For the past 60 years, antifreeze used to be employed successfully in order to protect sprinkler systems installed in areas where adequate heat is not provided, should it be in commercial applications as well as in residential applications.
However, a recent fire incident involving an antifreeze system occurred in a sprinklered home kitchen, which resulted in a single fatality and a serious injury to another person. The antifreeze solution was highly concentrated.
As a matter of fact, the antifreeze used (mainly propylene glycol and glycerine) are flammable liquids, which – even for a short time – increase the magnitude of the initial fire, and even may initiate an explosion. Since this tragic accident, the phenomenon could no longer be ignored.
This led the National Fire Protection Association to initiate a research project with the Fire Protection Research Foundation, which included a number of fire tests. Notably, the FPRF observed that highly concentrated antifreeze solutions (more than 40% of propylene glycol or 50% glycerine) may ignite when discharged through sprinklers.
The main consequence of this investigation is that the latest issues of NFPA 13 (standard for the installation of sprinkler systems) and NFPA 13 R (standard for the installation of residential sprinkler systems) require that antifreeze solution be listed for their sprinkler application. To our knowledge, there is to this day no listed antifreeze solutions on the market.
Alternatives include dry-pipe sprinkler systems and heat trace systems. However, those alternative are not always feasible : for instance, the use of dry-pipe for in rack sprinklers is prohibited. As well, ESFR sprinklers can be used on wet pipe only. Heat tracing at the moment is seldom used on sprinkler networks, for it is expensive and requires more maintenance. In addition, in many areas, contractors are not used to installing properly those systems.
The biggest issue one has to face is with existing systems. For systems protecting one- and two-family dwellings, the 2013 edition of NFPA 13D requires the antifreeze solution to be premixed (in order to mitigate mixing errors), with the following maximum concentrations :
- Propylene glycol to a maximum concentration of 40% by volume
- Glycerine to a maximum concentration of 50% by volume
- Other solutions must be specifically listed for use in sprinkler systems
For all other applications subject for compliance with NFPA 25 (sprinkler maintenance standard), the use of listed solutions will be mandatory in 2022. Until then, existing systems may remain in service, provided the following conditions are met :
- The concentration of glycerin shall be limited to 50% and of propylene glycol to 40%
- Newly introduced solutions shall be premixed
- Antifreeze solutions with concentrations superior to 38% glycerine and 30% propylene glycol shall be subject to a risk assessment
Such a risk assessment will require to be based on the fire tests done by the FPRF, which will considerably reduce the extent to which they may be used.
Considering the fact that the alternatives to antifreeze do not cover the full spectrum of sprinkler applications, and that there is a global issue concerning existing sprinkler systems subject to low temperatures, there is a strong need for the development of non-combustible antifreeze systems. Some manufacturers are in the process of developing non-combustible antifreeze systems, possibly based on calcium chloride or potassium acetate.
Recent research by Factory Mutual showed that the water spray distribution in a sprinkler was not affected by the use of a fluid with a greater density and viscosity did not affect the water spray distribution, which is most encouraging.
Current issues with the development of non-combustible antifreeze systems are the solution stability as well as the issue of corrosion which requires corrosion inhibitors.
Although there are still technical challenges to overcome, the pressure on the industry is strong to identify alternatives to existing antifreeze systems. We therefore can be quite confident that new non-combustible antifreeze systems will be launched in the coming years. However, the listing, which is a quite slow process, will delay the roll-out of new products.
Brice Franc - SPK Engineering