Underground » Health and Safety
The risks associated with the use of aluminium alloys are due to the possiblity that of high energy impacts of aluminium alloys on rusty steel objects can cause an incendive spark. Twelve incidents occurred between 1950 and 1955 in which such a spark was the source of an ignition of methane. Of these 6 occurred in the UK, 4 in Germany and 2 in Japan.
Ten were attributed to the roof supports in a longwall face utilising aluminium and steel friction wedges. Of the remaining two, one was caused by a hand held drill (made from 93% magnesium alloy) dropped onto a rusty roof support girder and the other by a stone passing through a ventilating fan and striking an aluminium alloy fan blade.
A further explosion occurred in 1962 in which it was thought, but not conclusively proven, that aluminium wrappings on rusty steel rails may have been one of the ignition sources. It was for these reasons that the use of aluminium was restricted, but not prohibited, in the UK. Legislation practices in New South Wales and Queensland reflect the UK position.
Aluminium Use in U.S Coal Mines
A study tour of coal mining operations in the United States of America was undertaken to assess the use of aluminium alloys underground. This showed widespread use in applications which ranged from the coal face to outbye areas. The only prohibition is on its use as a ventilation control device (stopping). There is also a restriction on the alloy content of external rotating parts on permissible electrical equipment (<0.6% magnesium).
Aluminium was used where it was considered to be the most appropriate for the nature of its application. Factors considered important were its lightness, and therefore its potential benefits in reducing manual handling injuries, its machinability and castability for engineering manufacturing purposes.
Examination of MSHA's ignition database showed that in the period from 1959 - 1991, there were 2071 ignitions recorded in the United States.
None of these ignitions were attributed to incendive sparks caused by aluminium contacting rusty steel. The study shows that the level of risk associated with the use of aluminium alloys in underground coal mines in the United States of America is extremely low (high uncontrolled use - no ignitions). It is proposed that where similar equipment and conditions exist in underground coal mines in Australia, the level of risk is comparable.
There is no prohibition on the use of aluminium in the oil and gas industries. No data could be obtained as to the extent of the use of aluminium, or whether any ignitions had been attributed to its use in the oil and gas industries.
Risk Management for Aluminium
However, where there is the potential for an ignition source, a system of control must be implemented appropriate to the level of risk. The intent of the project was to provide a definitive answer as to the risks and benefits of using specific aluminium products in underground coal mines. However, it was recognised during the project that the risk will vary from mine to mine. Therefore a generic risk benefit assessment process was developed to allow individual mines to make their own assessment.
To enable this, an assessment procedure has been developed which considers all the factors relevant to the use of aluminium alloys below ground, any benefits associated with its use and gives a ranking of risk and benefit. The procedure uses standard risk ranking techniques and accounts for factors associated with:
- the environment in which an aluminium alloy may be used;
- the nature of its design and use;
- benefits, if any, in either manual handling, engineering or cost reductions.
This procedure is an effective first step in the managment of aluminium risks and provides a conservative ranking or risk/benefit. It is not in itself a complete managment tool for the effective control of risk, but it can be used to assess if barriers are necessary, and if so assess the effectiveness of such barriers.
Benefit of Low Weight Materials
A recently completed study by the Victorial Institute for Occupational Health and Safety and Health (VIOSH) showed that there is overwhelming evidence that overstrain injuries are a significant problem to the underground mining industry both in Queensland and New South Wales. The study identified in Queensland and New South Wales that the highest priority for underground workers, is 'Ergonomics of manual handling tasks'
Weight of items is a contributory factor in strain related manual handling injuries. Significant benefits may be obtained in terms of reduced injuries by investigating the use of aluminium to make equipment lighter and easier to handle. Reduced mass and bulk when carrying items can also assist in the reduction of slip/trip incidents. Weight savings on individual components could be up to 60%, although on complete products, where only some components are substituted in aluminium, reductions may only be in the order of 10-20%.
It is recommended that the risk benefit process, developed as part of this project, be conducted on all aluminium equipment where significant OH&S benefits can be achieved to assist in reducing the incidence of occupational injuries in the underground coal mining industry. These assessments need to be conducted on specific applications at specific mine sites.
As well as OH&S benefits, there are engineering benefits from using aluminium:
- less weight reduces mechanical stress and inertia and improves power to weight ratio;
- it is easy to cast and machine;
- has good heat transfer characteristics;
- can reduce noise and vibration in some applications.
Additionally, there are cost and convenience benefits in being able to use commercially available equipment (used in general industry) in the coal industry.
Conclusions and Recommendations
There is overwhelming evidence to show that overstrain injuries are a significant human and cost problem to the underground coal mining industry, both in Queensland and New South Wales.
Significant benefits may be obtained in terms of reduced injuries, and therefore flow-on reduced operational costs, by the use of aluminium to make selected equipment lighter and easier to handle.
There is evidence that in some selected cases, direct and immediate cost savings on capital equipment of between 2.5% and a massive 66% could be achieved.
Mass savings on commonly used (individual) items could be up to 20%. Items repetitively moved or lifted, such as inspection covers, are probably an ideal target, and they are in common place use overseas.
To obtain more detailed and more specific examples of where aluminium products are lighter and provide significant benefits requires completion of a full study. As the manufacturers in Australia cannot use aluminium in colliery machines, the majority have not completed the engineering required to produce detailed information as to the exact benefits. Only by accessing manufacturers who have supplied equipment to coal mines where aluminium is freely allowed (USA, and to some extent South Africa) can we provide fully engineered data to adequately define the benefits.
This relatively small survey has confirmed the difficulty in obtaining information on a subject which few people/organisations in Australia have any experience in. It has therefore reinforced the need to directly obtain valid overseas information.
The lack of detailed information on applications has highlighted and confirmed that the proposal risk analysis will be flawed unless further data on aluminium applications is gained from countries/organisations familiar with the issue. We therefore recommend that the original project submission is followed, and that the risk analysis cannot proceed until a more complete applications study is undertaken and that the current use of aluminium in the USA is more fully understood by the project team.
This would also need to include gathering specific data, particularly any evidence attributing aluminium to any mine fires, explosions etc and also contrasting relevant injury statistics between mine/industries.
Given the nature and sensitivity of this issue, it may be appropriate that an industry representative accompanies a project engineer on any overseas visit. Ideally, this representative would then be made available to be a part of the industry risk analysis team.