When a fire occurs on a roof of a commercial building, it is often a spectacular event. Thick, black smoke is usually showing, often from miles away, and at first glance it can appear that the building itself is well involved in fire. This may or may not be the case, depending on what is actually burning. The incident may prove challenging to handle or may be able to be quickly controlled if you have done a bit of homework and know what to expect at the location that is on fire.
Commercial building roofs have a variety of construction types. In this column, I will concentrate on roofs with one of the most common construction types used in commercial occupancies, the flat metal deck roof with asphalt or other built-up roof covering. However, many of the items covered in this column may apply to roofs of other construction types as well. I’ll touch on the construction to help firefighters understand it a bit more, but the focus will be more on the tactics needed to fight a fire involving or on the top of the roof.
Breaking it down, this roof type starts from the bottom up with a steel truss that supports everything. The trusses normally rest on columns or walls to transfer the weight of the roof and anything on it to the foundation and the ground below. This steel truss is normally exposed to whatever is below it, whether that is simply open to the occupancy below or to some type of suspended ceiling that is below the trusses. If open to below, the roof structure will be directly exposed to any fire involving the occupancy, presenting the potential to rapidly weaken the roof support structure. The truss holds up the decking above, which is most commonly steel, although it could be of another construction. The metal deck normally has ribs or channels that can permit fire to move horizontally under the sheathing, insulation, and weather membrane installed on top of it. The type and thickness of the insulation can vary, depending on the climate of the area in which the building is located.
Insulation, sheathing, and membrane are secured to the deck by various means including adhesive (which may be readily combustible) and screws or other fasteners. Rock or similar ballast may be placed on top of the membrane material that is intended to help “hold” the roof down. The membrane, asphalt, or other material on the top is intended to shed water. Roof drains are often located at various points on the roof surface. These features are all important for firefighters to understand when responding to fires on these roofs.
Roof structures have some original design parameters that hopefully take into account snow loading on top of them (where applicable) and perhaps additional top loading with some consideration for things such as utility services [heating, ventilation, and air-conditioning (HVAC), sprinkler, other piping] that may be hung underneath the deck. Over the building’s life, additional loads may be placed on top (HVAC equipment, solar or other alternative energy equipment, and signs) or hung from underneath that may or may not have been considered in the initial design. During construction, both construction materials as well as construction equipment may be on the roof. There was likely a safety factor considered for this during the initial design, but what that safety factor actually is must be obtained from the designer or design documents and is likely not readily known to the normal building occupants or even facilities operations personnel. Firefighters operating on the roof also add to the loading.
WHAT CAN BURN?
Fires on the roof can involve the roof itself, items installed or located on the roof, or both. Often, the insulation or roof covering itself will burn, but it normally needs an ignition source to burn. This could be the heat from a fire inside the building that causes the roof above to ignite or some type of ignition source from equipment or construction on the roof. Equipment on the roof may be gas fired and become involved in a fire that could be contained to the equipment or spread to adjoining equipment or the roof itself.
Construction materials on the roof, whether for building/rebuilding the roof or for some other reason, may also become involved in a fire. These materials may not be easily visible from the ground/street and can add a significant additional fire load on the roof. Involvement of these materials will require stretching one or more hoselines to the roof. Rapid extinguishment is important to avoid further damage to the roof/building. Solar panels can certainly cause or be involved in a fire. (See “Tackling Solar Power Challenges,” May 2014, www.firefighternation.com/article/firefighting-operations/tackling-solar-power-challenges.)
If equipment on the roof is on fire, extinguishing the fire might be as simple as shutting off the gas supply or electric to the equipment on the roof. To do this successfully, you need to know what is on the roof and where the shutoffs are. Fuel supplies and shutoffs may be on the roof or leading to the roof.
If the roof covering material is burning, it can be a challenge to extinguish. Fire can smolder and burn, running horizontally under the roof covering through the metal roof deck channels. A tactic that can be successful in this case is to cut a “fire break” on the insulation/membrane ahead of the fire down to the metal deck itself to prevent the fire from spreading farther laterally. You will be cutting asphalt, polyisocyanate, insulation board, membrane, or other roof covering material, so be sure you have a saw capable of doing that. You do not need to cut the metal deck itself. Pulling tools will then be needed to pull up the burning material so that it can be extinguished. Use a very small smoothbore nozzle tip (½ inch is a good choice) to discharge water into the space between the deck and the covering above to help break the adhesive and remove the burning membrane or insulation material.
Most roof fires will require getting water to the roof. The most obvious method is to stretch a hoseline from an engine company to the roof using a stairway or ladder. Larger buildings may have a roof standpipe with outlets on the roof or inside a stairway or space that leads to the roof. Firefighters need to know not only where these are but also how they are activated. Sometimes there is a valve at the standpipe itself; other times there may be an activation valve inside the building for the roof standpipe. Even if there is not a specific roof standpipe, there may be a regular standpipe in a stair tower that can be used to make a hose stretch to the roof. An additional means to get water to the roof would be using an aerial apparatus to function as a flying standpipe, connecting the attack line to the aerial tip at roof level.
Beware when working on these roofs of either visible or hidden translucent corrugated roof panels. There is a possibility that they were on the roof at some point and membrane or another covering is installed over the top of it but they still present a weak point for operations on the roof. The best way to know if they are there is to conduct building walkthroughs with facility personnel before a fire starts.
There are likely hundreds of thousands of buildings with this general roof construction type. There are also variations on this type, and it is quite likely that designers of construction materials are coming up with or have already come up with alternative construction methods that are both lighter in weight and less expensive to install than this common roof type. A fire on or involving one of these roofs will generate a great deal of attention because of the smoke it will generate. Tactical generalizations for firefighting on these roofs can be made based on the presumed roof type, but the only way you will understand how best to handle a fire on one of these roofs is if you are out looking at these buildings while they are being built, as well as during any building modifications/changes that occur during their lifetime. It is incumbent on you to make sure that this information is documented and shared with your colleagues, officers, and mutual-aid organizations.