Before starting an inspection, individuals tasked to do so need to be sure that the vehicle is in a safe location that is out of the way of other moving or working equipment and does not have a lot of distractions for the vehicle operator or for you. Many operations will say where the equipment can be inspected safely.
In a mine, generally the dump area is an excellent spot for an inspection. It is usually safest to inspect haul trucks and loaders after they have dumped their loads and their beds and buckets are empty to eliminate any chance of a rock falling on an inspector. Also, any load might give false tire pressure readings.
Many surface mines as well as some construction sites have highwalls, benches and overhangs. (A highwall is any vertical or extremely steep slope on a job site.) Working around highwalls can be very dangerous due to falling rocks, dirt and debris that can let go at any time, fall to the base and roll for quite a distance.
If an inspector is standing at the base of a highwall, he or she could be in for a very bad day if this happens. In fact, 9% of fatalities in mines are due to accidents from highwalls.
Even though a highwall has been in place for years, environmental changes like freezing and thawing, blast damage, heavy machinery, water drainage, plant growth, etc. can affect the stability of the wall.
Therefore, make a thorough inspection of the wall for any safety issues before beginning work. Check the joints, faults, fractures, mud seams, overhangs and loose rock and report any concerns to the foreman for his immediate inspection.
Then the vehicle should be moved away from the highwall. There is a calculation to determine how far away from the wall to be. For every foot of height, stay two-thirds of that distance from the highwall. So if the highwall is 100 feet high, move 65 feet away from it.
Have the equipment parked so that you are working on the side away from the highwall. That way, if rocks do fall, the vehicle becomes a shield for you. If the vehicle can't be moved, park another truck between you and the highwall so that you have a barrier between it and you. Never turn your back to the highwall since you will want to see falling objects that can roll a great distance from the wall coming at you.
If you are going to work on top of a highwall, remember that rocks and dirt can give out under foot easily and result in a fatal fall. Fault lines can extend well beyond the edge of the wall and can give out unexpectedly. Therefore, give yourself and the vehicle a wide margin of safety and move well away from the edge of the highwall.
Remember it is your responsibility to ensure the vehicle is safe to inspect and/or service. Make sure it comes to a complete stop and the engine is shut off. Follow whatever procedures the site has established as well. Never approach a vehicle or begin an inspection until you are sure it is safe. Chock the tires or have the vehicle parked in a safety ditch.
During an inspection, check the tread for:
- Embedded objects (They should be removed since they eventually will work themselves through the tire and puncture it if allowed to remain in the tread.);
- Cuts that expose steel;
- Tread worn down to the belts;
- Chunks of rubber torn from the lugs;
- Tread detaching from the belts;
- Tread depth (follow the location's tread-depth requirements); and
- Wear patterns: Look for uneven wear that could result in ride disturbances and shorten tire life.
Check the sidewalls for:
- Cuts, bulges and cracks that expose ply cords; and
- Oil leaks that will degrade the sidewall rubber.
Check the bead for:
- Bead deformation;
- Cracks; and
- Proper seating.
Check the wheel for:
- Missing or loose lug nuts;
- Broken studs;
- Cracks in the rim or wheel base;
- Cracks in the side rings;
- Flange wear;
- Missing valve caps;
- Damaged valve stems; and
- Inflation pressure.
Once the inspection is complete, the person in control of the operator must then ensure that everyone is accounted for and is in a safe area prior to signaling the operator it's safe to move the vehicle.
Servicing OTR tires poses many potential dangers to technicians, and there have been many accidents that bear this out. Many OTR vehicles and machinery are equipped with multi-piece rims/wheels that have 16 large nuts that hold the inner and outer rims in place and 48 small bolts that attach the assembly to the hub. Not too long ago a technician was killed when he loosened most of the 16 large nuts with the tire inflated to 90 psi. The remaining nuts could not hold the outer rim, which blew off and smashed the technician between the tire and his truck. This is why it's necessary to always completely deflate multi-piece assemblies before removing them from the vehicle.
Heat is a major cause of tire failures and explosions. It is not unusual to find cracked rims on heavy mining and construction equipment. Many technicians think they can repair these cracks and in many cases are encouraged to do so by the equipment owners.
