Kitchen Table Debriefs - Hostile Fire Events (Part II)
Edward M. Raposo
When I left off in PART 1, I was talking about two things to do if you suspect that a flashover hostile event may occur. (Someone pointed out that there is actually a third thing to do: Put the fire out! It took several minutes before the urge to smack him in the back of the head passed.) The two things that you can do are: vent and cool.
If you are in the fire room early, before the massive buildup of heat and smoke, then horizontal ventilation may be useful. If the fire room is already charged with smoke and becoming superheated, you would want to either perform vertical ventilation, or no ventilation at all (closing the doors and windows in the fire room) until a hoseline can be stretched. The rationale behind not venting is to create an oxygen-depleted environment so the fire is oxygen starved. This slows the burning process (doesn’t stop it, though) and thus, reduces heat buildup. Of course, it must be determined that there are no victims or firefighters left in the room!
Unfortunately, if you are seeing indications of a flashover (intense heat pushing you to the floor; thick, black, rolling/boiling smoke; vent-point ignition also called rollover), and if you haven’t vented yet, it is probably too late to vent. Cooling the fire is still an option.
If you are on a search-and-rescue team, and unescorted by a hose team, then get your can-man busy! (If you are doing search-and-rescue without a hose team, and you don’t even have an extinguisher with you… what are you thinking?!) This is probably the last opportunity for the extinguisher to be of any use to you, though, if the building is about to flash, or close to flashing. By the way, the can-man should be holding a water-type extinguisher (the silver one!), not dry-chemical.
If you have a hose or hose team with you, some of you may be fans of multi-setting fog nozzles. In Europe, the Swedish Fire Departments have been researching the flashover phenomenon for many years and have given the rest of us some practical techniques for combating/delaying this killer. The Swedes have adopted a narrow fog in short bursts. Aimed at the hottest layer near the top of the compartment, they swear by this technique (discussed in detail in PART I). In my opinion, it depends on just how hot it is. As the temperature climbs over 1000’F (538’C), … and beyond, short bursts from a fog pattern may vaporize before they reach the upper layers, where you need them. A more substantial burst from a solid bore nozzle or a straight stream may be better suited. You also want to be careful of how much steam you actually produce!
We learned in the academy (or in NFPA 1001 Firefighter Level I) that the water to steam ratio is 1::1700. In other words, one cubic foot of water converts to 1700 cubic feet of steam, HOWEVER, that is at 212’F (100’C). The ratio expands as the temperature goes up. At 500’F (260’C) the ratio is 1::2400 and at 1000’F (538’C) it is close to 1::4000.
The backlash of steam application obviously needs to be considered. The average house size in the US is between 3750 and 13500 cubic feet per floor. Opening a fog nozzle for one minute into a room that is 1000 degrees F (538’C) will produce enough steam to fill the whole floor level with steam several times over (42,800 cubic feet of steam).
Survivability of victims must be considered. Better stated, there are no longer survivability considerations for victims. At these temperatures, survival is not an option. Consideration must also be made for interior crews. Any one on the fire floor, not just the fire room, will be saturated in a steam bath almost instantaneously. Steam is very unforgiving of loose straps and covers. Any exposed skin becomes painfully scorched.
Fog streams are very useful to us; don’t get me wrong. In an indirect attack from outside the fire room or even from the exterior, through a window, fog and steam are useful tools in moderation. I am not against the use of fog nozzles; I am against the use of fog nozzles without the calculation of risk/benefit being made.