A wet fire-sprinkler system must be protected from freezing when any portion of it is located in spaces with temperatures that cannot reliably be maintained at or above 40°F. Water-filled pipes must stay above that temperature to avoid leakage, a pressure decrease that causes a system malfunction, or significant damage when pipes freeze and burst. There are numerous design approaches to avoid freezing, but one longstanding option – the use of antifreeze – is in most cases no longer a viable option because of its potential to make fires worse.
Propylene glycol and glycerin have been used for decades as antifreeze solutions for fire protection systems. Propylene glycol and glycerin are combustible liquids with flash points of 210°F and 350°F, respectively. The National Fire Protection Association (NFPA) has limited use of these liquids in fire sprinkler systems because 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.
This was demonstrated in a number of fire incidents in recent years in which antifreeze that contained too high a concentration of propylene glycol or glycerin in water intensified or even caused a fire when it discharged from sprinklers. In 2002 at a restaurant in Monmouth Beach, NJ, a heater at the ceiling of an outside porch activated sprinklers, which then discharged what is believed to have been 100% antifreeze solution on the heater. The resulting flash fire spread flames across the porch ceiling and into the restaurant's interior. In 2010, a cooking fire set off the fire-sprinkler system in an apartment complex in Truckee, CA. The proportion of glycerin sitting in the pipes was too high when the sprinkler above the stove deployed, causing an explosion. The solution that came out of the sprinkler reportedly had a 71.2% concentration of glycerin.
Following these and other antifreeze-fueled fires, an NFPA study assessed the flammability of antifreeze solutions in commercial sprinklers. 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. Therefore, the conclusion was that limitations are warranted on the use of 50% glycerin or 40% propylene glycol antifreeze solutions in nonresidential sprinkler systems. Based on its findings, NFPA subsequently incorporated changes into NFPA 13, Standard for the Installation of Sprinkler Systems, and NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems.
The following was incorporated into the 2016 Edition of NFPA 13:
188.8.131.52* Except as permitted in 184.108.40.206, antifreeze solutions shall be listed for use in sprinkler systems. (220.127.116.11 in 2019 edition)
18.104.22.168 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. (22.214.171.124 in 2019 edition)
Early Suppression, Fast Response (ESFR) sprinklers are high-output sprinkler systems intended for use in warehouses with "High Piled Storage." This exception was included because it may be impossible to completely control the climate in these types of industrial settings.
New sprinkler systems are allowed to use antifreeze but must use listed antifreeze solutions. A solution that is "listed" means that it's been safety tested and approved for use in commercial sprinkler systems. To date, there are no listed antifreeze solutions, so the NFPA has effectively banned the use of antifreeze solutions in new fire-sprinkler systems.
Existing fire-sprinkler systems installed prior to Sept. 30, 2012 can still use antifreeze at certain maximum concentrations while also following extensive safety and maintenance requirements. A basic decision-making guide for existing antifreeze systems can be found at the end of this article.
NFPA 25 outlines the same major requirements: that an antifreeze solution must be listed for new installs (none are listed), 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 details on the exceptions for older commercial sprinkler systems:
The 2017 Edition of NFPA 25 states the following:
126.96.36.199.1* 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% glycerin), 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 conditions like ceiling height, sprinkler type, the occupancy use group of a structure, the size of a structure, and other factors.
This is not ideal because even the government-approved higher concentration may not 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."
By September 30, 2022, all existing antifreeze solutions must be replaced by alternative means of freeze protection. This will mark the end of antifreeze in fire-sprinkler systems and designers will be forced to use alternative means to continue protecting fire sprinklers in unheated spaces.
Multiple methods of freeze protection exist. However, none are always appropriate. Designers must evaluate each scenario to determine the most reliable, cost-efficient solution to ensure the proper operation of fire sprinklers in unheated spaces.
The following are alternative means of freeze protection:
- Install special scenario (dry) heads from a wet-pipe system (recommended if possible)
- Install a dry-pipe or pre-action system (recommended)
- Wrap pipe with listed constantly monitored heat trace
- Insulate and apply heat to maintain spaces above 40°F
- Tent insulation over pipe (where there is a heated space below)
- A combination of the previous techniques
Contact Risk Logic to answer any questions regarding the use of antifreeze in fire protection systems or to explore alternative means of freeze protection.
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*Diagram courtesy of National Fire Sprinkler Association
- Quick Response Fire Supply (QRFS) "The Use of Antifreeze in Fire Protection Systems"
- Willis Towers Watson "Antifreeze Sprinkler Systems in Cold Climates"