Fire engine pump activation en route?

Factual Questions
1

Why can’t fire engines activate the pumping apparatus on the way to a confirmed fire? They have to wait until they arrive, then the driver/engineer gets out to start the pumps that charge the lines. This can cause a brief delay with firefighters standing at the ready with a hose and waiting for the pumps to ramp up and pressurize the hoses.

If they had the pumps running already and used the onboard water supply until hooked to a hydrant, wouldn’t that eliminate the delay for a pressurized hose? And couldn’t the first due engine apply water from a deck gun immediately as it rolls up? If I recall correctly, that’s how airport crash trucks work, with the pumps already running as the truck runs to the crash site.

Fire departments strive for even marginal increases in response times, so I’m sure there must be a mechanical reason this isn’t practical. I’m asking what that is.

2

The engine that operates the fire pump is the same engine that moves the truck. The engineer has to line up the power to the pump, if the pump was connected continuously to the truck engine it would be dead heading on the way to the fire taking power from the truck. Also with the pump dead heading, no water flowing through the pump. the pump would be damaged. Also a tanker truck will have a limited amount of water on it to handle small lines. A pumper truck will not carry water on the truck. Tanker trucks are common in the country but few pumpers. Pumpers need a source of water. Pumper trucks are common in cities but no so in the country.

When the engine gets to the fire while other firemen are hooking up lines to to the truck the engineer begins to line up the truck manifold. The officer in charge will have told him how many and the size of the lines to be run and what pressure he wants at the nozzles. When the truck has water the engineer will engage the pump and bring it up to desired pressure. And as water begin to flow through open hoses he will have to make adjustments to keep the pressure up. If the truck has a nozzle someone will also climb up to the stand and aim the nozzle at the fire. The stand is designed for the truck to be stationary.

Airport fire trucks are a completely different animal. 1 they are LARGE tanker trucks, no hydrants along side the runways. Many times they have more than one nozzle and they are controller from inside the truck. IN fact the nozzle man and the engineer both stay inside the truck.

In summation fire trucks on the street normally do not carry water on the truck, and if they do it is only a small amount enough for a 1 inch line not a 2.5 inch line. Airport fire truck are very large and very heavy not a good idea to drive on a city street.

3

Basically the OP is answered in the first reply, the engine that powers the truck also powers the pump. There is a power take off (PTO) where power can be routed to one or the other. We call it pump gear. However there are a rare few configurations which would allow what the OP asks, but no modern pumper would be able to do that.

But to correct the above a pumper certainly can and most do carry water. 500 gal in the city is common and 1500 to 2000 gal in the sticks (which ours are). What makes it a pumper is the gal/minute it can pump. IIRC it must be over 1500 or 2000 g/m to get the class A rating. As opposed to a tanker which is rated by the amount of water on board, and the ability to ‘dump it’. A pumper with the required amount of water on board and the ability to dump it is know as a pumper-tanker.

4

To further elaborate on the solid answers above…

A “regular” fire engine uses the same pump to drive and to pump. The engine drives the transmission, but instead of the transmission connecting directly to the rear end, there is an additional gearbox in between called a transfer case (not to be confused with a 4-wheel drive transfer case). The transfer case sends power either to the wheels or to the pump’s gearbox. There’s a selector in the cab, usually an air operated switch, that the driver engages the pump.

The whole process, from the driver’s standpoint is:

  • Stop the truck
  • Apply parking brake (usually an air brake)
  • Transmission to neutral
  • Move the pump selector to the middle, neutral position until the air stops hissing (about a second)
  • Move the pump selector to “pump”
  • Shift the transmission into drive
  • The speedometer will ramp up to 15-20 mph, even through you aren’t moving

It literally took you longer to read that than it does to engage the pump.

Once the pump is engaged, engine speed control how fast the pump turns, which changes your pressure (and volume based on pressure).

There are some pumps, very common on smaller fire engines but also in use on a traditional “standard” fire engine, that run off of a PTO output from the side of the transmission. Pierce’s PUC is one of the more highly marketed ones, as is one from Darley. Those will “pump and roll,” but the faster you drive the higher your pump pressure - you can’t change either independently of the other.

