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Turning the building envelope into a fire prevention shield

The role and importance of active fire protection systems such as sprinklers is well known in most industrialized countries. However, the importance of fire-limiting construction for the entire building envelope is not as well understood. Complicating matters further are the exterior building components that often may be overlooked when it comes to fire and natural hazards loss prevention.

The building envelope of commercial and industrial buildings is critical to limiting fire spread, minimizing fire-induced property damage and mitigating business interruption. The use of rigorously tested and certified products and adherence to loss prevention guidance derived from scientific research and field study are important steps in not only limiting such losses, but preventing them from ever occurring.

At commercial property insurer FM Global and company member FM Approvals, the deep belief – backed by research and nearly two centuries of property loss experience and testing – is that the majority of losses from natural and man-made causes can be prevented. Companies that choose to embrace this philosophy can benefit from the use of planning tools, performance-tested FM Approved products, and proven installation and maintenance guidelines from FM Global to create well-protected facilities with significantly reduced potential for property loss due to fire and other hazards. FM Approvals, which provides third-party certification of property loss prevention products, is the only organization in the world that assesses performance of complete wall assemblies when subjected to multiple perils, including fire (interior, exterior and any wall cavity), wind, hail and windborne debris.

This article provides a brief overview of how performance-tested and certified building envelope products and assemblies can prevent or significantly reduce losses to commercial and industrial buildings.

Engineering the building envelope

The critical components that comprise the protective shell or building envelope for a “typical” industrial or commercial building are shown in Figure 1. From a loss prevention perspective, the building envelope is the outer shell that protects the interior from fire and natural hazards such as excessive heat/cold, moisture, wind, hail and snow /ice. The basic building envelope usually includes the following:

  • Roofing Assemblies (e.g., decking, insulation, fastening system, membrane, flashing),
  • Roof-mounted Systems (e.g., cooling towers, photovoltaic panels).
  • Exterior Wall Assemblies (e.g., solid walls, cavity walls)
  • Fenestrations (e.g., windows, doors, skylights, shutters)

Roofing Assemblies

Roofing assemblies are perhaps the most important first line of defense against fire and natural hazards in the complete building envelope. They must be able to protect a structure from natural hazards, including rain, hail, snow, high winds and temperature extremes. They are also required to limit fire spread from external fire risks (e.g., flying embers from adjacent buildings, rooftop hot work) and from internal fire risks (e.g., presence of combustible materials, failure of electrical or mechanical equipment).

Roof components that have been tested individually, but not as a total system, should not be relied upon to provide the highest level of fire and natural hazards protection; rather, roof assemblies that have been tested and certified as complete systems should be considered. Assembly testing should include multiple perils such as fire testing above and below the deck, wind-uplift testing, hail-damage testing, accelerated weathering, water leakage, foot traffic and corrosion-resistance testing of metal parts.

Figure 1: The “building envelope” on most industrial/commercial buildings is a complex system of components and assemblies that make up the outer shell of the structure and provide the first line of defense against manmade and natural hazards. The building envelope may include not only insulated wall and roof assemblies, but also skylights, solar panels, HVAC systems and other roof mount equipment.

Figure 1: The “building envelope” on most industrial/commercial buildings is a complex system of components and assemblies that make up the outer shell of the structure and provide the first line of defense against manmade and natural hazards. The building envelope may include not only insulated wall and roof assemblies, but also skylights, solar panels, HVAC systems and other roof mount equipment.

Roof-Mounted Systems

Cooling towers and photovoltaic systems are often mounted on roofs of commercial and industrial buildings to save footprint space and take advantage of the elevated location. All can, and do, contribute to increased fire risk.

Cooling towers are widely thought to be safe from fire because water flows through them. In fact, cooling towers are vulnerable to fire as they contain dry areas, electrical equipment and one or more combustible materials such as PVC, fiberglass reinforced plastic and ABS. Fire risks are increased during regular maintenance as water flow may be turned off allowing hot work, human element issues or electrical arcing to potentially trigger fires.

Cooling towers should be tested and certified as a complete system and evaluated for fire risk, as well as static and cyclic air pressures (i.e. wind) and debris impact. Resistance to seismic loads should also be determined.

Photovoltaic (PV) systems are increasingly specified and used on commercial and industrial rooftops due to the need to satisfy the latest energy efficiency and sustainability regulations. PV systems are specialist installations that can adversely affect the fire performance of any given roof assembly. FM Approvals standards can be used to evaluate both rigid PV modules, which typically require a metal rack system for roof mounting and flexible PV modules, which can often be integrated directly with roofing membranes.

Exterior wall assemblies

Exterior wall assemblies are another major element in the building envelope. They must be able to protect a structure from fire and natural hazards associated with the local environment, including rain, hail, high winds and temperature extremes. They are required to limit fire spread from external fire risks (e.g., fire from adjacent buildings or vehicles), from ignition sources within the cavity (e.g., hot work, grinding sparks and electrical shorts) and from internal fire risks (e.g., presence of combustible materials, failure of electrical or mechanical equipment).

Over the past 20 years, intermediate- and small-scale testing has replaced much of the costly and time-consuming full-scale fire testing previously required for walls and ceiling panels. For instance, full-scale 25 ft. and 50 ft. (7.5 m and 15 m) corner fire tests have been replaced, in most cases, by the small-scale Fire Propagation Apparatus – also known as ISO 12136/ASTM E2058 – and intermediate-scale tests such as the Parallel Panel Test and Room Fire Test.

Figure 2: When things go wrong. Fire is fast and devastating. Certified building envelope products help to prevent disasters.

Figure 2: When things go wrong. Fire is fast and devastating. Certified building envelope products help to prevent disasters.

Fenestrations

The building envelope is only as strong as its weakest link. Windows, doors, skylights, shutters, and impact resistant films – fenestrations – should not be overlooked when designing a building to withstand fire, hurricanes, powerful windstorms, hail and windborne debris. Damage to fenestrations can lead to serious damage to the building contents and the building structure itself.

Skylights, for example, are not only susceptible to damage from the natural hazards noted above, but also to foot traffic. Skylights made from various plastics also pose a fire risk from both internal and external sources. Fire tests should evaluate the ability of the skylight to limit flame spread, and measure the sample’s propensity to melt and drip, which could adversely impact the performance of sprinklers located just below.

Conclusion

The majority of all property loss is preventable when risk engineering best practices are followed. Products that have not been evaluated for loss prevention performance by a reputable testing agency may not provide the long-term loss protection expected or required. Loss prevention engineering and services provide added benefits by helping organizations prevent property losses in the first place. By avoiding losses due to fires, floods, hurricanes and other natural and man-made disasters, companies can significantly impact their business resilience and drive down their overall cost of risk.

For more information, go to www.fmapprovals.com

References

www.fmapprovals.com website Provides comprehensive information, including all available to download Approval Standards. www.approvalguide.com, The Approval Guide, a searchable online database of over 70,000 FM Approved products. www.roofnav.com RoofNav, a searchable online web-based roofing design tool for roofing professionals. FM Global Property Loss Prevention Data Sheets www.fmglobal.com/research-and-resources/fm-global-data-sheets.

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Jean-Philippe Roisin is Assistant Vice President, Manager New Business EMEA for FM Approvals based Paris.

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