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Reducing Risk: Water Supply & Fire Department Access

(Appeared in June 2017 issue of The Dispatcher)

There have been some recent questions and confusion regarding fire flow calculations for water supply. Fire flow calculations are made to assure there is enough available water for firefighting at specific structures. While there are five separate mathematical formulas to estimate the amount of water needed, there is no single “correct” method for establishing fire flow in the structural fire protection world. The overall objective is to provide enough water to effectively control and extinguish the fire. Most of the formulas were developed as quick use for an Incident Commander confronted with an emergency. So, which formula is the best to use?

Both NFPA 1 – Fire Code and the International Fire Code reference a fire flow formula calculated by construction type and square footage of the structure. These methods utilize a chart for the various square footage ranges and construction types, resulting in an amount for gallons per minute and duration needed. This information helps fire prevention officials determine whether there is sufficient water available to control and extinguish a fire in the building. Both code organizations, the National Fire Protection Association and International Code Council, see the benefits of fire sprinkler systems and give credit when a building is protected by them. The credit equates to a seventy-five percent reduction in the amount of the water needed by emergency response crews since the fire sprinkler system will activate early in the fire, thus requiring less water from the responding fire department.

The other fire flow formulas, however, do not credit for fire sprinkler systems and thereby require larger amounts of water to be available. Part of the argument for those formulas is that they treat all structures the same, as if they were not protected. By doing so, it is supposed to help the incident commander determine immediate resources (staffing, equipment, and water) to effectively control the fire and reduce further damage to the structure or neighboring buildings.

An example of two of the fire flow calculations: A building is a 200-by-300-foot, mixed-used building of type II (non-combustible) construction provided with a fire sprinkler system designed for the occupancy classification. The NFPA fire flow formula (Table 18.4.5.2.1 from NFPA 1) determines the building would require a fire flow of 3,500 gallons per minute (gpm) for three hours before the reduction for fire sprinkler protection. With the reduction, the gpm would be lowered from 3,500 to 1,000 (actual reduction results in 875 gpm, but we must use the code’s minimum required fire flow of 1,000 gpm). In sharp contrast, the National Fire Academy’s formula simply multiplies the length and the width of the building and divided that number by 3. This would result in a required fire flow of 20,000 gpm. The difference is substantial for the property owner who must provide the required fire flow for the fire department.

The NFPA 1 and International Fire Code calculations, though not scientific, provide a reasonable approach to fire flow determination when planning new construction. Once the fire flow requirements are determined, the next step is looking at fire department access. Access should be assured first to fire protection devices (hydrants, fire department connections) onsite for vehicles and staff. The access lanes for vehicles and equipment to assure access for firefighting are next most important. This information will assure fast, effective response by emergency response agencies.

Ensuring adequate water supply and fire department access reduces risk, both risk of occupant injury or death and risk of property loss. These are important components of the fire prevention bureau to assure business continuity.

For information on how fire sprinklers save lives and property, please email me or visit National Fire Sprinkler Association – Wisconsin Chapter, National Fire Sprinkler Association, and Home Fire Sprinkler Coalition.

-Marty King, State Coordinator, NFSA-WI

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