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Initiatives to address new technology and maintain safety requirements for fire sprinklers

Fire sprinklers have been used for over 100 years. Due to changes in their application and installation, on-going monitoring and assessment of their construction and performance are required to maintain high levels of safety.

Photo of a fire sprinkler

Introduction

For decades fire sprinklers have proven to be an effective and invaluable tool for protecting property and life from the potentially devastating effects of fire. With the increased awareness and public concern for building safety, there is a growing need for buildings to be fitted with reliable security and safety systems. While fire sprinklers have been used to reduce the loss of life and property from fires for more than 100 years, the expanded end-use applications and changing installation environments for these products require ongoing monitoring and assessments of the construction and performance requirements included in safety standards to maintain the desired high level of safety.

The Underwriters Laboratories Standards development process routinely considers new technology and performance in field use environments to assess the need for revision of product requirements or installation standards. Since the year 2000, improvements have been identified that enhance the performance requirements for fire sprinkler products.

Sprinkler Standards and requirements

On a global basis, there are a number of product standards for sprinklers published by various organizations. For example, the International Standards Organization (ISO) publishes four different international standards for fire sprinklers including ISO 6182-1, “Fire protection — Automatic sprinkler systems — Part 1: Requirements and test methods for sprinklers”1; ISO 6182-7, “Fire protection —Automatic sprinkler systems — Part 7, Requirements and test methods for early suppression fast response (ESFR) sprinklers”2;  ISO 6182-10, “Fire protection — Automatic sprinkler systems — Part 10: Requirements and test methods for domestic sprinklers”3 and ISO 6182-13, “Fire protection — Automatic sprinkler systems — Part 13: Requirements and test methods for extended-coverage sprinklers”4. The ISO Technical Committee (TC) 21/SC 5 is currently undertaking an effort to consolidate the requirements included in these four sprinkler standards into a new edition of ISO 6182-1 that will include an expanded range of fire sprinkler technologies compared to those described in the current versions of these standards. 

The European standards for sprinklers published in the English language include British Standards (BS) EN 12559-1, “Fixed firefighting systems — Components for sprinkler and water spray systems — Part 1: Sprinklers”5  and BS EN 12559-14, “Fixed firefighting systems- Components for sprinkler and water spray systems — Part 14: Sprinklers for residential applications.”6 

This paper is focused on requirements included in UL Standards. Although a number of UL Standards have been published over the year, the three most prominent UL Standards include:

  • UL 1997, the Standard for Automatic Sprinklers for Fire-Protection Service 
  • UL 16268, the Standard for Residential Sprinklers for Fire-Protection Service
  • UL 17679, the Standard for Early-Suppression Fast-Response Sprinklers 

In 2020, seven separate UL Standards, including UL 16268 and UL 17679, were consolidated into UL 1997. As a part of this effort, several revisions were made to achieve closer alignment of the test methods and requirements applied to the various types of sprinklers now covered by UL 1997. The sprinklers currently addressed by UL 1997, including the latest sprinkler technologies, include the following:

  • Conventional (old style)
  • Standard spray — standard coverage area
  • Residential
  • Extended coverage — light hazard
  • Extended coverage — ordinary hazard
  • Specific application (window and horizontal concealed spaces)
  • Storage sprinklers — control mode/density area (CMDA)
  • Storage sprinklers — extended coverage  
  • Storage sprinklers — control mode specific application (CMSA)
  • Storage sprinklers — early suppression fast response sprinkler mode (ESFR)

These sprinklers are generally intended to be installed in accordance with the nationally recognized installation standards published by the National Fire Protection Association (NFPA), including the standards for Installation of Sprinkler Systems, NFPA 1310; Installation of Sprinkler Systems in One-and Two-Family Dwellings and Manufactured Homes, NFPA 13D11; and Installation of Sprinkler Systems in Low-Rise Residential Occupancies, NFPA 13R12. The Standard for Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, NFPA 2513, contains comprehensive requirements for assessing the ability of the sprinkler system to operate as intended on an ongoing basis.
  
