ROCHESTER HILLS, Mich. (Oct. 13, 2003)—Guys, how many times have you walked out of the men's room and forgotten to check your pants zipper?
You were probably lost deep in thought and had a momentary lapse in concentration as you prepared to exit. Whatever the reason, it's an embarrassing moment, for sure, when someone shocks you back to reality with the words, “Hey, buddy, your fly's open!”
BOOM! There you are, out in public, in front of God and everyone to see. Unless you're a flasher, this is a sure way to get humiliating attention.
Zippers are a problem for commercial truck tire people both personally as well as professionally—and I'm not just talking about having your fly open while calling on your best fleet account. Sure, that's probably not good for business. But circumferential fatigue ruptures—known in the trade as “zippers” in steel radial truck tires—are the problem to which I'm referring.
Revisiting the problem
Now unless you've been living in a cave for the past 10 years, you know what a zipper rupture is. But for those of you who have been “on an extended leave of absence,” a zipper rupture is a tire failure in which the tire blows out in the upper sidewall, leaving an even line of broken steel cords exposed, which gives it the appearance of an open zipper. They are typically 10 to 12 inches long but can extend up to 36 inches in length.
When the tire blows out with this condition, the rupture begins at one point and then opens in both directions due to the instant transfer of load to adjacent steel body plies until the air pressure is evacuated. Only one side of a tire ever ruptures.
Typically, zipper ruptures occur in tires that have been run flat or severely underinflated in a dual wheel position. Low inflation pressure and the resultant increased sidewall flexing create fatigue in the cords.
With the proper inflation pressure, tire cords are always kept in tension as they traverse through the tire footprint on the road. However, as the inflation pressure decreases and gets closer to 0 psi, the cords are compressed as the tire rolls through the footprint area. This produces severe bending of the cords. Since the wire cords are bent hundreds of thousands of times as the tire runs, they are severely weakened and may even break.
Continued or extensive operation in an underinflated condition weakens one or both steel radial sidewalls to some degree. When the tire is re-inflated, the pressure put back in the tire pushes against the cords that no longer have the strength to hold it. The tire then blows out, often with an explosion. Tire pressure usually exceeds 40 psi when a zipper rupture occurs.
The blast of air that is released when the tire blows out can cause serious injury and even death. It's not unusual when a zipper rupture occurs for people to permanently lose their hearing, get hit with flying tools, the tire cage or the tire and rim/wheel itself. They also can get hurled across the room or into the air and impaled on equipment or building structure, or just be killed by the concussion of the air blast itself.
We are talking about a tremendous, lethal force here.
The root cause of the zipper rupture is loss of inflation pressure. This is most often caused by a puncture in the tire but can also be produced by a leaking valve stem, poor bead seat, bent flange, cracked rim or any other condition that will cause the tire to lose air.
Anytime a tire comes in flat, has a repair or needs a repair, everyone in the tire shop, retread shop or service truck that comes in contact with that tire should be on heightened alert and examine the tire closely for a potential zipper. Tires that have been repaired should be serviced with the utmost care. While a tire is being inflated—always in a safety cage—everyone at a service location must stay out of its trajectory—that's the sidewall area of the tire—to avoid being in the tire's dangerous blast zone.
Zipper problems were first recognized in the early 1990s.
An industry task force organized by the former American Retreaders Association (ARA), now known as the Tire Industry Association (TIA), conducted studies and developed training materials—booklets and videos—to advise retreaders, truck tire servicers and truck tire users of the dangers of zipper ruptures and how to identify them. The Rubber Manufacturers Association also de-veloped technical bulletins and warning posters on servicing tires that could be zipper candidates.
Many articles also were written in trade publications, passing along this information to the industry. In addition, retread equipment and rubber suppliers made these training materials available to their dealers and provided warning labels to put on newly retreaded and repaired tires to help minimize zipper-related accidents, too.
The inspection procedures developed then are still good today. They require you to feel the tire, listen to it and look closely at it. If you know what to look for, a potential zipper can sometimes be detected very easily.
If the tire has serious damage in the sidewall plies, the weakness can usually be felt by pressing the suspect area with your fingertips or thumbs and listening for a crunching or popping sound which can be heard as the broken sidewall cables move. The sidewall may also feel soft, and bumps and blisters may be felt on the sidewall surface.
Some tires that have been run low or flat show obvious signs of innerliner distress and fatigue—including wrinkles, discoloration and/or cracking—while others show no signs at all. The use of an indirect or grazing hand-held light can often reveal sidewall distortions, bumps and blisters indicating broken plies.
Unfortunately we don't work in a perfect world. Real world commercial truck tire work environments are not normally quiet. So it's often difficult to hear popping and crunching sounds when inspecting tires in the shop with equipment running and compressed air in use, or on the side of the road with the roar of traffic going by, and the use of a hand-held grazing light is impractical.
Further, some tires are very insidious. They hide the fact they contain potential zippers and make detection very difficult. However, I'll wager that most of the tires that zipper are the ones that didn't get inspected too well.
Step up prevention
In the early to mid '90s much press and attention was given to zippers. Now, about a decade later, I think people are getting lackadaisical about this condition.
Very few articles are written about zippers now, and you only hear about this condition when, for instance, a teenager or young father gets killed. And even then, I know we don't hear about all the accidents that occur.
Heck, what I've found lately is that tire dealers and retreaders don't even keep track of the zipper ruptures they have unless their own employees get injured by one. Then a report is made out primarily to meet workers' compensation re-quirements.
Few people are using this information to improve the level of inspection and tire service procedures to prevent future zipper blowouts, accidents, injuries and deaths.
Every commercial truck tire dealer and retreader should document every time a tire zippers. That should include not only at his own business locations with his own employees, but at his customer's locations and where the fleet's employees are involved as well—even when no injuries occur.
Zippered tires that blow out at customer locations should be returned to the tire dealership so they can be examined to determine whether they are indeed zipper ruptures. Complete information can then be recorded on the tire, as well as any vital information on injuries or damage. This just makes sense in case a lawsuit should result.
All tires that zipper should be presented to the individuals responsible for inspecting them. If they passed through a retread plant, all employees should inspect them and be reminded of how important each is in detecting potential zippers. In order to heighten their awareness and improve their detection techniques, anyone who repairs tires and services them should have the opportunity to examine zippered tires that should have been caught prior to airing them up.
These are important training tools that cannot be used too much.
Also, by keeping a record of the zippers your dealership experiences, you can track them better—and determine if a specific customer is more prone to these conditions than others, perhaps due to inherently poor maintenance. Then you can take special precautions with that customer's tires.
You can also go to the source and work with customers to improve their maintenance routines and help them reduce the potential for future zipper ruptures. At the least, you can determine if you're making any progress in reducing the number of zippers you have by keeping records month to month and year to year.
This could come in handy especially if, BOOM, you find yourself in court.
Open zippers can certainly be embarrassing as well as fatal. Use every opportunity you can to remind and train your company's associates to prevent them. Their very lives may depend on it.