Metal Deck Roofs...
Metal Deck Roofs: Do you have an operation?
The WCO recently had the pleasure of running the boys up in Kent Ohio through our flat roof operations for corrugated metal deck with significant layers of "built up" roof covering. Looks like the boys are off and running! See attached video. Strong work by a very hard working, dedicated group of Firefighters! Special thanks to G. Lane, Jeff Diedrich, Dave Moore, and Jeff Schupe for the hospitality and accommodations.
Let's get into it...
Points to consider when operating on flat roofs & opening up Metal Deck:
Rule #1: We travel at RIGHT ANGLES !! This is our operation for both walkable pitch & flat roofs. We do not "bee-line" to the center of the roof to begin the ventilation operation. This is done for several reasons all resulting in an increased level of safety for the roof team. Staying near the load bearing walls as we travel puts us in the most advantageous and sound area of the roof in the event a collapse were to occur. The roof team also gets a good view of the top floor window conditions, victims, etc. while traveling this line...
Rule #2: Perform Inspection Cuts: As shown in the video, we perform inspection cuts on every flat roof we ascend to. In general, although not always 100% accurate due to add ons and age of roof, this does a pretty damn good job of undressing the roof decking, roof system including direction of travel and height of truss (critical in pre-engineered), thickness of covering and the fire condition within the truss loft. We've found tremendous success using these diagnosing cuts to exposeand recon the system below our feet prior to committing into the involved area.
"Checker boarding": We've found great success in removing thick, built up, layers of roof covering by creating a"checkerboard" layout of cuts through the various layers of underlayment. This exposed area should be larger than your ventilation opening will be. There are many styles of cuts. We perform this style to make the sections more manageable when pulling or "J-Hooking" them out of the area. This may seem like it adds time to the evolution but in the end you'll see that you're taking time to make time and your firefighters will be less fatigued as this is only the first step to the openng of these roofs.
When cutting corrugated metal deck roofs remember that the corrugation runs the opposite direction as the trusses that support it. This will be identified by removing the covering when performing the inspection or "plug" cut.
When cutting begins on metal corrugated deck, try to refrain from running the rotary saw blade into the deeper, press or crease of the corrugation. Keep the blade up on the flat sections. This will ensure you've cut all the way through due to the shallowness of the rotary saw blade. If you end up down into the valley of the press the cut can get squirly, causing flex on the blade, and may restrict the rotary saw blade from cutting completely through the metal due to the blades shallowness.
If using the Stihl 460 Rescue chainsaw with the RDR (Rapid Duro Rescue) blade like the one in the video, the only considerations are to get rid of the depth gauge entirely so maximum depth can be achieved and when cutting "against construction" keep the saws chain away from the steel open web trusses. This will prevent the chain from "throwing". This is one advantage over the Stihl 460 chainsaws that the rotary saw blades have. This video is yet another example of how dominant these Stihl 460 Chainsaws are and how durable the new design of the Stihl RDR chain is.
The above video demonstrates several important techniques and observations. Notice that the saw operator (Not a Sawyer.. This is not the logging or wildland industry...) performs a full inspection cut through the ballast rock, butly covering, poly-iso foam and finally the metal deck. A whole is made large enough to insert his arm and grab the steel open web truss.
Carpet knves or exacto blades come in very handy when dealing with ballast rock. Cutting an pulling will make overcoming this obstacle much more manageable. You do not want to leave rock of this size in the way. It wont really stop your ability to cut but it will begin to fall into holes potentially dropping large, heavy amounts of rock onto interior firefighters as well as simply displacing large amounts of weight from the area over the fire.
Notice the "checkerboarding" of the underlayment. 2 saws working in unison cutting against each other will speed this process up. Give each other some room.
Always remeber when deciding how large to make the hole that yes, bigger is better but you havent done anything for the relief of interior companies and truss loft assessment until you get the roof opened and ceiling punched in. It is often more beneficial and very simple to get an inital louver completed and then expand upon it until sufficiently large enough or the the roof in that area becomes untenable.
The peformance of the Stihl 460 is quite impressive throughout the cutting of this metal deck roof... Well done lads!!
Some info on Corrugated Metal Deck roofs: Corrugated roofs and walls come generally in 18 to 22 gauge thicknesses which equates to roughly 1.2 to 1.6 mm of thickness. This is not at all thick and in fact a well maintained, sharp axe blade can cut right through it. Just ask Diedrich... Why the corrugation? Strength. Imagine taking a piece of unpressed, noncorrugated sheet metal and laying it across steel trusses at 4' on center. It would not resist load very well and our weight would generate considerable sag in between the trusses. The corrugation is created to add load bearing strength to the decking. The span of the Steel open web trusses (Steel Bar Joist) will either be at 4' o.c. or 8' o.c for corrugated metal decks. The depth of the corrugation determines which on-center distance is used much the same way the thickness of OSB or Plywood determines the on-center spacing of the trussed roof system that supports it.
The metal deck is fairly easy to remove once cut due to spaced out tack welds that run along the top chord of the truss. Make 4 cuts, smack and pull the piece out of your way. On 4' "centers", perform a simple louver much the same way we would on a wood deck, plywood roof. Perform your head cut "against construction" rolling the truss and stopping at the next one felt. Then your outside "dice" or "down" cuts just to the inside of each perimeter truss. Make these cuts sufficiently long and then make your fourth bottom cut, rolling the center truss again and intersecting the two outside cuts. ON these types of roofs with truss spans at 8' o.c., try to work off of them. Working off the perimeter trusses at 8' o.c. spans will increase the likelihood of capturing sound roof as you open larger sections of this roof. It may also behoove your operation to leave one corner connected much the same way we cut paneled, residential garage doors to prevent them from collapsing on us as we cut downward. The connected corner will keep the piece from falling into the structure and potentially injuring interior firefighters. Once all 4 sides are cut, smack the cut the section in the hopes of breaking the welds and pull it up and out of the opening. Then spin it to and on the remaining connected corner and lay it down on the roof...
Communicate with the hose team to "COOL THE OVERHEAD". Make no mistake, this will not be a fast operation. It is critical that the roof company communicates what type of roof system they encounter when it is out of the norm for the area and also when the opening will be delayed based off the roof decking encountered and size of the interior layout = large commercial warehouse.
Remember that this decking is not very thick at all and significant fire will heat and weaken the decking rapidly once the fire enters the truss loft. Yes, these truss lofts are of a non or limited combustion make up but fire gas ignition in a smoke charged loft from a living space fire below will be more than sufficient to heat and weaken the metal decking. Furthermore, steel truss elongation is a very real thing! Do not take it lightly.
4' o.c. is more than enough space for a firefighter to fall through. Once the metal deck has been exposed, it will be fairly easy to sound the decking and locate the trusses.
Lastly, many firefighters are turned off from roof operations for a myriad of reasons. The most common reason heard is that it takes too long. Well it most certainly will take long and lack effectiveness if the company performing the operation does not posses the right equipment and understand how these roofs are put together. Metal deck roof operations are a 2 saw minimum operation. 1 Rotary saw of sufficient power and proper blade: 960 on up with aluminum oxide or any other type of metal cutting blade and a Stihl 460 magnum chainsaw with the RDR chain for the thicker covering and eventually to help out the rotary saw with the decking. For more information on the spec's of this chain saw shoot us a message.