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NIST Wind Driven Fire Part Duex
The second part of the NIST Wind Driven Fire Conditions reports has been released. This part details the experiments and results from the Governor's Island tests. The lengthy report is a must read for those who desire to better understand not just high rise firefighting, but positive pressure ventilation as well. We should also be aware that as recently as Sunday in Loudoun County (VA)[1] and last month in Houston[2], the impact that wind conditions have on private dwellings as well. To encourage you to read this report, excerpts from the second part are below.
"NIST Technical Note 1629 Fire Fighting Tactics Under Wind Driven Fi..."
"Each of the 14 experiments started with a fire in a furnished room. The air flow for 12 of the 14 experiments was intensified by a natural or mechanical wind. Each of the tools was evaluated individually as well and in conjunction with each other to assess the benefit to fire fighters, as well as occupants in the structure. The data collected used to examine the impact of the PPV fans, WCDs, and the exterior water application tactics were temperature, differential pressure,and gas velocity inside the structure. Each of the experiments was documented with video and thermal imaging cameras. These experiments also captured video of specific fire phenomena that are not typically observable on the fire ground."
"All of the fires were ignited in furnished rooms of an apartment. Due to excess fuel pyrolysis/generation (lack of ventilation) the room of fire origin could not transition to flashover until windows self-vented and introduced additional fresh air with oxygen to burn. Without a wind imposed on the vented window, the fire did not spread from the room of origin and never left the apartment of origin. Even with no externally applied wind, creating a flow path from the outside, through the fire apartment into the corridor and up the stairs to the open bulkhead on the roof increased the temperatures and velocities in the corridors and in the stairwell resulting in hazardous conditions for fire fighters and untenable conditions for occupants on the fire floor and above in the stairwell."
"With an imposed wind of 9 m/s to 11 m/s (20 mph to 25 mph) and a flow path through the fire floor and exiting out of the bulkhead door on the roof, temperatures in excess of 400 ºC (752 ºF) and velocities on the order of 10 m/s (22 mph) were measured in the corridor and stairwell above the fire floor. These extreme thermal conditions are not tenable, even for a firefighter in full protective gear."
"If the fire has vented a window, important information can be gained by observing the behavior of the flame at the window. If the fire apartment has a high pressure relative to the outside due to an imposed wind, the flame will “pulse” out of the window to balance the overpressure. If the flames are being forced out of the window a flow path has been established through the building and the flow direction maybe favorable to interior fire fighting. If the flames are pulsing or being forced into the window, condition may not be favorable to interior firefighting and caution should be used on the approach to the fire floor. Even if flames are being forced out of adjacent windows in the fire apartment with a high amount of energy, there could still be sufficient energy flows on the fire floor to create a hazard for firefighters."
"Door control is the most basic means to interrupt or control the flow path in the building. The fire floor stair door should be checked for heat or hot gases flowing around the edges. The door should only be opened a few inches at first to look for rapid changes in smoke volume or velocity and/or thermal conditions. If the thermal environment changes quickly, close the door to interrupt the flowpath. In a smoke filled environment, visual changes to conditions may not be apparent with out a thermal imager. A similar approach would be used on the door to the fire apartment."
"In these experiments, the externally applied water streams were implemented in different ways; a fog stream inserted into the fire room window, a fog stream flowed from the floor below into the fire room window opening, and a solid water stream flowed from the floor below into the fire room window opening. In all cases, the water flows suppressed the fires, thereby causing reductions in temperature in the corridor and the stairwell of at least 50 %. The water flow rates used in these experiments were between 125 gpm and 200 gpm, demonstrating that a relatively small amount of water applied directly to the burning fuels can have a significant impact."
"Another factor Norman [16] identifies is that the fire does not have to be 20 stories or more above ground for wind to be a factor. Table 1.1-1 demonstrates that these FDNY wind driven fire incidents have occurred as low as the 3rd story above ground. NFPA data shows that the majority of fires in high rise buildings occur below the 7th floor [2]."
