Engineers Help Fight Wind-Fanned Flames


September 2011

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Real-world tests, observed by firefighters from around the country, were conducted in a building on Governors Island.

When a fire breaks out, members of the fire service do whatever it takes to put out the blaze and usher the victims to safety. While they are highly trained professionals with state-of-the-art gear, one still wonders, “Who has their backs?”

The answer: Engineers from the Polytechnic Institute of New York University. Since 2007, they have been working with the fire departments of New York City and Chicago to study the dynamics of wind-driven fires. This collaboration has resulted in a fundamental change in firefighting practice to protect those we rely upon to keep us safe.

Mitigating Risk at High-Rises

Wind makes all fires more dangerous but particularly on the upper floors of tall buildings, where the spread of smoke and heat can make it difficult for inhabitants to reach safety on the ground. While many new high-rises are equipped with stairwell-safety and automatic-sprinkler systems, most residential high-rises in cities are not, elevating the threat to firefighters and residents alike. 

The hazards were made all too clear in December 1998, when a Brooklyn high-rise ignited. Several fire companies answered the call, including three members of Ladder 170, who headed to the apartment where the fire had started to close the door and contain the blaze.

As they neared the door, one of the windows in the apartment shattered, creating 26 mph wind gusts. Simultaneously, wind from open windows down the hall swept the extreme heat and smoke toward the three firefighters, who never made it out alive. Though they followed procedure, the men were unprepared for the wind’s effects.

That unpredictability caused the staggering majority of civilian fatalities—92%—in fires that originated in apartments in 2002.

Positive pressure ventilation fans were shown effective at keeping stairwells clear of smoke and combustion gases, making them safe for occupants and firefighters.

The Chicago and New York fire departments responded by experimenting with a variety of tools. Covering windows with fire-retardant sheeting and limiting the fire’s oxygen flow seemed promising, as did using large fans to keep stairwells free of smoke and combustible gases and spraying water from high-rise nozzles through windows upwind of the fire.

But with no way to test these innovations, firefighters couldn’t be sure they’d found a solution—until 2007 when the National Institute for Science and Technology (NIST) and the Polytechnic Institute researchers offered to help.

NIST conducted eight laboratory experiments in Gaithersburg, MD, where fires were set in a simulated apartment so engineers could study what happened when a controlled wind blew through a window into the apartment blaze.

The results illuminated the perils firefighters face: The heat the fire released after the window was opened was 14-20 times greater than that emitted when the window stayed closed. And if the door to the apartment was left open, in only 30 seconds, hallway temperatures shot up over 600 °C (1,112 °F).

While some of the methods the Chicago and New York fire departments tried were proven helpful, such as covering the windows, thereby reducing hallway temperatures by half within 60 seconds, firefighters don’t fight fires in labs.

Live-Burn Experiments

The next step was a series of live-burn experiments that NIST, Polytechnic Institute, and the FDNY conducted by “setting” fires on the seventh, fifth, and third floors of a building on New York City’s Governers Island, which was wired to measure temperature, pressure, and velocity. Representatives from major fire departments across North America observed how well the new tools performed.

The high marks the wind-blocking devices, portable fans, and high-rise nozzles earned in the lab were confirmed. Used in tandem, these tools kept conditions in stairwells safe for residents and firefighters. Findings also forced observers to rethink a standard firefighting tactic.

When left open according to the usual procedure, stairwell doors on the first floor, the fire floor, and out to the roof actually put firefighters entering the fire floor right in the path of the hot fire gases. Using portable fans to pressurize the stairwell and keeping the roof door closed until firefighters were ready to access the fire floor was proven to be much safer.

Before fire departments could fully implement the new tactics, they needed to learn to implement them. Having gone as far as they could with live burn experiments, engineers validated the new tactics by running them through fire scenarios using Fluent 6.3 software and the NIST’s Fire Dynamics Simulator.

Computer simulations are now being used to train firefighters to use the new tactics and tools via an interactive web-based tool developed by the Polytechnic Institute.

Thanks to this research, fires in New York City high-rises are now approached quite differently. With help from FEMA, the FDNY purchased positive-pressure ventilation fans as well as wind-control devices and high-rise nozzles, and its officers continue to collaborate with researchers from NIST and the Polytechnic Institute to further the state-of-the-art.

Fire departments around the world are reviewing the data and observing New York’s success with great interest.

[Adapted from “Wind, Fire, and High Rises,” by Daniel Madrzykowski, Stephen Kerber, Sunil Kumar, and Prabodh Panindre, for Mechanical Engineering, July 2010.]
 

Wind makes all fires more dangerous but particularly on the upper floors of tall buildings, where the spread of smoke and heat can make it difficult for inhabitants to reach safety on the ground.

 
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by Daniel Madrzykowski, Stephen Kerber, Sunil Kumar, and Prabodh Panindre