The fire sprinkler community is generally aware that the industry has been particularly active within the last 20 years in developing new sprinkler technology, including a broad range of large K-factor storage sprinklers. While it is important for the product standards to be updated to address new technologies, it is also critical that standards be updated to take into consideration new information learned from the use and application of these fire safety products. Over the years, several new and revised requirements have been adopted into UL Standards that are intended to enhance the general operating performance of sprinklers in field environments. 

As would be expected, UL Standards contain tests to evaluate the capability of these products to distribute water in such a manner that will control or suppress fires. However, many are not aware that these Standards also include a broad range of tests to investigate the ability of sprinklers to operate and perform as intended under stressed and adverse field conditions. In fact, each of these Standards contains more than 35 different performance tests. The following is a brief description of just a few of the tests that have been in UL Sprinkler Standards for decades:

  • Resistance to leakage and rupture
  • Tests to evaluate the ability of a sprinkler to control or suppress a fire
  • General corrosion tests that expose samples to salt spray, hydrogen sulfide and carbon dioxide-sulfur dioxide atmospheres
  • Stress corrosion tests for copper alloy and stainless steel components.
  • Exposure of samples to 98% relative humidity at 93 degrees Celsius (200 degrees Fahrenheit).
  • High-temperature exposure tests for each temperature rating
  • Vibration exposure 
  • Impact resistance 
  • Rough usage 

Although these tests are considered to be very challenging, it is important to continuously monitor the performance of sprinklers in actual field use environments to maintain a level of confidence that the sprinkler standards continue to be relevant and effective in achieving the desired level of safety and performance.

Examples of revisions to UL Sprinkler Standards adopted in recent years to enhance sprinkler operation performance

Based upon reports from property owners, sprinkler contractors, code authorities and others, fortified by UL’s testing of thousands of sprinkler samples from hundreds of installation locations, two key areas for enhancing sprinkler operation performance were identified in the early 2000s. These revisions included new additional construction and performance criteria related to the release of the water seal assembly and resistance to premature (unwanted) sprinkler operation.

Release of the water seal assembly

Until the early 1960s, the prevention of leakage from sprinklers was primarily achieved through the use of a metal-to-metal compression seal arrangement, typically employing the use of a copper gasket. Today, a conical spring with a polytetrafluoroethylene (PTFE) film gasket is the most prevalent means used in sprinklers to prevent leakage. A schematic of typical water seal configurations used over the years is provided in Figure 1. 

Depiction of different water seals

Figure 1: Typical sprinkler water seal designs that have been used over the years. Note the small annular clearances between the O-ring water seal assembly and sprinkler orifice.

Since the late 1990s, UL has conducted operational tests on a large number and type of O-ring sealed sprinklers sampled from field installations. While the operational test results of these sprinkler types varied substantially after being installed in the different installation locations, UL’s testing of these sprinklers revealed that a large percentage of sprinklers utilizing a dynamic O-ring type seal required elevated inlet pressures for the water seal to release from the sprinkler and allow it to discharge water. In fact, in some cases, the O-ring type water seal did not release even when 6.8 bar (100 pounds per square inch gauge (psig)) was applied to the inlet.

deposits found in sprinkler inlets
Figure 2: Photograph illustrating the level of deposits commonly found in sprinkler inlets.

While O-ring seals were utilized in both wet and dry type sprinklers, the majority of dry sprinklers manufactured between 1970 to the early 2000s were constructed with O-ring water seals. Accounting for a small percentage of all installed fire sprinklers, dry sprinklers are generally found in locations having harsh environmental conditions, characterized by wide variations in temperature, humidity and corrosive conditions, such as car ports, parking garages, loading docks, outdoor canopies and walkways. Results from operational tests conducted on thousands of O-ring sealed dry sprinklers sampled from field installations indicate that approximately 50% of the sprinklers experienced inhibited operating characteristics primarily due to the water seal assembly not releasing in the intended manner.

dry sprinkler construction
Figure 3: Typical dry sprinkler construction incorporating an O-ring water seal. Note the areas where deposits can collect and inhibit sprinkler operation.

The analyses of wet and dry sprinkler samples received from the field installations indicated that a broad, but not clearly defined spectrum of materials and chemicals may reside within sprinkler inlets, including various types of oils, surfactants, chemicals associated with water potability and pipe sealing compounds, hard water deposits, sand and dirt. These materials and chemicals may act to accelerate the corrosion process and inhibit the intended movement of sprinkler operating parts.

