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Simulation of the Dynamics of a Wind-Driven Fire in a Ranch-Style House – Texas

Wind Driven Fire in Home, Texas, 2009. Aerial view of damage to the structure. (Photo credit: Houston Fire Department)
Wind Driven Fire in Home, Texas, 2009. Aerial view of damage to the structure.

On April 12, 2009, a fire in a one-story ranch home in Texas claimed the lives of two fire fighters. Sustained high winds occurred during the incident. The winds caused a rapid change in the dynamics of the fire after the failure of a large section of glass in the rear of the house. At the request of the National Institute for Occupational Safety and Health (NIOSH) and the Houston Fire Department (HFD), NIST assisted with examining the fire dynamics of this incident. NIST performed computer simulations of the fire using Fire Dynamics Simulator (FDS) and Smokeview, a visualization tool, to provide insight on the fire development and thermal conditions that may have existed in the residence during the fire.

The FDS simulation that best represents the witnessed fire conditions indicates that the critical event in this fire was the creation of a wind-driven flow path between the upwind side of the structure and the exit point on the downwind side of the structure: the front door. The flow path was created by the failure of a large span of windows in the den, in the rear of the structure. In a simulation that excluded wind, the thermal environment surrounding the location of interior operations was improved. Based on the analysis of this fire incident and results from previous studies, adjusting fire fighting tactics to account for wind conditions in structural fire fighting is critical to enhancing the safety and the effectiveness of fire fighters.

Impact of Exterior Suppression with Floor-Below Nozzle (00:56). No audio.

Prior to water application, flames can be seen in the bedroom and also flowing across the floor in the public hallway outside of the apartment. Once the water is applied into the bedroom window, notice how quickly the flames in the hallway are extinguished. The water has reduced the heat release rate and cooled the fire gases throughout the flow path.

Impact of Wind Control Device Deployment (00:58). No audio.

Note that when the wind control device is deployed, the flames coming out of the living room window (side window) stop and the color of the smoke changes from black to white (uncombusted, pyrolyzed fuels).

View of Temperatures at 5 ft Before and After Solarium Glass Fails - No Wind (00:12). No audio.

Simulated temperatures at 1.5 m (5 ft) above the floor throughout the house without wind.

View of Temperatures at 5 ft Before and After Solarium Glass Fails - With Wind (00:12). No audio.

Simulated temperatures at 1.5 m (5 ft) above the floor throughout the house with wind.

View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - No Wind (00:45). No audio.

Simulated temperatures at 1.5 m (5 ft) above the floor throughout the house without wind.

View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - With Wind (00:30). No audio.

Simulated temperatures at 1.5 m (5 ft) above the floor throughout the house with wind.

View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - No Wind (01:31). No audio.

Isometric view of the movement of heat at a level 5 ft above the floor. This video is annotated with labels that show when there are changes in ventilation. The temperature scale on the right is in degrees Fahrenheit. Any region that turns red indicates that is 500°F or above. Once the windows on the glass enclosed patio break, the hot gases vent out of the that area and the other portions of the structure cool down.  Note the cool air flow into the front door.

View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - With Wind (01:31). No audio.

The only change between this simulation and the previous one is the addition of a 10 mph wind. Notice how the roof ventilation provides some cooling in the front hallway, but once the glass wall in the rear of the structure (side c) fails the flow path in the structure changes. Now the inlet is the opening in the rear of the structure which is also the upwind side of the structure. The flow path extends into the den and then splits with some of the hot gases flowing out of the front door and some of the hot gases flowing out through the open garage door.

View of Temperature and Flow Path Development Throughout Incident - No Wind (00:51). No audio.

On the left is a view of the inlet to the flow path, the bedroom window, exposed to a 15 to 20 mile per hour wind. On the right is a thermal imaging camera view of corridor. The camera is looking north toward the vent. Prior to the window failure, a two layer environment exists with the hot gases flowing out of the living room door and cool gases in the lower 4 ft of the corridor. Note that the flow exits the living room and flows North toward the open vent. The thermal conditions in the corridor at that time are typical fire fighting conditions that PPE was designed to protect fire fighters from. After the window fails, the HRR of the fire increases rapidly and the high flow rate causes hot gases to fill the flow path, floor to ceiling. Firefighters have referred to this as the “blowtorch effect”. There is no escape from the thermal insult by getting low. The thermal conditions generated in the corridor after the window failed were approximately 1500°F, floor to ceiling, with heat flux measurements in the corridor just out side the living room doorway at 3 ft above the floor in excess of 100 kW/m2. These thermal conditions are not consistent with fire fighter survival. Also, note that even with the wind entering the bedroom window and the open flowpath, the pressure within the structure increased to the point where the flames pulse out of the window against the wind.

View of Temperature and Flow Path Development Throughout Incident - With Wind (01:01). No audio.

Here is another example. In this case, the door between the living room and the corridor is closed. After the window fails, the only inlet and exit for the flow path is the open window. For the fire, this is very inefficient. Once the door is open, completing the flow path through the structure, the heat release rate increases and the conditions in the corridor become very similar to those in the room of fire origin.

Wind Driven Fire - Texas (51,604 KB)

This PowerPoint presentation contains the following sections regarding the One Story, Single Family Home in Houston and wind-driven fires: introduction, objectives, summary on wind-driven fires, incident summary, fire dynamics simulator model, and a presentation summary.

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Impact of Exterior Suppression with Floor-Below Nozzle (00:56) No audio.

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Impact of Wind Control Device Deployment (00:58) No audio.

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View of Temperatures at 5 ft Before and After Solarium Glass Fails - No Wind (00:12) No audio.

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View of Temperatures at 5 ft Before and After Solarium Glass Fails - With Wind (00:12) No audio.

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View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - No Wind (00:45) No audio.

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View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - With Wind (00:30) No audio.

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View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - No Wind (01:31) No audio.

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View of Temperature and Flow Path at 5 ft Before and After Solarium Glass Fails - With Wind (01:31) No audio.

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View of Temperature and Flow Path Development Throughout Incident - No Wind (00:51) No audio.

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View of Temperature and Flow Path Development Throughout Incident - With Wind (01:01) No audio.

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Wind Driven Fire - Texas (51,604 KB)

Click here to download the PowerPoint presentation (PPT)

*** NOTE: The above video files must be in the same folder as the PowerPoint presentation in order to play most of the videos embedded in the presentation.

 

Download the complete report, NIOSH 2009-11

Download the complete report, NIST 1729

Contact

General Information:

Daniel Madrzykowski
madrzy@nist.gov
301 975 6677 Telephone

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NIST Engineering Laboratory (EL)