Using Antifreeze Solutions Today

By Victoria B. Valentine, P.E.

Sometimes the cold environments that fire protection systems have to endure are forgotten, since the systems are typically thought about in terms of a fire scenario that generates its own heat. Yet many parts of the world have periods of the year when cold temperatures have to be endured. Many systems are installed within structures that can offer protection from cold temperatures, but there are plenty structures that are not heated or even systems installed without structures present.

Given the spectrum of fire protection systems and equipment used to protect lives and property, not all of system components are affected by cold temperatures. One of the primary concerns is water-based fire protection systems, such as fire sprinklers, that could be at risk of freezing in cold temperatures and not able to operate should a fire occur in that window of time.

Water freezes at 32 ºF (0º C). Many codes and standards indicate that temperatures for water-based systems have to remain at 40º F (4º C) surrounding the components to make sure that the water within remains in a fluid state. Yet there are circumstances in which maintaining the temperature at that level is just not possible. One of the options for addressing these situations with temperatures at or below the freezing point of water is to use an antifreeze solution.

Antifreeze has been a topic of discussion in the fire protection community for some years now. Common antifreezes used in fire sprinkler systems, and at times adapted to other water-based fire protection systems, such as water-spray fixed systems described in NFPA 15, have been either propylene glycol or glycerine solutions. Both of these solutions are flammable, but have been used even with this knowledge due to the understanding that the antifreeze is diluted with and followed by water so it can offset any contribution of fuel to the fire. A couple of fires demonstrated the concern about using these solutions to protect life and property from fire. Examining these situations, along with research, led to changes in using antifreeze solutions in both new systems and existing installations.

Pure antifreeze should not be used to fill a sprinkler system; in this case, more is not better. The restrictions on using only a listed antifreeze solution have resulted from fires with high concentrations of antifreeze in the piping, which added to the fuel load before the pure water reached the fire source.

The Fire Protection Research Foundation conducted numerous studies to evaluate concentrations of propylene glycol and glycerine solutions in fire sprinkler systems. Different fire sprinklers and operating pressures were among the variables explored. Installation standards were modified based on this research.

New Fire Sprinkler Systems Using Antifreeze

The goal for this type of system is to avoid freezing the water used for fire protection. Fire sprinkler systems are the most common type of system that have used an antifreeze solution for fire protection, which is why NFPA 13, Standard for Installation of Sprinkler Systems, provides detailed information about how to accomplish this.

Other methods also can be used to protect from freezing conditions. When antifreeze is selected (even within the current limited instances), there has to be a balance in the appropriate concentration levels for the system—between the minimum amounts of antifreeze concentration necessary to allow the water to remain in a fluid state and minimizing the flammable liquid that, if too great, could contribute to the fire itself.

As of the 2013 edition of NFPA 13, antifreeze used for a new system installation has to be a listed solution. This is a modification to the standard after decades of permitting antifreeze solutions to be installed without listing the solutions. Under a listing, the antifreeze is required to demonstrate that the fluid will not ignite and add to a possible fire scenario. (UL 2901, Outline of Investigation for Antifreeze Solutions for Use in Fire Sprinkler Systems, is an example of the listing criteria the solution would have to meet).

There is an exception for propylene glycol solutions that have been listed for use in specific applications with early suppression fast-response (ESFR) sprinkler systems. Even with a listing, though, the antifreeze solution will still have to comply with any state or local health regulations.

For the small number of instances where a new installation is permitted to use unlisted antifreeze solutions, typically through a detailed risk analysis, the solution must be a premixed antifreeze solution. This would be a mixture of antifreeze and water, mixed to the appropriate concentration by the manufacturer. This maintains a level of quality ensuring that the solution is homogeneous at the correct concentration. The manufacturer’s instructions should be adhered to for filling (or refilling) procedures, along with the number of test ports necessary to maintain the system over its lifespan.

Existing Fire Sprinkler Systems Using Antifreeze

In general, once a fire sprinkler system is installed, it is measured only against the original installation standard. NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, is used to make sure that the fire sprinkler system maintains its functionality over its lifespan. When the allowances of using antifreeze in new installations were changed, the language of NFPA 25 was also modified to address antifreeze in existing systems.

If the type of antifreeze is not readily known, the first step would be to identify which type of antifreeze is present. Maintenance records, chemical tests, or information from the owner can be used if there is no information sign on the system. Should it not be possible to determine the type of antifreeze in the system from existing information, it will have to be replaced with an acceptable solution. The new solution also has to conform to state and local health regulations.

