Know Your Enemy #46

We continue with our pictorial discussion of trusses which started with Know Your Enemny #44, Previous units are archived.

We continue with hazards you might not be aware of In roof support systems. Steel Trusses can fail readily and kill firefighters.

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Photo By Frank Brannigan

Photo R299 - Unprotected steel trusses have long been used for clear spans in theaters, churches and halls. They are often hidden in the attic and may not be noticed on a routine inspection. The worst fire service truss disaster in our history occurred in Brocton MA in 1946 when 13 firefighters died when a fire in the balcony sneaked up the wall voids to the attic. We are now accustomed to finished masonry walls on the interior of buildings . In past years the grubby interior masonry was concealed by a lath and plaster wall on 2x4 studs providing a path for fire spread to the attic.

Photo R315 - Wakefield MA firefighters had preplanned that the building would be evacuated if fire reached the attic of a lodge hall which had typical steel trusses. They evacuated shortly before the roof collapsed with a 60 ft high burst of fire. Thanks to Chief Parr for the story and picture. Near misses are important training tools and infinitely better than fatality reports. Please send any such stories and pictures to Fbrannigan@comcast.net

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Photo By Frank Brannigan

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Photo By Frank Brannigan

Photo R303 - The light weight trusses were braced to the block wall. Fire elongated the brace and pushed down the gable just after firefighters had left the area below. How would you like to explain to a family that their loved one died in the collapse of a roof of a waste paper storage building? If possible cool the steel from a position outside the collapse zone, otherwise the building is doomed. In an unprotected steel building cooling the steel may be infinitely more important that putting the "wet stuff on the red stuff." There are still those who believe and teach the myth that cooling steel causes collapse See p 259-60 BCFS3 for the facts. I watched a Southwestern FD fight a hay fire in a metal storage shed, they concentrated on the fire. The result was a load of wet burned hay and a destroyed building.

Photo R304 - Four Wichita, KS firefighters died in the collapse of this bowstring steel truss on an automobile shop. Loads of heavy spare items on the bottom chord of the trusses was a significant factor. Cool exposed steel with heavy caliber streams from a safe location outside. The trusses are tied together for wind resistance so a collapse may cover a wide area. A second alarm was ordered as they turned out due to the heavy smoke column . I hope that you would accept that sign as a DOA (Defensive on arrival) fire in a light steel building.

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Photo By Frank Brannigan

We will continue our discussion of trusses in successive columns.

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