Apparatus Body Materials: Read Between the Lines


Choosing a body material for a new fire apparatus, particularly a pumper, can be challenging and frustrating for an apparatus purchasing committee. Making rational decisions may require committees to sort through the sales hype, advertising claims, and marketing tactics of apparatus manufacturers and their dealers. Smart purchasers are the ones asking questions. Be inquisitive; educate yourself. You may want to know more information than may be offered in nebulous statements and vague specifications. This article does not detail technical and sometimes confusing data and possibly misleading specifics such as weights, tensile strengths, corrosion resistance, flame resistance, mixing dissimilar metals, and the like. Instead, it highlights various body materials, different construction methods, and some common claims a purchasing committee may want to carefully evaluate.

To be able to evaluate available materials, you must understand basic body construction methods. A pumper body of years past was just that—a true four-sided body on which optional compartments could be added. Today, with storage space at a premium, bodies have—simply put—evolved into side and rear compartment modules tied together by a front panel with upper hosebed side sheets sized to fit the water tank and hose load. Mild or untreated steel is seldom used in today’s bodies and is not addressed here. Galvanized steel (also known as galvanneal or treated steel), stainless steel, and aluminum are common body materials; nonmetallic bodies are available in polypropylene and composite materials. The apparatus purchaser may want to consider more than the advertised material. How bodies are put together and what the entire body is fabricated of may be relevant in the decision-making process.

Bolted-together vs. welded bodies. As an example, a steel or aluminum body can be fabricated by welding or bolting the assembly together. Bolted-together bodies usually have bolt holes predrilled, so the component pieces must fit together very precisely. Welded bodies may be continuously welded or strip-welded together. Although continuous welding is prudent in the lower areas of a body to prevent corrosion, some manufacturers promote and advertise continuous welding throughout their body fabrication. Proponents of the bolted body laud the fit, noting there is no chance for distortion or warping that is common with the welding process. Advocates of welded bodies advertise no seams and no chance of leakage as well as no visible nuts and bolts that may loosen. Both bolted and welded body builders state their own methods of construction are easy to repair. Determining which claims are legitimate is up to the purchaser.

Formed vs. extruded aluminum bodies. Formed body pieces are fabricated and shaped in hydraulic brakes and presses and then are welded or bolted together as previously described. Extruded aluminum bodies are framed using extrusions, formed structural members with unique and sometimes proprietary designs such as angles, curves, and slots. With extrusions, heavier-gauge aluminum plates can be used for the body work instead of thinner formable sheet aluminum. The plates slide into the slots in the extrusions and are welded in place to make an extruded body. Formed aluminum bodies are marketed as lighter in weight than extruded bodies; extruded bodies are promoted as being heavy duty. Again, the choice is yours. Manufacturers can provide information on the alloy makeups, differences in tensile strengths, costs, weight variances, and differences in warranties (if any). Read it carefully.

Aluminum profile construction. Another method of aluminum construction uses aluminum profiles. Domestic manufacturers build their compartments where the material itself lends strength, support, and rigidity to the entire body. Some European manufacturers design bodies using a method of interlocking, bolt-together profiles. The profiles are lightweight aluminum extrusions that form an integral internal framework for the compartments and body. The profiles give the body strength and rigidity internally; the outer skin, attached to the profiles, merely provides protection from the elements.

Body substructures. Domestic body substructures should be addressed before discussing polypropylene and composite materials. The substructure is the framework that helps hold together component parts of a body, including those points of attachment where the body is physically connected to the chassis. In many cases, a substructure encompasses or cradles the bottom of a water tank. Whereas profile type bodies incorporate internal substructures, most domestic manufacturers use tubing, channels, and angle irons to form an external substructure.

Not all manufacturers use independent substructures. Some describe structural members as part of the body assembly. Still others define any member above the frame rail height as a superstructure. Although the principle and intent are the same, terminologies may differ among manufacturers. Ask your vendor to explain them in detail. And read the specifications carefully.

Let the buyer beware: Just because a manufacturer advertises an aluminum or stainless-steel body, it does not necessarily mean the entire body will be of the same material. Some manufacturers of stainless-steel apparatus offer galvanneal substructures as a cost savings. Some manufacturers of aluminum bodies also offer galvanneal substructures, promoting the strength of the steel.

Polypropylene bodies are usually supplied with aluminum substructures. Pump enclosures are mostly free-standing fixtures separate from the apparatus body. Again, in this area, purchasers should take note: Regardless of whether built in-house or purchased from an outside vendor, the pump enclosure and its substructure may not necessarily be made of the same material as the body. The mixing of dissimilar metals is a common but not well-known practice. Ask your dealers where it is done and the reasons for doing so.

Polypropylene (also called copolymer) is a thermoplastic material produced in sheets, similar to steel and aluminum. It is normally cut and electronically welded to similar material. It is lightweight, and the concept of forming and welding sheets of polypropylene has been extensively proven for years. Manufacturers of aluminum and stainless-steel body fire apparatus are hesitant to be too negative against polypropylene bodies; probably 90 percent of the booster tanks they use are manufactured from this material. However, they are usually unabashed to point out the polypropylene body must be supported by an aluminum or stainless-steel substructure.

Composite bodies are being reintroduced to the marketplace. Some manufacturers using metal readily refer to the composite bodies as “fiberglass, just like your motorboat.” That is not a fair statement. Granted, the original composite bodies built decades ago were molded type construction. Fabricated primarily of short or chopped fiberglass strands and resin, the body required a sturdy substructure, usually of steel. Although some molded body work may be found today, the latest composite fabrication is a laid-up type construction. Using combinations of continuous and woven fiberglass strands and resin, the material is vacuum injected and formed in large sheets. Similar to metal and polypropylene, composites are manufactured in various thicknesses, depending on the application. Construction is similar to metal and polypropylene bodies in that the material is cut and attached to each other. Laid-up composite body components are fabricated together with continuous and woven fiberglass strands and resin. Some refer to composite bodies in a derogatory manner as being bonded. The terminology does not reflect the strength of the product, since composite bodies are strong enough to be self-supporting and do not require a substructure.

Separate tanks are not necessary with polypropylene and composite bodies, and water and foam tanks are commonly incorporated as part of an integral body configuration—a true unibody. The pros and cons of integral tank technology and the use of metallic vs. nonmetallic bodies are left to the marketing people.

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This article does not favor the use of one body material over another, nor does it promote any one method of construction. It encourages the purchaser to be inquisitive. Don’t be afraid to ask why and to learn the advantages and disadvantages of each. Do not hesitate to ask vendors questions until you are satisfied.

BILL ADAMS, a 40-year veteran of the fire service, is a former fire apparatus salesman. He is a past chief of the East Rochester (NY) Fire Department.

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