If the temperature can or will be below 40°F, the sprinkler piping or heads need to be protected against freezing. There are several methods of automatic sprinkler protection that should be evaluated.
Antifreeze
Because water freezes at 32°F, additives such as glycerin and propylene glycol can be added to the sprinkler water to prevent freezing. Both additives in the pure form are combustible liquids, Propylene glycol having a flashpoint of 210°F and glycerin having a flashpoint of 350°F. Depending on several variables, the additives need to be between 30 – 70% of the total volume of water in the wet sprinkler system.
There has been some recent debate on the continued use of antifreeze. A fire in Herriman, UT in June 2010 involving antifreeze caused a flash fire. The fire started on the couch in an apartment, one sprinkler opened and a conflagration occurred where the window was shattered and items were shot out of the window. As a result there have been three phases of tests involving the performance of antifreeze. The tests involved a variety of antifreeze solutions, water flow pressures and types of fires. The final test was sponsored by NFPA in August 2012. The results were not good and NFPA indicated in a TIA that no new antifreeze systems should be installed utilizing propylene glycol and glycerin. The exception is if a sprinkler is specifically listed, such as the Viking ESFR with propylene glycol.
There are certain jurisdictions such as the State of New Jersey, which are allowing the use of antifreeze in new installations. This is a contradiction to NFPA and the International Fire Code.
Antifreeze systems that are existing should strictly adhere to the following design solution:
- 50% glycerin
- 40% propylene glycol
- Propylene glycol premixed solutions will be permitted to be used with ESFR sprinklers when the ESFR sprinklers are listed for the antifreeze
- Solutions over 38% glycerin or 30% propylene glycol need to be justified with “approved deterministic risk assessment” This was added per a NFPA 25 TIA on October 30, 2012.
The risk assessment should consider the following items:
- Occupancy use group per NFPA 13 and size of structure
- Ceiling height
- Antifreeze solution concentration and type
- Maximum system pressure (normal static pressures)
- Sprinkler type, including k Factor
- Potential and actual fuel load (Christmas trees)
- Type of structure (construction types)
- Ability of the sprinkler system to control the fire
- Occupied spaces -vs.- unoccupied space
- Adjacent occupancies and Separation
- Ventilation of areas protected with an antifreeze
- Duration of antifreeze discharge
Dry Pendent Automatic Sprinklers
Dry pendent sprinklers are intended to extend into an unheated area from a wet pipe system such as in a freezer. The sprinklers are fed from a drop where the drop is free of water. A seal is provided at the entrance of the dry sprinkler to prevent water from entering until the sprinkler head activates.
The Appendix of NFPA 13 states that under certain ambient conditions, wet pipe systems having dry pendent (or upright) sprinklers can freeze due to heat loss by conduction. Therefore, due consideration should be given to the amount of heat maintained in the heated space, the length of the nipple in the heated space, and other relevant factors.
Dry-pendent sprinkler heads are located within the compartment to avoid the cost of a refrigerated area sprinkler system. The dry pendent sprinkler system would be on a wet-pipe system with all piping located outside (above) the enclosure. The penetrations into the chambers (through the ceiling) would be protected by the use of dry-pendent sprinkler heads.
One of the problems with dry pendent sprinklers heads is that they are not FM approved for storage occupancies utilizing K11.2 heads. A UL listing is provided. Also the drop connection needs to be properly sealed. Drops are usually 12 in. This arrangement can cause ”sweating” of the portion of the dry pendent sprinkler above the roof, with resultant corrosion of the metal roof surface. If this problem exists, consider the following: tightly caulk the hole cut in the roof and wrap thermal mastic tape (or equivalent) around the dry pendent sprinkler nipple above the roof. Dry pendent heads need to be replaced every ten years.
Dry pipe and preaction sprinkler systems the two most popular options, but both systems are more expensive and a challenge to properly maintain. Dry systems are used in larger unheated spaces. An example would be an unheated warehouse. Preaction systems are typically found in computer rooms where there is an uneducated concern about sprinkler leakage.
Risk Logic can conduct your Antifreeze Risk Assessment per NFPA 25. We can also determine what the correct protection should be for your sprinkler system in a refrigerated or non-heated space.