"Every experiment began with all of the doors and windows closed with the exception of the door to the furnished bedrooms and the main entrance door from the public corridor to the fire apartment. After ignition, the fire was allowed to grow until it failed the windows in the room or became ventilation limited. The purpose of the experiments was to get a wind driven fire condition. Therefore when an apartment became ventilation limited because of lack of window failure additional doors were opened remotely such as the stairwell door to provide additional air for the fire to grow. In some cases, windows were manually vented to provide additional air flow."
"Once wind driven conditions were achieved many different openings were made to simulate the operations of a fire department. These operations included opening the front lobby doors for access, entering the stairwell, opening the door from the stairwell to the fire floor, and opening the bulkhead door at the top of the stairwell. In addition to these operations each of the tools to be tested, PPV fans, Wind Control Devices and Floor Below Nozzles were deployed and evaluated."
"Wind is a factor. As shown in these experiments, wind can significantly increase the thermal hazards of a fire in a structure. Wind conditions will vary at different elevations above the ground floor, on different sides of a building, due to the effects of surrounding structures or topography, or just changes in the wind itself. Therefore wind needs to be considered as part of the intial “size-up” of the fire conditions and continue to be monitored and reported on throughout the fire incident."
"Smoke is Fuel. A ventilation limited (fuel rich) condition developed prior to the failure of the windows. Oxygen depleted combustion products, containing carbon dioxide, carbon monoxide and unburned hydrocarbons, filled the rooms of the structure. Once the window failed, the fresh air provided the oxygen needed to sustain the transition through flashover, which caused a significant increase in temperature."
"Venting does not always equal cooling. In these experiments, the cool air forced into the broken upwind window resulted in an initial period of cooling in the room of origin, typically followed by a transition to flashover, if a flow path was available."
"Fire induced flows. Velocities within the structure exceeded 5 m/s (11 mph), just due to the fire growth and the flow path that was set-up between the window opening and the open bulkhead door on the roof."
References
1. "Photos from Loudoun County: Two-alarm house fire on Sunday morning in Broadlands." STATter911, May 2009
2. "Wind Driven Fires, Houston" Carey, April 2009
Additional Reading
"Examining Firefighting Tactics under Wind Driven Conditions" USFA, revised May 2009
"Wind Driven Conditions - Lab Experiments" Carey, March 2009
"Breaking Down NIST's 'Fire Dynamics'" Carey, Firehouse.com, September 2008
"Fire Dynamics for the Fire Service" Carey, September 2008
"NIST Technical Note 1629 Fire Fighting Tactics Under Wind Driven Fi..."
"Each of the 14 experiments started with a fire in a furnished room. The air flow for 12 of the 14 experiments was intensified by a natural or mechanical wind. Each of the tools was evaluated individually as well and in conjunction with each other to assess the benefit to fire fighters, as well as occupants in the structure. The data collected used to examine the impact of the PPV fans, WCDs, and the exterior water application tactics were temperature, differential pressure,and gas velocity inside the structure. Each of the experiments was documented with video and thermal imaging cameras. These experiments also captured video of specific fire phenomena that are not typically observable on the fire ground."
"All of the fires were ignited in furnished rooms of an apartment. Due to excess fuel pyrolysis/generation (lack of ventilation) the room of fire origin could not transition to flashover until windows self-vented and introduced additional fresh air with oxygen to burn. Without a wind imposed on the vented window, the fire did not spread from the room of origin and never left the apartment of origin. Even with no externally applied wind, creating a flow path from the outside, through the fire apartment into the corridor and up the stairs to the open bulkhead on the roof increased the temperatures and velocities in the corridors and in the stairwell resulting in hazardous conditions for fire fighters and untenable conditions for occupants on the fire floor and above in the stairwell."
"With an imposed wind of 9 m/s to 11 m/s (20 mph to 25 mph) and a flow path through the fire floor and exiting out of the bulkhead door on the roof, temperatures in excess of 400 ºC (752 ºF) and velocities on the order of 10 m/s (22 mph) were measured in the corridor and stairwell above the fire floor. These extreme thermal conditions are not tenable, even for a firefighter in full protective gear."
