MFA #4 - The New Rules: 1. Water Flow is Good 2. Air Flow is Bad

Simplistic as these statements are, most of the recommended tactical changes that have resulted from the fire dynamics research are ultimately related to those two general findings.  They summarize the reality of the effects of our primary fire control tactics.  Certainly, the implementation of these “rules” will be situation-specific and in no way as cut and dried as such a short list suggests, but they do represent the themes, so to speak, of how the approach to structure fire control is being modified.  Below, under each of these general categories, I have created a more specific and practical list of some key “reversals of opinion” related to these topics that the fire service is now trying to get its collective head around.

Water Flow is Good

Traditional North American firefighting theory held that water application from the exterior of a structure is appropriate only as a defensive strategy as it can push fire into uninvolved areas, injure occupants with steam, and has no benefit on interior areas beyond the reach of a hose stream.  The (false) corollaries of this myth are that the best way to extinguish fire is from the interior, and the quickest way to aid victims is to search the building.  I was one of a generation of incident commanders who would direct hoselines to the "unburned side" of a structure in order to prevent extension, even if it required stretching to the far side of the building and penetrating locked doors.  I earned my AIA (Aggressive Interior Attack) credentials on hoselines in the smoke-filled hallways of many a fire where flames were also showing on the exterior from a window or door.  Our department has routinely deployed search teams before hoselines were in place, even though all of our apparatus are equipped with pumps and water tanks.  Finally, we denigrated fire companies that frequently utilized external streams, labelling them "outstanding firefighters" because they were "out standing in the front yard".

In fact, researchers were never successful in "pushing fire", even when they attempted to do so by spraying water into a fire-involved room that had an exhaust vent behind.  (Products of combustion can be pushed by a hose stream set at fog pattern - although things actually are not so much “pushed” as generally churned up - but a solid or straight stream, which is recommended, causes no such effect.)  While we all know that water turns to steam and expands when it is applied to a fire, the experiments instead demonstrated that, in a compartment fire, decreasing temperatures resulting from the absorption of heat lead to a contraction of the gases, not an expansion.  Still, even steam at 212 degrees F/100 C, is an improvement on flashover temperatures, which are over 1100 F/600 C, and temperatures continue to drop as more water is introduced.  Finally, applying sufficient water (180 g.p.m. flows through smooth bore nozzles were used, but never for more than 60 seconds, and often less) into an involved room, or even the exhaust flow path, caused a significant drop in temperatures throughout the communicating areas of the building.  That included adjacent rooms and those of the floor above - every space that wasn’t separated by a closed door.

Bottom line: everything gets better when water is applied to a fire (i.e., cooling throughout the structure and immediate decrease in heat production), with no downside (i.e., no increased danger to occupants or extension of fire to uninvolved areas).  It follows, then, that the fastest route for application of water should be utilized.  When possible, first applying water from the building exterior is the quickest, and therefore most effective, approach.  In situations where an initial exterior attack is not an option because the fire compartment is out of reach of hose streams, as in a windowless building or on a higher story, water still should be applied as soon as fire, or even only heated fuel (i.e., smoke), is encountered, to immediately begin the heat reduction process. 

Air Flow is Bad:

Conventional fire tactics include the performance of ventilation, horizontal and/or vertical, passive and/or active, in order to remove products of combustion (heat, smoke).  The expected increase in visibility and decrease in heat in the involved structure was intended to facilitate locating and reaching the fire, as well as to improve the survivability of any victims present.  Standard teaching was that this should be performed just prior to the application of water, as it was recognized that ventilation increased fire intensity.  The practiced sequence was to rapidly stretch a hose line just as the windows and/or roof were opened, reaching the seat of the fire in time to benefit from the smoke and heat lifting.  Firefighters in my department are adept at opening roofs, and often need to be constrained from accomplishing it before hoselines are in place.  Anyone who has witnessed the effects of ventilation cannot help but be impressed by the amount of fire that can come out of a roof vent, seemingly decreasing the energy, and therefore the hazard, within the structure. 

What was not appreciated, and the fire dynamics research demonstrated, was that ventilation increases a fire's heat and smoke production faster than it can be released through the new exhaust paths.  Making larger openings merely results in larger fires.  The smoke and flames we saw coming out of vented roofs or windows were being pushed out by more of the same, the bad stuff essentially overflowing versus being emptied.  This deterioration occurred with any ventilation increase, even that resulting from just opening a door to enter the structure.  Further, the worsening interior conditions (higher temperatures, toxic gas production) that were found to result from ventilation would lead to a decrease in survivability of any victims within the structure.   The reverse was also demonstrated, in that closing an intake and/or exhaust opening - stopping how air enters or exits the burning structure - lead to a decrease in interior temperatures.   (Ventilation remains a viable tactic for removing smoke, just not for fire control, a topic for future discussion.)

The other key finding about air flow, actually first demonstrated through LODD investigations, is how deadly it can be to persons caught within its exhaust - the route the products of combustion take as they exit the building.  Identifying flow paths allows us to avoid that danger, even if we can't always control it, though such maneuvers as leaving entry doors open only enough to allow a hose line to pass through, and immediately closing bedroom doors when performing Vent-Enter-Isolate-Search (VEIS), are effective ways to minimize this danger.

A combination of these rules were applied to recommendations for controlling basement fires: the interior cellar stairs were identified as a flow path in such situations, and best avoided by firefighters.  Initiating water flow from the exterior, either through a window or below-grade door to the exterior, controlled basement fires quickly, then allowing entry by firefighters for complete extinguishment to be more safely performed.

Fire dynamics-based tactical revisions are much more complex and nuanced than just these two rules, and I’m not suggesting otherwise.  On the other hand, firefighters must accept these basic scientific facts before they can progress to a more comprehensive understanding of Modern Fire Attack methods.

MJC