Fatal Deception
SAN FRANCISCO, CALIF.
—
Heavy dark smoke,
pushing from doors, windows, cracks and crevices, sometimes
reversing itself, would signal the potential of a backdraft.
Although a backdraft is rare, the warning signs are etched into
every firefighter’s brain. We are taught that before making entry
into a structure exhibiting these signs, vertical ventilation must
take place.
Imagine
you arrive on the scene of a reported fire in this structure and
backdraft conditions are unmistakable. You, as the truck officer,
know exactly what to do. A quick survey of the building is
made and the masonry walls with composition shingle roof indicate
you are dealing with a Type- 3 building (ordinary construction). You
order your crew to the roof to “make an 8’ x 8’ opening then get
off.” Sadly, you may
have just sent your crew to their deaths. No question that all
outside appearance would indicate a Type- 3 building, where exterior
bearing walls are masonry and the roof system is of standard wood
construction (Photo 1). In actuality, the building is a Type- 2,
where the exterior bearing walls are masonry, but the roof system is
steel (Photo 2). The
building underwent renovation — its corrugated steel roof covered
with plywood then topped with composition shingles giving it the
illusion of ordinary construction. Furthermore, the corrugated steel
decking is supported by unprotected steel trusses with very little
mass. The rapid collapse potential of trusses, steel’s failure
temperature of 1000o F and the low mass of this roof
system is a prescription for disaster. Exacerbating the
problem is the fact there are no windows or doors other than the
steel roll- up type. What appear to be shutters over windows are in
reality nothing but a facade covering concrete blocks. The most
logical tactical option in this case would be to go with an indirect
attack, keeping off of the roof. Photos by Ted
Corporandy
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