If a system was installed before 30 September 2012, it will not necessarily be required to use a listed antifreeze solution until 30 September 2022. This hinges on the concentration of the antifreeze solution: The volume of antifreeze cannot be more than 30% for propylene glycol or 38% for glycerine. An exception is if an approved deterministic risk assessment, prepared by a qualified professional and accepted by the authority having jurisdiction (AHJ), would allow up to 40% by volume for propylene glycol or up to 50% by volume for glycerine. One other exception is specific to (ESFR) sprinklers: Propylene glycol solutions over 30% by volume can be used when ESFR sprinklers are listed for this application, similar to the exception for new installations.

Based on current requirements, the antifreeze solution must be tested annually. The concentration value is determined during the initial design phase of the system. Once the antifreeze solution in the existing system is known (provided on the information sign at the main valve) or determined, test samples are taken to confirm that concentration of the antifreeze within the system. These values should match, within tolerances, the original concentrations planned for the system; if they do not, the solution will have to be drained and the system refilled with the appropriate concentration of antifreeze. Until corrected, the system would be classified as having either an impairment or a critical deficiency.

Even when working with an existing system, it is important to confirm many of the same details that apply to new installations. These items are stated in NFPA 25. For example, antifreeze solutions are required to be a listed antifreeze, unless complying with the exception noted above. Where it is permissible to refill a system using propylene glycol or glycerine, only premixed solutions are allowed. Details such as solutions that are compatible with the piping material have to be maintained. Keep in mind that CPVC piping is incompatible with propylene glycol and can only be used with glycerine solutions as applicable.

Antifreeze Alternatives

At publication of this article, there were still no antifreeze solutions listed for use in fire sprinkler systems. Therefore, other means to protect against freezing would have to be employed.

One way of protecting the water from freezing would be to keep it in a heated space. This may mean heating specific areas or an entire building, depending on the arrangement of the space and its system. This could also be done by tenting insulation over the sprinkler piping so the pipe remains within the heated envelope of the space. This type of application is particularly useful for piping in an attic type space, since it would be typical for the remainder of the building to already be heated.

For applications where heating may not be a viable option, a dry-pipe sprinkler system could be used. This would keep the water out of the piping until needed for a fire scenario. Again, this would achieve the goal of preventing the water that would control a fire from freezing in the piping network.

Another option would be to use listed heat tracing on the piping to make sure the temperature does not freeze the water. There are separate listings for heat tracing that protects mains versus branch lines. When used properly, heat tracing will keep the water fluid, allowing it to be ready should a fire occur.

As long as the system is installed so it can function year-round in the space, enduring cold temperatures if necessary, the option is up to the user. Of course, each option has aspects that may or may not make it more desirable, depending on the specifics of the area being protected.

Residential Sprinkler Systems

For residential applications that use fire sprinkler systems installed in accordance with NFPA 13R, Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies, or NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, the rules for using antifreeze vary slightly from those in NFPA 13.

NFPA 13R parallels the requirements for new installations of antifreeze systems found in NFPA 13. The antifreeze solution is required to be listed. However, there are no exceptions to this rule for new installations (ESFR sprinklers and their requirements are not in this standard). When working with an existing NFPA 13R-type sprinkler system, the guidance is the same as for NFPA 13 systems.

NFPA 13D systems are traditionally smaller, since they are protecting one- and two-family dwellings. For these systems, new antifreeze systems are still permitted, but with restrictions. The default, like the other sprinkler installation standards, is to use a listed antifreeze solution. However, there is an allowance for use of premixed solutions of either propylene glycol up to 38% by volume or glycerine up to 48% by volume. This is limited to use only in areas that need freeze protection and must have approval by the AHJ. It is anticipated that this avenue will not be used unless other options for freeze protection are not viable.

Existing NFPA 13D systems are also treated differently. The solution has to be premixed as noted in the other systems and installations, yet propylene glycol solutions are permitted up to 40% by volume and glycerine solutions up to 50% by volume. This means the majority of existing systems do not have to be modified to protect them against freezing temperatures. Since NFPA 25 does not cover NFPA 13D systems, there is currently no fixed date for no longer permitting the use of either propylene glycol or glycerine solutions.


Antifreeze solutions have long been a method for preventing potential freezing in fire protection systems using water. When fire situations arise, they are studied and changes are made as needed. In general terms, this means that antifreeze is not a simple solution to protecting against freezing temperatures anymore. For new installations, other alternatives are being used to ensure that fire protection systems function as intended. For existing installations, it was thought that the problem would be solved by 2022 and systems could be modified accordingly. As the NFPA 25 technical committee enters its next revision cycle (to produce the 2020 edition), this topic will be evaluated for both solutions and timelines.

There is great hope for a new antifreeze product to arrive on the market that can be used in both new and existing installations, but not contribute to a fire. At this point, that resolution is still a waiting game.

Victoria B. Valentine, P.E. is with SFPE


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