Based on these analyses, UL identified four key factors considered to be contributing to the inhibited sprinkler operation, particularly in O-ring sealed sprinklers:

  • The collection of corrosion and other products in the small annular clearances between operating parts  
  • Transfer (sticking) of the O-ring material to the mating sealing surface
  • Dezincification
  • Micro-leakage past the O-ring water seal causing corrosion and deposits to form on the nonwater side of the seal

To address these concerns, several revisions to UL Sprinkler Standards were adopted in 2001. Table 1 summarizes the revisions that were adopted related to enhancing the operating performance characteristics of the water seal assembly. Extensive data generated as a result of UL’s operational testing of sprinklers from field installations subsequent to the implementation of these revisions have confirmed the need for these additional requirements. 

TABLE 1: Summary of revisions to the UL Sprinkler Standards related to enhancing sprinkler operating characteristics.

Revisions adopted in 2001

Rationale for new requirement

Hydrocarbon and water immersion exposure

Significant levels of hydrocarbons and water deposits have been found in sprinkler inlets sampled from field locations. Sprinklers are required to operate as intended after these exposures.

Ban on use of dynamic O-ring water seals

The primary contributor to elevated operating pressures measured in O-ring sealed sprinklers were (1) the collection of corrosion and other deposits in the small annular clearances provided between the operating parts, (2) transfer (sticking) of the O-ring material to the mating surface and (3) small leakage past the O-ring water seal causing deposits to develop. Figure 1 illustrates the small annular clearances typically associated with O-ring sealed sprinklers. Figure 2 illustrates the level of deposits commonly built-up in the inlet of a sprinkler. This type of water seal has not been permitted in UL certified sprinklers since 2003.

Dry sprinkler deposit loading test

Dry sprinklers can be installed in harsh environments, and corrosion deposits have been observed on the internal operating components. Figure 3 illustrates the areas within the dry sprinkler assembly where deposits have been observed. Figure 4 is a photograph of a dry sprinkler that was subjected to the laboratory deposit-forming test. After this exposure, the sprinkler is required to operate as intended.

Dezincification test

Some sprinklers received from field installations showed evidence of dezincification, which is the selective removal of zinc from a copper alloy. Dezincification can weaken the pressure retaining capabilities of sprinkler parts, and potentially cause leakage, loss of structural integrity or inhibited operation. This test establishes a minimum level of resistance to dezincification and is applicable to all copper alloy materials containing more than 15% zinc exposed to the sprinkler system water.

Resistance to premature sprinkler operation

In the early 2000s, UL received an increased number of field reports of sprinklers discharging water without an apparent cause for the operation. These situations are commonly referred to as premature sprinkler operation. Dry sprinklers installed in cold storage facilities and glass bulb sprinklers were the focus of many of those concerns.

Photograph illustrating the level of deposits created by the new laboratory deposit-forming test.
Figure 4: Photograph illustrating the level of deposits created by the new laboratory deposit-forming test. After exposure to the deposit-forming atmosphere, the water seal assembly is required to release as intended with an inlet air pressure of 0.48 bar (7 psig).

Regarding dry sprinklers installed in freezers, it was determined that ice build-up external and internal to the sprinkler had the potential to apply excessive stresses to the operating parts. Proper installation of the sprinkler is important to prevent external ice build-up around the sprinkler. It is critical for the hole that accommodates the installation of the dry sprinkler to be properly insulated and sealed. If the annular space between the sprinkler and freezer is not sealed properly, substantial quantities of ice can build-up around the sprinkler due to condensation and hot, moist air entering the freezer. Figure 5 is a photograph of a dry sprinkler that was not properly sealed around the sprinkler penetration. These situations should be readily visible during periodic sprinkler system inspections.

sprinkler with ice building
Figure 5: Photograph of dry sprinkler not properly sealed around the sprinkler penetration causing external ice build-up. This condition should be readily visible during an inspection of the sprinkler system.

