– 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?
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because they are not able to get to a safe distance to “shoot at the base” of the fire. so you do what you can from a safe distance. and the hose pressure isn’t high enough to have it point down and shoot at the base, so it needs to shoot up and take an elliptical trajectory.
Well by that point the fire has grown big and consumed most of the building. Fires burn and spread upward. So the aim is to try and prevent it from spreading further to upper floors and then putting it out below. If they were to focus on putting out the fire from the bottom to top floors then that won’t stop the fire from growing and traveling further upwards in the meantime.
Fire extinguishers and water used by firefighters are not the same.
Most fire extinguishers are ABC dry chem extinguishers. They have a chemical powder that disrupts the chemical reaction of burning. So disrupting the reaction needs to occur as close to the source of the fire as possible.
Firefighters use water. The water in liquid form hits whatever is burning absorbing its heat energy and converting to steam. Raining down water and getting coverage, even on things that aren’t burning, cools the material, creates steam, and absorbs energy. There is also the consideration that large streams of water have the force to penetrate burning material.
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”.
For the same reason that doctors don’t perform surgery with the rules for basic first-aid.
The idea behind a fire extinguisher isn’t to make sure everyone knows everything there is to know about how to professionally fight a fire. It’s something simple everyone could learn that will help with many minor problems.
Real firefighters, fighting a huge, out of control fire, are trained in all the specific things they should be doing in any given circumstance. That is way more than the sort of instructions that will fit on a label in large-print.
Airial units are there to suppress. This will generally happen when the threat of explosions are possible or the entire structure is compromised, thus risking life of a first responder. (Life before building & stop it spreading)
EDIT: Summary death in or close to buildings, use airial brigades.
On a side note the USA has a higher fatality rate for firefighters than most other countries. (Or so I was once told). Mainly due to the fact we try to save buildings other countries would have written off and just contained the burn.
Could also be types of structures (high rise vs single family, etc) or building materials or design, etc.
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