Best practices: Sprinklers and unrated glass partitions

Fire protection insights

• This article will teach how active fire protection (in this case an automatic sprinkler system) with unrated glass paneling can achieve a fire-resistance rating or a code compliant alternative to a fire-resistance rating.
• NFPA 13: Standard for the Installation of Sprinkler Systems defines design requirements for fire sprinkler systems. 

Building compartmentalization plays a pivotal role in the building’s overall fire and life safety strategy. With fire-resistance rated construction, buildings can be effectively separated into multiple areas that limit the spread of fire and/or smoke from one compartmentalized area to another. This can keep occupants and building contents protected for a longer duration in a fire event, which allows more time for a safe evacuation, allows more time for first responders to arrive and mitigate the fire’s effects and can keep critical parts of a building safe and functional.

Traditional walls with a fire-resistance rating have been given that rating after undergoing an ASTM E119: Standard Test Methods for Fire Tests of Building Construction and Materials test. This test exposes one side of the barrier to fire following the ASTM E119 time-temperature fire curve while closely monitoring the temperature on the other side of the wall and the structural integrity of the wall.

The fire rating of these walls is typically provided through noncombustible materials on the outside of the wall assembly with insulating materials on the inside. Passive fire protection like this is seen in a vast majority of buildings.

However, in buildings or spaces where certain architectural visions may be desired, the use of traditional fire-rated construction may not be appropriate or preferred. Interior glass paneling is frequently used to separate different rooms. Without any additional protection, it is expected that unrated glass paneling would be compromised due to an adjacent fire, which would render the partitions useless in providing the required fire-resistant separation between the adjacent spaces.

Figure 1: An example of a modern atrium bounded by glass partitions. Courtesy: Arup

Atriums and atrium separation

Atrium spaces are required to be separated from adjacent, nonatrium spaces by either a one-hour fire barrier or a horizontal assembly per the 2021 edition of the International Building Code (IBC Section 404.6). This boundary separating the atrium is required to aid a smoke control system (also typically required for atriums by the IBC) in exhausting smoke from just the atrium space and protect occupants located throughout the rest of the building. In most cases, the use of a one-hour fire barrier does not present an issue.

However, in cases where glass partitions are used as barriers, a possible issue can arise. There is quite a significant cost difference between an unrated interior glass partition and a one-hour rated glass partition that would be compliant with IBC Section 404.6. As such, in cases where a glass partition is used along the boundary of an atrium, IBC Section 404.6, Exception 1 details the prescriptive path to code compliancy.

In lieu of a one-hour fire barrier, a glass partition forming a smoke partition can be used. If an unrated glass partition is desired, then it needs to comply with the following:

• Automatic sprinklers shall be provided on both sides of the separation wall and doors (or only on the room side if there is not a walkway on the atrium side). These sprinklers shall be between 4 and 12 inches from the glass and no more than 6 feet apart from each other. The system shall be designed such that the entire surface of the glass is wet upon activation of the adjacent sprinkler (i.e., no mullions).

• The glass partition shall be installed in a gasketed frame such that the frame deflects without breaking before operation of the sprinkler system.

• All glass doors provided along the glass partition shall either be self-closing or automatic-closing.

From a fire protection standpoint, the first clause is an incredibly rigid set of design parameters. IBC requires sprinklers along an atrium boundary to be no more than 6 feet apart. However, NFPA 13: Standard for the Installation of Sprinkler Systems Section 10.2.5.4 sets the minimum distance between sprinklers to 6 feet. That means the distance between sprinklers along the atrium boundary must be exactly 6 feet unless baffles are provided to prevent cold-soldering between sprinklers.

Because of these stringent requirements, the architect and other engineers need to coordinate their design around the sprinklers along the atrium boundary.

Additionally, the requirement that sprinklers are a minimum of 4 inches laterally from an adjacent wall (NFPA 13 Section 10.2.5.3) can compound the issue. Consider a length of unrated glass along an atrium boundary that is 6 feet, 6 inches in length. One sprinkler is not sufficient to protect this length of glass — one sprinkler can only protect a maximum of 6 feet (see Figure 2).

Figure 2: A noncompliant sprinkler installation along glass partitions; one sprinkler is only sufficient to protect 6 feet of glass partition. Courtesy: Arup

Therefore, two sprinklers are sufficient to protect the length of glass, however, note that sprinklers need to be 6 feet apart per NFPA requirements to prevent cold soldering. That means that one or both sprinklers will be placed within 4 inches of the adjacent wall, which is no longer compliant with NFPA 13 (see Figure 3).

Figure 3: A noncompliant sprinkler installation along a glass partition. Though the two sprinklers are adequate to protect the length of glass, both sprinklers are located too close to the adjacent wall. Courtesy: Arup

This leaves two options that will be code compliant. Option 1 is to install a baffle between the two sprinklers in accordance with NFPA 13 Section 10.2.5.4.2 (see Figure 4). Though this is technically an option, it may not be aesthetically preferable to install a baffle in this area and may be a deal breaker from an architectural standpoint.

