Blog by Ed Hadfield
As firefighters, we are often faced with challenges out of our control. When tasked with vertical ventilation, we must deal with the roof assemblage we are dealt with. In the case of the metal deck roof, (also known as Robertson decking, or Q-decking) specific challenges are thrust upon the ventilation group. Obviously, if we had the opportunity to completely pre-plan all of the occupancies we might face in a commercial structure fire, we would have some prior knowledge of the roof assembly. But we don’t, so we must be prepared to react to the circumstances we encounter.
In most cases, once the ventilation group identifies the roof assembly is a metal-decked roof, a number of actions must occur for the mission to be safe and successful. The first item would be to indicate to command and interior operations that the structure has a metal deck roof assembly. This is important for all personnel operating within the structure due to the potential of a catastrophic collapse as the heat generated from the fire weakens the roof assembly, and support structures. The second key factor is to identify to all interior companies where specific heavy machinery on the roof may be located. This additional load may be critical in firefighter safety and survival.
Heavy Machinery Poses a Hazard to Interior Crews
The ventilation group supervisor may want to readily identify natural, or man-made ventilation points, such as skylights, and other openings that may assist in the ventilation of the structure without the need for actual cutting of ventilation openings in the roof. Of course this would be incident driven, and based upon the need, and amount of ventilation required to accomplish the task.
Cutting an Inspection Hole Four Feet from an Exterior Wall
Of course the ventilation group may not know the roof assembly is metal decked until we place an inspection cut into the roof itself. The inspection cut is the single most critical element to the vertical ventilation operation on a commercial or industrial occupancy. It will give the ventilation group five key elements in the vertical ventilation operation:
1. Roof covering
2. Roof decking
3. Rafter or truss type and direction
4. Conditions immediately underneath the ventilation group at that moment
5. Determines the operations of the ventilation group
Once the inspection cut is placed into the roof assembly the formal process begins to take action. In the case of the metal deck roof, a number of critical factors come into play. The first is the ability of the ventilation group to be successful in performing vertical ventilation on this type of roof assembly. The metal deck roof offers certain specific hazards and inhibitors to the ventilation group. The first is the ability to successfully open the roof up with the equipment on hand.
In most West Coast Fire Departments, the chainsaw, with a 20-inch bar and carbide tipped chain is the tool of choice for vertical ventilation operations. Although the advent of the newer Terminator and Raptor type chains has increased performance in this area, they still provided limited ability to be successful in the vertical ventilation operation on the metal deck roof. The primary problem occurs when firefighters run the chain into the metal trusses that support the metal deck roof.
Generally, no matter how experienced and careful the firefighter may be, the inability to feel the truss until it is too late causes the loss of multiple teeth on the chain, and in many cases causes the chain to be thrown from the bar itself, thus rendering the saw useless.
Utilization of a Rotary Saw with a Metal Cutting Blade
It is important for the ventilation group supervisor to acquire a minimum of two rotary saws immediately for the operation to be successful. As stated, most west coast fire departments don’t normally take rotary saws to the roof. This lends itself again to the need to spot your apparatus close to the occupancy so it doesn’t delay the operations longer than necessary. If the ventilation group is staffed well enough to send a runner back to the truck company to acquire the rotary saws, this would allow the ventilation group to possible begin ventilation operations on skylights, or other man made ventilation openings.
Pulling the Plug with a Rubbish Hook
As stated, the chainsaw is not the tool of choice in most cases. However, often times it is needed to skin the roof covering to expose the metal decking itself.
The best method of removing the top roof covering is to simply cut ventilation plugs the area or size of the ventilation hole the ventilation group wishes to accomplish. To accomplish this task utilize the chainsaw and make a plug cut the area or size of the ventilation opening.
If needed, the plug can be diced into smaller portions to make it more manageable for the pullers to handle. Be careful not to allow the chainsaw to sink into the metal decking, as this might cause the chain to be thrown, and thus rendered useless for further operations.
The goal is to simply skin the roof covering in an effort to expose the metal decking. Once the plug has been established, the best method of opening up the metal deck roof is with the use of rotary saws utilizing either a metal cutting blade, or for greater use the multi-cut or DAX type of blade. The use of the multi-cut blade offers longer duration of operations, without the repeated needed for changing blades.
Working Toward Your Means of Egress
When performing the cutting operations, always work back toward your means of egress. The ventilation group supervisor or Company Officer should remain in an EYES-UP position. This simply means the company officer should refrain from becoming actively involved in the ventilation cutting operations if at all possible. Of course this will be dictated by the staffing levels of the company.
If it is necessary for the officer to become involved in cutting operations he/she should limit the amount of cuts necessary to accomplish the task and then return to the EYES-UP position. This size and location of the ventilation opening is incident driven and specific to the location, and volume of fire within the structure.
A good rule of thumb is to operate in an area nearest to the fire without being directly over the involved area. It is important to note that heat will affect the structural stability of the roof assembly, and operation over the involved area may place the ventilation group in extreme danger.
The goal is to increase visibility and tenability by reducing the rapid build-up and spread of fire within the location. This can safely be accomplished from an area not directly involved in fire activity.
Teamwork and communication with interior crews is essential, and important for overall fire ground safety and survivability. As for the amount of ventilating required, this is incident specific. A good rule of thumb is to communicate with interior crew on their ability to suppress the fire and make headway on the assault. Also, heavy pressurization from a ventilation hole, or fire self-venting is generally an indication of inadequate ventilation, and further ventilation needs to occur.
The key items to remember when faced with metal deck occupancy are:
>> Vertical ventilation on metal deck roofs requires addition equipment in the form of rotary saws, and often multiple blades.
>> Vertical ventilation operations on metal deck roofs do not follow the same type of cut procedures as conventional and light weight engineered structures.
>> Vertical ventilation operations on metal deck roofs take greater time to accomplish. So plan wisely.
>> Natural and man-made openings should be the first choice in vertical ventilation openings.
>> Communications with the interior crew is essential for safe and efficient operations.
>> Preplanning of commercial and industrial occupancies is the best way to lessen the surprise of the metal deck roof on structure fires.
About the Author
Ed Hadfield has more than 26 years of fire service experience after rising through the ranks from firefighter to division chief. He is a frequent speaker on leadership, sharing his experiences within the fire service and also with corporate and civic leaders throughout the United States. For more on Hadfield, please check online at www.firetowntrainingspecialist.com.