The National Institute of Standards and Technology (NIST), the Fire Department of New York City (FDNY), and the Polytechnic Institute of New York University with the support of the Department of Homeland Security (DHS)/Federal Emergency Management Agency (FEMA) Assistance to Firefighters Research and Development Grant Program and the United States Fire Administration (USFA), have conducted a series of wind driven fire experiments in a seven-story building on Governors Island, New York.
The objective of this study was to improve the safety of firefighters and building occupants by developing a better understanding of wind-driven fires and wind-driven firefighting tactics, including structural ventilation and suppression. A series of 14 experiments were conducted to evaluate the ability of positive pressure ventilation fans (PPV), wind control devices (WCD), and exterior water application via floor below nozzles (FBN) also known as high-rise nozzles to mitigate the hazards of a wind-driven fire in a structure.
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 firefighters, 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.
During these experiments a public corridor and stairwell area was exposed to a wind-driven, post-flashover apartment fire. The door from the apartment to the corridor was open for each of the experiments. The conditions in the corridor and the stairwell were of critical importance because that is the portion of the building that firefighters would use to approach the fire apartment or that occupants from adjoining apartments or adjacent floors would use to exit the building. Fires in high-rise buildings create unique safety challenges for building occupants and firefighters. Smoke and heat spreading through the corridors and the stairs of a building during a fire can limit building occupants' ability to escape and can limit firefighters' ability to rescue them. In 2002, there were 7,300 reported fires in high-rise structures (seven stories or more). The majority of these high-rise fires occurred in residential occupancies, such as apartment buildings. In fires that originated in apartments, 92 % of the civilian fatalities occurred in incidents where the fire spreads beyond the room of origin.
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 firefighters 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 C (752 F) 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.
These experiments demonstrated the "extreme" thermal conditions that can be generated by a "simple room and contents" fire and how these conditions can be extended along a flow path within a real structure when wind and an open vent are present. Potential tactics which could be implemented to interrupt and control the flow path are door control from inside the structure and or a WCD from the floor above the fire. From the floor below the fire, external water application was demonstrated to be effective in reducing the thermal hazard in the corridor and stairwell.
Identify the Potential for Wind-Driven Conditions. Wind conditions should be considered as part of initial size-up of the incident. Wind conditions can vary widely in an urban environment due to wind flows around buildings, or shielding by buildings that give the perception on the ground that no significant wind is present, but another side of the building or a higher elevation in the building may be exposed to wind conditions. Wind speeds on the order of 10 mph to 20 mph are high enough to create a wind-driven fire condition in the structure with an uncontrolled flow path.
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 firefighting. 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.
Wind-driven fire conditions. The wind-driven condition can be described as hot gases or flames flowing horizontally out of the room of fire origin. The wind-driven fire condition has been described as a "blow torch" by firefighters. For our purposes, a wind-driven fire condition existed when the fire gases were well mixed and of equally high temperature from the floor to the ceiling, on the order of at least 400 C (752 F). For this condition to occur inside a structure, the fire must be in a flow path. In these experiments the inlet to the flow path was the upwind window in the room of fire origin. The flow path then went through the apartment, into the corridor, and exited out of the bulkhead door on the roof, via the stairwell. Without a flow path, the wind-driven fire condition inside the structure cannot occur.
Door Control. 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 flow path. In a smoke-filled environment, visual changes to conditions may not be apparent without a thermal imager. A similar approach would be used on the door to the fire apartment.
Impact of PPV. PPV fans alone could not overcome the effects of a wind-driven condition. However, when used in conjunction with door control, WCDs, and FBNs, the PPV fans were able to maintain tenable and clear conditions in the stairwell. The key to successful use of PPV fans was to mitigate the wind-driven fire condition via door control or other tactics. Then the PPVs can be used to clear the stair and then pressurize the stairwell to provide a safe working environment. Although the PPV fans, when used alone, could not reverse the flow of a wind-driven fire, PPV fans always improved conditions in the stairwell.
Impact of WCDs. In these experiments, the WCDs reduced the temperatures in the corridor and the stairwell by more than 50 % within 120 s of deployment. The WCDs also completely mitigated any velocity due to the external wind. The WCDs were exposed to a variety of extended thermal conditions without failure.
Impact of externally applied water. 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.
Stored Energy. Wind-driven fire conditions can generate and transfer energy throughout the flow path. When doors or WCDs are used to stop the wind-driven fire conditions, energy and fuel may be trapped on the fire floor. These experimental results indicate that the thermal conditions due to the residual heat on the fire floor were still of a level which could pose a hazard to firefighters in full PPE. However, when used in combination with PPV fans to force cool air into the stairwell and out through the fire floor, and or with the cooling effect from water streams, the fire floor temperatures were reduced to tenable conditions for firefighters in full PPE within minutes.
The data from this research will help provide the science to identify methods and promulgation of improved standard operating guidelines (SOG) for the fire service to enhance firefighter safety, fire ground operations, and use of equipment. If the demonstrated technologies continue to prove effective in the field trials and pilot programs, the next step may be to examine the need for standards and standardized test methods to define a minimum level of acceptable performance of these devices.