Because it can ignite, NFPA has limited the use of antifreeze in fire sprinkler systems
Protecting the integrity of pipes in fire protection systems is a challenge in regions that are subject to harsh winters, specifically in structures or areas of buildings that aren’t climate controlled. Water-filled pipes must stay above 40 F to avoid leakage, a drop in pressure that causes a system malfunction, or significant damage when pipes freeze and burst.
Whether it’s installed in a commercial space in which climate control is difficult or a home that is left empty on winter vacation, a wet fire sprinkler system must be protected from freezing. There are a variety of ways to address cold temperatures, including through the installation of preaction and dry systems, thorough insulation of pipes, and creative system design. But one longstanding option – the use of antifreeze – has fallen out of favor in the past eight years because of its potential to make fires worse.
In this blog, QRFS will outline the issues surrounding antifreeze, the National Fire Protection Association’s (NFPA) guidance on using it, and highlight alternatives to safeguard fire protection systems from falling temperatures.
Important update (2/5/19): A new antifreeze has been listed for use in sprinkler systems. Keep reading to understand the issues with flammable antifreeze, and then visit this blog to learn about the first UL-listed antifreeze for use in sprinklers.
Antifreeze in fire sprinkler systems
You use it in your car and you may use it in your HVAC system, and the principle is the same in a fire sprinkler system: A solution of a water and an active antifreeze ingredient is flooded into wet pipe systems to keep the water from freezing. These antifreeze solutions typically contain a mixture of water and either propylene glycol or glycerin at specific ratios.
The issue is that propylene glycol and glycerin are flammable substances that can ignite at a high enough concentration. Not all solutions are mixed at proper proportions, and solutions that are do not always stay that way; since water and the active ingredients have different densities (antifreeze is heavier), they naturally tend to separate over time due to gravity.
Thus, when the proportion of the active ingredients near a sprinkler becomes too high relative to water, an antifreeze solution can actually serve as fuel for a fire when the sprinkler discharges.
A Truckee, CA family learned this tragic lesson in 2010 when a cooking fire set off the fire sprinkler system in their apartment complex. The proportion of glycerin sitting in the pipes was too high when the sprinkler above the stove deployed, causing an explosion. One woman, Isela Minutti, was killed. Her husband, who was standing right below the sprinkler when it deployed, was burned over about 45 percent of his body. Their three children suffered minor injuries but survived.
Investigators later concluded that the sprinklers were “discharging a solution of glycerine-based antifreeze which was ignited by the flames coming from the burning onions in the frying pan and resulting in the explosion of the glycerine solution.” The solution that came out of the sprinkler reportedly had a 71.2% concentration of glycerin.
In another incident in 2002, ceiling-mounted heaters on the outside porch of a Monmouth Beach, NJ restaurant set off sidewall sprinklers. They sprayed a propylene glycol-water solution which “resulted in a flash fire.” The “flames … traveled across the ceiling and continued into the inside of the restaurant” and “several restaurant patrons received medical treatment for smoke inhalation and thermal skin burns.”
And in 2010, a mother and her three-year-old son suffered second- and third-degree burns when fire sprinklers deployed in their Herriman, Utah apartment. A propylene glycol solution had caused the fire to spread rapidly.
NFPA launched an investigation into the antifreeze issue in 2010. Its Fire Protection Research Foundation conducted a series of tests that evaluated the flammability of different mixtures of antifreeze hitting fires of different sizes.
The results of several tests were reported in a December 2010 report, Antifreeze Solutions in Home Fire Sprinkler Systems Phase II:
- Results of the Scope A testing indicate that concentrations of propylene glycol exceeding 40% by volume and concentrations of glycerin exceeding 50% by volume have the potential to ignite when discharged through residential sprinklers.
- The results of this research suggest that antifreeze solutions of propylene glycol exceeding 40% and glycerin exceeding 50% by volume are not appropriate for use in home fire sprinkler systems.
A subsequent study was done to assess the flammability of antifreeze solutions in commercial sprinklers. It found that the ignition of a solution was dependent on several factors, including droplet size and distribution, solution concentration, and the initial fire’s heat release rate (HRR), which is “the rate at which fire releases energy,” measured in Watts. The primary factors that determined whether antifreeze fed a fire were the solution’s concentration and a fire’s HRR (essentially, its size and power).
The commercial sprinkler study’s main conclusions were that antifreeze solutions at 50% glycerin or 40% propylene glycol did not usually ignite smaller fires with a heat release rate of 1.4 MW – but did ignite them at 3.0 MW. For points of reference, a burning upholstered chair has a peak heat release rate of about 2.1 MW, whereas a burning sofa has a peak HRR of 3.12 MW.
The authors concluded that “[t]he results of this test program indicate that limitations should be considered on the use of 50% glycerin or 40% propylene glycol antifreeze solutions in non-residential sprinkler systems.”
Remember, the antifreeze mixture that burned the family in Truckee, CA was 71.2% glycerin.
