LIGHTWEIGHT STEEL TRUSSES (bar joists) ROOFS
Steel trusses can elongate and push on supporting walls, which can collapse. If the wall resists failure the truss will buckle. At higher temperatures they start to soften and fail.
If supporting a tar and gravel roof on corrugated steel sheets, they can develop heavy fire under the roof from gases coming from the tar above. This is called a Combustible Metal Deck roof (COMB).
Heavy streams directed from a safe location onto the underside of the roof can cool tar and cut off gas. Overhead streams on the roof are useless. A tower ladder or squirt can be used to provide a stream through a doorway. Keep the bucket clear of a possible front wall or cornice collapse.
It is unsafe and useless to attempt to ventilate manually. Keep personnel off and out from under the roof.
Twenty St. Paul, Minnesota firefighters were evacuated from a strip mall store because of high heat and smoke, 60 seconds before the COMD roof collapsed. Reference BCFS3, pp. 302-9. And, Firehouse Magazine, Feb. 2002, "Combustible metal Deck Roofs", by Brannigan.
There are not many literature references because this problem is not recognized and heat is ascribed to "gases from contents", or, as an "attic fire". Take the tower ladder out and systematically look down on the roofs for flat roofs. Then determine if the covering is a "Built Up Roof".
With the help of son Christopher who is a Power Point whiz, I am developing a Power Point presentation for this serious hazard, which I discovered in 1946, for instructors.
AN IMPORTANT CORRECTION
BCFS3 p. 447 states 537 BTU is generated for each cubic foot of oxygen delivered to the fire. I learned this years ago and have no idea of its origin or accuracy. A competent authority has informed me that the word delivered is incorrect. It should be, consumed, by the fire.
The point of course is that there is a direct relationship between heat produced and oxygen available to the fire.
However, this is the sort of obscure item beloved by exam writers. I wrote BCFS3 to help firefighters survive in a most hostile environment, not as an exam text.
I did not write a "Study Guide" because I feel that everything in the text is important to somebody somewhere. A promotion exam is designed to rank candidates, and multiple "guess" questions are quick and easy to correct.
Their serious defect in this life safety subject is that one answer must be provably wrong in court, but give a strong appearance of being correct. At a 2 a.m. fire, the wrong answer may be the one which flashes up on the officers mental compute screen, with possible fatal results for the officer and his crew.
After the test the training officer, at the very least, should make every effort to expunge the wrong answers from the consciousness of those who took the test. In today's litigious society failure to do so may be regarded as serious negligence.
To those who say, "I read your book when I studied for promotion, and not since", I urge you to dust it off. Keep it handy and read a page or two daily. You never know when some bit of information will help to get the job done or save a life, possibly your own.
In my own case, one bit of information had been on my hard drive for several years. In another, I got the information on Wednesday and used it to good advantage on Friday.
Would you like your doctor to brag that he had never read a book after leaving school because his experience was enough?
THE BUILDING IS YOUR ENEMY. KNOW YOUR ENEMY