"If the fire has vented a window, important information can be gained by observing the behavior of the flame at the window. If the fire apartment has a high pressure relative to the outside due to an imposed wind, the flame will “pulse” out of the window to balance the overpressure. If the flames are being forced out of the window a flow path has been established through the building and the flow direction maybe favorable to interior fire fighting. If the flames are pulsing or being forced into the window, condition may not be favorable to interior firefighting and caution should be used on the approach to the fire floor. Even if flames are being forced out of adjacent windows in the fire apartment with a high amount of energy, there could still be sufficient energy flows on the fire floor to create a hazard for firefighters."
"Door control is the most basic means to interrupt or control the flow path in the building. The fire floor stair door should be checked for heat or hot gases flowing around the edges. The door should only be opened a few inches at first to look for rapid changes in smoke volume or velocity and/or thermal conditions. If the thermal environment changes quickly, close the door to interrupt the flowpath. In a smoke filled environment, visual changes to conditions may not be apparent with out a thermal imager. A similar approach would be used on the door to the fire apartment."
"In these experiments, the externally applied water streams were implemented in different ways; a fog stream inserted into the fire room window, a fog stream flowed from the floor below into the fire room window opening, and a solid water stream flowed from the floor below into the fire room window opening. In all cases, the water flows suppressed the fires, thereby causing reductions in temperature in the corridor and the stairwell of at least 50 %. The water flow rates used in these experiments were between 125 gpm and 200 gpm, demonstrating that a relatively small amount of water applied directly to the burning fuels can have a significant impact."
"Another factor Norman [16] identifies is that the fire does not have to be 20 stories or more above ground for wind to be a factor. Table 1.1-1 demonstrates that these FDNY wind driven fire incidents have occurred as low as the 3rd story above ground. NFPA data shows that the majority of fires in high rise buildings occur below the 7th floor [2]."
"Every experiment began with all of the doors and windows closed with the exception of the door to the furnished bedrooms and the main entrance door from the public corridor to the fire apartment. After ignition, the fire was allowed to grow until it failed the windows in the room or became ventilation limited. The purpose of the experiments was to get a wind driven fire condition. Therefore when an apartment became ventilation limited because of lack of window failure additional doors were opened remotely such as the stairwell door to provide additional air for the fire to grow. In some cases, windows were manually vented to provide additional air flow."
"Once wind driven conditions were achieved many different openings were made to simulate the operations of a fire department. These operations included opening the front lobby doors for access, entering the stairwell, opening the door from the stairwell to the fire floor, and opening the bulkhead door at the top of the stairwell. In addition to these operations each of the tools to be tested, PPV fans, Wind Control Devices and Floor Below Nozzles were deployed and evaluated."
"Wind is a factor. As shown in these experiments, wind can significantly increase the thermal hazards of a fire in a structure. Wind conditions will vary at different elevations above the ground floor, on different sides of a building, due to the effects of surrounding structures or topography, or just changes in the wind itself. Therefore wind needs to be considered as part of the intial “size-up” of the fire conditions and continue to be monitored and reported on throughout the fire incident."
"Smoke is Fuel. A ventilation limited (fuel rich) condition developed prior to the failure of the windows. Oxygen depleted combustion products, containing carbon dioxide, carbon monoxide and unburned hydrocarbons, filled the rooms of the structure. Once the window failed, the fresh air provided the oxygen needed to sustain the transition through flashover, which caused a significant increase in temperature."
"Venting does not always equal cooling. In these experiments, the cool air forced into the broken upwind window resulted in an initial period of cooling in the room of origin, typically followed by a transition to flashover, if a flow path was available."
"Fire induced flows. Velocities within the structure exceeded 5 m/s (11 mph), just due to the fire growth and the flow path that was set-up between the window opening and the open bulkhead door on the roof."
