When Keith Fally sees news that a trailer has gone up in flames on a highway, he knows there’s a chance he’ll get called out to investigate the cause. And, according to the national OEM account and national service manager for Stemco, he knows there’s an even better chance the driver was to blame.

“It’s kind of like a CSI investigation where you’re putting pieces together to fill in all the blanks to determine what occurred,” Fally said in an interview on wheel-end fire prevention with Today’s Trucking. “And not to pick on drivers, because there’s good ones and bad ones. But if they all actually did their pre- and post-trip inspection every day like they’re supposed to by federal law, there wouldn’t be as many issues.”

Most wheel-end fires occur on often overlooked trailer positions and begin with either overheated brakes, underinflated tires, or inadequately lubricated wheel-ends. The nearby tire serves as a willing accelerant when temperatures exceed certain thresholds.

Fally explains a common sequence of events: “The brakes will start dragging and it generates heat in the brake drum. The brake drum starts glowing cherry red and the distance between the brake drum and the tire is, maybe, three inches. That tire gets so hot that it melts the bead of the tire and the tire blows out. Now you have a tire that’s running basically flat and then the steel belts are slapping the ground and sparks are flying off it. Then, once the tire’s on fire, it’s pretty much ‘Adios’. You can’t really put out a tire fire with a fire extinguisher.”

What to look for

Overheated brakes will often leave signs behind that should alert an observant driver to potential problems during their pre- and post-trip inspections. An overheated brake lining will turn a whiteish color, and may crack and crumble.

Brake drums will turn cherry red when they reach about 1,200 F (649 C). When they cool back down, they will retain a pink hue that should also serve as a warning.

“Sometimes we’ll investigate these fires months — if not years — later and that brake drum will still be pink in color which is a telltale sign of a brake thermal event,” Fally explained.

Stemco hubcaps contain a window that turns white and opaque when the bearings are running hot, often due to lack of lubricant. The discoloration occurs at about 260-280 F (127-138 C), offering a warning of impending problems before the window melts completely at about 300 F (149 C). An aluminum hubcap typically won’t melt until it reaches 1,200-1,400 F (649-760 C).

In normal conditions, a wheel-end will run about 50-80 F (10-27 C) above ambient temperature.

“If you have a wheel-end above 200 F (93 C) [on a 100 F day], you know there’s something going on in there.”

Ken Kelley, vice-president of engineering and development with P.S.I., agrees drivers should be looking for telltale signs of overheating during inspections.

“When a driver looks at the wheel, if it has seen heat in the past, it’s going to talk to you,” he said. “It’s going to look different. If a wheel-end has been very hot, generally surfaces that contain lubricant will show signs of stress. Where the hubcap is bolted onto a trailer hub, it might start to leak. You might see discoloration of the rims if it’s seen enough heat.”

Technology can help

Technology is available to help drivers and fleet maintenance managers to prevent wheel-end fires, and not all of them are expensive. Fally recommends drivers travel with a handheld heat gun that they can point at each tire position while doing a walkaround. It’s a low-tech, low-cost early warning system.

“You can buy them for less than $50,” he said. “Point it at the hub and get an idea.”

Wheel-end fires typically don’t happen suddenly, Fally said, and in most cases drivers have an opportunity to eliminate the risk before a thermal event occurs. A driver who doesn’t get under the trailer with a flashlight may not discover a leaking wheel seal.

“If that lubricant is leaking, you’re not going to have as much lubricant on the bearings, and the bearings are going to get hot over time,” he warned. “That heat is eventually going to cause a bearing failure to occur. That typically doesn’t happen overnight.”

Fleets wanting to take the extra step toward avoiding wheel-end fires may focus on tire inflation pressures systems, such as those provided by P.S.I. (now owned by Clarience), which comes standard with the ThermAlert warning system.

A screw installed into the press plug contains a eutectic material that will melt at a certain threshold – typically 100 F (38 C) above the normal operating temperature of a wheel — causing pressurized air to vent through the hubcap vent. This produces an audible whistling noise that the driver should notice as soon as they exit the vehicle. The science behind it isn’t entirely unlike that of a pop-up turkey timer.

“Our system uses pressurized air within the axle to maintain the tire pressures,” explained Craig Smith, P.S.I.’s vice-president of marketing and communications. A warning light mounted to the front of the trailer and visible from the driver’s seat will also illuminate when a heat issue is detected.

The newer Digital ThermAlert also gives fleets control over the thresholds at which warnings will be issued, and sends them to the fleet or maintenance manager via P.S.I.’s TireView portal. Not a bad idea, thinks Fally, who has investigated trailer fires and discovered the driver has covered up the ThermAlert warning light on the trailer.

“That light is to get the driver’s attention,” he said. “But I’ve actually been on investigations – probably three or four – where the driver puts a piece of tape over the light.”

In one such instance, an entire 40,000-lb. load of 15-terabyte hard drives valued at about US$6 million was lost. All because of a piece of tape, and a driver who didn’t want to be bothered with the warning system.

Kelley acknowledged fleets should work with P.S.I. to set alert thresholds that won’t result in too many false positives or become an irritant for drivers.

The maintenance manager also has a role to play in preventing thermal events, including training drivers on what to look for and being there to provide advice if a warning system such as ThermAlert flags an issue that’s then spotted via the portal.

Kelley said it’s not always obvious whether a trailer with a hot-running wheel-end can be limped to the shop or must be towed to safety. “If I could put my hand on the wheel-end and it hurt a little bit, yeah, I may limp somewhere. That’s a subjective call. If it’s hot – like paint starting to peel and all that – I would say it’s a tow event. It’s a judgement call.”