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Determining Water Supply Requirements for Rural Firefighting

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An underlying firefighting assumption building codes make is that firefighting measures (full time or volunteer) are available to all buildings. Building codes do not assume that a specific level of firefighting protection will be provided (i.e. minimum equipment available, water capacity, pumping capacity, manpower, response time, etc.). The code assumes that between 10-30 minutes could elapse between the outbreak of fire and can result in high radiant heat energy to adjacent buildings. During that period, the spatial separations required by building codes should be sufficient to prevent fire spread to buildings on adjacent properties. If manual firefighting is determined not to be readily available within 30 minutes, additional fire protection measures above the minimum requirements should be considered for a building (reference Notes to Part 3, A-3 Application of Part 3 – Firefighting Assumptions).

The NBCC indicates that every building shall be provided with an adequate water supply for firefighting. Other provincial building codes, such as Ontario and Alberta also indicate that water supplies shall be adequate as well (Reference OBC, 3.2.5.7., NBCC 2015, 3.2.5.7.1.). Smaller buildings that fall under Part 9 of the NBCC do not have firefighting water supply requirements, though fire insurance companies may require certain water supply requirements.

An adequate water supply is not defined in the Code but is required to be readily available and of sufficient volume and pressure to allow firefighters to control fire growth, conduct search and rescue operations, and prevent fire spread between buildings. Water supplies can be natural sources (such as ponds, lakes, creeks, etc.) or constructed source such as municipal water supplies, storage tanks and cisterns for example.

If a building is of such a size (building area, number of storeys) to require an automatic sprinkler or standpipe system, determining an adequate water supply is straightforward. The water supply needs to be of sufficient volume and pressure to allow the sprinkler or standpipe system to operate as designed. For small residential buildings, protected with just a residential sprinkler system, an adequate water supply could be as little as 150-200 gpm at 40-50 psi. For larger buildings with more severe fire hazards and more complex sprinkler and standpipe systems, an adequate water supply could be 500-3,000 gpm or more.

If a building is not protected with a sprinkler or standpipe system, determining an adequate water supply is not straightforward. However, accepted standards and other guidelines exist to help identify an adequate water supply. The Alberta and Ontario Building Code (ABC, OBC) as well as NFPA 1 “Fire Code”, and NFPA 1142 “Standard on Water Supplies for Suburban and Rural Fire Fighting” all have methods for determining firefighting water supplies.
The methods discussed in the codes and standards above vary, but the following factors are consistent in determining a water supply:

  •  The size/volume of the building (OBC, ABC, NFPA 1142 methods),
  •  Spatial separation distances between buildings (OBC, ABC methods),
  •  A building coefficient or construction classification number which considers building construction and occupancy (OBC, ABC, NFPA 1142 methods).

NFPA 1, instead of a formula-based method, determines a base fire water flow rate (in gpm) first, by considering the building area and construction; then permits reductions to the flow rate by percentages for features such as sprinkler protection, and increased spatial separation. NFPA 1 also indicate minimum and maximum water flow rates for smaller buildings such as residential one- and two-family dwellings.

Some municipalities in Canada also require that the “Fire Underwriters Survey” (FUS) method be used to determine water supplies. The FUS method is often used by fire insurance companies.

Regardless of the size of buildings, all standards referenced in this Article state minimum flow rates that should be provided. 450-500 gpm is about the minimum recommended water supply for firefighting. Considering that most rural areas are not supplied by municipal water systems, flowing 500 gpm through multiple attack lines would deplete the water supply from a fire department’s responding tanker in 2-3 minutes. Often, not enough apparatuses are available to provide a water shuttle capable of delivering a tank of water every 2-3 minutes. Therefore, establishing a nearby water pumping area would be vital in delivering a sustained water supply to the fire scene.

Reference: https://my.firefighternation.com/forum/topics/889755:Topic:1861034?commentId=889755%3AComment%3A6365774#gref

 

The bottom line is there are methods for determining what an “adequate” water supply should be by applying industry-accepted codes and standards. When applied, the results should satisfy the property owner, their insurer and the local AHJ. However, being a firefighter myself, I’ve been to structure fires involving single-family dwellings where the fire was controlled using less water flow than that recommended by standards. Every fire is different, with endless variables that could increase or decrease the amount of fire water needed to suppress, control and protect property.
PLC Fire Safety Solutions has the knowledge and expertise to help Owners, municipalities, towns and villages develop or identify adequate fire water requirements for all buildings.

PLC provides sprinkler design services and we can help identify what an adequate water supply should be for a non-sprinklered building.

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