Occupants of buildings often assume that a fire sprinkler system is the only line of defense against a fire. Non-combustible concrete and masonry construction resists fire, does not burn, and provides fire containment through compartmentation or unit division. These passive fire protection benefits do not change during the life of the structure and do not require routine inspection and maintenance to assure proper operation.
Most occupants will presume that fire safety installations meet building codes, without being aware that passive fire protection is equally important, particularly in case of fire sprinkler system failure.
There are two types of reliability reported for fire sprinkler systems: operational reliability and performance reliability. These are explained in “Estimates of Operational Reliability of Fire Protection Systems,” a paper by R.W. Bukowski, senior engineer for the National Institute of Standards and Technology Building and Fire Research Laboratory; E.K. Budnik, vice-president of the National Institute of Standards and Technology Building and Fire Research Laboratory, and C.F. Schmel, chemical engineer of Hughes Associates.
Usually performance reliability is based on full scale tests of a sampling of fire sprinkler systems components and sprinkler heads. When tested in the laboratory for full-scale fire events, the reliability is very high for fire sprinklers, often as high as 98 or 99 percent.
Operational reliability, on the other hand, is the performance of fire sprinkler systems in the field. There are two categories of operational reliability: “failed-safe” and “failed-dangerous.” Failed-safe means that the fire sprinkler system discharged water when there was no fire event. Failed-dangerous means the system did not operate during a fire event or it did not control or extinguish the fire. Bukowski, Budnik and Schmel’s investigations of operational reliability only address “failed-dangerous.”
The work of Bukowski et al. was based on data from the United Kingdom, Australia, and Japan. The reliability of sprinklers to operate was found to be between 95 and 99 percent. However the ability to extinguish a fire varied greatly — as low as 48 percent in the United Kingdom and as high as 96 percent in Japan.
Bukowski et al. identified a variety of causes for failures of sprinkler systems to operate:
- Manufacturing/equipment defects
Equipment defects have been the cause of a number of fire sprinkler system failures in the United States, including two notable incidents in 1995 when Omega sprinklers failed to release water despite activation of their fusible element by the heat of a fire: one at a Marriott Courtyard Hotel in Michigan, and the other at a Veterans Administration Medical Center in New York. During Federal investigations in 1990 and 1998, the Consumer Product Safety Commission was informed of 20 fires in which Omega sprinklers did not function.
Data on the operational performance of fire sprinklers from the United States Fire Administration is presented in a report published by the National Fire Protection Association: “U.S. Experience with Sprinklers.” This study only considered fires large enough to have called upon the fire sprinkler system to operate. The data for multi-family structures reported the following percentages of fires where sprinklers did not operate:
- Hotels and motels: 17.3 percent
Other constructions that may include multi-family type occupancies were reported to have the following failure rates:
- Educational properties: 20.4 percent
- Health care or correctional facilities: 20.0 percent
Sprinkler systems may not operate when needed the most, during large disasters. Earthquakes, hurricanes and other high wind events, floods, or explosions may disrupt water supply, making fire sprinkler systems ineffective at a time when the demand for fire services is above normal and response is impeded by lack of traffic control or lack of passable access routes. Water supplies may also be disrupted by arsonists, breaks in water lines, or routine water supply system maintenance. During any of these conditions, if sprinkler trade-offs were exercised at the time of construction, the building occupants are at an increased threat to life safety and property protection in the event of a fire.
Sprinkler trade-offs, permitted by some building codes, reduce the number of fire separations and/or the fire resistance rating of passive fire protection in buildings equipped with fire sprinklers. If sprinkler trade-offs were used, properties with defective sprinklers may be without adequate fire protection. They may have been without adequate fire protection for years, clearly an unacceptable risk for building occupants who are likely to presume that fire safety installations meet code and that they are safe in buildings.
Clearly sprinkler trade-offs should not be acceptable in building codes. Multi-family residences should be constructed with:
- Automatic fire detection systems
- Automatic fire suppression systems (fire sprinklers)
- Minimum two-hour fire resistance-rated non-combustible concrete and masonry separations between living units
- Minimum two-hour fire resistance-rated non-combustible concrete and masonry between living units and public spaces
- Minimum one-hour fire resistance-rated non-combustible exterior walls
When it comes to building construction that provides fire protection over the life of the building without disruption, there is no comparison to non-combustible concrete and masonry construction. For more information about combining smoke detectors, fire sprinklers, and passive fire protection visit the Pennsylvania Fire Safety Construction Advisory Council.