Up on the Roof … Fire Safety

By David Laks, P.Eng.

Every year there are a significant number of roof fires resulting from installation errors, neglected maintenance or poor housekeeping. This article, which includes case studies, discusses how the design, installation and maintenance of roof systems affect the likelihood and severity of roof fires.

Design

Most jurisdictions have design requirements for the fire performance of roofing systems. Many require a Class A, B or C roof rating. This rating is a measure of external spread of flame on the roof covering surface.¹ The test procedure as outlined in NFPA 256, Standard Methods of Fire Tests for Roof Coverings consists of exposing the top surface of the roof system to gas flame and measuring the distance of flame propagation. A Class A rating (highest degree of protection) is achieved if the flame spread is ≤ six feet, Class B, ≤ eight feet and Class C, ≤ 13 feet. For roof systems with combustible decks, two additional tests may be required: Burning Brand Test and Intermittent Flame Test.

If the roof assembly has a steel deck and incorporates plastic foam insulation, most codes require a thermal barrier or the complete assembly to pass an internal fire performance test. This test addresses the contribution of the roof components to the spread of fire. A common test procedure is outlined in NFPA 276, Standard Method of Fire Test for Determining the Heat Release Rate of Roofing Assemblies with Combustible Above-deck Roofing Components.²

Moreover, some jurisdictions or insurance companies require roof systems that are classified as Class 1. This classification can be obtained from FM Global. Besides meeting the external flame spread test, the whole roof assembly is evaluated against more comprehensive tests, including wind, hail, corrosion/leakage, flame spread on the underside of the deck, etc. It should be noted that all Class 1 roof assemblies are Class A, but not all Class A roof systems meet Class 1 requirements.

Installation

There are many commercial “flat” roofing systems available. Some of the most popular include BUR (built-up roofs), modified bitumen, single plies (thermoset/thermoplastic) and metal roofs. There are many others, but this article only focuses on fire risks related to BURs and torch-applied modified bitumen systems.

BURs are usually applied in “shingle” fashion using three to four plies with felts that are hot asphalt/tar or cold adhesives. They can be finished with a top coat and gravel or smooth finished (painted). The bitumen (asphalt or coal tar) is heated in kettles and applied with mops or spreaders on the roof.

A heat source such as propane or natural gas is used to heat/liquefy the bitumen in the kettle to proper application temperature. This process also releases flammable vapors. The bitumen can also be heated to its flashpoint, so precautions must be employed by properly trained personnel.

Modified bitumen systems can also be classified as BURs. These systems usually have a 1-2–ply base and a smooth or granulated cap sheet. The base sheet(s) can be “peel and stick,” adhered with hot asphalt or cold adhesives, and the cap sheet can also be torch-applied.

Clearly, using an open flame for torch-applied roofing systems creates unique fire risks, and specific precautionary measures must be taken. There are many documented fires that have caused extensive property damage, two of which are discussed below.

Case Study—Torch-applied Roofing #1

Heflin, Alabama, 2006: Contractors were working on the roof until late afternoon, and the fire broke out shortly after they left for the day. This resulted in the complete loss of the plant and several million dollars in property losses. As the roofers were applying a tie-in of the new torch-applied roof system to the existing roof system, the open flame was likely drawn below the deck, where it ignited the wood supports for a metal panel drop ceiling. The fire in this concealed space (below the metal roof deck and above the metal drop ceiling) worked its way undetected throughout a large area of the plant. When firefighters arrived on site the fire was so extensive that it was impossible to save the facility.

Wood studs were installed to support the metal panel drop ceiling. The wood studs in the approximately two foot-high drop ceiling space and the lack of fire-stopping would have contributed to the spread of fire within that space.

Case Study—Torch-applied Roofing Case #2

A contractor was re-roofing a dollar store on March 17, 2011, in Listowel, Ontario. During the installation of a torch-applied roof, a fire started below the metal roof deck. Combustible material and lightweight construction that were not visible fueled the fire, which was masked by a drop ceiling. The investigation revealed that the fire may have been burning for up to 40 minutes before 911 was called. These conditions were only discovered when the firefighters started battling the fire. Tragically, as the call was made to vacate the property, the roof collapsed, resulting in two firefighter fatalities.

As a result of this incident, local fire codes were changed to include items related to open flame torches, bitumen kettles and fire watches.

More emphasis within the codes should focus on ensuring the system is installed safely, with a consideration for fire safety. As code changes are being considered, input should be sought from fire protection engineers, insurance underwriters, brokers, roof consultants, roof manufacturers, roof specifiers and roof inspectors.

Maintenance

According to a 2012 NFPA report,³, grease-related hood/duct system fires cost restaurant owners approximately $50 million per year. One in five fires indicated “failure to clean” as a contributing factor.

Proper design that includes appropriate consideration of fire safety, installation by qualified installers who follow proper safety procedures, and a regular roof inspection/maintenance program will go a long way toward reducing the likelihood and severity of roof fires.

David Laks is with HUB International Risk Services Division.

References

¹NFPA 256, Standard Methods of Fire Tests of Roof Coverings. National Fire Protection Association.

²NFPA 276, Standard Method of Fire Test for Determining the Heat Release Rate of Roofing Assemblies with Combustible Above-deck Roofing Components. National Fire Protection Association.

 ³Structure fires in eating and drinking establishments. National Fire Protection Association, 2012.