MITTENDORF: CUT IT
Applying heavy streams to the underside of a roof to cool the steel decking can be a successful tactic. But it also has its drawbacks: Working inside the building depends on the tenability of the structure’s interior; deploying hose streams through heavy smoke that obscures that target might not be as effective as planned; and the volume of water can cause substantial damage to the building’s contents.
Let’s consider another tactic that can be used in conjunction with or instead of hose streams from inside: cutting a strip through the layers of composition and insulation only. This will vertically vent the gases from the liquefied tar, removing the source of fuel which makes the fire self-sustaining. Here’s how it’s done:
- Using a chain saw or a rotary saw with a wood-cutting blade, make two parallel cuts (three to six feet apart) ahead of the rapidly moving fire. (See Photo 3, center left.) You need cut through only the composition and insulation; let the teeth of the saw “ride” on top of the metal corrugations.
- Make cross cuts every four feet between the parallel cuts. This makes the cut sections of composition and insulation easy to remove.
- If the metal decking under the cut sections that are to be removed is cold, strike the cut sections with an axe, pike pole, or similar tool. This will loosen the tar’s adhesive
- bond between the metal corrugations and the material above.
- Remove the cut sections (see Photo 4, bottom left) and place them away from the fire.
- Make two parallel cuts through the metal decking, similar to the first cuts made in the layers of
- composition and insulation.
- Make cross cuts between the metal joists. (See Photo 5, center right.) This way, each of the metal sections to be removed will be attached to just one metal joist, making them easier to remove. (See Photo 6, bottom right.)
The strip in Photo 4 is 4 feet by 40 and took 6 minutes to complete. Once the strip is removed, a hose line on the roof can extinguish any fire that’s crossing the opened area and cool the metal decking from the top.
If additional ventilation of the roof fire or the building’s interior is necessary, the metal decking can be removed—although it will take time. It should be done with a rotary saw and metal-cutting blade:
Although easily accomplished, this process consumes blades as well as time. The cut in Photo 6 destroyed three metal-cutting blades.
Knowing you can vent the fire’s fuel without necessarily cutting conventially sized holes through the metal roof gives you a second tactical option. Whether to work from the top, from underneath, or both will depend on the conditions you find at the scene.