Figure 4: Option 1 for a compliant sprinkler installation along a glass partition: a baffle separates the two sprinklers located less than 6 feet apart. Courtesy: Arup

If the installation of a baffle is not an option, then the only option that is left is to increase the length of glass to a minimum of 6 feet, 8 inches or to shorten the length of glass to a maximum of 6 feet (see Figure 5). To facilitate a code-compliant design, it is best to bring this up earlier rather than later in the course of a project to give others ample time to react and assure the design is compliant with IBC and NFPA.

Figure 5: Option 2 for a compliant sprinkler installation along a glass partition: the glass partition has been lengthened to 6 feet, 8 inches to allow compliant distance between sprinklers and between a sprinkler and the adjacent wall. Courtesy: Arup

Another item to consider is the provision that “the entire surface of the glass is wet upon activation of the adjacent sprinkler.” It is this clause that helps the glass partition perform like a one-hour fire-rated assembly. This clause does not detail exactly how the entire surface should be wet upon sprinkler activation.

However, IBC commentary notes that curtain rods, draperies and similar fixtures would impede the wetting of the entire surface; as such, any of those fixtures should be located at least 12 inches from the window surface.

Furthermore, the presence of mullions along the glass paneling may obstruct water spray and could prevent the wetting of the entire surface. As such, the use of mullions should be closely examined by the design team to confirm that the system still meets the intent of the code. It is also important to take note of manufacturer specific guidelines pertaining to obstructions to sprinkler spray, like vertical and horizontal mullions in a glass panel wall.

Lastly, the use of closely spaced sprinklers along atriums does not classify the boundary as a one-hour fire barrier in all other situations. Rather, it is an alternate approach for providing code allowed atrium separation. As such, the glass partition with closely spaced sprinklers cannot be used as a fire-rated wall/barrier/partition in any other situations where needed.

In lieu of unrated glass paneling walls with closely spaced sprinklers, standard fire-rated barriers should be used as enclosures for fire pump rooms, exit passageways, shaft enclosures and control area separations among others.

Other types of fire-rated separation

Atriums are not the only features that need to be separated by fire-rated assemblies in buildings. Fire-resistance rated walls, partitions and barriers, along with smoke partitions and barriers, are found in practically every building. If one is trying to use a sprinkler system to achieve a proper fire-resistance rating, then these fire-rated elements need to be analyzed differently when not located along an atrium boundary. If unrated glass partitions are being used along an element of fire-rated construction (which could be seen along control area separation, exit passageways, walls separating the building into multiple alarm zones and along horizontal exits, etc.), then a different approach is required.

There is a solution that can be used to provide a true fire rating to otherwise unrated glass paneling. Special application sprinklers can be used so that, when activated, water discharges directly onto the glass it is protecting. When installed in accordance with the manufacturer’s precise design criteria, these sprinklers wet the entire surface of the adjacent glass and can provide a two-hour fire-resistance rating to the glass panel. This assembly with the special application window sprinklers requires testing and passing of the ASTM E119 test, the same test that typical rated assemblies must go through.

As mentioned above, the installation requirements for window application sprinklers are very strict, far stricter than those prescribed for closely spaced sprinklers by IBC. Though the specific requirements vary between manufacturers, there are some general criteria that need to be followed. There are a few less stringent requirements for sprinkler spacing for window sprinklers than closely spaced sprinklers, such as manufacturers allowing 6 feet and to up to 12 feet between the sprinklers. Also, depending on the manufacturer, the sprinklers need to be between 4 and 12 inches from the glass.

When designing for the use of window sprinklers, it is important to coordinate the details of the glass paneling with architects. Vertical mullions within the glass paneling create an obstruction of water spray on the glass. If not accounted for in the design, vertical mullions may prevent the wetting of the entire glass surface, therefore compromising the integrity of the fire-rated assembly. Vertical mullions are still allowed on the glass paneling, but each individual section of glass between the mullions needs to be protected individually.

Horizontal mullions, on the other hand, are not permitted within the rated assembly, as there is no feasible way for water to wet the entire surface. Window sprinklers are required to be within a certain distance of the protected glass as well. There is also a maximum height of the glass partition that is allowed, as well as glass type characteristics that need to be followed.

To mitigate the risk of a fire compromising the atrium boundary before the sprinklers can activate, there is also a manufacturer’s requirement to prevent the buildup of combustibles along the glass partition. Manufacturers recommend the use of a 36-inch pony wall up against the glass; however, other methods could be considered acceptable to the authority having jurisdiction (AHJ). All of these stipulations should be discussed with the architect to make sure that their design is copacetic with the window sprinkler requirements.

The long list of requirements for window sprinkler installation should not deter one from specifying their use in spaces where they may be necessary.

However, because of the amount of coordination needed between the fire protection engineer and the architect, code consultant, AHJ and others, it is vital that this topic is brought up early in the design process. The earlier this topic is discussed and resolved, the less stressful the late stages of design will be.

Additionally, it is important to note that this approach is not allowed prescriptively unless it is specifically approved by the AHJ through the means of an alternate means and methods request per IBC Section 104.10.

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