For the second time this year, someone serviced a truck tire as part of their normal day-to-day routine for the last time. While I don't have any specific details on either accident, I know that two people didn't come home from work because a tire separated under pressure. To make matters worse, I also know that the second accident involved a tire that was initially inflated in a restraining device (safety cage) and then separated after it was removed.
As bizarre as the most recent fatality may seem, it is very believable. For the past 13 years, I've dedicated my life to educating technicians on the importance of using a restraining device when inflating tires, yet it didn't matter. Adding to the hopelessness of the situation is the fact that this isn't the first time a tire separated after it was removed from the safety cage. It would be easy to throw my hands in the air and let fate decide who goes home and who doesn't, but I know that restraining devices save lives, so nothing has changed as far as I'm concerned.
Out of respect for the deceased, I won't speculate as to what happened in the recent accidents. But rather than wait for the answers on how something like that is even possible, I'll provide a few examples of how using a safety cage can still get someone killed. First, if it was a multi-piece (split rim) assembly, then mismatched, worn or improperly seated rim components can easily separate after the tire has been inflated in a restraining device. As ridiculous as it may seem, not all 20-in. rim components are compatible. When technicians fail to match the identification stamps or use worn parts, the risk is significantly greater even if the assembly had been initially inflated in a restraining device.
I've also personally witnessed a zipper rupture occur during the overinflation stage of the inspection process, which means that a technician who inflated such a tire to operating pressure and then removed it from the cage would definitely be at risk. Inspection procedures for radial truck tires returning to service require overinflation because the additional stress applied to the body cords will usually identify any weaknesses. The only caution is that the maximum inflation pressure of the rim or wheel cannot be exceeded. It's definitely possible that a damaged tire could zipper rupture after it's removed from the cage if the technician failed to inspect it properly.
Perhaps the most troubling risk is associated with heat damage to disc wheels. When a wheel is operated overloaded or exposed to excessive heat for an extended period of time, the diameter is actually reduced to the point where it won't support one of the beads after the tire is pressurized. Unfortunately, the actual pressure at which it explodes is totally unpredictable so technicians either don't know what to look for or are simply rolling the dice. Since the damaged side is opposite the valve stem, the unsuspecting or uneducated technician may not become aware of a problem until after the assembly has been removed from the restraining device.
Inflating a truck tire to 100 psi is an inherently dangerous procedure that should never be taken lightly. Many of the related inspection and safety procedures put in place by the industry are in direct response to serious and fatal accidents. But while restraining devices definitely play a major role in protecting technicians from injuries when inflating truck tires, they are only part of the answer.