Deck guns have limited utility on most fires. If you can’t get water onto the fire, the fire doesn’t go out. Most building fires need to be put out with hoselines, as deck guns can’t go down hallways. They’re sometimes useful to darken things down before you go in, but if you’re using a deck gun for the whole fire you will also need an excavator - to put the building in a dumpster when you’re done.

Airport fire engines (ARFF vehicles) pump entirely differently from structural trucks. The mission of an ARFF vehicle is to be able to constantly reposition a turret flowing up to 1200 gpm of foam around a crash site. And do it with minimum staffing (minimum = 1). To accomplish that goal, there are two big differences - pump and water tank.

The water tank of a small ARFF vehicle is 1500 gallons (these have 4 wheels). The next size up is 3000 gallons (6 wheels) followed by 4500 gallons (8 wheels). The turrets flow 750 gpm on a 1500, 1200 gpm on the 3000s and 4500s. And they do it while driving. Off of tank water, not a hydrant. A regular fire engine can do 400, or maybe 500 gallons per minute off the water tank (and that tank is likely 500 to 1000 gallons total).

The drivetrain in an ARFF vehicle is odd. My career was on a brand built in Wisconsin, but the other two manufacturers have similar designs. The engine drives a power divider, which can selectively power two output shafts. One shaft goes to the transmission, the other to the pump gearbox. If you drive with the pump not engaged, the truck drives like any other vehicle, although the power divider is just allowing the engine to drive the transmission directly. When you engage the pump, the power divider splits which component gets the power, giving preference as required. The pump immediately starts turning, but only really kicks up when flowing a turret. When the truck senses water flowing, the engine goes to full rated rpm and the gas pedal acts “funny.” The first half of the pedal’s travel doesn’t make the truck move, rrslly nothing happens. Once you cross the halfway point, the power divider spools up and dumps a ton of power to the transmission, rocketing the truck off the line. You can tell a driver knows their stuff if they can feather that pedal position to smoothly start moving.

Engaging the pump in an ARFF vehcile is very simple. Drop the engine rpms to less than 1500 and push the “water” or “foam” switch on the dash. That’s it. Drive, neutral, reverse, doesn’t matter. Turning the pump off is the same, push the switch off (no rpm restriction for off).

Tactically, when you’re about 300 feet from the fire, you engage the pump and open your turret of choice. As said above, driving deadheads the pump, building up pressure that can break things.

Once a turret is flowing, pressure is controlled by a relief valve that dumps excess pressure back into the pump intake piping, not by varying pump speed.

The newest version of that manufacturer’s 4500 gallon truck has two engines that are coupled together, feeding a common power divider. The truck weighs something like 130,000 pounds, and has to meet the NFPA 414 acceleration time - 0 to 50 in 35 seconds. The newer Tier 4 engines don’t quite have the power of the older engines, so they did some engineering magic to make it all work. You can also engage the pump at any rpm with it.

Marvelous machines. And to think they actually paid me to drive them.

5

Fantastic answers from both of you. Thanks for such clear explanations.

KCB615, I’m curious if you ever experienced an airport crash that required the full response by your truck. Saw a video online once of an airport firefighter who had gone his entire career without working a crash, and then responded to a major airliner fire on his last shift, or maybe it was one of his last.

Also, what’s the turnaround time once you’re exhausted your water/foam supply? I’m guessing that by the time you go back to refill and return to the site, it’s not likely you’d be needed by then.

That’s a hell of a cool job to drive one of those for a living.

6

At one time (early 20th Century), there was a kind of fire truck called a chemical pumper. In a era where a hydrant might not exist at the fire location, and steam-powered pumpers took some time to ramp up to pressure, the chemical pumper was pretty innovative. On the way to the fire, a chemical reaction was induced in the enclosed tank, which built up pressure rapidly. By the time the truck pulled up to the fire, they could shoot the entire tank instantly instead of having to wait until the water boiled.

This innovation was short-lived. Some of the drawbacks were [ol][li]a small tank (80 gals), []no easy way to refill it, []the C0[sub]2[/sub] didn’t help put out the fire as much as they hoped, [*]the chemicals tended to erode the tank from the inside.[/ol] This scheme was superseded by motorized pumpers, which carried much larger tanks (150-750 gals), and could hook up to a hydrant, pond, cistern, or lake as well.[/li]
There is a short video about the history of firefighting in the 1800-1950 era in a small Wisconsin town. 13:20 starts the chemical pumper talk.

