Sprinkler System Design to Mitigate Loss

Most sprinkler systems are engineered to control fires from spreading to adjacent areas. These types of systems distribute water to reduce a fire’s heat release rate and pre-wet surrounding combustibles. Although a sprinkler system can be designed to suppress fires originating from a specific target, the average system is designed to prevent the spread of fire from its point of origin until the local fire department can extinguish it. Thus, it’s crucial to determine the water flow and pressure required to control a fire. If a sprinkler system is unable to control a fire, the fire will spread, actuate additional heads and further deplete system resources. This leads to fires spiraling out of control, causing significant loss of property, services, revenue and possibly life. Retaining a quality Fire Protection Engineer (FPE), to produce or review sprinkler system design documentation, is important to avoid such loss.

In the State of New Hampshire, a quality engineer will design a commercial sprinkler system in accordance with the State of New Hampshire Building Code (RSA 155-A). Specifically, the International Building Code (IBC-2009). A quality engineer will also design a commercial sprinkler system to comply with the New Hampshire State Fire Code (Saf-C 6000). Including, but not limited to, the Standard for the Installation of Sprinkler Systems (NFPA 13-2013) and the Life Safety Code (NFPA 101-2015).

A designer may use one of two methods to calculate a sprinkler system’s water requirements. The density/area method or the room design method. To utilize the room design method, the protected structure’s rooms must be enclosed by walls having a fire-resistance rating equal to the water supply duration requirements for hydraulically calculated systems. This commonly requires a structure’s walls to have a fire-resistance rating of at least 1-hour. For this reason, it’s customary to implement the density/area method as it doesn’t require the protected structure to comply with specific requirements.

When utilizing the density/area method, a quality engineer will determine the water flow and pressure required over a pre-determined area, for a set amount of time. To do this, the designer must first determine the protected structure’s occupancy classification. NFPA 13 occupancies differ from those listed in IBC and NFPA 101. They range from Light hazard to Extra hazard (Group 2) and are determined by the quantity and combustibility of contents. A quality engineer will make an accurate assessment of these occupancies. This is crucial as their design requirements vary wildly.

Once initial water requirements are determined, they must be adjusted to account for site specifics. The following details increase the amount of water required: the use of dry heads, steep sloped ceilings, adjacent hazards, obscurations and hose stream allowances (water required by the local fire department). If any of these details are bypassed, a system’s sprinkler heads may not be provided enough water to control a fire.

In closing, the retaining of a quality FPE, to produce or review sprinkler system documentation, is important to ensure a structure’s characteristics and fire load are accurately assessed. A proper assessment is crucial as an under engineered system may not be able to control a fire, leading to significant loss of property, services, revenue and possibly life.

Written by: Mark R. Richards, PE

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