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MFA Tools and Rules: Put the Wet Stuff on the HOT Stuff

"Don't spray water on smoke" has been uttered as a dismissive command from generations of instructors, officers, and senior firefighters attempting to stop what was viewed as a useless action, and to instead encourage progress to reach and extinguish the seat of a fire.  A result of the fire service's movement from using almost exclusively exterior streams to the currently-standard interior attack (an evolution that has been ongoing for the past 50 years or so, and which, by the way, required coincident improvements in PPE, SCBA, hoselines, and training), it reinforced the rapid entry mindset that was thought to be required for that strategy.  We now know that strict adherence to that rule can lead to firefighter injuries or death.

Modern furnishings and finishes burn much more rapidly than their predecessors, and can deplete the available oxygen for combustion just a few minutes after ignition, creating a "vent-limited" fire.  In this state, the process of combustion becomes inefficient and incomplete, with the still-significant heat causing the continued conversion of solid fuels to their gaseous states, but lacking the third leg of the fire triangle required for the production of flame.  When attacking such fires, the smoke that comes out to meet us is a hot and rich mix seeking a breath of air in order to complete its transition to "the red stuff".  Waiting for that process to resume before intervening can allow anything, or anyone, within that environment to be consumed.

In order to prevent the ignition of the heated fuel swirling above and around interior fire crews, it must be cooled, and the former cardinal sin of spraying water into smoke is the only method for accomplishing that temperature reduction.  Using a Thermal Imaging Camera (TIC) can indicate the presence of heated fuel overhead, but just injecting a brief water stream and listening for the sound - sizzle or splat - is a pretty clear indicator of the presence of sufficient heat for ignition.  Of course, not all smoke needs to be cooled (the old rule wasn’t all wrong), but just that which is already heated, and to which crews are in close proximity.  The impressive fireball produced when ventilating an attic fire is an example of hot smoke that suddenly ignites, and, whether a follower of modern methods or not, it’s still a bad idea to spray water into it.  Alternatively, trying to cool the lazy smoke emanating from a distant or newly extinguished fire has no benefit.  The new rule, then, might read: “Don’t spray water on some smoke”.

So, once again, MFA principles have made fireground decision making a little more difficult.  I attempted to counter this additional complexity via this post’s title, using a variation of that intentional oversimplification of the process of fire extinguishment: "Put the wet stuff on the red stuff".  While that slogan is less of a "rule" and more of a "Firefighting for Dummies" guideline, our current knowledge has informed us that this light-hearted saying perpetuates a dangerous oversight.  In order to better protect ourselves and anyone else, we need to expand and refine our water flow target to anything hot enough to ignite.

MJC

The author can be reached at markjcotter@comcast.net

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