By Kerry M. Bell, principal engineer, Fire Sprinkler and Pump Equipment; Corporate Fellow – William Henry Merrill Society
For several decades, UL Solutions has examined and tested sprinklers sampled from field installations in accordance with the recommendations and requirements of applicable National Fire Protection Association (NFPA) standards.
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. For example, the amount of water required to be discharged from a sprinkler protecting a warehouse with high-piled storage is multiple times greater than the amount of water required to be discharged from a sprinkler protecting an office facility with a smaller fire load. 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 maintained to help ensure that the system equipment will perform as intended if a fire occurs. The primary focus of this article is on the examination and testing of the sprinklers sampled from a sprinkler system as referenced in the 2023 edition of NFPA 25, Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems.
Inspection, testing and maintenance requirements for sprinklers
Periodic inspection of field-installed sprinklers is an important element of a comprehensive maintenance program for fire 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 and corrosion or loading considered detrimental to sprinkler performance must be replaced. These conditions can lead to the degradation of sprinkler performance during a fire condition.
In addition to the periodic inspection of field-installed sprinklers, the 2023 edition of NFPA 25 also requires replacement or representative sample testing of sprinklers based on the length of time in service. Sample testing or replacement frequency depends on the sprinkler type and installation environment. While many sprinklers do not require representative testing or replacement until they have been in service for 50 years, sprinklers having fast response elements must be tested or replaced at a shorter time interval. Early suppression fast response (ESFR) and control mode specific application (CMSA) sprinklers that have fast response elements must be tested or replaced after 20 years in service and 10-year intervals thereafter. Other types of sprinklers that have fast response elements must be tested or replaced after 25 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 must be tested or replaced after 20 years of service and 10-year intervals thereafter regardless of the sprinkler response type. It is also worth highlighting the fact that NFPA 25 indicates that sprinklers installed in extraordinarily harsh environmental conditions, such as foundries, fertilizer facilities or areas exposed to outside weather conditions, must be replaced or representative samples tested on a five-year basis. The frequency for sample testing or replacement of some of these sprinklers has been revised over the years in consideration of the overall performance during representative sample testing.
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% of the number of sprinklers per sample area, whichever is greater, are to be tested. The sprinkler samples removed from the system for testing must be immediately replaced with new sprinklers. Each sample received by UL Solutions 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 manufacturer. The condition of the sprinkler is also noted based on 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 and allow the discharge of water.
Process for submitting samples for testing
UL Solutions field sprinkler testing program is intended to assist property owners and other interested parties in assessing the operating characteristics of fire sprinklers in service. The UL Solutions online Field Sprinkler Testing Tool for requesting operational testing of sample sprinklers provides a quick, simple means for initiating this process. This tool can also be accessed by visiting our fire sprinkler testing dashboard on the UL Solutions website. Following the menu prompts provided within the tool, basic information on the submittal is requested.
As a part of UL Solutions 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 also be requested using the online Field Sprinkler Testing Tool.
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 ANSI/CAN/UL/ULC 199, the Standard for Automatic Sprinklers for Fire Protection Service. During this test, the inlet of the sample is pressurized to approximately 5 psi (0.35 bar) and quickly plunged into an oven that circulates heated 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. If the heat response element functions but the water seal does not release, the sample is exposed to a water supply to determine if the sprinkler’s water seal releases at 7 psi (0.5 bar). A diagram and photo of an example of a test oven apparatus is provided in Figure 1.
Diagram and photo of sensitivity oven test apparatus – Figure 1
The test report for the samples is provided to the submitter and describes the condition of each sprinkler and results of the operation test as either normal or abnormal. The as-received condition of each sprinkler sample described in the report is based on a visual examination. The information included in the report is intended to be considered by other parties in determining the need to replace other sprinklers in the system.
