Case study: Combined compartmentalization strategies

A new research laboratory building is currently under construction in Massachusetts. This building contains seven stories above grade, six of which are connected by an atrium in the center of the building. Because this is a research laboratory, there are relatively high amounts of hazardous materials that may be present in the building.

As such, the building owner and architect chose to separate the building into multiple control areas. Please note that the complete design of this building is not yet available to the public and, as such, images and figures of this building will be diagrammatic by nature.

The figures show a very simplified version of how each floor is separated. The floor is generally separated into three separate control areas (see Figure 6). Control area 1 is a nonlaboratory space and is also shared across floors (as it encompasses the six-story atrium). Control areas 2 and 3 on each floor are the laboratory spaces where most of the hazardous materials are expected to be found.

Figure 6: Typical control area layout for a new research laboratory in Massachusetts. Courtesy: Arup

The floor is also separated into spaces that are and are not a part of the atrium (see Figure 7). Some of the separations between the control areas and the separation between the atrium spaces and nonatrium spaces entirely consist partially of glass paneling.

Figure 7: Typical atrium separation for a new research laboratory in Massachusetts. Courtesy: Arup

The presence of an atrium and multiple control areas in the building, compounded by the vast amount of glass paneling, made this a complex situation from a life safety and fire protection standpoint. It was determined early in the building design that the use of sprinklers would be used where possible in lieu of common passive fire protection measures to achieve the required fire resistance ratings.

The most basic part of the design for this space was the fire-resistance rated separation between control areas 2 and 3. The boundary between these two spaces did not consist of any glass paneling with the exception of a few glass doors. The glass doors were required to be made of rated glass because window sprinklers cannot be used for operable openings. The remainder of the separation between the spaces was provided by the standard fire-resistance rated fire barriers, with no need for additional protection by the automatic sprinkler system.

For the separation between nonatrium and atrium regions encompassed within control area 1, the closely spaced sprinkler rule detailed by International Building Code Section 404.6, Exception 1 was applied. The glass doors along the boundary were specified to be self-closing and gypsum soffits were provided along the glass boundary so that concealed pendent sprinklers could be spaced every 6 feet along the boundary. These sprinklers are installed within 4 to 12 inches of the glass they are protecting.

Though the design and installation requirements for these closely spaces sprinklers are quite rigid, it was determined that this was the significantly more cost-effective and aesthetically desirable than the use of rated glass partitions.

Lastly, the most complex part of the design was the boundary between the atrium and the lab spaces. Practically the entire boundary between these two spaces consisted of glass paneling. Though it is an eye-catching design, it obviously presents issues when it comes to compartmentalization and separation. The glass paneling makes up the boundary between atrium and nonatrium spaces.

However, it is not correct to use the same rules from IBC Section 404.6, Exception 1 because the control area separation requirement is more stringent than the atrium separation. Separation between control areas does not allow for the same sprinkler alternative that is accepted for atrium separations with closely spaced sprinklers.

As such, the window sprinklers that provide a listed two-hour fire-resistance rating were used instead. The two-hour fire-resistance rating of these sprinklers provided a sufficient fire-resistance rating to separate adjacent control areas, and exceed the minimum required one-hour fire-resistance rated atrium separation.

On the ground level, window sprinklers were designed to wet both sides of the glass surface. On higher levels, the window sprinklers only had to wet the entire surface of the lab (nonatrium) side of the glass, as there were no occupiable walkways on the atrium side. Having no occupiable walkways mean that there does not exist the reasonable threat of a fire on the atrium side to the glass, which would have already been mitigated by the window sprinklers on the lowest level. This approach was specific to the variance associated with this atrium protection.

Because the use of window sprinklers to achieve a fire-resistance rating is not a prescriptively compliant approach in Massachusetts, a variance application was submitted and accepted to confirm this approach with the authority having jurisdiction as providing an equivalent level of fire protection and life safety intended by the code.

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