WESLEY D. CHESTNUT

This massive amount of weight rests on the tire and wheel assemblies of these vehicles, which are held to the axles by several wheel-attaching nuts, more commonly known as lug nuts. Having something so small, in comparison to the overall size of emergency vehicles, to keep critical components attached to the vehicles is quite impressive. It takes all of the lug nuts working together at the proper torque to keep the tire and wheel assemblies attached to the vehicle.

Importance of Proper Tightening

The required torque equates to clamp load, which keeps the wheel attached to the emergency vehicle. It takes appropriate torque on all lug nuts to keep the wheel attached. A single lug nut coming loose may have a domino effect on the remaining lug nuts or lead to damage on the wheel or wheel stud.

Inspecting the lug nuts and verifying torque are critical to the integrity of the wheel mounting. If a loose lug nut goes without notice and damage to the wheel stud or wheel occurs, a wheel could separate from the axle. The National Highway Traffic Safety Administration (NHTSA) has investigated previous incidents in which this may have occurred, and manufacturers have issued safety recalls in certain cases.

New Vehicles

During assembly, a new emergency vehicle's wheels and tires are installed on the axles, then tightened to the appropriate torque. In many cases, the axles' supplier may specify the appropriate torque for the lug nuts. These torque values equate to the clamping force intended to keep the tire and wheel assembly attached to the axles. Manufacturers may use a calibrated torque tool to achieve the appropriate torque in the appropriate sequence. After the emergency vehicle has gone through the assembly process and subsequent road testing, manufacturers ensure the lug nuts are tightened, again using a calibrated torque tool.

In certain cases, an emergency vehicle may be built in two or more stages, with the chassis cab being built in one facility and final assembly occurring at a separate facility that may be miles away. The chassis cab manufacturer may recommend that the lug nuts be inspected and torque verified on all lug nuts after receipt of the chassis cab and prior to delivery to the end customer. This is a precautionary measure to ensure the lug nuts have remained properly tightened to their recommended torque value.

Once "In Service"

After the vehicle is placed in service, it is even more important to inspect, or verify torque on, the lug nuts. The wheel studs and lug nuts often experience dynamic conditions such as impacts from traversing various types of terrain and heat generated by vehicle braking. Over time, these conditions may adversely affect the wheel, wheel studs, or lug nuts.

National Fire Protection Association (NFPA) 1911, Standard for the Inspection, Maintenance, Testing, and Retirement of In-Service Automotive Fire Apparatus, indicates that lug nuts are to be torqued to the manufacturer's recommendation. The frequency of this inspection may depend on an emergency vehicle's use. However, there is guidance within the standard that suggests verifying torque between 50 and 100 miles after wheel removal.

Federal regulations promulgated by the Federal Motor Carrier Safety Administration (FMCSA) include a minimum periodic inspection standard that departments can use as baseline criteria for emergency vehicles. This standard includes inspecting wheels and fasteners for loosening, cracks, stripping, or elongated holes in the wheels.

Lug Nut Torque Indicators

There are various methods of inspecting for loose lug nuts that include visual inspection or applying a

Chris Mc Loone

There was also an unfortunate coincidence in that this was the second time in several months a rig from this station was involved in a rollover. There were many who jumped to conclusions regarding this most recent incident. Although it's easy to make assumptions, it's important to remember not to react so fast.

Whenever an accident occurs, a department will conduct its own investigation to arrive at the accident's root cause. In many cases, this will involve an emergency response vehicle failure analysis, which columnist Chris Koop covers in this month's Apparatus: the Shops.

The fire department here conducted an investigation quickly and determined the cause of the accident to be the failure of five spring hanger bolts that connect the truck's frame to the axle. According to media reports, the apparatus's operator and passengers heard a pop, then felt the truck sag. The spring hanger bolt failure caused the axle to move slightly inward, resulting in the tire rubbing against the wheel well and making it extremely difficult to steer.

There are a number of lessons to be learned from this incident. First, I believe the injuries sustained in this accident were not more severe because the operator was driving the truck in a controlled manner. It was responding to a reported structure fire, but had he been driving recklessly, the results may have been much worse. My high school English teacher was fond of relating Latin expressions to us. One of his favorites was "festina lente," which translates to "make haste slowly." We all have a job to do, but we have to get there to do it. Should the unexpected occur, being in control of the vehicle will help reduce the chances of severe injuries or death.

Second, know your trucks. I know that sounds obvious, but who among us doesn't know our personal vehicles well enough to know when there is an odd vibration that wasn't there before or notice when a new sound emanates from the engine compartment? One of the items Koop discusses is that when investigating the failure of an apparatus component, a department must ask the right questions, and the apparatus operator can be of great help. In the above example, the operator and firefighters were all able to cite very specific things that occurred prior to losing control of the vehicle. Although they were very specific items, when you know your trucks, you'll know every shimmy and every odd sound. Report them immediately.

I will never forget when I had a truck stall on me, luckily in our highway yard, on a fuel run. The truck just died and would not start again. As I was driving it to the yard, I noticed it was hesitating-not enough to make me really nervous, but enough to be noticed. After it died, and was subsequently flatbedded to the repair facility, I relayed this to my chief engineer, who replied, "Do me a favor. The next time it's doing that, turn it around and bring it back."

The third lesson is not to jump to conclusions too quickly. No department wants to experience an apparatus rollover, much less two within months of each other. Operator error was not to blame in this rollover. Moreover, I believe the operator saved the four firefighters riding that truck from more severe injury. As difficult as it was to steer the truck, had he been going too fast, the crash would