Acceptance criteria for the operational testing of sprinklers sampled from field installations
UL Solutions has implemented several changes over the years to the service for testing sprinklers sampled from field installations. One of the changes recently implemented was to align the acceptance criteria values with NFPA 25, which included guidance for the criteria to be used for evaluating the operating performance of the various types of sprinklers. Table 1 summarizes the suggested criteria that is described in A.5.3.1.1 of NFPA 25:
| Criteria description and sprinkler type | Criteria |
|---|---|
| Maximum RTI for standard response sprinklers | 350 (meters-sec)1/2 |
| Maximum RTI for quick response and residential sprinklers | 65 (meters-sec)1/2 |
| Maximum RTI for ESFR sprinklers | 50 (meters-sec)1/2 |
| Minimum release pressure for all sprinklers | 0.5 bar |
This NFPA 25 Annex information provides guidance for testing laboratories to determine whether a sprinkler is considered to operate in a “normal” or “abnormal” manner. The UL Solutions test report references the response time index (RTI) for each sprinkler tested in the plunge oven test. The RTI is calculated using the operating time and marked temperature rating for the sprinkler, as well as the standardized velocity and temperature conditions used during testing. The test report also provides information as to the visual observation of the condition of each sample sprinkler received.
Statistical information on test results
The results from the testing of sprinklers sampled from installation sites also provide valuable information to UL Solutions 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 concerns associated with the operating performance of dynamic O-ring sealed wet- and dry-type sprinklers. This data and subsequent research led to substantial revisions to UL Standards for sprinklers that included a ban on the use of a dynamic O-ring water seal and more stringent corrosion exposure testing of dry-type sprinklers, which were implemented in early 2003. If sprinkler inspection, testing and maintenance was performed in accordance with NFPA 25 since 2003 for all installation sites, every field installed O-ring sealed sprinkler would have been identified and likely replaced by this time. However, a substantial number of dynamic O-ring sealed sprinklers remain in existing facilities even though UL Solutions has not certified these sprinklers since 2003. In fact, during 2023, approximately 15% of the dry-type sprinklers received for testing incorporated a dynamic O-ring seal.
In more recent years, the data on testing sprinklers sampled from field installations was useful in identifying a level of degraded operating performance of ESFR sprinklers. This finding provided technical support for revisions to ANSI/CAN/UL/ULC 199 that added requirements for more challenging corrosion exposure testing for ESFR sprinklers and revisions to NFPA 25 that referenced new thermal sensitivity acceptance criteria.
To assist the NFPA 25 technical committee members in understanding the operating characteristics of in-service sprinklers, UL Solutions has shared statistics from our testing of sprinklers sampled from field installations with the technical committee and others within the fire protection community. For the year 2023, an extensive analysis of the data from samples tested during that year was conducted. Table 2 provides an overview of the test results for the various types of sprinklers that were submitted to UL Solutions from existing facilities. 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. Most of the standard response (SR) sprinklers tested were at least 50 years old. Most of the quick response (QR) and ESFR sprinklers were at least 20 years old, and most of the dry-type sprinklers were at least 10 years old.
| Sprinkler type | Percentage of tested samples with normal operation |
|---|---|
| Wet-type QR (no ESFR or O-ring sealed) | 99.4% |
| Wet-type SR (no O-ring sealed) | 97.4% |
| ESFR without O-ring seals | 90.6% |
| Dry-type without O-ring seals | 99.2% |
| Wet-type with O-ring seals | 62.8% |
| Dry-type with O-ring seals | 44.3% |
Summary
NFPA 25 includes detailed requirements for the inspection, testing and maintenance of sprinkler systems (as well as other water-based fire protection systems) that are intended to provide a level of confidence that the system will provide the desired level of safety. The operating characteristics of sprinklers can degrade over time when exposed to a broad range of internal and external environmental conditions, and a cost-effective means to assess the operating characteristics of field-installed sprinklers is to conduct representative sample testing. Our service for testing sprinklers sampled from systems is intended to be a valuable tool to assist property owners, inspection authorities, the insurance industry and others in making important assessments of the operating characteristics of sprinklers in existing facilities.
The statistical analysis of the data generated from testing sprinklers sampled from field installations indicates that a 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 ANSI/CAN/UL/ULC 199 and NFPA 25. Based on the data collected, several revisions have been made to UL Standards that have been instrumental in maintaining the extraordinarily high level of performance that sprinkler systems have demonstrated over decades of use.
Learn more about UL Solutions field sample sprinkler testing program.