A little bit of fire science for ya. I will always be a student of my profession and never take for granted that I know it all. This video allows me to explain just what exactly is going on inside a structure that is on fire and when there is an aggressive interior attack occurring. I have had people ask me why do we go inside to put out a fire when we can just “shoot the water from the outside into the windows”. The reason why is because you can not search for or find and rescue any victims from the outside and you can not effectively put the fire out. The logical order to a fire attack is to Locate, Confine,Extinguish the fire. If you aim a stream through a window you are not confining the fire but rather pushing it into uninvolved areas. It’s sloppy and unprofessional and ultimately very dangerous to anyone trapped inside.
At about the 1:30 mark you will see flames going over the top of the firefighters. This is called Roll Over. At this point in a fire there is a natural phenomena called thermal layering that occurs. As the fire burns , the products of combustion, smoke and gases , are located at the ceiling level of the room while the firefighters are crouched low in the safer cooler air near the floor. As they watch the flames roll over their heads they are seeing the super heated gas and carbon monoxide laden smoke being burned off.
It looks cool to watch but this is a temporary state and this rollover is a signal to the firefighters that the fire is burning its way toward the next stage. What happens is all of the contents of the room are beginning to heat up and those heated items, furniture, walls and anything else start to feedback the heat into the room thus making the temperature increase more rapidly. At some point if the firefighters do not open up the nozzle and cool the room down, the smoke will begin to bank down to the floor and everything being heated in the room will reach ignition temperature. When this happens the fire has reached the flash over stage. The flash over stage of a fire is where the whole room ignites in flame and it is not survivable , even by firefighters.
When firefighters open up the line they will cool the superheated gases but they will also disturb the thermal layering. The water is turned to steam and along with it the hot gases get pushed down onto the firefighters. If the nozzle man doesn’t understand this and keeps the line open for too long the steam can burn the firefighters because the wetness has a way of penetrating the protective turnout gear they are wearing. So to prevent this from happening the firefighters use controlled bursts that are directed at the ceiling and at the object(s) that are on fire.
Also it is hoped that this is a well coordinated fire attack and a crew of firefighters have begun ventilation of the fire room. When a firefighter on the outside is told to take out the window this firefighter has to time it accordingly. If he or she takes the window too early (before the interior attack team has water and is in place) the addition of fresh air can cause the room to flash over too early thus taking away any chances of finding any living victims. If the outside vent firefighter breaks the window too late the steam that banks down along with smoke and gases will also kill any victims. But a well timed vent will produce stellar results in knocking down the fire and pushing the dangerous products of combustion and steam out the window and allow rescue crews to grab the victim and deliver them to EMS for medical aid.
What does all this mean to someone who is not a firefighter? It means that you can also understand the way fire works inside a structure and use your knowledge the same way we do. If you can stay low and not panic (I know, easier said than done) then you can find your way out of the fire room and shut the door behind you. You just confined the fire !
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