaska. (Marty Katz for The New York Times)