Feature Articles
Corrosion Resistance and Environmental Exposure Testing of Fire Sprinklers
by Kerry M. Bell P.E.
March 31, 2008
UL 199 incorporates a full range of performance tests for one reason — to ensure product reliability and durability.
Fire sprinklers have proven to be a highly
effective tool in reducing the loss of life and property from fires for more
than 125 years. The usage, as well as the end use applications of these
products, continues to expand and, according to the International Fire
Sprinkler Association, an estimated 100 million fire sprinklers were installed
worldwide in 2006. Because the application and installation environments are
expanding and changing, on-going performance assessments of these products in
the field are instrumental in maintaining a high level of
effectiveness.
Underwriters Laboratories Inc. (UL) has been listing fire sprinklers since
1902. As a part of UL’s third-party certification program, qualification and
surveillance testing is conducted to evaluate the ability of sprinklers to
comply with specified criteria. In addition to this testing, UL closely
monitors the field experience and performance of sprinklers, and regularly
updates the standards to address new technology and information learned from
the use of these products in the field. In recent years, a number of revisions
have been introduced into UL’s sprinkler standards to enhance the operating
performance characteristics of both wet and dry-type sprinklers.
UL 199 and Other Sprinkler Standards
Currently, UL publishes three standards for sprinkler products described as
follows:
• UL199, Standard for Automatic Sprinklers for Fire-Protection Service
• UL1626, Standard for Residential Sprinklers for Fire-Protection
Service
• UL1767, Standard for Early-Suppression Fast-Response
Sprinklers
The products covered by these standards are intended to be installed in
accordance with the nationally recognized installation standards published by
the National Fire Protection Association (NFPA).
UL’s fire sprinkler standards include nearly 40 different performance tests and
a limited number of prescriptive construction-type requirements. The
performance tests in UL’s sprinkler standards fall into five categories, as
indicated in Table 1. While all of these tests are important to provide a high
level of confidence that fire sprinklers will perform as intended, the focus of
this article is on the requirements that are intended to address the potential
adverse affects of exposure to anticipated environmental conditions.
Because fire sprinklers are a critical property protection and, in some cases,
a life-safety tool, the construction of these products consider both
reliability and durability. As a part of UL’s certification program, an extensive
series of corrosion resistance and environmental exposure tests described in
Table 2 on page 15 are conducted to investigate the ability of these products
to resist degradation when exposed to a wide range of field environments.
It is important to understand that many of these tests are accelerated under
controlled laboratory test conditions to simulate extended service time in the
field. To limit the duration of these tests to a reasonable time frame, the
techniques used to accelerate the corrosion, loading or degradation processes
include the use of aggressive atmospheric exposure conditions and high test
temperatures.
While all fire sprinklers are constructed to incorporate a significant level of
corrosion resistance, sprinklers identified as “corrosion resistant” are UL
Listed for use in corrosive external atmospheres. These sprinklers typically
utilize a wax or other coating to achieve this designation. Corrosion resistant
sprinklers are subjected to more challenging salt spray, hydrogen sulfide and
carbon dioxide-sulfur dioxide test conditions as described in Table 2.
Dynamic O-Ring Water Seals in Fire Sprinklers
One of the critical construction requirements recently introduced into UL’s fire sprinkler standards was a prohibition on the use of dynamic O-ring water seals. Based upon reports from property owners, sprinkler contractors, authorities having jurisdiction and others (which was supported by testing thousands of sprinkler samples from hundreds of installation sites across the country), UL concluded that sprinklers incorporating dynamic O-ring water seal assemblies might not operate as intended in a fire condition.
The construction requirement prohibiting the use of O-ring sealed sprinklers was adopted into UL’s sprinkler standards as a result of UL’s extensive research indicating that a broad range of environmental conditions could adversely impact field performance.
As a result of these findings, UL recommends that property owners take action to have O-ring sealed sprinklers located in existing installations replaced or representative sprinkler samples from these systems be periodically tested to determine acceptable performance.
Field Inspection, Testing and Maintenance
While fire sprinklers are constructed to provide a substantial level of corrosion resistance, periodic inspection, testing and maintenance of a sprinkler system is critical to provide assurance that the system will perform when challenged with a fire. In this regard, UL Listed sprinklers are intended to be serviced and maintained in accordance with the NFPA 25, Standard for Inspection, Testing and Maintenance of Water-Based Fire Protection Systems.
The useful life of a sprinkler is highly dependent upon the installation conditions. When installed in non-aggressive environments, fire sprinklers have demonstrated an ability to remain functional for 50 years and longer. When installed in environments known to be corrosive, corrosion-resistant sprinklers should be used and closely monitored since the useful life can vary.
When sprinklers are installed in environments that present unique challenges to maintain sprinkler functionality, additional measures to protect fire sprinklers may be appropriate. For example, NFPA 33, the Standard for Spray Application Using Flammable or Combustible Materials, permits the use of cellophane bags having a thickness not greater than 0.08 mm be placed over the sprinkler to provide enhanced protection against overspray residue loading, which could adversely impact sprinkler performance.
For all fire sprinkler systems, NFPA 25 includes detailed criteria relative to inspecting fire sprinklers on a regular schedule and the time interval for fire sprinkler replacement or representative sample testing.
Accounting for a small percentage of all installed fire sprinklers, dry-type sprinklers are generally found in locations having harsh environmental conditions, characterized by wide variations in temperature, humidity and corrosive conditions such as attics, car ports, cold storage structures, and parking garages. In consideration of these harsh conditions — as well as operational test data generated on a large number of these sprinklers removed from field installations — NFPA 25 requires replacement or representative sample testing of sprinklers from the system after 10 years in service.
Summary
Table 2. Selected UL 199 Corrosion Resistance and Environmental Exposure Tests.
As is the case with most products that are expected to have a long service life, periodic inspection, testing and maintenance is critical for fire sprinklers. NFPA 25 includes detailed information and requirements related to properly maintaining fire sprinklers and associated system equipment.
Kerry M. Bell P.E.
Kerry Bell, P.E., is a principal engineer at Underwriters Laboratories Inc. (UL), specializing in fire sprinkler and pump equipment. Since 1976, he has been involved in UL’s testing and certification activities related to a variety of fire suppression products, including fire sprinkler system equipment, portable fire extinguishers and special hazard extinguishing systems. Bell is a member of several technical committees of the NFPA, American Water Works Association and ASTM International. He is currently a member of NFPA’s Residential Sprinkler Systems, Sprinkler System Discharge Criteria and Technical Correlating Committees; chairman of the NFPA Technical Committee on Water Spray Fixed Systems, and vice chairman of UL’s Fire Council.
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