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High Rise Buildings and Wind, A Perfect Storm?

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We know that high-rise fires can be challenging, to say the least, due to the complexity of the buildings themselves, as well as the all the bases that must be covered in these incidents to ensure a successful outcome. One of the most difficult challenges that we as firefighters can face when responding to these incidents is a wind-driven fire in a high-rise building. This is an extreme and very serious situation.

Wind was a factor in this high-rise fire that the Chicago Fire Department responded to several years ago. Photo courtesy Keith Witt

Wind was a factor in this high-rise fire that the Chicago Fire Department responded to several years ago. Photo courtesy Keith Witt

Wind-driven fires don’t actually occur in every high-rise fire, but the potential does exist for a seemingly routine fire to turn into a wind-driven fire when a number of factors come together. And when that happens, it will create one of the most dangerous and challenging fires you will ever encounter.

Wind-driven fires aren’t limited to huge, luxury high-rise buildings; they can occur in smaller public-housing high-rises as well. As a matter of fact, some of the most deadly wind-driven fires have occurred in these “projects,” under conditions we would normally consider routine. But we in the fire service cannot, and should NEVER classify any situation as routine.

Documenting the Effects

In 2007, the National Institute for Standards and Technology (NIST), in conjunction with the Chicago Fire Department and the FDNY, conducted research on the affects of wind in high-rise fires. The research started in Chicago in November 2007 using live-fire experiments in a vacant 16-story high-rise building that was slated for demolition. These experiments were highly successful in obtaining a wealth of information on the fire dynamics in these buildings when wind becomes a factor.

However, the Chicago experiments just scratched the surface, and left a lot of questions unanswered. The following year, the research continued on Governors Island in New York City in an attempt to gain more information about these deadly fires. The research has provided some valuable data about the dangers these fires present to firefighters, and how firefighters can better prepare to deal with them.

Fire Dynamics

Wind-driven fires are the result of wind entering the fire apartment through windows that have self-vented due to heat, or have been prematurely vented by firefighters. As the wind enters the building through the opened window and comes in contact with the smoldering or burning material, the rate of heat release is dramatically increased, very similar to using a bellows in a fireplace.

If the door of the apartment is left open by the escaping occupants or is forced by firefighters and not properly controlled, the once seemingly routine fire will suddenly and without warning blow torch out of the fire apartment and into the public hallway. According to NIST, temperatures can escalate in excess of 2,500 degrees F in the most severe cases. This is not a gradual build-up of heat, but happens with lightning-bolt speed, making escape very difficult if not impossible without severe or fatal injuries.

Once this occurs, it’s physically impossible to extinguish this fire using a direct frontal attack. We must either implement an alternative tactic or wait for the fire to reduce the fuel load to be able to eventually make the hallway and the fire apartment. The latter seems almost unthinkable. However, if we do not have an alternate tactic to implement, then that may be our only option.

The best means to protect ourselves in high-rise fires is to become familiar with the fire dynamics and recognize the warning signs of a potential wind-driven fire by conducting a thorough and educated size-up.

The first thing to understand is how heat and smoke travel through the building. We must understand that fire is a pressure-driven event—fire always moves from the burning compartment (the high-pressure area) to other parts of the building such as hallways, stairways or apartments on the opposite side from the fire apartment (the low-pressure areas). This is called the flow path.

One of our primary functions in this situation is to reduce the flow path by controlling and coordinating our ventilation, and controlling the opening and closing of doors. This will minimize the air currents within the building until we can get the fire under control, thereby reducing the likelihood of rapid fire spread.

5 Key Factors

For a wind-driven fire to occur, five key elements must come together. In the absence of anyone of these elements, a wind-driven fire will not occur.

  1. A fire in the apartment.
  2. An open apartment door—either left open by the occupant, or forced open and not controlled by firefighters.
  3. Smoke in the public hallway. Although this would indicate that the apartment door has been left open, there have been wind-driven fires that have occurred where the hallway was clear until firefighters have forced entry to the fire apartment and lost control of the door.
  4. Wind. One would think that we would need a strong and powerful wind to cause such extreme conditions; however, according to NIST, a wind speed of as little as 10 to 20 mph can cause serious problems for firefighters. As we keep this in mind we must also realize that the wind conditions at grade level may seem light or even nonexistent; however, as we ascend above grade level, the wind speeds can change.
  5. A failed or open window. This is probably the most crucial element. The window can be left open by the occupants, vented prematurely by firefighters or fail suddenly due to heat conditions.

When this perfect storm comes together, conditions will change within seconds, causing firefighters to scramble for safety, and possibly incur serious injury.

Anticipate & Prepare

As previously stated, wind-driven fires don’t occur at every high-rise fire. However, we must always anticipate the worst-case scenario. The best way to protect ourselves is to recognize when these factors begin to come together as we arrive on the scene. In my next article, we will take a look at how we can best size-up this situation for a safe and successful operation.

Authored By: BFC Keith Witt

Keith Witt is a 32-year veteran of the Chicago Fire Department (CFD) and currently holds the rank of battalion chief, assigned to the 18th Battalion in Chicago’s Englewood neighborhood. He holds a bachelor’s degree in fire protection and safety engineering technology from Oklahoma State University and a master’s degree in public safety management from Lewis University. Witt is also a lead instructor in the CFD’s Officer Training Program, a Field Staff Instructor for the University of Illinois Fire Service Institute, and the National Fire Academy. Firefighter safety and survival has become one of his top priorities and motivations.

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