Based upon the same air movement principle, ice may build-up internal to the dry sprinkler if a sprinkler’s water seal assembly and extension nipple connection is not completely sealed. To prevent air interchange within the sprinkler and the resulting build-up of ice internally, UL sprinkler Standards require this connection to be completely airtight. More detailed information on dry sprinklers installed in freezers is contained in a paper titled “A Technical Analysis: The Use and Maintenance of Dry Type Sprinklers.”14 

While glass bulbs have been used as heat responsive elements in sprinklers for decades, these bulbs have been miniaturized in recent years to enhance the sensitivity to fire conditions. Considering the typical phases of a sprinkler’s life, there is ample opportunity for damage or overstressing of the glass bulb to occur. Figure 6 illustrates several potential sources of damage to the glass bulb heat responsive elements and causes for the premature sprinkler operation. 

Chart of several potential sources of damage to glass bulb heat responsive
Figure 6: Chart of several potential sources of damage to glass bulb heat responsive elements and causes for unwanted discharge of sprinkler system water.

To address the potential source of damage related to manufacturing, UL sprinkler Standards include a test to determine that the integrity of the glass bulb is maintained after the sprinkler has been fully assembled and subjected to all the other production testing at the factory. This requirement provides a level of assurance that sprinklers are shipped from the factory with a damage-free, fully functional glass bulb. Also, to minimize the potential for glass bulb damage due to the extensive handling that typically occurs after the sprinkler has left the manufacturing facility, UL sprinkler Standards require all glass bulb sprinklers to be fitted with protective covers.

The requirements referenced in Table 2 were adopted into UL sprinkler Standards in 2003 and are believed to have been instrumental in substantially reducing the number of premature sprinkler operation occurrences in field installations in recent years.

Table 2: Summary of the revisions to UL Sprinkler Standards related to reducing the potential for premature sprinkler operation

Revisions adopted in 2003

Rationale for new requirement

Dry sprinkler air tightness/leakage test

Air interchange through the sprinkler can cause internal ice build-up. Requiring the sprinkler’s water seal assembly and extension nipple connection to be completely airtight reduces the risk for ice build-up on the internal parts of the sprinkler assembly.

Protective covers for glass bulb sprinklers

Extensive handling of sprinklers after shipment from the manufacturing facility creates the potential for unprotected glass bulbs to be damaged by coming in contact with other sprinkler components and objects. Requiring a protective cover for glass bulb sprinklers reduces the potential for damage to occur.

100% glass bulb integrity testing

Requiring each fully assembled sprinkler to undergo a test to evaluate the integrity of the glass bulb provides a higher level of assurance that sprinklers shipped from the factory will not have a damaged glass bulb.

Degraded thermal sensitivity characteristics of ESFR sprinklers

NFPA 2513 includes requirements for periodic inspection, testing and maintenance of sprinkler systems. To provide a level of assurance that field-installed sprinklers continue to operate as intended, sprinklers are required to be replaced or representative sample testing conducted at specified time intervals based upon the sprinkler type. For ESFR and other quick-response type sprinklers, the required time interval for replacement or representative sprinkler sample testing is 20 years after installation. If representative sample testing is conducted, retesting is required to be conducted at 10-year intervals thereafter. Representative sprinkler samples removed from the system are required to be subjected to a thermal sensitivity/operational test. Since this testing is destructive, samples removed from the system are to be immediately replaced with new sprinklers.

For several decades, UL has been conducting thermal sensitivity/operational testing on sprinkler samples removed from field installations. This testing service is intended to assist property owners, enforcement authorities and other interested parties in assessing the operating characteristics of sprinklers in service. UL’s online tool to request testing be conducted on sample sprinklers submitted to our facilities provides a quick, simple means for initiating this testing process. This tool can be accessed by visiting UL’s website at www.UL.com/fieldsprinklertesting

ESFR sprinklers began to be used extensively to protect storage facilities in the early 1990s. Since replacement or representative sample testing of ESFR sprinklers wasn’t required until 20 years after installation, UL didn’t receive samples for testing until the last few years. After testing a significant quantity of ESFR sprinklers sampled from field installations, UL observed that a large percentage of these samples had a response time index (RTI) greater than the required 36 (m·s)1/2 [65 (ft·s)1/2] that was apparently caused by exposure of the sprinklers to the range of environmental conditions associated with storage facilities. 