References
1. "Photos from Loudoun County: Two-alarm house fire on Sunday morning in Broadlands." STATter911, May 2009
2. "Wind Driven Fires, Houston" Carey, April 2009
Additional Reading
"Examining Firefighting Tactics under Wind Driven Conditions" USFA, revised May 2009
"Wind Driven Conditions - Lab Experiments" Carey, March 2009
"Breaking Down NIST's 'Fire Dynamics'" Carey, Firehouse.com, September 2008
"Fire Dynamics for the Fire Service" Carey, September 2008
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Replies to This Discussion
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Permalink Reply by Mike Walker on
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NIST Tests Wind-Driven Firefighting Tactics
Jun 1, 2009 2:46 PM
By Mary Rose Roberts
Fire engineers at the National Institute of Standards and Technology tested the effect of wind-driven fires and developed related firefighting tactics for use in residential and high-rise buildings. Wind-driven fires create dangerous fire conditions that penetrate firefighters’ turnout gear and lead to loss of life, said Dan Madrzykowski, a NIST fire protection engineer.
Researchers at NIST, a non-regulatory agency under the Department of Commerce, initially began to study how firefighters died of thermal shock in high-rise fires. In each case, burn injuries weren’t necessarily inconsistent with life.
“They weren’t that bad,” Madrzykowski said. “But yet there was an extreme heat condition they were overcome by, and it seemed to happen very quickly. We needed to get a better understanding of why that happened.”
Madrzykowski said researchers conducted a series of experiments to study the effect of wind on high-rise fires or buildings with seven or more floors. He said eight experiments were conducted at the agency’s Large Fire Laboratory.
Tests demonstrated that a fire expands when wind and an open vent are present. Madrzykowski explained that wind conditions push hot gases and smoke from the apartment of origin into public corridors and stairwells. Typically, a firefighter on scene opens a door, or a series of doors, to create a vent path through the structure. Now, the opened window is the inlet for the fresh air. As a result, flames blow horizontally and force their way through the apartment into the corridor.
Usually, the firefighting environment has hot gasses on top and a cool layer on bottom. That’s not the case in wind-driven fires, Madrzykowski said. Sometimes they remain as flames creating a blowtorch effect — which some firefighters have described. Other times, fires still don’t have enough oxygen and exist as super-heated gases.
“It’s taking these well-mixed hot gases and basically creating a near uniform temperature from floor to ceiling,” Madrzykowski said. “So there’s no way for these firefighters to get low and get out of the hot gas flow.”
During the test, the flow path’s temperature reached at least 750°F, Madrzykowski said. Because the wind is blowing, super heated gases flow over the turnout gear. The gear is designed to absorb the heat but it has a finite limit. The next layer affected is the firefighter’s skin.
“The temperatures we saw in our experiments would have been lethal, even to a protected firefighter,” he said.
Researchers collaborated with the Fire Department of New York to create a wind-driven fire in abandoned buildings on Governor’s Island, N.Y. The live tests confirmed laboratory findings.
What researchers found prompted NIST to release several recommendations about wind-driven fires. First, Madrzykowski said wind awareness during a size up is crucial. “To the best extent you can, you want the wind behind you,” he said.
Second, control the flow path. The absence of a flow path prevents wind-driven fire conditions throughout the building. Be aware of which windows may fail, which windows are opened and to try and maintain control.
Equipment and tactics also are used to prevent wind-driven fires. Madrzykowski said use a small amount of water at the fuel source or initial burn room that caused the window to fail. In a high-rise, a high-rise nozzle is used. Firefighters use the tube from the floor below by opening the window, placing the nozzle outside and throwing water overhead. The wind helps push the water into the apartment to cool the hot gases and removes the wind-driven fire conditions, he said.
Another strategy is to deploy wind-control devices, Madrzykowski said. Firefighters deploy heat-resistance material from one floor above the fire over the window on the fire floor in order to block wind. He said it diminishes the velocity of the hot gasses through the space. It also blocks oxygen and smothers the fire.
“You drop the temperature throughout the fire floor at least by 50% within 60 seconds or so,” he said about the technique.
A third technique is the use of positive-pressure ventilation fans. They do an excellent job of pressurizing the stair and stabilizing it so firefighters have a safe refuge or a place to start their fire attack, Madrzykowski said.
“They don’t create enough pressure to overcome the wind-driven fire condition,” he said. “But when the other devices or techniques are used — the positive pressure can be affective with the blowing the smoke out of the corridors and adds cool air behind the firefighter’s back to work with.”
NIST now offers its finding on a set of DVDs. They are free of charge to public-safety agencies for firefighter training. E-mail Madrzykowski to request a copy. -
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