7

Made it through my career there without a large fuel fire caused by an aircraft crash. Not a ton of incidents that needed a turret. I did a study of 10 years’ worth of responses in our department, only 0.4% of our incidents “needed” a turret. Really, those trucks are only there for a once-in-a-lifetime incident. They’re the wrong tool for nearly everything else. As I said at a capital budget meeting, it’s like giving an electrician a sledge hammer and saying “use only this tool to do your job.” It will work for a couple things, but it’s wrong and dangerous the rest of the time. A “regular” structural fire engine is far more appropriate for 99.6% of our incidents. Most other ARFF departments I have trained, worked, conferenced, or shared beverages with - and that’s a very long list - have a similar experience.

I have had two fuel trucks on fire, and a lot of major fuel spills that I have used turrets for, though. And plenty of other fires where we used turrets because we had them and they’re easy - a shuttle bus, grass fires, a shed on fire, etc. Never had an aircraft on fire where we used turrets (four planes on fire where we used handlines, though).

Water supply is one of the two biggest challenges with aircraft firefighting. Manpower is the other. If you open your turret and just flow, you will be out of water in 2 minutes, give or take. Turrets have two switches to open the valves: an on/off toggle switch, and a momentary switch. I always told my guys that I’d whack their hand if they reached for the toggle switch. That’s a guaranteed way to waste your water. One of the best lines I was ever taught was “water that isn’t moving is wasted,” and there’s a lot of truth to that. Foam puts out a fuel fire instantly when it hits it, and it isn’t coming back for 3 to 10 minutes. If you move the turret and give the fire a few quick shots, you can put out a lot of fire with a surprisingly small amount of water. Shoot quick, reassess, and hit any remaining fire.

ARFF vehicles have to carry enough foam concentrate to make foam out of two tank fulls of water. Most have enough for four tanks full (if you didn’t get it out with 4 water tanks full, maybe it’s time to consider other careers). After you dump your first water tank, there are a few options for more water:

  • Drive to the closest fire hydrant and refill. Time at the hydrant just waiting for the tank to fill can be 4 to 10 minutes, plus your travel time there and back, plus time to hook the truck up, plus the time for the first truck there to dress and open the hydrant. Plan for an 8 to 15 minute round trip.

  • Get filled from a tank truck that followed you to the incident. The military uses this option. Usually the tanker holds 5000 gallons, so you can fill one to three trucks, depending on sizes. That’s quick, but the tanker is going to run out and have to refill. Plus that’s another body that the airport has to pay for (remember, manpower is a Big Problem).

  • Have your friendly neighbor lay a supply line from a hydrant to the incident. If you have a good amount of help on the way, this can be a good option. Takes about 8 minutes per 1000 feet of supply line to get set up, and assumes you can get to a hydrant.

Usually the water resupply ends up being a mix of the first two that can migrate into the third.

In theory, you should have the fire 90% out in one minute and 100% out in 2 minutes. It has never worked that way, but that’s the theory. The federal regulations (14 CFR 139.315, 317, and 319 if you need some light bedtime reading) are set up with that theory in mind. The FAA specifies how many trucks and how much water is needed, based on the length of the air carrier aircraft regularly scheduled into an airport. The quantities needed will frighten you - because they’re so low.

[Soapbox]
The ARFF industry is engineered firefighting. Most regular fire departments can brute force a solution, and have some time to make it work. Airport firefighting is highly tuned - and I mean razor thin, no room for error tuned - to one problem, to the exclusion of all others. If you don’t do it right the first time, there is no second chance. There is essentially zero redundancy or resiliency in a system that demands both to function properly. The big incidents in the past ten years - Asiana 214, the engine fires at O’Hare, Las Vegas, and Ft. Lauderdale, the B17 at Bradley - were remarkable in that they happened at well staffed, well equipped, and highly trained departments. Of the 550 or so air carrier airports in the US, there are about 40 that can really do some solid work right out of the gate. The rest, which includes my former department, are behind the 8-ball before the tones ever go off. [/soapbox]