Protecting automatic fire sprinkler systems from cold temperatures has many challenges. As was demonstrated in February’s Texas power crisis, the formation of ice in a piping system containing water will lead to catastrophic failures.  

Automatic fire sprinkler systems rely on water to flow through pipe and discharge from fire sprinklers to control or suppress fires. If water is unable to flow, fires will not be addressed, resulting in catastrophic losses. 

National Fire Protection Association (NFPA) standard NFPA 13:2019, Standard for the Installation of Sprinkler Systems, Section 16.1 establishes the requirements for the protection against freezing when any portion of a system cannot be reliably maintained at or above 40 F (4 C). This section identifies methods of addressing freeze protection that includes using a dry or preaction system, using antifreeze, insulating the pipe or using heat tracing. Similar requirements are in NFPA 13R and 13D.  

This column will focus on the use of antifreeze. 

Antifreeze in Fire Protection Applications

Various antifreeze solutions have been used for many years in automatic fire sprinkler systems. Significant changes occurred in 2010 following a 2009 fatal incident involving the discharge of highly concentrated antifreeze during a fire event. This resulted in NFPA 13, 13R, 13D and 25, making significant changes to the use of antifreeze in fire sprinkler systems. 

Firstly, the types of antifreezes allowed in existing systems were significantly reduced to premixed solutions of 48 percent glycerin and 38 percent propylene glycol. Secondly, for new systems, a requirement for the use of a listed antifreeze was established. Thirdly, NFPA 25 established a sunset date of Sept. 30, 2022, for the use of nonlisted antifreezes in existing sprinkler systems. However, a major obstacle to implementing these requirements was the lack of a commercially available listed antifreeze. 

In response to the new NFPA antifreeze requirements, Underwriters Laboratories (UL) established UL 2901, Standard for Safety — Antifreeze Solutions for Use in Fire Sprinkler Systems. This standard provided for a number of critical tests to validate the safe and effective use of a listed antifreeze in automatic fire sprinkler systems.  

While the main use of antifreeze is to prevent freezing within the piping system, it must do so in a manner ensuring that the sprinkler system fluid will flow through the pipe and discharge from a sprinkler so that a fire can be properly addressed. Key attributes validated by UL 2901 include long-term stability, material compatibility, corrosion resistance, electrical conductivity, toxicity, exposure to fire, firefighting effectiveness and resistance to leakage.  

In 2018, Johnson Controls (JCI) introduced into the market the first UL-listed antifreeze for fire sprinkler systems, JCI’s LFP Antifreeze. This solution is UL-listed with a minimum use temperature of -10 F (-23,3 C). In 2020, JCI launched a second UL-listed antifreeze, LFP Antifreeze+, with a minimum use temperature of -25 F (-32 C). 

Several considerations must be taken into account when using listed antifreezes. As part of the listing requirements, UL established maximum volume allowances of antifreeze in fire sprinkler applications. These allowances are shown in Table 1. It should be noted that manufacturers of listed antifreeze solutions continue to work with UL to expand volume allowances, so it is recommended to check the manufacturer’s installation instructions for updated information. 

Because the viscosity and density of listed antifreeze solutions are different from water, hydraulic calculations must be performed to adjust the sprinkler K-factor and determine friction loss. The Hazen-Williams formula for water and the Darcy-Weisbach formula are used to account for the antifreeze solution properties.  

Another important consideration is thermal expansion, given that antifreeze solutions have a greater thermal expansion rate than water. Inadequate thermal expansive provisions will result in significant system pressure increase that can cause leakage or potentially catastrophic failure. NFPA 13, 13R and 13D provide recommended methods to account for antifreeze thermal expansion. 

Also, manufacturers’ installation instructions provide the antifreeze’s physical properties that can be used to calculate the amount of volume increase expected due to a temperature change.  

Usage Steps

Listed antifreezes are premixed per NFPA 13, 13R and 13D. They are not to be diluted with water as this will adversely impact the performance and properties of the solution. When using listed antifreeze in a new fire sprinkler system, the following steps are followed: 

1. The system shall be installed with materials as indicated in the manufacturer’s provided compatibility list.  

2. Verify the required backflow prevention and cross-connection control is in accordance with state and local requirements. 

3. The system shall be outfitted with air vent valve(s) and fluid sampling valve connections as required by the applicable NFPA standard.  

4. The system should be determined to be airtight before introducing antifreeze into the system to prevent loss or spillage of product.  

