The “When”, Understanding What Happens
During fire growth, the products of combustion in today’s fire environment create “bad” air at a rapid rate. That bad air (CO, Hydrogen Cyanide, CO2 and Carbon) replaces the needed “good” air (Oxygen enriched) that the fire uses. Two things must happen for the fire to continue to grow. First, more good air must be introduced and second the bad air must be moved (vented) or consumed (Flashover/Smoke Explosion).
A number of events out of our control can and do occur to maintain the “balance” needed by the fire to allow the growth to continue. The occupants leave a door open into the fire compartment/structure or the heat and/or pressure breaks a window(s).
When these events happen the fire growth is allowed and the heat (BTU’s) increase. As the fire grows it uses more O2 and produces more of the other crap, consuming more contents and more structure. In order to keep it simple (KISS method), we won’t get to into all the dynamics but you should have the picture.
After we (the fire service) arrives, if any of the above listed has not occurred it soon will! What is the first thing most of us do in order to initiate an interior aggressive fire attack?
We force the front door or other entry way to the involved area!
You my friend have just created the first VENT point. Is this the best “tactical” vent point? Really doesn’t matter because we always do it, so let’s just go with it. Now the heat and bad air move toward and out of the top of our vent point and fresh cool air rushes in at the bottom.
Fire growth now has the needed elements to happen and sometimes at a rapid pace. As we move into the structure, unless we have created another or additional vent points, things tend to get nasty. The point of all this is that; we as firefighters must make considerations to venting opposite the attack crew before they or anyone else gets “jacked” up.
Creating the opposite vent point from the attack crew is essential to our survival. It should be accomplished before we enter the fire compartment.
It also should be at least 2/3rd the size of the initial opening to be fully effective. The reason I emphasis this method, it saves use from getting caught in the rapid fire growth most of the time. In our business there are NO absolutes or guarantees!
There are a number of videos available online for your viewing/learning pleasure. The best are ones show conditions prior to our arrival and what happens when we arrive.
As we go through this learning curve, I hope to give you a full understanding of the need for Tactical Ventilation not hap hazard ventilation. In the next segment we will go deeper into the “when” to vent process. Until then be safe my brother!