NFPA issues new guidelines
In August of 2010, NFPA issued three Tentative Interim Amendments (TIAs) that included prohibiting the use of antifreeze in new automatic residential sprinkler systems. This was followed by several more TIAs over the next few years until NFPA settled on its current guidance in 2013:
The use of antifreeze in commercial fire sprinkler systems
NFPA 13: Standard for the Installation of Sprinkler Systems sets the requirements for the installation of commercial fire sprinklers.
From the 2016 Edition of NFPA 13
126.96.36.199* Except as permitted in 188.8.131.52, antifreeze solutions shall be listed for use in sprinkler systems.
184.108.40.206 Premixed antifreeze solutions of propylene glycol shall be permitted to be used with ESFR sprinklers where the ESFR sprinklers are listed for such use in a specific application.
A solution that is “listed” means that it’s been safety tested and approved for use in commercial sprinkler systems. ESFR stands for Early Suppression, Fast Response. These are high-output sprinkler systems that are intended for use in warehouses with “High Piled Storage.” This exception makes sense, as these types of industrial settings may be impossible to completely climate control.
The issue with this NFPA 13 guidance and the lengthy code that follows it – which details various components that need to be installed along with an antifreeze system, the arrangement of supply piping and valves, etc. – is that it could imply that the use of antifreeze is still possible in newly-installed systems under NFPA code.
In truth, it’s not.
There is a key bit of text that explains the change to NFPA code: “The use of antifreeze in new NFPA 13 sprinkler systems was prohibited unless the solution use was listed and the listing indicated illustrated the inability for the solution to ignite.” In the eight years following NFPA’s first TIA on the matter, no non-flammable antifreeze solution has been developed and listed. Thus, antifreeze is essentially banned for use in new systems.
The use of antifreeze in residential fire sprinkler systems
NFPA 13D: Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes sets the guidelines for the installation of most residential fire sprinklers.
From the 2016 Edition of NFPA 13D
220.127.116.11 Except as permitted in 18.104.22.168, antifreeze solutions shall be listed for use in new sprinkler systems.
Again, no new antifreeze solutions have been “listed,” thus stopping their use in new systems. The guidance is similar in NFPA 13R: Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies: all antifreeze solutions must be listed.
There is an exception which still allows the use of antifreeze in older commercial and residential systems – but even this loophole will sunset by 2022.
Antifreeze may be used in certain existing fire sprinkler systems at specific concentrations
Existing fire sprinkler systems which were installed prior to Sept. 30, 2012 can still use antifreeze at certain maximum concentrations and while following extensive safety and maintenance requirements. The keys here are:
- Existing systems installed before Sept. 30, 2012
- Solutions that are premixed from a manufacturer at maximum concentrations
- Subject to the approval of the authority having jurisdiction (AHJ; the local governmental authority overseeing the approval of a system)
From the 2016 Edition of NFPA 13D
22.214.171.124.1 For existing systems, antifreeze solutions shall be limited to premixed antifreeze solutions of glycerine (chemically pure or United States Pharmacopoeia 96.5 percent) at a maximum concentration of 50 percent by volume, propylene glycol at a maximum concentration of 40 percent by volume, or other solutions listed specifically for use in fire protection systems.
126.96.36.199* Premixed solutions of glycerine (chemically pure or United States Pharmacopoeia 96.5 percent) at a maximum concentration of 48 percent by volume or propylene glycol at a maximum concentration of 38 percent by volume shall be permitted to protect piping that is supplying sprinklers in a specific area of the dwelling unit, where acceptable to the authority having jurisdiction.
188.8.131.52.1* Documentation shall be presented to the AHJ to substantiate the use of the antifreeze solution.
Similar guidelines were outlined for commercial systems. These guidelines are confusing, as they seem to be overridden by NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. This may be because the latest edition of NFPA 25 was released one year later than the various forms of NFPA 13.
NFPA 25 outlines the same major requirements: that an antifreeze solution must be listed for new installs (none exist), that it must be premixed from a manufacturer, and that ESFR sprinklers may be able to use antifreeze under certain conditions. But it has slightly different detail on the exceptions for older residential and commercial sprinkler systems (emphasis added by QRFS):
From the 2017 Edition of NFPA 25
184.108.40.206.1* For systems installed prior to September 30, 2012, listed antifreeze solutions shall not be required until September 30, 2022, where one of the following conditions is met:
(1)* The concentration of the antifreeze solution shall be limited to 30 percent propylene glycol by volume or 38 percent glycerine by volume.
(2)* Antifreeze systems with concentrations in excess of 30 percent but not more than 40 percent propylene glycol by volume and 38 percent but not more than 50 percent glycerine by volume shall be permitted based upon an approved deterministic risk assessment prepared by a qualified person approved by the authority having jurisdiction.
Basically, older systems can still use antifreeze at lower proportions of active ingredients (30% propylene glycol or 38% glycerine), or at somewhat higher concentrations – if a local government-approved expert states the latter is necessary. This expert’s “deterministic risk assessment” will look at factors like ceiling height, sprinkler type, the occupancy use group of a structure, the size of a structure, and other factors.
