There’s been a lot of discussion of late about which pump is better and offers more value for the money. Determining the size of the pump you should buy can be boiled down to a few questions that, if answered honestly, will determine the correct size – no magic, no egos involved and, most importantly, no money wasted.
First, the most important question: Is there a need for a specific minimum pump rating to comply with any specific regulation? Those might include a recent Insurance Services Office (ISO) or state fire marshal’s inspection, which has identified a need for an additional pump rating.
Other reasons to specify minimum pump size include buying an apparatus to comply with USDA forestry category or an apparatus for airport use to meet standards set forth by National Fire Protection Association (NFPA) 414, International Civil Aviation Organization and Federal Aviation Administration (FAA) standards and meeting NFPA 1901 and 1906 standards.
Sometimes departments must specify minimum pump ratings to meet agreed upon mutual aid tanker shuttle standards and also to replace existing apparatus that is part of the ISO pump capacity ratings.
Whether your department needs to meet a specific minimum pump size due to regulations or not, the next step will be to look at the fire loads. This includes specific supply and relay activities needed to cover fire loads.
Checking The Charts
To answer this question, departments need to identify the type of apparatus that is needed, the type of apparatus that will be dispatched with it, the mutual aid apparatus available and the specific jobs the apparatus will be required to perform.
Fire load is normally based on a building’s square footage divided by three. For example, a 1,000 square foot house needs a fire flow of 333 gpm and a 3,000 square foot house needs 999why not 1,000 gpm fire flow and so on.
A petroleum fuel spill fire is also based on the square foot area of the pool of fuel, or the area of the containment space. Charts normally supplied by foam manufacturers then determine the fire flow rate. The chart will help determine the application rate and the proportions of foam and water to extinguish the fire.
Once a fire department has identified its largest and most potentially hazardous fire load, it then needs to determine the kind of apparatus needed to effectively handle a fire at that location.
Looking At Assignments
Let’s say a community’s biggest homes are in the 5,000-square-foot range, and it has only a few small stores that are no bigger. Given those parameters, an attack pumper with a 1,750 gpm pump would make a lot of sense.
If a department needs a rig that will handle auto accidents and grass fires, a 750 gpm pump would be ideal. That figure is based on the fact that at least 125 gpm is needed, plus a back up line. For forestry, a flow rate of 150 gpm at 250 psi is needed to supply a Type 3 forestry apparatus.
With that same vehicle, firefighters could fight a fire at a small summer home of 1,000 square feet. For an interior attack house fire, it’s common to have a minimum of two lines and a flow rate of at least 300 gpm. Therefore, the 750 gpm pump would be required for state rating.
For apparatus with an assignment to fill other apparatus for a mutual aid tanker shuttle system – requiring a minimum of 300 gpm, with all tankers having a direct fill capable of handling at least 500 gpm – a 500 gpm pump will fill this role nicely.
Planning For Growth
For the department in the market for a ladder tower with a 2,000 gpm waterway and twin monitors, depending on some variables, a 1,500 gpm mid-ship pump will do the job, provided the community has a water system with the lowest residual hydrant pressure of 45 psi and all flowing 2,000 gpm or more. To get the 1,500 gpm pump to work adequately might require a little trickery the pump supplier should be able to explain.
Communities also need to plan for future population growth, especially if the trend is people moving into rural areas from metropolitan areas. Those communities should brace for a boom in homes of 5,000 square feet. They should also plan for shopping malls and box stores to quickly follow.
If the department that finds itself faced with that kind of development has the staffing to respond to fires with several apparatus, the question will center on whether the department will continue to have the necessary personnel to sustain that approach. In the future, the department may find it needs to respond with fewer apparatus and in that situation each apparatus will need to have a bigger pump.
Taking those variables into consideration will help determine the minimum size pump the department should purchase. But, the formula isn’t that simple, taking into account reality and practicality.
Reality is, every department I have encountered in my 36 years in the fire service wants to do the job and make things happen. Their efforts are often thwarted, however, by lack of personnel, lack of sufficient water supply, limiting hose size, limiting engine size and the list goes on and on. Add in lack of training, experience and leadership, and the situation deteriorates even further, but those are not equipment related and we don’t need to get into that discussion here.
