FYI - Accidental Discharge of Fire Sprinklers

Automatic fire sprinkler systems are widely considered the single most effective tool for protecting life and property from unfriendly fire. There has never been a multiple loss of life from fire among building occupants protected by a properly designed, installed and maintained fire sprinkler system. Having an automatic sprinkler system protecting your home or workplace has been compared to having firefighters at the ready 24 hours a day. Automatic sprinklers respond individually to heat from a fire, distributing water under pressure at the source of a small fire before it can become large and deadly.

The idea of having water at the ready can be a concern to some due to the prospect of water damage. It is increasingly recognized that less water is needed to suppress small fires than large fires, and that a sprinkler system typically uses less than one-tenth the water to control a fire than the fire department would use in a nonsprinklered building. But what happens if there is accidental leakage from the automatic fire sprinkler system?

The fire sprinkler industry takes many precautions to ensure than accidental leakage does not occur. The automatic sprinklers and other system components are tested and listed by Underwriters Laboratories and Factory Mutual Research Corporation to make sure that these devices are not prone to leakage. Component designs are typically tested for integrity at four to five times the maximum water pressures they will see in service, and every single sprinkler is tested at twice its maximum service pressure before it leaves the factory. As a final step in the installation process, the entire sprinkler piping system is also tested under an elevated pressure for a two-hour period, and any leaks must be located and corrected.

There have been some instances where the performance of an automatic fire sprinkler has been so efficient that it is not immediately apparent that a fire took place. But if an automatic sprinkler has discharged water in the clear absence of a fire, an investigation should be undertaken to determine why the sprinkler operated. In almost all cases, a reason can be found. Typically, the reasons include inadvertent overheating, freezing, mechanical damage, corrosion, or deliberate sabotage.

Overheating - Automatic sprinklers respond to heat, and cannot differentiate between "good heat" and "bad heat". Where sprinklers are located very close to unit heaters, under skylights and in other areas exposed to high heat, the applicable rules of NFPA standard 13 - Installation of Sprinkler Systems require that higher temperature rated sprinklers be used. This means that the solder elements or glass bulbs used as the operating mechanisms will be designed to activate at temperatures of 200-300^oF (93-149^oC) instead of the normal 155-165^oF (68-74^oC). If new sources of heat are added, a qualified contractor should be hired to make the necessary modifications. Temporary heat-producing sources such as construction lighting and television cameras have also been known to activate sprinklers.

Freezing – Although special types of sprinkler systems are available for use in areas subject to freezing, most sprinkler systems are wet pipe systems, meaning that the piping is normally filled with water. If a system or even a small portion of a system is exposed to freezing temperatures, water in the piping can turn to ice, expanding in volume and producing thousands of pounds of pressure. Such pressures can break fittings, but can also force open the valve caps of sprinklers, resulting in apparent accidental discharge or leakage when the system subsequently thaws.

Mechanical Damage – The frame, the seat and the operating mechanism (solder link or glass bulb) of an automatic sprinkler together form a sealed unit that is expected to maintain its integrity, but also to operate efficiently if a fire ever threatens its protected area. The sprinkler parts are joined somewhat like a coiled spring, holding the energy needed to activate when released by heat from a fire. Mechanical impacts to sprinklers can result in damage and separation of parts. Although it is obvious that a large force can immediately open a sprinkler, it is less obvious that a smaller impact can do the same thing over time. For this reason, it is important that sprinklers be carefully handled during the installation process, and that the proper wrenches be used during their installation. Special wrenches are often required by the manufacturers' literature to reduce the possibility of slippage that can damage the sprinkler operating mechanism, potentially resulting in a release of parts weeks or months later. Building renovations can also result in impacts of sprinklers, leading to an inadvertent discharge or leakage at a later date.

Corrosion – Corrosion can result in a weakening of parts, and a subsequent release of water. This can occur among very old sprinklers, or sooner with sprinklers installed in a harsh environment. Many fire codes require enforcement of NFPA 25 - Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. This standard requires that the building owner replace sprinklers that exhibit corrosion, loading or other damage.

Deliberate Sabotage - Deliberate acts of sabotage must also be considered when investigating the reasons for sprinkler discharge. Vandalism and insurance fraud have been found in the past to be motivations for tampering with sprinklers.

Manufacturing Defect - The likelihood of an automatic sprinkler opening in the absence of the above reasons was historically found to be extremely low - on the order of one per year per sixteen million sprinklers in use. These statistics were based on the use of traditional sprinklers, however, not the more sensitive sprinklers of today that feature lighter operating mechanisms for enhanced fire performance. Although very rare, the possibility of a manufacturing defect can be considered when all other potential reasons for inadvertent operation have been ruled out. This could take the form of a problem in loading or tolerances on the parts. The sprinkler manufacturer should be contacted, and arrangements can be made for professional analysis.

Keys to proper analysis of the reasons for unexpected sprinkler discharge:

1. Salvage of all sprinkler parts. Pieces of the sprinkler operating mechanisms can often be located during clean-up activities and, like the sprinkler frame remaining in the piping, are extremely valuable in helping to determine the reason for sprinkler operation.

2. Complete observation of the surrounding physical environment. The history of the sprinkler is important. For newer sprinklers, this includes the conditions under which it was shipped to the jobsite, stored and installed. For sprinklers that have been in service for some time, the conditions of use include the possibility of damage from materials handling equipment, the potential exposure to freezing conditions, and the possibility of temporary heat sources.

Following an unexpected operation of a fire sprinkler, prompt and thorough collection of parts and data can mean the difference between an unexplained mystery and a documented problem. Better understanding of the reasons sprinklers operate accidentally will help ensure that fire sprinkler systems are there when needed…to protect lives and property.

c. 2000, Russell P. Fleming, P.E.