Open Cut » Health and Safety
The objective of this project was to identify materials that could be used to enhance the night time driveability of coal mine haul roads. Materials that could be used as either a reflective coating on haul roads or roadside berms or as part of the road bed itself were examined.
The literature review carried out by the Australian Road Research Board (ARRB) and ATD uncovered a number of articles dealing with retroreflective materials, guide posts and lane marking paint. Few relevant articles were found that related to haul road luminescence and design. These papers emphasised the need for thorough haul road design and maintenance and the influence of mobile lighting plant positions on truck productivity.
Many haul truck drivers have concerns about the safety of driving at night time. These mostly relate to visibility of the haul road and surrounding terrain. Glare from the various artificial light sources are also a concern to some drivers.
About 79% of accidents which occur at night are due to haul road conditions. During daylight operations a similar proportion of accidents are also related to haul road conditions (Queensland Dept. of Mines safety records). These figures are limited in scope and do not include any events where no immediate damage to persons or machines occurred. No data was found that could be used to determine the possibility (or extent) of long term damage that night time driving conditions may be having on workers (e.g. eye strain).
Several different delineation methods were investigated, these included: glass beads; paint; roadside markers; light sensitive dyes and various white minerals. Roadside markers such as bollards, guideposts and reflective cones were thoroughly investigated. Further investigation was carried out on the two most promising surface coating options: fly-ash, a by-product of coal combustion; and light sensitive dyes.
The production benefits to be gained from improved night time driving conditions are small. It was determined that the reduction in productivity at night is about 0.5% on main haul roads, and about 4% on in-pit temporary roads. The investigation did not assess the production losses due to equipment wear and damage. This damage could affect production in two ways: reduced operating efficiency; and increased maintenance time.
The cost of the small productivity increase gained through improved night time vision is high. Total costs for using fly-ash are anticipated to be $770 000 pa, and for light sensitive dyes to be $252 000 pa, with a $50 000 set up cost for this option. It is estimated that these road enhancements would return about $250 000 by way of improved truck productivity. Due to the unfavourable economics, it is unlikely that mines would implement either option, regardless of field trial results.
Environmental testing revealed that run-off and seepage water could potentially be contaminated by fly-ash leachate, and would need to be carefully contained. Fly-ash may create dust problems in dry conditions, adversely affecting mine operations and worker safety.
This project was conducted in two stages. Stage one was planned as an evaluation of any work previously done which may assist in meeting the objective including:
>evaluating the production losses when driving at night;
>an assessment of delineation and surface treatments potentially available;
>evaluating the safety issues concerned with night time driving as opposed to daytime driving on mine haul roads.
This report outlines the outcome of stage one of the project. On the basis of stage one findings, it is recommended that the project be discontinued, with no field trials.
There are two safety issues related to night time hauling: the long term problem of driver comfort and fatigue; and the constant danger of a vehicle accident.
Experience suggests that for a variety of reasons a haul truck driver is more prone to experience discomfort and fatigue when driving at night. Due to the unnatural light conditions, such as isolated, high powered light towers and glare from oncoming trucks, drivers need to concentrate more to make out the edge of the road and irregularities in the road surface. This causes fatigue to set in more rapidly than during daylight operations. Because it is harder for the drivers to distinguish pot-holes and rises in the road surface, they inevitably have a rougher ride than drivers during day shift. Over a long period of time this can aggravate back complaints and other health problems.
The danger of a truck colliding with another vehicle or a stationary object (such as the road berm) is increased at night because it is harder for drivers to see where they are going. Locating the edge of the road and judging distances to oncoming vehicles were the principle concerns expressed by truck drivers.
Queensland's Dept of Mines attributes haul truck accidents as being due to either driver error or road conditions. A study of their safety records shows that approximately three quarters of accidents are caused by road condition, as opposed to driver error (table 1). These figures were calculated from lost time injury records for the Queensland coal mining industry since 1991.
It is likely that the lesser total number of accidents during the night is due to fewer numbers of vehicles operating during the night. Unfortunately it was not possible to collate these numbers to confirm this or to calculate the proportion of night time and day time accidents as a percentage of truck operating hours.
The ratio between the attributable cause of the truck accidents does not vary significantly between day and night driving. At first glance this suggests that night driving is not substantially different from day time driving. However there are many other factors that are not considered such as truck speed and it would be wrong to draw these conclusions. Certainly, most truck drivers feel that driving at night is more dangerous than during the day.
The accident figures also fail to take into account the effects of fatigue and stress that drivers experience driving at night.
A suitable surface treatment for in-pit haul roads could possibly deliver the following gains:
>up to 3% cycle time reduction on in-pit haul routes;
>as yet unmeasured, decrease in equipment damage and downtime;
>a possible increase in vehicle running efficiency;
>increased driver confidence;
>possible decrease in driver fatigue and long term back problems.
Improved use of roadside markers in the form of guideposts or reflective cones will help delineate the haul road, but is not a complete solution. Markers do not help the driver's perception of the haul road surface and irregularities. They merely guide the driver along the road by making the road edge more discernible.
The materials investigated for the purpose of treating the haul road surface are too expensive or difficult to obtain to make their use worthwhile. Further investigation showed the two most promising candidates - fly-ash and fluorescent dyes - to be uneconomical, and uncovered potential environmental problems.
It is recommended that the project not proceed to the field trial stage.
Roadside markers are not a complete solution, and in-pit haul routes are too transient for useful implementation. Surface treatments have been proved uneconomic and could create undesired environmental or safety problems.