Let’s look a little closer at engine horsepower as a factor in performance. It wasn’t that long ago that engines were the common limiting factors for many fire truck pumping applications. A reasonably priced commercial chassis 25 years ago had only a 210 horsepower engine with 600 foot pounds of torque. That was enough for a 1,000 gpm pump and no more.
Today, we commonly have 300 to 330 horsepower engines in apparatus developing 800 to 1,000 foot pounds of torque, which will drive a 1,500-to-1,750 gpm pump effortlessly.
Moving up to a 2,000 gpm, or more, size pump necessitates a jump up to the more expensive chassis. Fortunately, the percentage of the jump up is less than it was 25 years ago, but sufficient power to drive the selected pump is still needed. That decision is nearly always based on funds available for the apparatus.
Yet another limiting factor is the transmission pto. Since the early 1990s, apparatus manufacturers have had access to bigger transmission ptos which can drive the pump. Historically, splitting of the main driveline set up was common. Today, the engine might have sufficient power to handle a big pump, but the next question is will the pto handle it, and which one should be used.
Engines and Transmissions
No currently available pto will supply full engine power to the pump, unless the engine is very small and the transmission is oversized – an occurrence that just doesn’t happen in the marketplace. For that scenario to happen, a department would have to specify a 210 horsepower engine producing 520 foot pounds of torque mated to an Allison 3000EVS transmission. That setup would be close to handling full engine power. Reality is, however, a 210 horsepower engine would normally be mated to an Allison 2000 transmission that has a small pto opening limited to 500 gpm.
Along with the power limitations, there are also limits on operating lives on the pto based on duty loads and cycles. Specifying ptos for pumps is complicated, and it’s best to seek guidance from the pump manufacturers when comparing pto power and life limits.
Unfortunately transmission manufacturers, and even many chassis manufacturers, just don’t seem to understand fire pump requirements adequately and what it takes to drive a pump over the life of the apparatus. Most people in the fire service have a difficult time grasping this reality. Keep in mind our industry is very small by the standards of Allison, Detroit Diesel, Ford and International. The North American market for school buses alone is about five times larger than the fire service’s North American market for total usage of chassis with a gross vehicle weight rating (GVWR) over 20,000 pounds.
Still another very real limiting factor in pump specification is water supply. To help determine pump size, it’s important to consider what the community’s hydrant system will provide. If the biggest mains will only provide 1,000 gpm and there are no other mains to tap, then you might only need a 1,000 gpm pump.
If there are no open bodies of water from which to draft, a 1,500 gpm pump wouldn’t make any sense either. Nor would it be advisable to get a big pump if all the fire flow water would be supplied by a tanker shuttle. A shuttle seldom supplies big water.
Departments that draft from dry hydrants, open bodies of water, or off bridges should buy a 1,500 gpm pump, provided they have the supply hose available to deliver the big flows of 800 gpm or more. Big pumps at less than rated flows generate more maximum vacuum at impeller eyes.
Size Of The Hose
This extra vacuum permits drafting of water from a higher lift of a longer hose lay, up to as much as 70 to 80 feet to the water source.
Some departments face the reality of having only the water they bring available for fire fighting. There, the limiting factor on pump flow is the tank to pump line. A 3-inch line there will deliver 500 to 700 gpm, while a 4-inch line will deliver 700 to 1,100 gpm. The exact flow will depend on the pump model, plumbing and valve design. A good goal to aim for is a 4-inch line delivering 1,000 gpm.
Departments with commercial properties, apartments, big box stores and shopping malls, that also have good hydrant systems, should specify 1,500 gpm pumps just for the master stream capabilities.
Access to water in distance and the size of your supply hose will also play a role in the water supply side of the argument. During a relay, the number of inline apparatus and the size of the hose will determine the water available at the fire. In that scenario, flows in most practical cases are 1,000 to 1,200 gpm. To do better than that, departments will need to plan out the relay and actually try the relay before an actual fire. Some departments have spent time and money and launched big training efforts to successfully achieve big water flows.
Although it might not be as obvious, staffing can be a limiting factor in the size of the pump required. If an apparatus has a monitor, or an elevated waterway, achieving big flows with one or two people is possible.
