– If fire extinguishers are supposed to be directed at the base of the fire, why do large fires often have firefighters on extended ladders shooting water from above?
In: 13
Former volunteer firefighter here.
You are indeed supposed to go for the source of the fire and rob the fire of one of the things it needs to keep burning (the fire triangle. Oxygen, heat, fuel). This also what you do when it’s possible, using smoke divers to go into the house, find the source and spray it down.
Now if it isn’t possible to go for the source the only option you have with a fire extinguisher is Get Out. Regardless of what your fire extinguisher is loaded with (Powder, foam, CO2) you have a very limited amount of it. Not enough to do anything about the fire indirectly.
Firefighters on the other hand have a massive tank of water (or water and foam agent) which will last for a few minutes and is enough for a minor fire or until you’ve connected yourself to the public water grid through a firehydrant. Once you have access to all those vast amounts of water (even a small hose can deliver hundreds of liters per minute) you can attack the fire indirectly.
The fire is still limited by Heat, Oxygen and Fuel. Water requires energy (heat) to become steam (lots of energy), so by spraying water over a fire (preferably through a fog nozzle*) you’re robbing it of the heat it needs to ignite stuff, stopping it from sending flaming sparks all over the neighbourhood that can ignite nearby stuff and you’re lowering the air temperature to provide an effective screen for the firefighters doing their work (20 minutes in gear is heavy but no biggie, 20 minutes in gear while being treated like a kebab by the nearby fire is super exhausting, because it’s like performing a workout inside a finnish sauna).
In the best case by spraying the roof you’re giving your smokedivers an opening to hit the core or you’re giving firefighters on the roof an opportunity to vent out volatile gasses. In the worst case scenario you GTFO because the building is about to explode**. If neither of these things is about to happen you’re still containing the fire or at least robbing it of energy.
P.S: Shooting it from a ladder high up in the air gives you more range (safer) and often gives you a better trajectory to hit areas that you need to cool down.
*fog is small water droplets. Small water droplets have larger surface area compared to the amount of water, so it’s more effective at robbing the fire of heat (by quickly becoming steam) while using less water and causing less water damage.
**Solid&liquid things generally do not burn themselves, but when heated they emit flammable gasses. These flammable gasses burn when they hit the right temperature. If they have the perfect mixture between Oxygen and Fuel they go Woosh! like a bomb, a super fast combustion called a flashover which generally blow out windows, can blast out doors or even blast out the entire building. A decent flashover will kill even a fireman in protective gear, through sheer pressure. But even if it doesn’t you go from “Parts of the building is on fire” to “everything is on fire”.
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