UL examined and tested sprinklers sampled from field installations in accordance with the recommendations and requirements of applicable National Fire Protection Association (NFPA) standards for several decades. Currently, NFPA 25, Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems¹ includes requirements for the inspection, testing and maintenance of sprinkler systems. 

To be effective in controlling or suppressing a fire, a sprinkler system is required to be designed and installed to provide protection against the magnitude of the fire risk anticipated to occur. While it is critical for sprinkler systems to be properly designed and installed, it is equally important for these systems to be periodically inspected, tested and properly maintained to ensure the system equipment will perform as intended when a fire occurs. 

While the focus of this column is on the examination and testing of the sprinklers sampled from a sprinkler system, the requirements in NFPA 25 are comprehensive in that it includes criteria for inspecting, testing and maintaining all components of a fire sprinkler system. As indicated in NFPA 25, the responsibility for properly maintaining a sprinkler system resides with the owner of the property.

Inspection, Testing and Maintenance Requirements for Sprinklers

Periodic inspection of field-installed sprinklers is an important element of a comprehensive maintenance program for sprinkler systems. As specified in NFPA 25, sprinklers showing signs of leakage, field painting, physical damage, loss of fluid in the glass bulb heat-responsive element, as well as corrosion or loading considered detrimental to sprinkler performance are to be replaced. All these conditions can lead to the degradation of sprinkler performance during a fire condition.

In addition to the periodic inspection of field-installed sprinklers, NFPA 25 also requires replacement or representative sample testing of sprinklers based upon length of service. The frequency of sample testing or replacement depends upon the sprinkler type and installation environment. While many sprinklers do not require representative testing or replacement until they have been in service 50 years, sprinklers having fast response elements are required to be tested after 20 years in service and 10-year intervals thereafter. 

Due to the relatively complex construction of a dry-type sprinkler, as well as some of the challenging installation environments where many of these sprinklers may be installed, dry-type sprinklers are required to be tested after 15 years of service and 10-year intervals thereafter. It is also noteworthy that NFPA 25 indicates sprinklers installed in harsh environmental conditions such as foundries, fertilizer facilities or areas exposed to outside weather conditions are to be replaced or representative sample-tested on a five-year basis.

Sprinkler samples selected for testing are to be representative of the sprinklers installed in the system. As noted in NFPA 25, no less than four samples or 1 percent of the number of sprinklers per individual sample, whichever is greater, are to be tested. Because UL’s operational testing of sprinklers is destructive, the sprinkler samples removed from the system for testing need to be immediately replaced with new sprinklers. 

Each sample received by UL is visually examined before testing to ascertain the sprinkler manufacturer, model or sprinkler identification number, style, type of heat-responsive element, temperature rating and year of manufacture. The condition of the sprinkler is also noted, based upon visual evidence of corrosion, loading, leakage, physical damage, loss of fluid in a glass bulb heat-responsive element or field painting. The testing of the sprinklers involves an assessment of the ability of the sprinkler to operate as intended. 

Process for Submitting Samples for Testing

UL’s program for conducting operational tests on sprinkler samples removed from field installations is intended to assist property owners and other interested parties in assessing the operating characteristics of sprinklers in service. UL’s online tool for requesting operational testing of sample sprinklers provides a quick, simple means for initiating this process (fieldsprinklers.UL.com). Following the menu prompts provided within the tool, basic information on the submittal is requested. 

As a part of UL’s field sprinkler testing service, identification tags are available for use at no charge. Sprinkler samples submitted for testing should be identified with the name and address of the building’s occupant, type of room environment (office, warehouse, factory, etc.), location of the sample within the building, and information on the party submitting the samples for testing. These identification tags can be requested online as well. 

Sample Testing and Report

To assess the operating characteristics of sprinklers sampled from field installation environments, the samples are subjected to the Sensitivity-Oven Heat Test as described in UL 199, the Standard for Automatic Sprinklers for Fire Protection Service². During this test, the inlet of the sample is pressurized to approximately
5 psig and quickly plunged into an oven that circulates air at a constant temperature and velocity. 

The actual temperature and air velocity used for the test are selected based on the temperature rating of the sprinkler. Each sprinkler sample is observed for proper operating characteristics, including the release of operating components and time of operation. A diagram and photo of a test oven apparatus are provided in Figure 1.

The Annex of the 2020 edition of NFPA 25 provides uniform criteria for testing laboratories to apply in determining whether a sprinkler is considered to operate in a “normal” or “abnormal” manner. Table 1 summarizes the acceptance criteria described in A.5.3.1.1 of NFPA 25.

The results from the testing of sprinklers sampled from installation sites provide valuable information to UL in assessing the operating performance of the broad range of sprinkler constructions. In the late 1990s and early 2000s, this data was useful in identifying the concerns associated with the operating performance of O-ring-sealed wet- and dry-type sprinklers. 

This data and subsequent research led to substantial revisions to UL’s sprinkler standards, including a ban on the use of a dynamic O-ring water seal and more stringent corrosion exposure testing of dry-type sprinklers implemented in early 2003. However, a large number of dynamic-sealed O-ring, dry-type sprinklers still remain in existing facilities even though UL has not certified these sprinklers since 2003. In 2019, approximately 23 percent of the dry sprinklers UL received for testing incorporated a dynamic O-ring seal. 

In order to assist the NFPA 25 Technical Committee members in understanding the operating characteristics of aged sprinklers, UL shared statistics from testing sprinklers sampled from field installations with the committee and others within the fire protection community. Table 2 provides an overview of the test results for the various types of sprinklers that were submitted to UL from existing facilities in 2019. 

Except for the known concerns with sprinklers having dynamic O-ring seals, the test results indicate a high level of operating performance even after the sprinklers have been in service for many years. The majority of the standard response (SR) sprinklers tested were at least 50 years old. The majority of the quick response (QR) and ESFR sprinklers were at least 20 years old; most of the dry-type sprinklers were at least 10 years old. 

The statistical analysis of the data UL generated from testing sprinklers sampled from field installations indicates that a very high percentage of these sprinklers operate in a normal manner even after being installed in challenging environmental conditions for many years. The data generated from this testing is also useful in identifying opportunities for developing proposed revisions for safety standards such as UL 199 and NFPA 25. 

A number of revisions have been made to UL and other standards that have been instrumental in maintaining the extraordinarily high level of performance that sprinkler systems have demonstrated over decades of use. 

References:

¹ “Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems,” NFPA 25, National Fire Protection Association, Quincy, MA, 2020 Edition.

²“Standard for Automatic Sprinklers for Fire-Protection Service,” UL 199, Underwriters Laboratories Inc., Northbrook, IL, Twelfth Edition, April 28, 2020.

Kerry M. Bell is Corporate Fellow and principal engineer for fire sprinkler and pump equip¬ment at UL LLC. 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.