Perhaps one of the most seemingly straightforward but actually complex topics of fire protection is the use of fire sprinklers to achieve passive fire resistance requirements. This week I'm diving into an introduction of different methods of using sprinklers for passive fire protection and discussing some of the design abuse therein.
If you've encountered it, you're surely already familiar with how big of a topic it is.
Three Methods for Protection of Windows
Where windows are provided in fire-resistance rated components (a fire partition or barrier, as sprinklers are not permitted to be used for fire walls), the opening must be addressed in a manner that maintains the fire-resistance of the rated enclosure. The driver for these requirements is the building code.
Option 1: Rated Glazing
The first method to address openings in rated walls is provide a glazing assembly that is rated.
The International Building Code qualifies two types or ratings- fire-resistance-rated or fire protection rating. The former is tested to ASTM E119 or UL 263 and is not considered an opening. The later (fire protection rating) is tested to NFPA 257 or UL 9 and has limitations on overall size. (IBC 2018 Fire-Rated Glazing Definition)
Of the three options, this one is the most costly. Cited costs of fire rated glazing alone can be nearly $100 per square foot. For a large 10 foot x 6 foot window, for instance, that's over $6,000 for each panel.
Option 2: Closely-Spaced Sprinklers (for Atrium Enclosures)
Closely-spaced, standard sprinklers are used in glazing applications specifically for the protection of an atrium enclosure which contains glass.
The closely-spaced sprinklers, used in conjunction with specific requirements for glass and frame, are only permitted in the International Building Code as an alternative to a 1-hour enclosure for atrium spaces. (IBC 2018 404.6)
I'll discuss this in more detail, but the big takeaway here is that the building code only permits the use of closely spaced sprinklers as an alternative to a 1-hour enclosure for atrium enclosures.
Closely Spaced Sprinklers used in lieu of a 1-hour wall for atrium enclosures are the least-restrictive setup for sprinklers and glazing, with limited dimensional requirements and allowed use of multiple standard sprinkler types.
Option 3: Window-Style Sprinklers
The last method for treatment of windows in fire rated assemblies is to provide Tyco Window-Style sprinklers installed in accordance with their listing.
The proper use of these sprinklers can achieve up to a 2-hour fire resistance rating with the use of glass. This method is not a prescribed code application but rather an “alternative method of construction” which requires documentation & support as an alternative, and must be approved by the AHJ. (IBC 2018 104.11)
Fair warning - these sprinklers are roughly $400 each, and have major restrictions for their use (including specific sprinkler placement dimensions and glass requirements).
Window-Style Sprinklers (by Tyco) can provide up to a 2-hour rating for a fire barrier. With wider application, these sprinklers also come with a significant list of limitations outlined in the product listing.
Passive vs. Active Systems
Passive fire protection requirements, such as the fire-resistance ratings of fire partitions, fire barriers, and fire walls, are required by code to limit the spread of fire.
The term 'passive' is given as no intervention or dynamic activity is required in order for the system to function. Fire partitions, barriers and walls have a long history of successfully extending longevity of buildings in a fire, limiting spread, and increasing the ability of people to defend in place or escape a fire.
Active systems are identified by a dynamic "action" that is required in order to function effectively. Automatic fire sprinkler systems are one type of active fire protection system, which require open valves, clear pathways, and in some cases the electrical and mechanical operation of fire pumps.
Point-Counterpoint For & Against Fire Sprinklers for Passive Requirements
This area of application isn't without controversy. There's opposite viewpoints on whether sprinklers should even be used as an alternative to passive fire protection. Here's a summary of the pros and cons:
Use of sprinklers in conjunction with glass can afford many architectural opportunities without the expense of rated glazing, but restrictions are extensive, such as ensuring no combustibles are adjacent to the glass
The Common Misapplication
I’ve often heard architects ask about using “water curtains” or “deluge sprinklers” when they have a rated fire barrier and are looking to incorporate a window.
The request is commonly for "closely spaced" standard sprinklers to comprise a 1-hour or 2-hour fire barrier.
I’m fairly confident that some part of me dies inside each time I hear either term - mostly because I know the education effort that always has to follow.
The Basis for Closely Spaced Sprinklers
The basis for standard, closely-spaced and located near glass, is provided in the International Building Code specifically for the enclosure of atria.
An atrium is specifically an opening that connects two or more stories and is one method of interconnecting multi-level spaces and acknowledging vertical openings with fire safe goals in mind.
Atrium spaces are unique in that they require fire sprinkler protection, a fire alarm system, and a smoke control system. All three of these components work in conjunction with each other to detect fire early in the process, notify occupants, and keep smoke to a manageable level while occupants escape.
The International Building Code allows “closely spaced” sprinklers to be used with glass (with limitations) in lieu of a 1-hour enclosure specifically because of the other systems already provided for life safety. (IBC 2018 404.6)
Misapplication for Non-Atrium Spaces
While this section for atrium spaces has existing for some time, what has not existed in the building code has been the provision for closely spaced sprinklers to equate to 1-hour fire resistance rating. To put it simply, a documented basis for such an arrangement doesn’t currently exist.
Could it be proposed as a code alternative to a 1-hour fire barrier? Perhaps. But even without being an AHJ, I would question what technical evidence would support the use of closely-spaced sprinklers to be used in lieu of a 1-hour fire barrier.
If I were an AHJ and closely-spaced sprinklers were proposed as a code alternative, I’d require a fire alarm system and a smoke control system for the space – just as is required for the atrium arrangement.
Casual (Sloppy) Design
Unfortunately, in some jurisdictions there’s not enough resources and/or education for code officials and plan reviewers to monitor and police applications like this.
Locally, I know of several jurisdictions who would immediately (and correctly) pounce on issues like this. I also know others where there is total reliance on the engineer for code compliance and proper design as there hardly is a plan review process.
This sloppy design causes issues for everyone, especially for me when I have to be the bad guy and educate an architect or general contractor on future jobs. It's the common excuse of "that's what we did on the last job" that of course justifies continuing down the wrong design path. This is one reason I really enjoy working with knowledgeable and thorough AHJs as opposed to more "hands-off" jurisdictions.
Free PDF Companion
Download our free PDF comparison between these three applications, with major design implications outlined.
I'm very interested in what your experience has been with the use of sprinklers to meet passive window fire protection requirements.
Help us by sharing your experiences on the topic in the comments section below. I look forward to the discussion.
References & More Reading
Arsenault, Peter. “Window Sprinklers as an Alternative to Fire-Rated Glass.” Continuing Education Center, Tyco, continuingeducation.bnpmedia.com/courses/tyco/window-sprinklers-as-an-alternative-to-fire-rated-glass/3/.
Kim, A.K., and G.D. Lougheed. “Fire Protection of Windows Using Sprinklers.” Construction Technology Updates, 15 Mar. 2018, www.nrc-cnrc.gc.ca/ctu-sc/en/ctu_sc_n12/.
Model WS-5.6 K-Factor Specific Application Window Sprinklers, Horizontal Sidewall and Pendant Vertical Sidewall. Tyco Fire Products Research & Development, 2016, Model WS-5.6 K-Factor Specific Application Window Sprinklers, Horizontal Sidewall and Pendant Vertical Sidewall, www.icc-es.org.
Tyco Window Sprinkler, tyco-fire.com/index.php?P=detailprod&S=6200.
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.