What Are the Trade-Offs When Specifying a Large Tank on a Pumper?
Considerations when specifying large booster tanks for pumpers are categorized as operational, physical, and immeasurable. They are interwoven, but not necessarily compatible, with each other. They can be affected by personal preferences and emotional decisions of apparatus purchasing committee (APC) members.
DETERMINE THE MISSION
The primary operational consideration when specifying a tank size is defining the pumper’s mission and the amount of water required to accomplish it. That in-house determination should be made prior to meeting with prospective vendors. Asking vendors for firematic advice on how much water a pumper should carry could generate responses favorable to individual product lines rather than realistic operational needs. After the mission and tank size are established, the committee can evaluate operational and physical trade-offs necessary to successfully complete the mission. Experienced vendors’ expertise is helpful when merging tank size with physical limitations such as wheelbase, turning radius, overall length, and overall height.
Physical considerations are measurable factors such as water weighing 8.34 pounds per gallon and a gallon occupying 231 cubic inches. They are constant values regardless of how much is carried or who builds the truck. A slide-in rear enclosure to store a particular ladder and pike pole complement requires an area 28 inches high by 14 inches wide by 144 inches long. Requiring accessibility from ground level creates a situation where multiple features (water and ladders) compete for the same space. Through-the-tank storage displaces 244 gallons of water. To maintain a tank capacity, possible trade-offs can be a longer wheelbase, a higher body, using a hydraulic ladder rack, or sliding the ladders alongside the tank and losing about 33 cubic feet of exterior high-side compartmentation.
Immeasurable concerns are unknowns not always considered beforehand. Trade-offs to accommodate a large tank are sometimes not realized until after delivery. The safe and expedient accessibility of hose and equipment is a major one. What looks good on a blueprint might not work well on the fireground. Another could be increasing a rig’s physical size to accommodate a large tank. Some drivers may be apprehensive about driving it. In the volunteer sector, they might refuse to. APCs don’t always seek the advice, wants, or needs of drivers. Mere black coats might not be given the opportunity to drive a demonstrator or similar sized vehicles. Determining a comfort level for drivers is an extremely important unknown. You tell the mayor the new half-million dollar pumper sits in the barn because the drivers will not drive it.
Any large liquid-carrying rig, baffled or not, may be difficult to maneuver and safely control during extreme weather conditions and, in particular, on challenging roadways. Vendors don’t like to demo new apparatus on back roads or during snowstorms and heavy rain.
REGULATIONS AND COMPLIANCE
Most APCs acknowledge that cab and chassis manufacturers will meet all Department of Transportation (DOT) rules and regulations. Many accept as gospel everything in National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus. When specifying a pumper with a large tank, some committees believe any rig meeting NFPA 1901 is acceptable, legal, and safe to operate. Use caution. NFPA 1901 is a nationwide minimum recommended standard. It does not evaluate or grade a rig’s performance in a given response area.
NFPA 1901’s rollover stability requirement requires apparatus to remain stable up to 26.5 degrees when physically tilted or calculated by a “computer.” It is a pass or fail test. A compliant pumper with a 1,500-gallon tank either passes or fails the same as a rig with a 500-gallon tank. Performancewise, the handling characteristics of a rig with 10,000 more pounds of water and tank material are going to be different. There is no guarantee a pumper with a large tank will perform exactly like one with a small tank. Negotiating narrow winding highways in the Adirondack mountains will be more challenging than driving on the flat plains in Nebraska. NFPA 1901 does not grade roadworthiness and handling characteristics on a 1-to-10 scale. It does say if the rig leans to one side more than 26.5 degrees, it’s likely going all the way over.
NFPA 1901 sentence 126.96.36.199 states, “When the fire apparatus is loaded to its estimated in-service weight, the front to rear weight distribution shall be within the limits set by the chassis manufacturer.” Good luck finding what that ratio is. I have not seen where an apparatus cab and chassis manufacturer has put that in writing. NFPA 1901’s appendix sentence A.188.8.131.52: “The distribution of the weight between the front wheels and the rear wheels should be a major consideration, because improper design will seriously affect the handling characteristics of the fire apparatus. Too little weight on the front wheels can cause a front-end skid and, on bumpy roads, can cause the front of the fire apparatus to veer from side to side. At the very least, it would be difficult to keep the fire apparatus under control. Too much weight on the front wheels reduces the traction of the rear wheels and can result in a rear-end skid or difficulty in traveling over unpaved roads or in mud.” I think the NFPA put those four sentences in the standard for a reason.
When a pumper, and especially one with a large tank, has to stay within defined wheelbase and overall length parameters, vendors are obligated to advise purchasers if a proposed rig is close to the maximum limits of both the individual gross vehicle axle ratings (GVARs) and the gross vehicle weight rating (GVWR). Those ratings are federally mandated DOT maximums that cannot be legally exceeded. Ask the vendor if the manufacturers of the axle, tire, rim, and suspension components have standards or recommendations for a maximum weight load intended to be carried 24/7/365. It could be significant. And, last but not least, is to weigh the total overall cost to carry the extra water—a trade-off the committee may have to justify to the bean counters in city hall. Good luck.
BILL ADAMS is a member of the Fire Apparatus & Emergency Equipment Editorial Advisory Board, a former fire apparatus salesman, and a past chief of the East Rochester (NY) Fire Department. He has 50 years of experience in the volunteer fire service.
