Glycol is a combustible liquid that has a history of being used as an antifreeze solution for freeze protection in fire sprinkler systems. Traditionally, the combustibility of glycol was offset by mixing it with water. The solution of glycol and water was thought to be safe, until 2009 when a fire intensified by the activation of a sprinkler system using antifreeze. Afterwards, the National Fire Protection Association (NFPA) issued a Tentative Interim Amendment (TIA) that was incorporated into the following codes: The Standard for the Installation of Sprinkler Systems (NFPA 13), The Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes (NFPA 13D), the Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies (NFPA 13R), and the Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems (NFPA 25). As a result, new sprinkler systems are required to use listed antifreeze solutions. To date, antifreeze solutions are not listed for such use. Thus, NFPA has effectively banned the use of antifreeze solutions in new fire sprinkler systems. In addition, NFPA 25 was updated to give an expiration date to antifreeze solutions in existing fire sprinkler systems. By September 30, 2022, existing antifreeze solutions must be replaced by alternative means of freeze protection. This marks the end of antifreeze in fire sprinkler systems. Thus, designers must use alternative means to continue protecting fire sprinklers in unheated spaces.
The following are alternative means of freeze protection:
- Insulate and apply heat to maintain spaces above 40 degrees Fahrenheit,
- Install special scenario (dry) heads from a wet-pipe system,
- Install a dry-pipe system,
- Wrap pipe with listed heat trace, or
- A combination thereof.
Per NFPA 25, the property owner or designated representative shall ensure that water-filled piping is maintained at a minimum 40 degrees Fahrenheit, unless an approved antifreeze solution is utilized. Thus, freeze protection can be accomplished by eliminating unheated spaces. This can be an appropriate solution for indoor areas (such as attics). However, it cannot be used to protect exterior canopies or similar building features.
Special scenario (dry) heads are fed from a wet-pipe system that’s located in a heated space. They can be a cost-efficient method to protect unheated spaces, including exterior canopies. However, these heads must be installed in accordance with manufacturer specifications. Generally, special scenario (dry) heads are manufactured with sprig lengths not exceeding four feet. Thus, their range of protection is limited.
The use of a dry-pipe system is a reliable way to provide freeze protection. A dry-pipe system keeps water out of a piping network, until needed in a fire scenario. Periodic flow tests require a dry-pipe system to be filled with water and emptied (reference Section 18.104.22.168.2.2 in NFPA 25-2011). Rust requires iron, oxygen, and water to form. The oscillating of water in and out of a system accelerates corrosion since pipes are never completely dry. Thus, dry-pipe systems use internally galvanized stainless steel, or another corrosion-resistant pipe, to prevent the onset of rust. Corrosion is unwanted as it can lead to blockages and system failure. Generally, chlorinated polyvinyl chloride (CPVC) pipe is not listed for systems using compressed gases. Therefore, its not used in dry-pipe systems. Converting an existing wet-pipe system to dry would require the following actions:
- Replace black-iron pipe with corrosion resistant pipe, as applicable.
- Replace CPVC pipe with corrosion resistant pipe, as applicable.
- Install a dry valve, quick opening devices (if required), and compressor, as well as any other applicable piping and appurtenances. The location of the dry valve would depend on the scope of the dry-pipe system install. Ensure the existing fire department connection is piped to the wet side of the dry valve.
- Install a reliable source of inert gas (reference Section 22.214.171.124 in NFPA 13-2013).
- Replace wet heads with listed dry heads. Dry heads must be tested or replaced more frequently than wet heads (every 10 years per Section 126.96.36.199.1.6 in NFPA 25-2011).
- Remove piping and apparatus associated with the existing antifreeze system. This includes, but is not limited to, fill cup, expansion chambers, etc.
- Verify all parts of the system can be properly drained. Piping must be properly pitched, low points must be equipped with auxiliary drains, etc. If installed correctly, the existing system should be able to be completely drained.
- In a wet-pipe system, water is immediately available upon the activation of a sprinkler head. In dry-pipe systems, it takes longer for water to reach a fire as it must travel throughout the system to reach its destination. Thus, a 30% safety factor (reference Section 188.8.131.52.5 in NFPA 13-2013) is required to be incorporated into the design of any dry-pipe system. The original system would not have included this safety factor. Therefore, hydraulic calculations must be performed to verify the new system demand.
Wet to dry-pipe system conversions are cumbersome. Instead of a conversion, it’s likely easier to install a new dry-pipe system. Either way, a designer must obtain site specific information, including hydrant flow data.
Listed heat trace can be used to protect wet-pipe systems in unheated spaces. However, it’s not the most reliable solution. Heat trace can be faulty or stop operating with loss of power, allowing pipes to freeze. Nortech does not suggests using heat trace unless other protection schemes are unavailable or cost prohibitive, and the owner understands all risks involved.
In conclusion, existing antifreeze solutions must soon be replaced by alternative means of freeze protection. 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.
Written By: Mark R. Richards, PE