Continued from page 94.

through-the-roof.” Your other choice on the foreground is to let the air get “sucked” into horizontal openings you make to complete the explosive triangle and have the vectors of force pound against building and firefighter. By opening the roof of a structure (or above the enclosure trapping the backdraft condition), you can choose where the explosive force that is going to happen will occur. The opening in the roof lets the gas and heat rush out to mingle with the air it needs. The triangle completed outside the building, the force vectors are just as strong but now go off relatively harmless into space as “fire

Smoke explosion. The fire building is opened and firefighters have entered and are operating an aggressive interior attack. Suddenly there is an explosive, flaming force in a cockloft or attic “blowing” ceiling material on firefighters below it, or the occurrence involves a remote (cold smoke) area. What is that? Is it forceful? Yes! But certainly not as forceful as a true backdraft. “Hey! Great pull,” one firefighter screams to his partner as one opening with a hook (or pike pole) blew down 200 square feet of lath and plaster ceiling material.

Hoselines are advancing from one street through an occupancy that is “L” shaped and has another facade on an intersecting street. The handlines are moving, extinguishing, and pushing fire and additional toxic and explosive vapor toward and through the connecting door. Outside, additional firefighters are forcing the roll-down doors enclosing the intersecting street front because of the direction of the handline attack at the rear of the fire. Suddenly an explosion blows the steel roll-down door assembly onto the forcible entry team, injuring seven firefighters. What was that?

Either before our entry or while we fight fire in the early stages, products of incomplete combustion are forced into enclosed areas—connected occupancies, between ceiling and roof space (or ceiling and floor above spaces), into refrigerated and other storage areas, or adjoining living spaces. It’s hot, but not hot enough. It has some air mix, but not enough. It’s explosive, but not as high into the upper explosive limits as the backdraft condition.

To ignite and explode, it needs a little more air (from the nozzle, the opening the hook makes, the first few feet a saw blade makes as it cuts the roof, the foot of a firefighter that cracks the flooring material above the trapped gases, or continuing supportive horizontal ventilation). It also may need “kickoff energy” that the rising lick of flame will give it, or the burning embers that the now-liberated gases can fall upon or rise to. It’s not classic. It’s not observable. It’s not recognizable. It is local as opposed to total building involvement. It occurs after ventilation operations and extinguishing commitment have been under way for some time. It is explosive. This is a smoke explosion, not a backdraft.

I’ve been jotting down these “random thoughts” of mine for many months now. I know that you have comments—I hear them from you in the field. Please take a few minutes and drop me a line on your thoughts about this or any other matter: Tom Brennan, P.O. Box 904, Sayville, NY 11782. I assure you that it won’t go unanswered! ■



What is backdraft? Is it the same as a smoke explosion? Why are we hearing so much about flashover today? What is rollover? Can we control these conditions?

“Backdraft/smoke explosion.” That’s how many fire service texts list or print these unique fireground phenomena. This implies that both occurrences are the same or that one occurrence has two names that are synonymous. Some books go so far as to define them as being the same.

Why would we give two actiondescriptive nouns to one phenomena? And, if they do describe the same thing, what do we call the explosive force that doesn’t fit into the classic description of backdraft?

Backdraft. Just what is backdraft? Our ability to describe it is surrounded mostly in myth. It happens, or could happen, or did happen —but not at the frequency that media, commercial entertainment, training films, and some training sessions would have us believe. Backdraft is a serious, structure-damaging explosion. As simple (or complex) as that. It is not inward and outward pufts of smoke and high heat. It is not a “whoosh” followed by a w all of heat, and it is not a local explosion in a remote room, enclosure, extension, or attic space that occurs after the firefighters have entered the structure and are engaged in fighting fire.

Firefighters, by and large, have “romanticized” backdraft into a “believed” common occurrence. It is like telling a story so often that soon you believe it yourself (an event that never happens in our job). Recently, I was in the company of a couple of firefighters—twoto three-year “veterans”—smart, cocky, and a couple of years away from the realization that they don’t know everything. My attempts to make friendly, brotherhood-type conversation were met with a macho “We, in our department, are the entire fire world. What could you possibly know?” attitude.

“Is your station very busy?” I asked in frustration.

“Why, last night I personally was in two backdralts,” was the jutted-jaw retort of one.

Out of patience, I said, “Oh, did the ambulance drop you guys off here?”

Funny? Sure. True? Unfortunately so.

A backdraft does not occur that often. It needs a structure tight enough and strong enough to contain fire and hold back sufficient oxygen until the fire process moves into its final stage. Explosive gases—carbon monoxide, mostly—are heated well above their ignition points, mushroom, and are pressurized. The gases are pushed into every nook and cranny of the structure. These combustion by-products creep out of every opening—brick joints, glass frames, shingle layers, and more. It’s hot inside — hotter than the real hell. Too hot for a human to survive—1,000° to 1,800°F and higher. The process needs only one additional thing—air. If the “fire” can get it through a horizontal opening, die rapid explosive force will * occur inside the structure and cause building elements to be subjected to severe concussion. The nowflaming gases explode out of the horizontal openings that you just made and that it itself is making.

A backdraft picks you up from w’here it catches you and tosses you, in pain, many feet into a location that you never thought you’d be that night. It is classic, defined, and, because of known observable signs, predictable—if you’re sharp.

Many think that this event is preventable—a myth! Backdraft condition, once formed, is not all that preventable. All other events on the fireground are. Therein lies the difference between backdraft and other , dangerous events during the firefight—smoke explosion, flashover, and rollover.

Continued on page 90.

No posts to display