Based upon the data and information gathered from our testing of ESFR sprinklers sampled from field environments, requirements in UL Standards for ESFR sprinklers were revised in 2015 to require more aggressive laboratory corrosion test conditions, and these requirements became effective in 2017. It is anticipated that ESFR sprinklers complying with these new requirements will exhibit a much greater resistance to thermal sensitivity degradation. Additionally, UL, with support from the sprinkler industry, undertook an initiative to generate large-scale fire test data that was used by the NFPA 25 Technical Committee to support an increase in maximum RTI allowed for representative ESFR sprinkler sample testing from 36 (m·s)1/2 [65 (ft·s)1/2]  to 50 (m·s)1/2 [90 (ft·s)1/2]. 

Summary 

The timely updating of requirements in safety standards is imperative to maintain the relevancy of test methods and requirements as it relates to achieving safety objectives. While UL sprinkler Standards were the first to include the requirements described in Tables 1 and 2, the importance of applying these requirements to sprinklers has been freely shared with the fire protection community. Many of the additional sprinkler construction and performance requirements described in this article have also been adopted into the latest editions of the previously mentioned ISO standards for sprinklers.

Fire sprinklers have established an outstanding record of protecting property and life dating back to the 1800s, and the overall effectiveness of sprinkler system protection continues to be at a very high level. With the vigilance and collaboration of enforcers, insurers, designers, installers, manufacturers, standards development organizations, certifying organizations and others, the high level of safety provided by fire sprinkler systems can be maintained and enhanced even though fire challenges and installation environments continue to evolve. The ongoing efforts to expand the usage of fire sprinklers as a protection tool will make our world a safer place to live. 

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    References

    1. ISO 6182-1, “Fire protection – Automatic sprinkler systems – Part 1: Requirements and test methods for sprinklers”, International Organization for Standardization, Geneva, Switzerland, Third Edition Dated 2014-01-15
    2. ISO 6182-7, “Fire protection – Automatic sprinkler systems – Part 7: Requirements and test methods for early suppression fast response (ESFR) sprinklers”, International Organization for Standardization, Geneva, Switzerland, Second Edition Dated 2020-04-01
    3. ISO 6182-10, “Fire protection – Automatic sprinkler systems – Part 10: Requirements and test methods for domestic sprinklers”, International Organization for Standardization, Geneva, Switzerland, Second Edition Dated 2014-05-15
    4. ISO 6182-13, “Fire protection – Automatic sprinkler systems – Part 13: Requirements and test methods for extended-coverage sprinklers”, International Organization for Standardization, Geneva, Switzerland, Second Edition Dated 2017-02-01
    5. BS EN 12559-1:1999, “Fixed firefighting systems- Components for sprinkler and water spray systems – Part 1: Sprinklers”, British Standards Institute, London, United Kingdom 1999-09-15
    6. BS EN 12559-14:2020, “Fixed firefighting systems- Components for sprinkler and water spray systems – Part 14: Sprinklers for residential applications”, British Standards Institute, London, United Kingdom 2020-01-31
    7. UL 199, The Standard for Automatic Sprinklers for Fire-Protection Service, Underwriters Laboratories Inc., Northbrook, Illinois, Twelfth Edition, 2020-04-28.
    8. UL 1626, The Standard for Residential Sprinklers for Fire-Protection Service, Underwriters Laboratories Inc., Northbrook, Illinois, Withdrawn in 2020.
    9. UL 1767, The Standard for Early-Suppression Fast-Response Sprinklers, Underwriters Laboratories Inc., Northbrook, Illinois, Withdrawn in 2020. 
    10. Standard for the Installation of Sprinkler Systems, NFPA 13, National Fire Protection Association, Quincy, Massachusetts, 2019 Edition.
    11. Standard for the Installation of Sprinkler Systems in One-and Two-Family Dwellings and Manufactured Homes, NFPA 13D, National Fire Protection Association, Quincy, Massachusetts, 2019 Edition.
    12. Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies, NFPA 13R, National Fire Protection Association, Quincy, Massachusetts, 2019 Edition.
    13. Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, NFPA 25, National Fire Protection Association, Quincy, Massachusetts, 2020 Edition.
    14. Golinveaux, James, A Technical Analysis:  The Use and Maintenance of Dry Type Sprinklers, Tyco Fire & Building Products, Lansdale, Pennsylvania, 2002.

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