A rollover crash involving fire apparatus is among the worst nightmares of any firefighter or fire chief. Unfortunately, such crashes continue to be too frequent across North America.
One contributing reason may be that fire apparatus has grown increasingly taller over the years. There are several factors contributing to this aspect in the evolution of fire apparatus.
Fire departments, due to the increasing scope of services they provide, need to carry and store more equipment than ever before. And, the amount of chassis space dedicated to the crew cab has increased dramatically in the past generation.
Yet, fire apparatus can only be so wide and so long — maneuverability restricts length and road lane size restricts width. That only leaves one place to go: up. This increase in the vertical profile makes an apparatus more susceptible to losing its vertical orientation — rolling over when struck by another vehicle or when it drops off the edge of the road.
The design and construction of custom fire apparatus in many ways mirrors that of top racing cars, like Formula I. In a racecar, the driver’ space is designed first with maximum emphasis on protecting the driver in a crash. After that, the rest of the car’s components are added around the driver’s protection capsule.
Current fire apparatus is being similarly designed with the crew cab designed for maximum protection with the rest of the apparatus built around the cab. The desired result is an area of safe refuge, not only for those firefighters during a rollover crash, but also from other physical hazards such as a building collapse, approaching severe weather, etc.
Building blocks
Previous generations of fire apparatus constructed of steel were subject to corrosion and rusting.
Then along came aluminum as the primary metal for apparatus construction; aluminum was heralded as a panacea for the rust and corrosion threat. Many departments, however, found aluminum to be lacking in strength, durability, and appearance — the metal oxidizes over time.
Enter stainless steel as a construction material that fire departments have increasingly specified in their new fire apparatus. Stainless steel offered better strength, resistance to rust and corrosion, and maintained its appearance better when compared with aluminum.
Stainless steel, also known as inox steel or inox from French inoxydable, is a steel alloy with a minimum of 10.5 percent chromium content by mass.
Unprotected carbon steel rusts when exposed to air and moisture. This iron oxide film, rust, accelerates corrosion by forming more iron oxide. And, because of the greater volume of the iron oxide, this tends to flake and fall away.
Stainless steel differs from carbon steel in that it has more chromium. This extra chromium forms a passive film of chromium oxide. This prevents surface corrosion by blocking oxygen diffusion to the steel surface and by blocking corrosion from spreading into the metal’s internal structure.
A better mousetrap
“One of the deficiencies with the stainless steel being used to build fire apparatus today is that it’s 100-year-old technology,” said Ken Grantham, executive vice president at Crompion International.
“A few fire apparatus manufacturers have begun using high-strength stainless steel in recent years, but for the most part the stainless steel that most department’s specify and that the manufacturers use is 300 series stainless,” he said. “That’s the same grade that’s used in the stainless steel stove or refrigerator in your kitchen.”
Crompion produces and distributes low-carbon, dual-stabilized ferritic stainless steel, which it markets as Cromgard. With 18 percent chromium, the steel has good corrosion resistance in moderately corrosive environments and good oxidation resistance at elevated temperatures. As a ferritic grade of stainless steel, Cromgard is not susceptible to stress corrosion cracking.
Another steel manufacturer’s product line, AK Steel’s Chromeshield 22 stainless steel, is dual stabilized with both titanium and niobium (columbium) to improve weld corrosion performance. Small additions of copper and molybdenum further enhance corrosion resistance.
“What you have is a stainless steel that’s stronger than 100-year-old technology stainless steel because the materials used and the design and manufacturing process is vastly different from traditional stainless steel,” Grantham said. “That means that we can create one gauge of Cromgard for structural components of the apparatus and a lesser grade for the body of the apparatus. So a manufacturer can drop down a gauge (in the metal thickness) in both the structural and non-structural components used in the apparatus.”
Lightening the load
This reduced thickness can equate to an overall weight savings of 600 pounds or more for a piece of fire apparatus.
“That weight reduction can mean greater fuel economy,” Grantham said. “Or, it can mean that the truck can be designed with more compartment space.”
This stainless steel also uses less price-volatile materials, meaning departments and manufacturers have better control over apparatus construction costs.
“Our production costs are not as susceptible to market fluctuations in alloy materials,” Grantham said. “A 20 percent increase in the price of nickel or chromium, for example, can bust the budget for a department getting their truck built with the older-technology stainless.”
Haven’t heard of this new grade of stainless steel until now? According to Grantham, Crompion is currently working with several major fire apparatus manufacturers.
One fire department, the Fire Department of New York, is already onboard. All new fire apparatus purchases by FDNY are specifying Cromgard for all structural and non-structural apparatus components.
For Grantham it just seems like common sense for departments to specify the use of the newer technology stainless steel. “Why would you want a fire truck that’s built with the same grade of stainless steel as your dishwasher when there’s something that’s infinitely better?” he asks.
