Fire Department Use of Sprinkler Systems
At the first NFPA meeting in 1896 the first consolidated set of sprinkler installation rules were established, becoming what is today known as NFPA 13, Standard for the Installation of Sprinkler Systems. Formalizing the sprinkler installation standards increased fire sprinkler effectiveness, however, a gap still existed in the use of fire sprinkler systems. In 1933 a brochure titled “Use of Automatic Sprinklers by Fire Departments” was published providing fire departments with guidelines on how to best capitalize on the effectiveness of fire sprinkler systems during incidents. This brochure evolved over the next 33 years into the Recommended Practice for Fire Department Operations in Properties Protected by Sprinkler and Standpipe Systems, NFPA 13E first published in 1966. Today NFPA 13E provides the information necessary to ensure fire departments are trained on and operate effectively with automatic fire sprinkler systems.
Although some fire sprinkler systems are designed to suppress a fire, most are designed to control a fire. The main difference between fire control and fire suppression is related to the fire sprinkler systems impact on the fires heat release rate. The graph below depicts fire control (dotted line) versus fire suppression (solid line). Fire sprinklers controlling a fire result in a steady heat release rate, keeping the fire from growing, and fire sprinklers suppressing a fire will result in a decreasing heat release rate.
The three principal causes of fire sprinkler system failures identified in NFPA 13E are a closed control valve, inadequate water supply for the system and occupancy changes that render the installed system unsuitable. Beyond the primary causes found in the recommended practice, NFPA has conducted research on the U.S. Experience with Fire Sprinklers to help understand fire sprinkler effectiveness. Let’s take a second to review the three main causes found in the recommended practice all of which responding fire department personnel can impact positively.
Closed control valve
Familiarization with the types of control valves and their layout in a system allows firefighters to both understand what valves will disrupt water flow and what position have they should be in for effective operation. Should they encounter a valve which is not in the correct position during a fire, placing that valve in the correct position may restore the system effectiveness. This is not a hard and fast rule however, since the fire may have already operated more sprinkler heads than the available water supply can support, making the system ineffective.
Additionally, fire departments should never turn off a sprinkler system that has activated until they have confirmed the fire is fully extinguished and overhaul has taken place. Even if ventilation is needed to increase visibility and conduct search and rescue, the system should remain operational to control the fire as these tasks occur. Once this occurs, steps should be taken to identify if only a portion of the system needs to be shut down (a zone) rather than the entire system. Anytime the system is shut down a firefighter with a portable radio should remain at the control valve to immediately open the valve should the fire not be fully extinguished.
Simply turning the system back on may not reestablish fire control. Fire sprinkler systems are designed to control a fire utilizing a specific number of sprinklers at a design pressure and flow. If the system is shut off prior to the fire being extinguished the potential exists for additional heads beyond the design to activate. When the system is turned back on the available water supply may not cover the operated heads leading to ineffective water application and a fire that is no longer controlled.
Inadequate Water Supply
The water supply may be inadequate due to a lack of available water flow, lack of available pressure or both. Since fire department pumpers often have the capacity to supply water at higher flow rates and pressures than the normal water supply, utilizing a fire department pumper to supply water to the fire department connection (FDC) can address most inadequate supply concerns. The FDC will often bypass many of the control and check valves in the system, supplying water directly to the operating sprinklers. NFPA 13E recommends a pressure of 150 psi (10 bar) to effectively suppl fire sprinkler systems, unless additional signage is provided to indicate a different pressure.
The fire department can also have a negative impact on the water supply to a fire sprinkler system. Although fire sprinkler systems are designed with a hose stream allowance or amount of water the fire department may potentially need to fully extinguish the fire, this may not be sufficient. For more information on fire flow check out this blog Calculating the Required Fire Flow.
The hose allowance accounts for water needed at the base of the fire, which if the fire department cannot effectively apply water to the base of the fire, more may be needed. Utilizing more water from the supply than accounted for has the potential to reduce the sprinkler system effectiveness, eliminating its ability to control the fire, resulting in fire growth and the need for more water. Supporting the system through the FDC ensures that even if more water is needed than the original allowance, the sprinkler system still has an available supply at an effective flow and pressure.
Although the fire department does not have an ability to impact occupancy changes during a fire incident, an effective preplan and inspection program has the potential to identify occupancy changes which can adversely impact fire sprinkler system effectiveness before fires occur. Training those conducting these inspections to understand what types of commodities would represent a high heat release rate fire and how to identify if a sprinkler system could be designed to deliver the necessary water density can reduce this potential cause of failure.
As with all NFPA recommended practices, the language is less rigid than a standard or code, utilizing “should” instead of “shall” as to not limit the individual fire departments, allowing them to adopt more effective procedures. Familiarization with NFPA 13E provides anyone who may be utilizing a fire sprinkler system the knowledge necessary to positively impact the systems effectiveness. Check out NFPA 13E to help your department identify the recommended training and operations for those responding to emergencies involving activated fire sprinkler systems.
Interested in learning more, check out the resources below for additional information on fire sprinkler systems and fire department access.