By Mark van der Feyst
Last month we focused on ventilating a structure by removing the windows and some of the considerations that need to be assessed before any windows are taken out. Taking out a window is a popular and consistent practice by most fire departments. Another consistent practice is vertical ventilation, although its popularity is slowly dying out, perhaps because of incidents in which firefighters fall through the roofs while trying to ventilate.
This occurrence has been happening far too often, and critics have raised the question of our need to be on the roof. There are many videos showing tests being conducted on different types of roof materials and the time it takes for them to fail under load. The City of Phoenix (AZ) Fire Department conducted some of these tests along with NIOSH showing two firefighters (test mannequins) standing on a roof with the structure on fire below it. It did not take very long before roof failure occurred, and the test mannequins fell through. The time varied depending upon the type of roof material being tested. If you conduct a search on YouTube, you will find many videos demonstrating the quick failure rate of lightweight trusses.
The roofing materials being used in modern building construction are designed to be lightweight for the construction industry and span greater distances for the building owner. Although technology allows us to have these advantages for building purposes, it is a great disadvantage for the fire service. The lightweight material being used is failing much quicker than did previous construction materials. A common time frame established for failure of a lightweight truss is between 5 and 15 minutes under fire conditions–not much time for fire departments to operate within to cut a hole for vertical ventilation.
Vertical ventilation is a quick method for the removal of hot gases and smoke from the upper portions of a structure. Seeing as heat rises naturally, all our smoke and hot gases will be travelling to the highest point within the structure as it starts to mushroom back down. By alleviating the smoke and hot gases through a vertical opening, we are allowing for the increase in visibility and decrease in temperatures inside the structure, the prevention of horizontal fire spread, and relieving public hallways and stairways of smoke.
To aid in quick ventilation, use existing openings found on roof tops. Common openings found on roof tops are skylights, scuttle hatches, HVAC equipment, stairway doors that exit to the roof, and vertical vent pipes. All these items are a good start to opening up the building for smoke and hot gas removal.
Cutting a hole in the roof is the best way to accommodate the need for quick ventilation. Sometimes a series of holes is needed to ventilate effectively. Before we go the roof to cut our hole, we need to consider a few items;
- Where is the fire located?
- Cut our hole directly above the fire as possible.
- How big is the fire?
- We may need to cut more than one hole.
- What operations are underway right now and where are they located?
- We do not want to be interfering with any interior or exterior operations.
- Is the fire already breaching the roof?
- If we see visible flames breaching through the roof, it will not be structurally viable to support our weight and will fail very soon.
The common tools that we use to cut a vertical opening are a combination of hand tools and power tools. Under our hand tool category, we have the ax, both pickhead and flathead, the haligan tool, pike poles, roof hook, sledgehammer, and any other combination hand tool such as the TNT five-in-one tool. Our power tools are going to be either a rotary power saw or a chain saw, both gasoline-powered tools that require clean air to operate, as it mixes with the fuel for internal combustion.
A drawback to the power tools is that if there is too much smoke exiting the structure, the power tool will not work properly and will sometimes stall. It is always a good practice to bring up to the roof both hand tools and a power tool. The hand tools will serve as a backup to the power tool.
Another item that firefighters need to consider is the roof ladder. The roof ladder is designed to allow for the weight of a firefighter to be dissipated along the roof. A roof ladder will only work if the top portion with the hooks is at the top of the roof ridge and the butt end of the ladder is hanging over the edge of the eave of the roof. These two points of contact ensure that the roof ladder is supported on the most structural portions of the roof. If a roof ladder is shorter than the roof span, it will still be useful but will not be as effective as it will not be supported structurally. A roof ladder is not always a requirement for conducting vertical ventilation. It will depend upon the conditions presented and the type of roof you’re dealing with.
Working on a roof ladder to make your cut can be a difficult and awkward task. Overreaching to make your cuts will make the job much more difficult. In photo 1, we can see a firefighter starting to make their initial cut with the saw and they are fully extended out with their arms. There is nothing wrong with stepping off the roof ladder to aid you in making your cuts. If the roof is not safe to be on in the first place, then you should not be up there to begin with. As long as you sound the roof with your hand tool or with your foot and it sounds structurally strong, step off the roof ladder.
When making multiple holes in the roof, moving the roof ladder into position every time from one spot to the next may not be convenient. The roof ladder may be too short to span the roof and therefore would only be window dressing for the operation. In photo 2, the span of the roof is too long for any roof ladder to be used. Here the firefighters need to rely upon the size up of the conditions, the “sounding” of the roof, and reports from the interior crews as to how the fire is progressing to ensure that it is still safe to be there.
Mark van der Feyst has been in the fire service since 1999 and is a full-time firefighter in Ontario, Canada. He is an international instructor teaching in Canada, the United States, and India, and at FDIC. He is a local level suppression instructor for the Pennsylvania State Fire Academy and an instructor for the Justice Institute of British Columbia. He is also the lead author of Residential Fire Rescue (Pennwell).
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