The primary objective of this project was to determine whether asbestiform fibres were present in kimberlite mines, mining both pipes and fissures. This research work was carried out in conjunction with another SIMRAC project OTH 410.
Dust control by means of water is undesirable due to the fact that blue ground swells and disintegrates when it comes into contact with water, rendering the ground still to be mined unstable and unsafe.
The dust caused by dry drilling is a cause for concern and a research project was undertaken to determine the risk to which this drilling method exposes employees.
A literature study revealed that asbestiform fibres are commonly found in rock formations world-wide, with chrysotile being the most prevalent form of asbestos fibre. It is commonly accepted that a background fibre concentration of 0,0005 f/ml would be representative for urban outdoor levels. It was therefore necessary to establish the background levels of fibre content in the atmosphere, which could have an effect on underground sampling.
Fibre counts did not differ much between the two mining methods (pipe and fissure mining) or between wet and dry drilling. However, during dry drilling, there was a tendency for dust to obscure the presence of fibres, resulting in possible inaccuracies during the fibre-counting process.
When the dust load was reduced by means of control measures, more fibres became visible for counting. High fibre counts were noted when samplers were programmed to sample at short intervals (10-minute cycles) during every 60-minute period. Less dust was then sampled and the asbestiform fibres were easily detectable by means of microscopy.
The extent of employee exposure was not established but the results obtained during this project revealed that asbestiform fibres are present in the working environment of kimberlite mines and this means that further monitoring of employees is necessary to determine their risk and personal exposure.
Monitoring of asbestiform fibres should form an integrated part of the monitoring programme for airborne pollutants. Structured routine sampling for airborne fibres should be conducted at all mines mining kimberlite, irrespective of the type of deposit mined (excluding alluvial deposits).
A cost-effective method of identifying the various asbestiform fibres and other fibres is
necessary for the whole mining industry in South Africa.