Trade-Offs for Fire Departments When Specifying Large Tanks on Engines
How much water do you need to carry? This is usually one of the first questions that needs to be answered when working on the specifications of any new engine. This decision needs to be based on your response area, water supply issues, staffing, and response times. All these factors play into how much water your next engine should carry.
DETERMINING THE AMOUNT
The amount of water that is carried can make the price of the rig decrease, or it can make the number go up. And, that price can go up a lot depending on the amount of water you have determined to carry. That cost usually comes from the components that are required to handle the tank size and the weight of the water. So, evaluate whatever amount of water you believe is necessary and the cost associated with that number.
Response areas that require departments to carry a large amount of water to the scene must be thoroughly evaluated. The more water carried requires a larger apparatus, and that apparatus has to be able to negotiate the road system in your geographic area. Carefully consider how this rig is going to maneuver and handle on the roads while responding to the call, then how well that rig will be able to position once on the scene. Small driveways, small roads, road composition, and area to maneuver all have to be considered when determining the size of the rig.
With most manufacturers, water tanks do not need to fit the standard sizes, which were usually in 500-gallon increments. Today’s tank sizes can be custom-designed to achieve the amount of water you need, along with fitting into the body design that your department requires. So, do not be talked into the standard size if you have other operational requirements on your apparatus that require space.
With water comes the weight, and that weight requires the appropriate axle ratings and possibly additional axles to handle that weight. These all cost money, and careful consideration should be given to not just specifying the axle rating that will meet the weight of your vehicle but also for possible additional equipment weight being added over the life of the vehicle. Along with axle ratings and number of axles, consideration needs to be given to the ride quality of that rig. There are a number of different options regarding ride quality with a variety of springs and air bag suspensions. And, each of these options has a different ride feel when maneuvering on streets and roads that must be evaluated by the department.
With any amount of water, but especially with high water volume, ride stability is important to the driver’s ability to properly maintain control of the rig. So, ensuring driver comfort with the weight and drivability of the apparatus is something that has to be carefully considered for the safety of the rig in your response area. I highly suggest road tests in your area with the manufacturer of your rig with the same water weight and different suspensions to ensure your department is happy with the ride quality. Doing this work ahead of time may save your department the headache of having to fix a ride quality issue after delivery.
Braking systems need to be closely looked at to ensure that the rig has enough brake for emergency responses and that any additional auxiliary braking systems are added to the rig to assist in the braking process. Anything that you can add to make sure you have brake left when you need it the most is a good thing.
Water takes up space, and space has to be managed on any fire apparatus purchase. So, once again the department will need to make decisions. Those decisions will determine what equipment is going to be carried on the unit, how much hose, and what functions the rig will be required to perform on incidents. A rig that is designed to perform many different functions and designed to handle all hazards can sometimes be built to perform none of those functions very well. So, the design committee must be ready to make hard decisions when it comes to the functionality and ergonomic design of the rig, all the while meeting the requirements for the community and department. Regarding the water, the amount has been decided, and the balance of the rig must be engineered. So, this is where the customer and the manufacturer must work together with the apparatus engineers to figure out what will fit and work and what will not. This process will require any number of trade-offs and designs to ensure the proper functionality of the rig.
There are endless ergonomic designs that can be worked into any rig that carries a large amount of water. These options may require everyone to think outside the box a little bit, and at the end of the day, the unit may not fit the cookie-cutter mold. But as long as it can serve your community and response area, that is truly what matters.
With rigs that carry a larger amount of water, many times the hosebed can be very high and not firefighter-friendly to retrieve hose or deploy attack lines. But with the proper design, even while carrying a lot of water these hosebeds can be lowered. This will help with the deployment of hose and will require firefighters to be less of an acrobat when trying to get hose off. But, it requires the trade-off. We need to push that water somewhere else on the rig. This may require higher side sheets, pushing the water up higher toward the center of the rig, or extending the overall length—all which are acceptable, as long as the rig still meets the mission of the department.
With the additional water on these rigs, they can be classified as tenders or tankers depending on what part of the country you are from and how well you like the National Incident Management System. But, do not let those titles affect your rig’s design. Most tenders/tankers have dumps built into the tank to allow rapid water offload. These dumps have a dramatic effect on the body design of the apparatus. And, you and your department have to consider if these are important to your operation. In my opinion, having compartment space is important, and these dumps take away from that space. So how do we get the water off, if that is a function of your engine with lots of water? A couple of designs that we have recently seen is for one increasing the tank-to-pump valves to dual three-inch lines or a single large valve to the pump. We can then offload the water quickly through the pump with large-diameter hose discharges at the pump panels and possibly the rear. This trade-off saves the compartment room and achieves the same result, but with just some added time to fully offload as compared to the dumps.
Don’t stay with a standard design or thought process when purchasing engines with additional water. Think outside the box and push the engineering process to build a rig that works for your firefighters, your response area, and your water supply needs.
RICKY RILEY is the president of Traditions Training, LLC. He previously served as the operations chief for Clearwater (FL) Fire & Rescue and as a firefighter for Fairfax County (VA) Fire & Rescue. He also currently serves as a firefighter with the Kentland (MD) Volunteer Fire Department. He also is a member of the Fire Apparatus & Emergency Equipment Editorial Advisory Board.