Usage:
- SUPPLEMENT: 11/26/79
SERVICE MAGAZINE, OCTOBER 8, 1979, PAGE 1. In the article "Warning: Excessive Heat Can Cause A Tire Explosion", change the first sentence of the last paragraph to read:
Wheel coolant is provided in Caterpillar wheel tractor-scrapers (all except 613, 621, 623 and 627 Tractor-Scrapers) in which excessive brake application could cause burned tire beads.
Also, change the illustration caption to read: APPROACH AREAS. Do not approach tire within 300 ft (91.4 m) from the side or within 15 ft (4.6 m) from the front, rear, or above.
--------------- END SUPPLEMENT ---------------
Earthmoving machine tires can, under certain special conditions, explode like dynamite. The explosion can expel the tire, rim assembly and other machine components for distances as far as 300 feet (91.4 m) or more from the machine. Both the force of the explosion and debris can cause personal injury or death, and property damage. Tire explosions are infrequent but due to the possible severity, all personnel should be made aware of the possibility and the actions to take to minimize the risk.
The danger of a tire explosion must be recognized as a distinct possibility whenever the smell of burning rubber or excessively hot brakes is detected. The danger is also present when a fire on the machine gets at the tire. Under such conditions, all personnel must avoid approaching the machine in a manner that injury could result should an explosion actually occur. Move the machine to a remote area only if it can be done without endangering the operator or other personnel in the area. Remove all personnel from the area where the machine is located.
If it is absolutely necessary to approach a machine with a suspected tire, do not get closer than 15 feet (4.6 m) to the tire tread nor closer than 300 feet (91.4 m) directly in line with the tire. The following sketch illustrates the high risk areas to avoid when approaching the machine, although there is no absolutely safe approach. Do not approach any tire on the machine if there is a brake fire, burning rubber or other indications that excessive heat was generated by the brakes on the machine. Brake-generated heat probably affects all other tires on the machine, even though the visual evidence is only at one tire.
A tire explosion is the result of excessive heat from any source (such as overheated brakes due to dragging or excessive usage, overloaded tires, machine fire, welding on tire rim with tire in place, etc.) causing auto-ignition of the gaseous mixture inside the tire. When a tire is exposed to excessive heat, the tire bead can burn due to heat transfer through the rim assembly. Deterioration of the rubber compounds in the tire bead by the heat can result in the release of a volatile gaseous mixture within the tire. Normally, the burnt bead causes loss of air and the tire goes flat without hazard to anyone in the vicinity. In a few rare instances, the gaseous mixture may reach auto-ignition temperature before the bead deteriorates sufficiently to cause tire deflation. The internal fire in the tire created by the auto-ignition of the gaseous mixture causes a very rapid increase in pressure, resulting in a violent tire explosion. The danger of a tire explosion is at its greatest after the machine stops because of loss of the cooling effect of the circulating air due to wheel rotation. The resultant explosion produces a blowout at the tire bead which reacts against the machine in most cases to expel the tire and rim assembly components, including final drives, a considerable distance from the machine. In some cases, the tire may explode without expelling wheel components.
APPROACH AREAS
Do not approach line within 300 ft. (91.4 m) from the side on within 15 ft (4.6 m) from the front, rear or above.
Wheel coolant is provided in Caterpillar wheel tractor-scrapers (all except 613, 621, 623, 627) in which excessive brake application could cause burned tire beads. The coolant minimizes heat transfer from brakes through the rim and to the tire bead on these machines. The coolant must be of the recommended type and concentration be at the proper level to be effective. The recommended coolant solution is 20% mixture of ethylene glycol type antifreeze and 80% water. Oil or any other fluid other than that recommended should never be used as a wheel coolant. The coolant level should be checked at least every 1000 hours as recommended in the Lubrication and Maintenance Guides for the machines. In addition on earlier machines which require the removal of a brake drum stud to add or check coolant level, cooling system sealant should be added every 2000 hours.