Here’s the thing in all cases where antifreeze would still be used, however: Concentrations should never be more than 40% propylene glycol or 50% glycerin, and antifreeze at such low concentrations might not even provide sufficient freeze protection. According to NFPA, “A concentration of antifreeze solution currently permitted by the standard might not provide sufficient freeze protection without additional measures.” And to continue using it, the maintenance requirements are extensive.
A summary of maintenance requirements for fire sprinklers using antifreeze
Fire sprinklers using antifreeze are subject to complex maintenances and inspection requirements. A basic summary:
- Because antifreeze solutions can separate in the pipes, creating different concentrations of water and active ingredients at different portions of the system, annual testing is required that takes multiple samples from the system and tests the specific gravity/concentration of each sample. “Where antifreeze systems have a capacity larger than 150 gal (568 L), tests at one additional point for every 100 gal (379 L) shall be made.” (NFPA 25)
- This may require the installation of an additional control/test valve, usually at the highest practical point in the system. And if any sample shows a mixture higher than allowable concentrations during a test, the system must be completely drained and refilled with an appropriate solution.
- Sprinklers using antifreeze need specific signs explaining the location of antifreeze systems that are remote from the riser, as well as the specifications of the antifreeze used in them. The signage must list the supplier as well as the concentration and volume of the antifreeze used.
- Systems with CPVC sprinkler pipe can’t use propylene glycol-based antifreeze, as it is absorbed into the pipe and causes “environmental stress cracking.” Only glycerin antifreeze solutions can be used with CPVC.
- “Some antifreeze systems are equipped with expansion chambers that allow the water: antifreeze solution to expand without rupturing the sprinkler pipe.” NFPA stipulates a series of formulas (NFPA 13: A.220.127.116.11) for determining the size of an expansion chamber. Antifreeze systems also require backflow preventers which stop the antifreeze from leaking back into the water supply.
Given these complex requirements, it’s not hard to see why the use of antifreeze is falling out of favor, even among older systems.
Fire sprinkler freeze protection measures: Alternatives to antifreeze
NFPA lists some other good options for protecting fire sprinkler pipes in cold weather:
From the 2016 Edition of NFPA 13
A.7.6 In cold climates and areas where the potential for freezing of pipes is a concern, options other than antifreeze are available. Such options include installing the pipe in warm spaces, tenting insulation over the piping … listed heat tracing, and the use of dry pipe systems and preaction systems.
Installing the pipe in warm spaces: This is pretty self-explanatory, though it can involve creative installation of systems to maximize the amount of pipe in a climate-controlled area. For example, a home fire sprinkler installer could exclusively put in sidewall sprinklers in the uppermost floors of a house – instead of pendent sprinklers in the ceiling – to avoid having to run horizontal pipe through an unheated attic.
Tenting insulation over the piping: Even if an installer did run horizontal pipe through an unheated attic, an option is to thoroughly insulate the exposed pipe. It’s very important to protect the insulation by nailing it down (e.g., with a wire mesh or flooring) to make sure it’s not disturbed, however.
Heat tracing: This method of winterizing pipes uses an “an electrical heating element run in physical contact along the length of a pipe,” often combined with insulation. Heat tracing is typically used in commercial applications. The heat tracing method must be listed.
Dry or preaction fire sprinkler systems: Dry systems are specifically designed for areas that are subject to freezing temperatures. Instead of having the pipes filled with water, they are filled with pressurized gas (air or nitrogen) which holds a control valve shut. When a sprinkler activates and releases the pressure, water floods the system.
Preaction sprinklers are similar, except a detector that senses heat or smoke opens the valve to release the water. The benefit of both dry and preaction systems is that much of the pipe is never filled with water, enabling it to be placed in freezing areas.
A drawback of these systems is that it takes longer for the water to discharge from the sprinkler. In addition, while these types of systems can be installed in homes, they are more complex and expensive than traditional wet systems, which is why they are uncommon in residential applications.
What about standpipe systems? Can antifreeze be used?
No. NFPA 14: Standard for the Installation of Standpipe and Hose Systems is very clear:
From the 2016 Edition of NFPA 14
18.104.22.168.1 Antifreeze solutions shall not be used to protect standpipe system piping from freezing.
The bottom line about antifreeze in fire sprinkler systems
Antifreeze can be used in older systems installed prior to Sept. 30, 2012, but it adds complexity to a system, carries risk if the solution is not mixed right or settles improperly in the pipes, and annually testing it and measuring samples requires the help of a professional – unless you happen to have a “hydrometer with a scale having 0.002 subdivisions” sitting around, plus the expertise to make the appropriate calculations.
Never mix your own antifreeze solution and add it to a sprinkler system – unless you want to risk an explosion when a system deploys.
It’s simpler and safer to make sure that all sections of pipes are properly winterized in a different way – or opt for a dry or preaction sprinkler system. If you have any questions about the use of antifreeze in fire protection systems or need help finding an item for your system, give QRFS a call at 888.361.6662 or fill out our contact form and we’d be happy to assist.
Important update (2/5/19): A new antifreeze has been listed for use in sprinkler systems. Visit this blog to learn about the first UL-listed antifreeze for use in sprinklers.