5. A pressure test shall be conducted per the applicable NFPA standard. This pressure test may be performed with water or antifreeze. It is recommended that systems with drops be tested with antifreeze to prevent water accumulation in the drops.  

6. For systems hydrostatically tested with water, they must be drained after the test per the applicable NFPA standard. Storing or carrying the antifreeze solution in any container other than the original may introduce contaminants and reduce the functional life of the solution.  

7. It is recommended that before filling the system with antifreeze, the antifreeze is tested to verify the specific gravity or refractive index is within the ranges. This test verification is not required if the antifreeze solution is from a new, unopened factory container. 

8. Fill the system with antifreeze. Avoid the use of contaminated hoses and equipment that have come into contact with fluids other than antifreeze or water. Using a pump with a backflow preventer and pressure capabilities to get the system to the supply pressure is recommended. For antifreeze to work correctly, purge as much air as possible from the system. Accelerated corrosion may occur where air pockets exist in the system.  

9. After filling the system with antifreeze, test samples to verify the solution has not been diluted. Take samples of the solution from a high and low point in the system. If not done so beforehand with water, perform the hydrostatic pressure test as applicable. 

When using listed antifreeze in existing systems, the following steps are required: 

1. Inspect all sprinklers for mechanical damage, corrosion and evidence of leakage. If any of these conditions are present, replace the sprinkler per NFPA 25.  

2. Verify the required backflow prevention and cross-connection control is in accordance with state and local requirements.  

3. The system should be airtight to prevent leakage. Air vents are recommended to reduce the oxygen in the system.  

4. Drain the existing antifreeze from the system per NFPA 25.  

5. It is recommended that before filling the system with antifreeze, the antifreeze is tested to verify the specific gravity or refractive index is within the ranges. This test verification is not required if the antifreeze solution is from a new, unopened factory container. Storing or carrying the antifreeze solution in any container other than the original may introduce contaminants and reduce the functional life of the solution.  

6. Fill the system with antifreeze. Avoid the use of contaminated hoses and equipment that have come into contact with fluids other than antifreeze or water. Using a pump with a backflow preventer and pressure capabilities to get the system to the supply pressure is recommended. For antifreeze to work correctly, purge as much air as possible from the system. Accelerated corrosion may occur where air pockets exist in the system. 

7. After filling the system with antifreeze, test the system to verify the solution has not been diluted by measuring the specific gravity or refractive index. Take samples of the solution from a high and low point in the system. 

8. If the specific gravity or refractive index is not within the allowable range, drain the system and repeat the steps or add antifreeze to displace the non-compliant antifreeze and achieve the required purity. Repeat the required tests to verify the specific gravity or refractive index is within the acceptable range. Repeat this process until the specific gravity or refractive index is within the acceptable range. 

Identification and ITM

 As required by NFPA 13, 13R, 13D and 25, a system tag must be present on the system main valve identifying the following information: type and manufacturer of the solution, volume of antifreeze used and the percent concentration by volume. If using JCI’s LFP Antifreeze or LFP Antifreeze+, the percent concentration is 100 percent since it is a premixed solution. A tag for inspection, testing and maintenance also can be hung on the system riser to record annual test data.

Fire sprinkler systems using listed antifreeze are required to schedule inspection, testing and maintenance (ITM) service at least once per year. The listed solution is tested during the annual ITM to verify that its physical properties are within specification. For JCI LFP Antifreeze and LFP Antifreeze+, the physical property measurements are conducted from a fluid sample taken from the system and checking the specific gravity or refractive index.  

Acceptable limits for these are provided in the manufacturer’s installation instructions. A hydrometer is used to measure specific gravity and a refractometer is used to measure refractive index. These devices are required to be calibrated before use to ensure accuracy. Both methods are acceptable per NFPA 25.  

Solutions meeting the specified requirements can remain in the system. The fluid must be replaced if either property deviates from the allowable tolerances. It is recommended that the testing be done before the cold weather season. 

The use of UL-listed antifreezes helps meet the intent of NFPA freeze protection requirements and the requirement of using an agency-listed antifreeze in both new and existing systems. 

With more than 32 years of engineering experience, Manuel Silva is the chief engineer for Johnson Controls fire suppression products business. For 21 years, he has developed numerous products for use in fire sprinklers systems and is named on 37 U.S. patents related to fire suppression devices. In his current role, Silva is involved with the research and development of new fire protection products and is a member of the NFPA 13, 30B and 1910 Technical Committees.