Window sprinklers, water curtains, sprinkler protected glazing: What is the difference
Window sprinklers and water curtains are similar in appearance, but quite different.
A water curtain is used in an exterior wall that is required to have up to a 1hr fire rating based on FSD (Fire Separation Distance). They include roughly adding standard sprinkler heads at 6′ on center, 6″ from the wall. Adding the water curtain allows for unlimited openings in that rated exterior wall where, without the water curtain, the openings would be limited. Water curtain systems are generally installed at the ceiling with the intent of applying water on the entire surface of the inside of the exterior wall.
Window sprinklers, on the other hand, are part of UL listed 2hr fire barrier assembly for use inside buildings where occupancies must be separated by a fire rated construction. Openings (windows and doors) in a fire barrier are generally limited to 25% of the length of the fire barrier wall and must be protected. Protected openings, in this context, mean that the opening assembly (door or window) has a fire rating or that the opening is protected with a roll up fire shutter. A properly designed window and window sprinkler system is not considered an opening, protected or otherwise. Rather, it is a 2hr rated wall assembly, tested to the same standards as, for instance, two layers of gyp. bd. on each side of a stud wall.
Windows that are part of this system must include metal (steel or aluminum) frames and a minimum of 1/4″ thick tempered glass. Special sprinkler heads are placed on either side of the windows and designed to wash the windows with water. They do not wash the entire wall, just the windows. If there is a bank of windows with horizontal mullions (that could interrupt the flow of water on the face of the glass), additional heads must be placed at each horizontal mullion.
ESR‐2397 is the ICC-ES Evaluation Report addressing window sprinklers. Below is a link to a continuing education program about window sprinklers.
2016 NFPA 13 address both window sprinklers and sprinkler protected glazing, the difference being that sprinkler protected glazing would be considered an opening in the fire barrier and subject to the 25% of the length of wall limitation from the IBC while window sprinklers are the rated assembly and not limited in length. Some references that may be applicable follow.
Table 7.7.8.4 provides guidance on positioning and K-Factor.
8.15.26 provides further clairification regarding the sprinklers and windows.
23.6 goes into more detail about applicability, design and limitations.
