Needed Fire Flow

Fireground size-up factors can have varying degrees of impact on a fire. Life safety is always the most important, but achieving all of our incident priorities is highly dependent on many factors:• Poor construction methods can accelerate a fire or...


Fireground size-up factors can have varying degrees of impact on a fire. Life safety is always the most important, but achieving all of our incident priorities is highly dependent on many factors: • Poor construction methods can accelerate a fire or make a building more prone to collapse...


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Fireground size-up factors can have varying degrees of impact on a fire. Life safety is always the most important, but achieving all of our incident priorities is highly dependent on many factors:

• Poor construction methods can accelerate a fire or make a building more prone to collapse

• The lack of clear distances between buildings can allow a fire to spread to adjacent exposures

• Height, occupancy, area, location, weather and lack of protective fire systems all can play a significant role in achieving or failing to gain fire control

• A shortage of personnel can cause a shift in strategies and tactics

• The location of the fire and the time it occurs can impact the situation

Yet, with all of the potential problems that accompany those size-up points, it has been my experience that a lack of or loss of water supply seems to always be followed by bad things happening. The water supply can be lost due to a burst length of hoseline or the engineer finding that the hydrant is out of service and the tank's water supply has been exhausted. In any case, fire burning unabated can spread rapidly, endangering occupants and firefighters. These situations can be compounded if ventilation activities have been initiated prior to the water supply being lost. The influx of fresh air can spread the fire to areas that seem to compound the problem the greatest.

Gauging Need for Water

A consideration at a fire scene for the initial incident commander is how much water will be needed for effective fire control. This information will impact the incident in terms of determining needed resources and the implementation of tactical operations.

Determining the amount of water needed to extinguish a fire in a specific building is best accomplished during the pre-planning stage. This can be achieved through a deliberate calculation of the occupancy considering conditions when establishing the needed fire flow. When pre-planned information is available to the initial incident commander upon arrival at an incident, strategic and tactical decisions can be made more readily and accurately.

Determining required fire flow during pre-planning activities requires the application of a "fire-flow formula" to conditions observed during an inspection of the premises. On many occasions, fire incidents are encountered where pre-planned fire-flow information is not available. Under these circumstances, experienced fire officers are able to determine the needed fire flow based on their experience and knowledge of similar situations they have encountered in the past.

There are occasions when a newly appointed or relatively inexperienced officer lacking the expertise of a seasoned officer must quickly judge the amount of water needed to effectively control a fire. The National Fire Academy (NFA) in Emmitsburg, MD, has developed a formula that allows for quick calculations. The formula was derived through a study of fire flows that were successful in controlling a large number of working fires along with interviews with numerous experienced fire officers from throughout the country regarding the fire flows they have found to be effective in various fire situations.

The NFA "quick-calculation" formula can be used as a tactical tool to provide a starting point for deciding the amount of water required at an incident scene. This will permit decisions to be made on the apparatus needed to deliver the water and the number of firefighters that will be needed to apply it. The information developed indicated that the relationship between the area which is involved in fire and the approximate amount of water required to effectively extinguish the fire can be established by dividing the square footage of the area of fire involvement by a factor of three. This quick-calculation formula is expressed as:

Fire flow = length times width divided by 3

This formula is most easily applied if the estimated square footage of the entire structure is used to determine an approximate fire flow for the total structure and is then reduced accordingly for various percentages of fire involvement.

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