The Metal Roof Tests

Every type of building construction poses challenges for ladder companies performing vertical ventilation. In this article, we take a closer look at Type 2 construction, specifically the metal roof, and determine how feasible it would be to vertically ventilate commercial-type structures with this type of roof. When conducting the research, we emphasized safety and efficiency, as well as the most common resources ladder companies have for vertical ventilation: chainsaws and circular saws.

Construction
In steel construction, columns hold up girders, which hold the joists that support the metal decking. The metal decking most often used in a commercial roof setting is “B-deck” and is corrugated for extra support and stiffens up the roof. The typical span between joists is in the area of four feet to eight feet, depending on the engineering of the structure’s roof. The walls in these buildings are made of tilt slab or masonry construction and usually don’t have many windows in them. Because Type 2 construction is consistent with newer buildings, most of these structures fall under modern building codes and possess sprinkler systems for fire protection. It’s also common to find skylights in these structures, and usually all the HVAC systems are on the roof surrounded by a parapet wall.

Hazards
Type 2 construction, also called non- or limited-combustible construction, usually has exposed steel members in the roof system. Where wood roofs require direct fire impingement to make structural members fail, steel roofs can fail with high heat alone and will collapse rapidly with little or no warning.

These structures are most often very large, have a big heat sink, and the fuel load can be massive. Most of the Type 2 construction we found was in larger commercial buildings, such as Walmart, The Home Depot, Lowes and structures that had a large fuel load inside. Although larger buildings may have roll-up doors in the rear, doors and windows can be scarce, and forcible exit will be a challenge in the event that a rapid escape is required.

To the Test
In our tests, we used the same “B-deck” found in commercial roofs, and we built the props using the same attachment methods normally used to attach the decking to the joists. The tests were broken into three main sections: cutting through just the metal decking, cutting through foam insulation, and cutting through both. Because most ladder companies carry both chainsaws and circular saws, we utilized these tools for all the tests, using both a steel blade and a multi-blade for the circular saw.

Metal Deck Test
During these tests, we stuck with the circular saws and tried both steel blades and multi-blades. When cutting through just the bare metal, both saws cut through the steel, but it was a slow process. The multi-blade cut through faster and seemed to keep a pretty sharp edge. Although the steel blade did the job, it wore out rather fast and would need to be switched out to make an adequate sized hole. Cutting against the corrugated portion of the roof took extra time, and it was more efficient to make the longer cuts going the same direction as the corrugation cutting. Although cutting the metal alone was not too difficult, it was extremely difficult to make the cuts while ensuring that the sawyers’ feet remained on structural members. The decking gets strength through the corrugation, so once that was cut through, the decking became very flimsy. Because we used circular saws, the reach was limited, forcing the sawyer to stay right on top of the saw during the operation.

Foam Insulation Test
The foam on these types of roofs is commonly applied in two ways–with foam placed directly on top of the metal deck with a thin membrane on top, or by covering the roof with plywood or gypsum, then placing the foam insulation and membrane over that (the less common method). Because foam is built up to create water run-off, foam depths can range from a few inches to a couple feet. When the circular saws were used to cut the foam, there were issues with being able to cut deep enough to penetrate all the foam. Even with the foam just “scored” with the saw, it was difficult to pull it up and expose the metal decking. After a few uses with both the metal and multi-blade, the foam heated up enough to create a gooey nightmare in the circular saws. The chainsaws cut better and did not create as much of a mess, but if the sawyer goes through the foam and into the metal, they can probably expect a thrown chain. When the foam was placed directly on the decking and filled the corrugation, it was very difficult to remove enough foam to expose enough metal to cut a decent sized hole. The method of placing foam over gypsum or plywood made removing sections of foam easier, but again, cutting/scoring through thick insulation while trying not to tap the chain on the metal roof made for a very inefficient process.

Deck & Foam Test  
The final test was to simulate a scenario where a ventilation foot hole needed to be cut. We went to several different local commercial structures of Type 2 construction to test our ability to effectively sound a roof. Due to the thick foam, it was next to impossible to feel any structural members, and all areas of the roof sounded hollow. A thermal imaging camera (TIC) was also used to visualize structural members, but nothing stood out. (Note: That outcome may be different if the building had fire in it and was heating up the metal.)

Back at the prop, we attempted to cut a 4′ x 8′ vent hole. Again, foam was the biggest challenge as it ate up a lot of precious time and made two of the saws inoperable. Even after the foam was removed, we only managed to cut a 3′ x 4′ hole, and the firefighters were fatigued. It was one of those operations that just didn’t flow and seemed like in a risk-versus-gain calculation, risk won out.

The Takeaway
If you throw enough time and resources at a roof operation, I am confident that a ladder company can open anything. That being said, firefighters are usually the casualties in commercial structure fires; typically, most of the people inside self-evacuate or the fire happens when the building is empty. So we need to ensure the safety of our personnel when considering our tactics.

As you begin a tactical approach on a metal roof, sounding is a huge concern; in our experience, sounding was largely ineffective, which imperils the ability to get your crew to the ventilation location safely. In wood roofs, smoke inspection holes can be easily placed and monitored for conditions underneath; on a Type 2 roof, there is really no way to tell what you and your crew are standing over.

In situations where fire sprinklers have been activated, you can expect cold smoke, and vertical ventilation probably won’t be effective. I have seen some metal roofs opened up by making 1′ x 1′ holes, but small holes in a commercial structure will not do much good for crews operating inside.

During a fire in one of these buildings, skylights are a great option for ventilation, but many of the structures we looked at didn’t have any, or had a sprinkler head directly under the skylight that makes the hole useless. Natural ventilation and/or positive pressure may be the best options for a working fire in these types of structures. If the structure has overhead doors, they can be opened to at least lift the smoke enough for a quick search.

From a tactical standpoint, if the fire is not extinguished quickly in this type of building, or it’s larger than the resources we have on scene, I would strongly recommend addressing life hazards, and then pull out of this building sooner rather than later.