Because the application and installation environments are expanding and changing, on-going performance assessments of fire sprinklers in the field are instrumental in maintaining a high level of effectiveness. As a part of United Laboratories’ third-party certification program, qualification and surveillance testing is conducted to evaluate the ability of sprinklers to comply with specified criteria.

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 StandardsCurrently, 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 inTable 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 inTable 2.

Table 1. Category of Tests in UL’s Sprinkler Standards.

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.

Table 2. Selected UL 199 Corrosion Resistance and Environmental Exposure Tests.


Fire sprinklers are subjected to a large number of corrosion and exposure type tests that are intended to represent a broad spectrum of field installation environments. While fire sprinklers are constructed to resist degradation during use, certain field environments can shorten their life. Corrosion-resistant sprinklers are available for use in external environments known to be corrosive.

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.