Another Day, Another Way
NFPA Journal®, November/December 2012
In these tough economic times, many companies are shying away from constructing new customized storage facilities and are scooping up empty warehouses for dimes on the dollar. In some cases, they aren’t even purchasing new space, but repurposing existing warehouse space to accommodate new products or new storage operations. The problem is that many of these owners do not understand that storage sprinkler protection is not one-size-fits-all.
If you’re part of the sprinkler community, you may already be well versed in the recent developments on antifreeze solution behavior in sprinkler systems. To recap: After several rounds of testing various types and concentrations of antifreeze solutions with various types of sprinklers, the NFPA technical committees responsible for writing NFPA 13, NFPA 13R, and NFPA 13D created new requirements that mandate the use of “listed” antifreeze solutions for new system designs. The critical component of the listing is that it needs to indicate that the solution will not ignite when discharged from a sprinkler. These requirements essentially prohibit the use of the traditional solutions, propylene glycol and glycerine, which are not listed.
While the prohibition on traditional antifreeze solutions has taken a tool out of the sprinkler system designer’s toolbox, many other freeze protection options exist. Most of them have been around for years, but they have not been explored and refined as palatable design approaches by many designers simply because antifreeze was extremely cost-effective and efficient. Or so we thought.
A frequently used alternative to an antifreeze system is a dry-pipe system, which eliminates concern about freezing pipes because the piping subject to freezing temperatures does not contain water. Instead, it contains pressurized air that is discharged when a sprinkler operates, allowing the “dry valve” to trip and water to flow. Dry-pipe systems have been around for decades and are a viable option for freeze protection where there are not extensive piping networks that may increase the water delivery time.
Other options include insulation or heaters. Insulating sprinkler piping runs in walls, interstitial spaces, and attics is common in wood-framed buildings, especially where NFPA 13R and NFPA 13D systems are installed. It is important to install the insulation so it cannot be easily altered, compromising its thermal resistance properties and potentially leading to frozen pipes. This is fairly easy to accomplish in walls and concealed spaces where there is limited access, but it can be trickier in attics. In areas where the freeze season may last days or weeks instead of months, one option for pipes in attics or large spaces is to provide heaters on thermostats.
The thermostat can keep the temperatures at 40 to 50°F (4 to 10°C), limiting the operating time and keeping costs down. For a Fire Protection Research Foundation literature review of insulation and sprinkler piping, visit nfpa.org/sprinkler_insulation.
Other options included in the 2013 edition of NFPA 13 include heat tracing and engineering calculations. Heat tracing, which consists of a wire heating element wrapped around the pipe, is used in many industrial applications, including oil refining processes and nuclear power plants, and is becoming more popular for sprinkler systems. A new requirement also allows engineering calculations to be used as a justification that piping will not freeze, even if temperatures drop below the 40°F (4°C ) threshold established by NFPA 13. If these calculations show that there is sufficient thermal resistance between the water in the pipes and the ambient air to prevent the piping from freezing, a wet-pipe sprinkler system may be installed.
While there will be some adjustments as designers phase out traditional antifreeze solutions, myriad options exist. With luck, the abolition of traditional antifreeze solutions will yield new, affordable freeze protection options that have not yet been conceived — another example of necessity as mother of invention. For more information, visit nfpa.org/antifreeze.
Matt Klaus is a senior fire protection engineer at NFPA and staff liaison on NFPA 13, 13R, 13D.