Thursday, April 16, 2009

My kind of firefighting

This week is all about pumps. Maybe that doesn't sound that exciting to you, but for me this is a great week. You see, most of the necessary skills for firefighting have to do with physical ability. You need strength to move a victim, balance to climb and work from a ladder, endurance to spend time working in the heat of a fire environment without collapsing. I'm not BAD at that kind of thing; in fact, I'm in pretty good shape. But working the pump on a firetruck is mostly about simple math and abstract thought -- yes!

For those who are not part of the fire service, you should know that using the pump on a firetruck is more than just turning it on and letting the water flow. There are at least 8 points from where an engine can be discharging water, and each one of them has to have their pressure adjusted properly for the task at hand. Let me give you a simple example:

For a house fire, you might have 2 lines deployed off of the truck, both 1 3/4 inches in diameter. One might be 150 feet long because it's going in through the front door, the other might be 200 feet long because it's being taken in through the side of the house. Each one needs water pressure of 100 PSI (pounds per square inch) at the nozzle, and they each are running 125 gallons per minute of water through the hose. How much pressure does the pump need to be discharging at?

Well, when you push water through a 50ft stick of 1 3/4 inch hose at 125 GPM, it loses 12 PSI. So if you are pumping 112 PSI, by the time it reaches the end of that 50 foot length, it's down to 100. The longer of the 2 hoses deployed off the truck is 200 feet, which is 4 50 foot lengths, so the pump will have to be discharging 148 PSI to make sure that the longer hose has enough pressure. However, the shorter hose (the 150 foot one) only needs 136 PSI to have 100 PSI at the nozzle, so you would have the pump discharging at 148 PSI, and gate the shorter hose down to 136.

Now, there are many more complicated scenarios than that when you get into having multiple hoses of different sizes at different flow rates, and when you start incorporating things like standpipes to raise water up to a higher story in a building, and managing the intake into the truck at the same time from the water supply operations. This is the kind of material a geek can really get into.

Moral of the story: don't go thinking that firefighters are just brute muscle, they need some brains to get things done as well.

1 comment:

  1. The pump operator is the most important person at a working fire and any mistake they make can be someones life at the end of the line. Screw up there and people notice...a lot of people.