As architecture and interior design of new construction continues to leverage creative means to provide an open look and feel, these more open designs often include glass in areas where rated construction is required. Windows serve as an opening in fire rated assemblies that are required to be rated based on the functionality of the assembly it protrudes. A common, but often cost prohibitive method to provide a fire resistance rating to windows is through fire rated glazing that is tested in accordance with NFPA 257 or UL 9. Another method that is frequently used is to utilize automatic sprinklers to protect the opening. This approach is often misapplied within the industry, but as long as careful consideration is provided to the design it can be an effective means of fire protection.
Code Requirements
The building code does not permit the use of active fire suppression in lieu of passive fire protection without an alternative means and methods request being developed. New language was added to the 2012 edition of the International Building Code (IBC) which clarified this requirement as follows:
Under the prescriptive fire-resistance requirements of the International Building Code, the fire-resistance rating of a building element, component or assembly shall be established without the use of automatic sprinklers or any other fire suppression system being incorporated as part of the assembly tested in accordance with the fire exposure, procedures, and acceptance criteria specified in ASTM E 119 or UL 263. However, this section shall not prohibit or limit the duties and powers of the building official allowed by Sections 104.10 and 104.11.
In order to utilize sprinklers in lieu of glazed glass in a fire resistance rated assembly , an alternative means and methods or variance in accordance with IBC §104.10 or §104.11 must be submitted and approved by the Authority Having Jurisdiction (AHJ). The variance / alternative means and methods request would include a performance argument that addresses how the alternative design complies with the intent of the provision of the code. In this case the intent is to show that use of window sprinklers there is potentially an overreliance on one type of system (automatic sprinklers) to accomplish two different defense-in-depth elements to achieve life safety in the building:
Prevent fire growth: relies on automatic sprinklers
Prevent fire spread throughout the building: relies on fire rated construction (and sprinklers if they are “rating” the wall)
In order to minimize the likelihood that window sprinklers will be out of service at the same time as general area sprinklers, serving the window sprinklers from an independent sprinkler zone valve should be considered.
As part of the alternative means and methods request, the registered design professional should consult new guidance in NFPA 13 (2016 Edition) that require specifically listed window sprinklers to be used when protecting glass, except where the building code specifically allows standard spray sprinklers (such as for atrium separation).
Equivalence Testing
The use of ANSI/UL10B: Standard for Fire Tests of Door Assemblies can used as an alternative testing standard. Section 10 of this standards comprises of a hose stream test to determine how a heated surface responds to water. During testing, the gas flow required to achieve the time/temperature relationship specified in ASTM E119 was established without sprinkler protection. A window assembly with window sprinklers was then installed in the test furnace and were applied over a two-hour period. The window assembly with window sprinklers did not show and cracking or visible damage during the testing period. This indicates that a window with listed window sprinklers provide an equivalent level of fire-resistance rating. This testing data should be considered in the development of an alternative means and methods request.
Design Criteria
When the use of window sprinklers is found acceptable to the AHJ, window sprinklers may be used in either sprinklered or unsprinklered buildings to protect non operable window openings. Window sprinklers have very specific listing conditions, including glass height, protected area, spacing of mullions, etc.. These requirements must be carefully reviewed by the design team prior to specifying glass and laying out the sprinkler layout.