Stupid question--but why do fire fighters vent the roof when a building is on fire?

Question

There has to be more to it than just letting the smoke escape.

And doesn't letting the air in just fuel a fire?

Is it to let the heat out in hopes the building doesn't explode?

Answer 1

The firefight is going to go into the building.

Before he goes in, they put a hole in the roof so that once air comes in, the fire and smoke and heat goi=es out the roof.

If they didnt, once the fire ate up all the oxygen, it would lie in wait until fresh air came in when the firefighter entered, and it would almost literally explode with new flames and heat.(so to speak) (AKA "Backdraft)

Answer 2

It has somehting to do with insurance claim. The bigger the hole the bigger the claim, my dad is an adjuster and he told me this years ago. Hope it helps, made me feel better.

Answer 3

Not a stupid question. It's called vertical ventilation. It's performed simultaneously with fire attack. With vertical ventilation, the hole, usually 4 foot by 4 foot, is cut directly above the fire. The smoke, heat and unburned gases will seek the path of least resistance which is up. They will evacuate the compartment through the hole.

This does several things. It helps to prevent backdrafts and flashovers. I clears the compartment of smoke and heat, and makes it easier to extinguish the fire. Ventilation is a practiced technique. If not done properly, it can spread the fire and even hurt or kill firefighters.

Yes, it does introduce fresh oxygen into the compartment as the fresh air entrains into the plume, but, with it being performed at the same time as the fire attack, ventilation helps limit the fire to just one compartment or room and limits the amount of damage.

Answer 4

It's to prevent backdraft.

Answer 5

Venting the roof allows heat and smoke to exit the building.  At the same time, fresh air is brought into the building at lower openings (Doors, broken windows).  By venting you can avoid back drafts (a very hot, oxygen starved compartment full of combustion gasses is suddenly given the last thing needed for combustion - oxygen - and rapid combustion occurs - EXPLOSION) and flash overs (burning room suddenly reaches a temperature that allows the majority of the material to release vapors and ignite - not an explosion but a sudden engulfing of fire) by changing the conditions in the compartments.  Yes, fresh oxygen will help the fire burn, but more importantly you make the conditions safer and more conducive for the Firefighters to safely and effectively extinguish the fire.

Peter D:  If the fan in the doorway is positioned to blow INTO the building, it is called positive pressure venting.  It can be dangerous if you do not have a clear and controlled path of ventilation.  If it blows OUT of the building, it is negative pressure ventilation (the same concept as cutting a hole in the roof, but under forced conditions).

Answer 6

because heat rises.

when a went is created the heat will rise and make it less intense so that the firefighters can work with less probability to burn their lungs (breathing in hot air) or their actual body. it also helps to  prevent passing out from heat exhaustion.

basically it helps to make the building a little cooler by providing a venting system.

Answer 7

I don't know the answer, but I saw a show once where they placed a very high powered fan in the door of a house that was on fire to suck all of the air and smoke out.  The hypothesis was it would make the fire even worse.  To their surprise, not only was it easier to see, but it also made the fire spread more slowly.  I don't recall their explanation of this.

Answer 8

You're right, but getting the smoke out is a calculated risk--you can't fight blind, and smoke kills more firefighters (and people) than fire does!