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This poses a real threat to the safety of the roof crew as well as to any nearby exposed buildings. The asphalt and plastic mixture liquefies and burns with the intensity of a Class B fire. A hoseline must be stretched to the roof position and operated as needed to protect the vent team and exposures, as well as for controlling flame spread across the surface. Naturally, standard practices to prevent hose streams from being operated into any roof ventilation openings still must be followed.
Membrane roofing poses another threat to firefighters operating at roof level. The reinforcing fabric mesh gives the material significant tensile strength, which means it does not tear easily when pulled from end to end or side to side. When the material is applied and sealed into place, it forms a relatively rigid surface which maintains its shape even when the roof deck beneath it is gone, such as from burning away.
The membrane acts like a surface of a bass drum, holding its shape with no support in the middle. Some manufacturers claim their fabrics have held up to over 200 pounds per feet before breaking. Of course, that's not counting on exposure to fire. The danger to firefighters, though, is that the material does not necessarily show any telltale sag if the roof decking below is weakened. In fact, at the scene of one recent fire, I watched several members step through a roof covering that looked perfectly sound but which had only roof joists left below for support. Thankfully, this was the day after the fire had been extinguished and when members returned to the scene to critique the fire. No one was injured but it taught us all a lesson: even in broad daylight, with no smoke or need for speed, it is impossible to judge the condition of these roofs by sight. You must probe ahead each and every step with a substantial blow from a tool. Remember to think of these roofs as being just like the skin of that bass drum.
Photo by John Norman
The roof covering at this fire shows evidence of fire spread across the surface, yet firefighters stepped through the roof in areas which appear untouched.
Photo by John Norman
The fire travel across this roof extended over 60 feet from its source, requiring hoselines on the roof to extinguish.
It is nearly impossible to differentiate between a membrane roof and an older tar paper and hot tar roof once each has been in place for more than a few months. The time to identify them is when they are being installed. This too is harder to detect than older roofing methods. In the past, the old tar kettle (a source of many fires in itself), with its fragrant aroma, would indicate a roofing or roof repair in progress. Membrane roofing does not require a layer of hot tar to be mopped or sprayed on it. Like that tomato sauce advertises, "it's in there."
If you are unsure of the type of covering, membrane or conventional, your fire tactics should prepare for the worst-case scenario. Fires in top floors and cocklofts should prompt a precautionary hoseline to be stretched to the roof as soon as possible.
As always, roof crews should have at least two separate and remote means of egress. They should be aware of the wind direction and avoid getting caught on the down-wind side of a hole that is showing fire without hose line protection. They must, however, not hesitate in their roof venting duties, otherwise the gases accumulating in the cockloft are likely to wreak havoc on all those on the top floor, firefighters as well as civilians. Cut early and cut large!
John Norman, a Firehouse® contributing editor, is a captain with the FDNY, assigned to Rescue Company 1 in Manhattan. He is also an instructor at the Nassau County, NY, Fire Service Academy and lectures nationally on fire and rescue topics. Norman is the author of Fire Officer's Handbook of Tactics, which may be ordered by calling 800-752-9768.