The Role of Insulation in Mission-Critical Design

Improve moisture control and fire performance with the right material
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Sponsored by Owens Corning
By Jeanette Fitzgerald Pitts

Fire Performance

Be it a mission-critical or average building, fire is one of the most planned for threats to a building. A three-pronged approach is usually employed to offer occupants the greatest opportunity to get to safety and minimize potential fire damage. These strategies include a detection system, an active suppression system, and passive fire-containment measures. The detection system alerts occupants and authorities to the presence of a fire and helps facilitate an urgent, safe evacuation. An active suppression system is also triggered by the presence of fire or smoke. Sprinklers are a common example of an active suppression system.

As an important redundancy, buildings also incorporate passive fire-containment measures that do not require a trigger to activate in the instance of a fire. If the passive fire systems are designed and installed properly, fire and smoke may be contained or slowed, allowing occupants crucial time for escape. Some insulation products work with other components to create passive fire containment assemblies.

Mineral wool insulation can be used as part of the curtain-wall assembly to create perimeter fire containment at floor line and roof locations. One of the most complex and least understood areas where a fire can propagate is at the exterior of the building, where a non-rated curtain wall bypasses a rated floor assembly. If a void exists between the non-rated exterior wall and the rated floor assembly, the IBC requires that designers extend the rating of the floor slab out to that exterior wall. This is accomplished by putting a system in the joint that has been tested to ASTM E2307: Standard Test Method for Determining Fire Resistance of Perimeter Fire Barrier Systems and rated to stay in place for the same length of time as the floor assembly. The reliable fire performance of specially engineered mineral wool is a leading material to create these perimeter fire-containment systems that will prevent or retard the spread of fire and hot gases through the opening.

The time versus temperature curve found in ASTM E119 indicates the response of multiple materials to fire exposure over time based upon years of testing and research.

ASTM E2307 is just one of several fire-assembly tests to indicate performance in the presence of fire. For mission-critical buildings, several factors like occupancy, building contents, or location increase the likelihood of fire-rated exterior walls or roofs being required. ASTM E119: Standard Test Methods for Fire Tests of Building Construction and Materials is referenced by IBC to meet these requirements. The test exposes a wall or roof assembly specimen to a standard controlled burner that achieves specified temperatures throughout a specified time period and evaluates the duration for which an assembly can contain the fire and retain its structural integrity. Results are plotted along a time/temperature curve.

Through decades of testing and fire science, the ASTM E119 time and temperature curve has become well-known as an indicator of fire behavior in materials. Of note is that a significant proportion of standard building materials present in wall and roof assemblies are compromised within the first hour of fire exposure. This includes common materials like foam plastics, glass fiber, zinc, aluminum, and glass. Yet these materials can be included in hourly rated systems. This is an example of where the system is greater than the individual parts. It is how these materials work together that matters most.

This highlights the need for taking a deeper look at the details. For example, gypsum sheathing is introduced into many wall assemblies as a means of providing a thermal barrier for more combustible products. Mineral wool insulation has also been identified as a thermal barrier for these applications and can be a particular problem solver for mission-critical buildings where other materials are not desirable or reasonable. Notice on the previously mentioned curve, mineral wool can potentially withstand fire exposure for hours.

Unfortunately, designing the envelope of a building to limit the spread and growth of fire is more complicated than simply choosing an insulation with good fire performance. In fact, it is not even as simple as meeting a single fire-assembly test requirement. The IBC requires buildings of Types I–IV construction (mission-critical buildings often falling into Types I or II) to have noncombustible construction. However, exterior walls subsequently are wrapped in multiple combustible materials, such as air and water barriers, combustible claddings, and possibly insulations.

The NFPA 285 testing procedure exposes a wall assembly to fire on a lower level and measures vertical and lateral propagation of the fire across the wall.

In order to help designers create building envelopes that control the spread of fire, a standard was developed to test the fire propagation of exterior wall assemblies. This standard is the National Fire Protection Agency (NFPA) 285: Standard Fire Test method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components. NFPA 285 measures what happens during a fire when a noncombustible building is wrapped in combustible materials. In order to pass NFPA 285, the wall assembly must resist flame propagation over the exterior face of the system, the combustible core or components in the panel must resist vertical flame from one story to the next, the interior (room side) surface of the panels must resist the vertical spread of flame from one story to the next, and the assembly must resist the lateral spread of flame from the compartment of fire origin to adjacent spaces.

Based on decades of research, similar to ASTM E119, general conclusions have been drawn about combining common materials to pass NFPA 285. For example, noncombustible claddings such as masonry veneer, stone veneer, and concrete may be combined with combustible insulations like most foam plastic continuous insulation as well as noncombustible insulations like mineral wool continuous insulation. However, when the cladding is combustible, such as aluminum composite material panels, hollow terra cotta panels, high-pressure laminate panels, or other metal composite material panels, designers must select a noncombustible insulation or very carefully design with specially engineered materials to provide thermal protection.

A Qualified Antiterrorism Technology

Many mission-critical facilities are considered higher-risk targets for acts of terrorism. Designers working on these types of projects can garner valuable liability protection for themselves and building owners by selecting products and delivering services that have earned the Safety Act designation from the DHS.

Due in part to the extraordinary fire performance demonstrated by some mineral wool products, this material has earned the Safety Act designation from the DHS. This means that incorporating the mineral wool products that have been deemed a “qualified antiterrorism technology” will extend a level of protection to the design team and building owners from claims implicating these products resulting from an act of terrorism.

There are a number of considerations incorporated into the review of a potential Safety Act product. One is demonstrated use and efficacy through sales or use by commercial or government customers. Four of the five tallest buildings in North America incorporated specific mineral wool products for fire protection into their envelope, and the fire performance of the material has been exhaustively tested in stand-alone and exterior assembly applications.

Additionally, the liability protections granted by earning the Safety Act designation can be retroactive, meaning design teams or building owners using these mineral wool products may have a level of protection on projects they worked on in the past if their security procedures/products are substantially similar to those covered under the SAFETY Act.

It is important to note that the Safety Act designation is product specific, not material specific. For more information about the specific types of mineral wool that have been recognized by the DHS as a qualified antiterrorism technology and offer this broad liability protection, please refer to www.safetyact.gov or contact the manufacturers of mineral wool directly.

Conclusion

In conclusion, insulation plays a powerful role in creating a design that meets the nuanced performance needs of a mission-critical project. Selecting materials that protect against moisture ingress and enhance the fire-containment abilities of the envelope equips these facilities to continue their important work without interruption, even when the extreme happens. Of the many types of insulation currently on the market, cellular glass can offer design teams an extra waterproof layer to create the redundancy that is commonplace inside a mission-critical building in the roof and compressive strength available that cannot be matched by other rigid board boards. Mineral wool offers an unparalleled performance when exposed to fire and allows designers the freedom to use the types of combustible cladding that have been gaining popularity, without sacrificing code compliance or safety. In short, selecting the right insulation for a project can help to fortify the envelope of a building against environmental elements, which is especially important when the mission inside the envelope is critical.

Jeanette Fitzgerald Pitts has written nearly 100 continuing education courses exploring the benefits of incorporating new building products, systems, and processes into project design and development.

 

Owens Corning<sup>®</sup> Owens Corning develops, manufactures, and markets insulation, roofing, and composites. The company’s businesses use their deep expertise in materials, manufacturing, and building science to develop products and systems that save energy and improve comfort in commercial and residential buildings.

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Originally published in Architectural Record


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