Saturday, April 25, 2009

Water Supply for the layman

Without water, it's going to be pretty hard to knock down a fire; that's why you need so many more people to fight a fire than just the few people running into the building with hoses. Where does all that water come from?

Well, you might say, the fire engine of course! That's where the hoses are coming from, so that's where the water is. Great job, you'd make an excellent detective! But consider this: each one of our fire engines contains 750 gallons of water. That sounds like a lot, but it actually won't last as long as you thing. One regular hand line (a hose carried into a building) is usually configured to spray 125 gallons per minute. That's about 6 minutes of water for 1 hose; that's not that long, and it's not likely that you're fighting a large fire with just one hose. On anything larger than a regular room-and-contents fire, you're going to need a little more than that 750 gallons showing up in the first engine.

That's one of the reasons you send more than 1 fire engine to a fire: you need to be getting your water somewhere, and the engine pumping water into the house (the "attack" engine) doesn't have time to find out where the best place to get water is. So the next engine to show up (the "supply" engine) hooks up a large supply hose to the intake of the 1st engine and sends all the water in it's tank shooting into the tank of the attack engine. Alright, now you have about 1500 gallons of water, that's pretty good. Except you might have 3 hoses being used by this point, so you could possibly be using somewhere around 500 gallons a minute. In fact, some of the larger deck guns can shoot up to 1000 gallons per minute just by themselves. If you have a hydrant around, that's super, and in most metro areas you do. A good hydrant can flow over 1500 gallons every minute by itself, which is pretty good. However, not all hydrants have that level of pressure, and if you're in a more rural area you may not have a hydrant near enough to hook the supply engine into. Now what?

Here's where the well-oiled machine of teamwork comes into play, and it's a pretty impressive operation when it's running smoothly. Picture this:

The attack engine is pumping water onto the house as fast as it can. The supply engine is sending every drop it has available into the tank of the attack engine. By the supply engine are 2 large "fold-a-tanks", big steel frames with tarps inside of them that basically form a small pool that can hold over 2000 gallons of water. The supply engine has a suction hose dipped into the nearest tank and is sucking water in from it, but how is the water getting into the fold-a-tank?

From the tankers. Tankers are big firetrucks who's main job is to shuttle large amounts of water from one place to another. Each one (on our department) holds about 1500 gallons of water, and can dump it all into one of these tanks in about 30 seconds. So you get 2-3 of these tankers that are driving a circuit to the nearest hydrant or other water source: Fill up the truck, drive to the supply engine, dumpt the water, drive back to the water source. As long your water source doesn't go dry and your trucks don't break down, you can now put water on the fire all day if you need to. It's a marvel to watch when it goes right and this system is clicking like an oversized bucket brigade.

So you see, the heros running into the building are depending upon a large team on the outside to keep them in action. Pretty cool, huh?

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