Investigation of ADT overturn events has identified the following causal factors as being common, either individually or in combination.
- Soft or sticky or un-compacted ground
- Tipping too close to an edge
- Tipping on an excessive gradient or on a cross-fall
- Moving/Reversing up a slope, stockpile or bund edge
- Carrying unstable loads such as silts and slurries
- Carrying sticky or cohesive loads such as clays and soils
- Excess speed or sharp braking, especially on corners and bends
- Poor haul road conditions
- Mechanical failure of key components such as the lifting rams, suspension
- Incorrect use of the differential lock
- Poor visibility/weather conditions
- Use of tailgates on cohesive materials
- Vehicle runaways
- Travelling on excessive camber and gradients
- Incorrectly inflated tyres or tyre blowout
- Failure of drivers or site supervisors to adequately identify and assess risk
Example photographs illustrating some of these are contained as Appendix 9.1
The importance and influence of these factors is usually relatively easy to identify in investigations carried out after an ADT overturn incident. The challenge is then for operators to identify them as risk factors before an incident takes place.
It is often the case that the root cause of an incident is simply attributed to ‘driver error’. While competence of the driver is always a key consideration, often this ignores the failure of site management to adequately assess the hazards associated with ADT operation on a site.
All of these factors can be incorporated in the overlapping concepts of Safe Driver, Safe Machine and Safe Environment. A failure to take into account one or more of these will mean that an operator of ADTs is exposing themselves and their workforce to unnecessary and preventable risk.