Automatic sprinkler protection is considered the single most effective tool in preventing loss and damage from fire. However some people still worry about the possibility of unexpected water discharge from defective sprinklers. Such an occurrence is extremely rare — the likelihood of an automatic sprinkler operating in the absence of a fire has historically been one for every 16 million sprinklers in use.
The manufacturers of the sprinkler systems take many precautions so that accidental leakage does not occur. Sprinkler designs are tested at five times the maximum water pressure they will see in service. In addition, every sprinkler is tested at twice its maximum service pressure before it leaves the factory. NFPA 13 requires that the entire sprinkler piping system be tested under elevated pressure for two hours and that any leaks be corrected.
Despite all the tests and precautions taken, sprinklers do sometimes operate in the absence of a fire. When this occurs, an investigation should be done to understand why. Most discharges are the result of inadvertent overheating, freezing, mechanical damage, corrosion or sabotage.
Automatic sprinklers are designed to respond to heat but they cannot determine what the heat source is. If sprinklers are installed in areas exposed to high heat, such as near unit heaters or skylights, NFPA 13 requires the use of sprinklers rated for higher temperatures. This means the sprinklers heads are designed to operate at 200°F to 300°F instead of the normal 155°F to 165°F. If new heat sources are added to the area after a sprinkler system has been installed, a qualified contractor should be hired to make the appropriate modifications.
There are special sprinkler systems designed for use in areas that are subject to freezing, but most sprinkler systems are wet systems. This means their piping is normally filled with water. The water in the piping can turn to ice if the system is exposed to freezing temperatures. The ice produces thousands of pounds of pressure which can force open the sprinkler heads or fittings resulting in accidental leakage or discharge when the system thaws.
It is important that sprinklers be handled carefully during installation and renovation, and that the proper wrenches are used according to the manufacturer's instructions.
A large force can open a sprinkler immediately, but a smaller force can do the same thing over time. The frame, seat and operating mechanism of a sprinkler form a sealed unit that's expected to operate efficiently when a fire occurs. If a sprinkler is hit, the unit may be damaged, or the parts may separate.
Corrosion can weaken the parts of a sprinkler system. Sprinklers that are old or installed in harsh environments are more susceptible to corrosion. Many building codes follow NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, which states that building owners should replace sprinklers that show signs of corrosion, loading, or other damage.
Vandals and people who commit insurance fraud have been known to tamper with sprinklers. This should always be considered when unexpected leakage or discharge occurs.
Although rare, manufacturing defects should be considered after all the other potential causes have been ruled out. The sprinkler manufacturer should be contacted and a professional analysis should be arranged.
A thorough investigation should be conducted after an accidental leakage or operation occurs. If a sprinkler system is new, one must consider the conditions under which the system was shipped to the site, stored and installed. For an older system, one must consider all of the potential causes listed above. Understanding why sprinklers operate accidentally will help ensure that the sprinklers systems work properly if and when a fire does indeed occur.
Acknowledgements: Excerpts from this article were taken from Russell P. Fleming's article "Unexpected Discharge of Fire Sprinklers" in the November/December 2000 issue of NFPA Journal.