A grass fire, auto fire or trash container fire may be manageable with three personnel, but launching an interior attack at a structure fire is a completely different story.
In that case, the “two in, two out” rule goes into effect, requiring a minimum of four firefighters. The hose size and nozzle design will limit how much water each person at the nozzle can deliver to the fire.
To deliver 300 gpm on an interior fire, with only two lines, will require straight bore tips and personnel who are very strong and well trained. Even then, you might fall short of being able to sustain that flow. Remember, there needs to be a back up line for each attack line deployed. The only bit of good news in this scenario is we normally see a room or two involved, needing a fire flow of 60 to 95 gpm. It’s critical for the incident commander to be proficient at flow requirement size-up.
Adding personal monitors to your apparatus will increase maximum flow per person considerably, usually up to 500 gpm with on person to deploy it.
Many departments can achieve big flows using Class A pumpers or aerials with monitor operations where staffing is not a limiting factor when considering pump size. Using monitors you may not save the building, but you may save the block.
Staffing may also be limiting when considering pump sizes for rescue pumpers, mini pumpers, tankers, initial attack apparatus, auto incident apparatus, or even wildland trucks. If there are only three people assigned to work fires with these units, and no monitors are available, a 300 gpm pump may be all you can use.
It takes a lot of hard work to determine true pump needs based on analysis of regulatory requirements and realistic limitations. When all is said and done, there will always come a judgment time where departments will need to make the decision of buying a bigger or smaller pump.
It doesn’t make sense to buy a 1,250 gpm pump when the state fire marshal told you to buy a 1,750 gpm and the fire load calculations show a 1,750 gpm fire flow requirement and you are already planning buy a 330 hp engine anyway. Even if you have limited staffing, remember you can always use a monitor. In reality you may only be saving $2,000 to $3,000 anyway.
You may be able to save more money with the insurance rates than you would by skimping on the pump And then, there’s always the chance of the really big fire hitting, and you’ll be faced with the reality of justifying a small savings on a pump versus the huge fire loss. Even if the fire was unstoppable with a bigger pump, you still should have been able to meet the accepted fire flow requirements of the regulatory agency.
If saving money governs your decision making, a better way of doing so is to eliminate every last trim item, decoration, chrome plating and gadgets and put it toward it the pump. To do otherwise might be very challenging to explain to the community. When making purchasing decisions, saving money as the primary reason to buy, or not to buy, can be dangerous. Buying something because it’s what you honesty need – bigger or smaller – is a lot easier to defend.
Generally speaking, pump manufactures do not charge extra for a higher gpm rating when the pump itself doesn’t materially change. All three U.S. manufactures follow a similar path and pricing is a competitive situation.
Common Product Sizes
Some common product sizes I have used as example are as follows: a pto pump is available in ratings of 300 to 500 gpm and the selling price does not change from 300 to 500 gpm ratings; a big body midship pump is available in ratings of 1,000 to 2,000 gpm with no change in the price for the pump itself; small body midship pumps are available in ratings from 750 to 1,250 gpm with no change in price for the pump itself.
That means if a department is buying a midship pump and requires only a 1,000 gpm rating, but it has the power and water to supply a 1,250 gpm pump, it should without hesitation. The only thing you need is enough outlets. In the real world, most small bodied pumps are 1,250 gpm. Very few have 1,000 gpm ratings.
My advice is if you can buy a bigger pump at no, or very little cost, and you already have the engine to power it, do it. Typically going up to 1,250 gpm means adding one 2.5-inch discharge as the only additional cost.
Bigger pumps typically wear less than overworked smaller pumps, and that alone can justify the extra cost.
And, going up to a 1,500 gpm or larger rating, the only consideration is adding a second drafting line during yearly service testing.
Next time you need to specify a pump, keep in mind the key questions, answer them honestly and it will become obvious exactly what pump is right for your department and your budget.
Editor’s Note: Gary Handwerk has been involved with the fire service industry for 36 years working for various fire apparatus or fire pump manufacturers. He is currently global pump product manager for Hale Products and has been a member of the National Fire Protection Association (NFPA) Fire Apparatus Standards Committee for 15 years.