In one documented case, a technician welded the rim on a vehicle with the tire deflated. However the heat resulted in the decomposition of the rubber inside the tire, which gave off flammable vapors. When he inflated the tire, a fire erupted inside the tire and it exploded, killing the technician.
The lesson to be learned here is never weld or attempt to repair a wheel. This is true whether a tire is mounted on it or not. Heat will also damage and weaken the heat treatment of the wheel, with potentially lethal consequences.
Another type of accident happens more than you would like to think. In this case a technician mounted a new radial tractor tire on a wheel on the floor of a service area that was under a metal canopy.
The bead would not seat so the technician kept adding inflation pressure to the tire/wheel assembly while he bent over it. The bead burst over the rim flange and sent the technician and the tire in the air where they both hit the canopy and then plummeted about 20 feet back down to the cement floor.
Needless to say, this was not a good day for the technician. In this case several OSHA procedures were ignored. Tires can only be inflated to 5 psi outside a safety cage. They must not be inflated on the floor or where any other surface is within 1 foot of the tires' sidewall.
And tires may never be inflated beyond 40 psi to seat the beads. If the beads are not seated at 40 psi, the technician must stop, deflate the tire and determine the problem.
In another instance, a radial OTR tire on a vehicle was inspected by the technician who checked the pressure and found that it was 30% underinflated. Instead of removing the tire and thoroughly inspecting it for a potential zipper rupture, he inflated it while standing in front of the wheel and in the tire/wheel trajectory.
The tire zipper-ruptured and blew the technician into his truck, killing him instantly. The potential for this scenario to occur is growing in the small OTR tire (up to 25-inch rim diameter) market as the market is shifting to radial from bias tires for haulage, loaders and graders.
When a tire explodes, the pressure it releases can exceed 1,000 psi and can hurl tools, people, debris and other material great distances and endanger anyone in the immediate vicinity, even those inside a vehicle.
Studies have shown that the primary injury associated with tire explosions is caused by the shock wave, which can result in eye injuries and damage to the lungs, ear drums and nasal sinuses. Injuries can also be caused by flying debris striking the victim at high speed.
A person can also sustain injuries from being thrown against objects such as walls, ceilings and trucks as a result of the force of the blast. The head and face are the most commonly injured as technicians normally are facing the tire when the explosion occurs.
To make this even clearer, a 26.5x25 tire at 90 psi has 373,650 foot-pounds of stored energy. If released instantly — as when a tire zipper ruptures — it can hurl an average size person 1,868 feet. Talk about the Force being with you.
This is why all tire/wheel assemblies must be inflated in a safety cage or some other type of restraining device using a clip-on chuck and an in-line valve with a gauge or a pressure regulator with a gauge preset to the desired value.
Tires that are too large to be put in a cage or are still installed on a vehicle must be inflated with a clip-on air chuck, an in-line valve with a gauge and a sufficient length of hose to enable the technician to stand outside the trajectory, which is 45 degrees from the center of the tire/wheel assembly in all directions.
In other words, if you are outside the trajectory, you should not be able to read the tire sidewall. It is wise to use the service truck as a barrier during inflation as well.
Never forget that according to the U.S. Occupational, Safety and Health Administration (OSHA), tires that are found to be driven underinflated at 80% or less of their recommended pressure must be considered flat, completely deflated, removed from the vehicle, demounted and inspected for potential zipper ruptures.
The beads should be checked for wear, cracks and grooves resulting from the rim flanges rubbing them, and the inside of the tire should be inspected for signs of dark lines and broken cords in the sidewall flex area that indicate the tire was run flat.
Also, all personnel in the work area need to be aware of the trajectory zone and know this is also a danger zone. It is the technician's responsibility to ensure everyone stays out of the trajectory zone and never sits or stands in front of a tire that is being inflated.
It is probably best to think of OTR tires as potential bombs and treat them with the deference they require and deserve. Never let your guard down in a mine or construction site and constantly be monitoring your surroundings to stay safe.
Always follow the site's safety protocols and proper tire servicing procedures. Especially in mines and large construction sites, have someone with you who can watch your back, call for help if needed and communicate with equipment operators. They just might save your life.