Heavy haulers, heavy responsibilities

Last year’s metals recovery affected local copper and gold producers most, interest in base metals and SA coal was high, and only African diamond miners really suffered throughout the period.

With Chinese purchases rebuilding many new heavy off-road haulers were needed here to satisfy the demand for both straight diesel (similar but much more powerful than their on-road cousins) and diesel electric (allied to railway locomotive) trucks.

This article looks at the operational safety requirements for what amount to rigid rough-terrain dumpers (strictly a construction industry term; mineral-winners prefer to talk of hauling and specialised mining trucks), typically weighing in at 30-150 tonnes apiece when empty (they can be much larger) and capable of shifting between 30 and 200t-plus of uncrushed ore or aggregate up a steep gradient, 12 hours or more a day. That needs engine power in the 350-2000kW range, at the top end delivered by a massive 16-cylinder unit, turbocharged and aftercooled of course. It also typically needs an automatic transmission system that is electronically controlled to allow the operator to concentrate on what’s important, some kind of payload management system to ensure this very costly machine is not misused (and not under-used either), and probably oil cooled disc brakes all round on four or six wheels too. It goes without saying that the all-independent suspension system needs to be extra tough and that the steering is likely to be based on hydraulic power. All this is why the unloaded weight starts at 30 tonnes.

Not covered here are the many variants of popular articulated dumpers, including top-quality models designed and built in South Africa, nor the specialised multi-axle heavy haulers used in the road transport business for moving massive items like hydro generators on flatbed trailers slowly around Africa. Both these categories of hauler bring with them their own very specific safety considerations.

All the H&S issues point to one unvarying conclusion about heavy haulers: never let an unskilled operator get his hands on one of these machines unsupervised, even moving it round the stockyard. Accidents usually fall into one of three main categories.

First, movement incidents, of which by far the most common is backing up. Some mine trucks are more than six metres high to the obligatory canopy rock-guard rail over the cab, so maintaining visual contact with on-the-ground workers when making any kind of a movement is difficult, to say the least. Clean and properly adjusted mirrors minimise the danger, as does an automatic reversing alarm system that works, but there’s really no substitute for having an alert spotter or banksman working with the operator at all times – and especially when backing up to receive or dump a load, or negotiate one of those tight bends that often link quarry galleries.

Second come accidents that typically take place when a load is being tipped. Obviously the hauler needs to be properly positioned before the gate is released and the load bay lifted, and the operator needs to make quite sure people on the ground – and their livestock - know what’s about to happen. But often overlooked is the fact that the whole loaded mining truck needs to be standing on reasonably level ground before the hydraulics are actuated. If its not the sudden change in weight and moment as part of the load is raised – remember these heavy haulers typically shift more than their own mass of payload – can cause the whole package to move unexpectedly, even turning over in some circumstances. By contrast loading is usually a much slower and therefore under-control process.

The third type of incident is the result of a collision. This often happens because the operator’s vision is impaired, especially when the truck is put into reverse or negotiating a sharp bend. A special danger arises because most mining trucks either have no fenders at the front at all (obviously rear ones interfere with unloading), or they are mounted very high up so as to provide the necessary ground clearance. So a small moving vehicle like a site dumper or pickup can easily be swallowed beneath that massive 1000hp-upwards powerplant without the operator even knowing what’s happened.

Alain Charles Publishing, University House, 11-13 Lower Grosvenor Place, London, SW1W 0EX, UK
T: +44 20 7834 7676, F: +44 20 7973 0076, W: www.alaincharles.com

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