Multi-Family Fire Safe Construction
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Reliability
Fire Sprinkler
Reliability
 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. These passive fire protection benefits
do not change over 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, 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
does not operate during a fire event or it does not control or extinguish
the fire. Bukowski et al.’s investigations of operational
reliability only address “failed-dangerous.”
The work by 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:
- Installation errors
- Design mistakes
- Manufacturing/equipment defects
- Lack of maintenance
- Exceeding design limits
- Environmental factors
 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 (1990
and 1998), the Consumer Product Safety Commission was informed of
20 fires since 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:
- Apartments: 12.4%
- Hotels and motels: 17.3%
Other constructions that may include multi-family type occupancies
were reported to have the following failure rates:
- Educational properties: 20.4%
- Health care or correctional facilities: 20.0%
 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 Fire
Safety Construction Advisory Council.
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