Silicosis is an occupational lung diseases (OLD) caused by the inhalation of free respirable crystalline silica dust.
Silica dust is present in many industries, including mining and quarrying where quartz concentrations are high, as is the case in many deep-level gold mines. If inhaled, crystalline silica dust may cause a fibrotic reaction (or scarring) in the lung, which results in a restriction of lung elasticity. Silicosis predisposes an individual to the development of pulmonary TB. The chance of this is increased when an employee is immuno-compromised – for example, if he or she is HIV-positive. Silicosis and TB in silica-exposed employees are considered to be compensable diseases in terms of the Occupational Diseases in Mines and Works Act (ODMWA).
As gold mining companies, we take seriously our responsibility to prevent the generation of dust at source – the areas where dust is created - and to protect employees from exposure.
As far as possible we prevent the generation of dust at source, that is, in the areas where people work. Dust may be caused by various mining activities, such as drilling and sweeping, and during transport among others. The dust that we are concerned with is minute particles that are often undetected by the human eye, and which comprise silica, a natural component of the orebodies we mine.
One of the most effective ways of managing the dust that is inevitably generated is through efficient ventilation, with fans and detailed ventilation plans in place to remove the dust from working areas.
Employees who are located in potentially dusty areas are also provided with and encouraged to wear personal protective equipment (PPE), including dust masks. All working areas are sampled on a regular basis to determine the exposure of employees to dust and potentially vulnerable employees are continuously monitored by wearing portable gravimetric sampling devices. These devices are able to gather and calculate the actual exposure to dust of an individual which, in turn, allows the rotation of employees across working areas should higher levels of exposure be detected.
Extensive research and development has been undertaken into appropriate technology (such as drilling and ventilation) and mine planning to reduce the generation of respirable crystalline silica at source. Some of these techniques and technologies include drilling, ventilation, dust allaying, filtration at tipping points and centralised blasting to prevent peak exposures.
We have also been constantly improving our standard of dust monitoring, sampling frequencies and dust analysis methods.
Collectively these efforts have resulted in the incidence of silicosis (the number of new cases in a study population in a given period) declining over time. This is also evidenced by the increasing period of exposure before diagnosis.
It's important to note that given the length of time it takes to contract silicosis, the dust management procedures put in place now are only likely to show results (fewer cases of silicosis) in about 20 years' time.
The 2003 Mine Health and Safety Council (MHSC) health and safety milestones agreed between government, labour and business committed companies to achieving, among other things, the target that 95% of all exposure measurement results would improve on current regulatory requirements and by 2014, be below the milestone level for respirable crystalline silica of 0.1 mg/m3. In aggregate, that ambitious target was close to being reached, according to MHSC data published in November 2014 by the Chief Inspector of Mines (see graphic below).
The milestones also set the goal of no new cases of silicosis among individuals unexposed prior to 2008. As far as we are aware, there have not at this stage been any such diagnoses. Of course, because of the lengthening post-exposure diagnosis period, it would be premature to assume that there will never be any such diagnoses.
In line with international trends towards even more rigorous dust controls, the renewed 2014 MHSC milestones set a new target - that 95% of all exposure measurement results will (by 2024) be below the milestone level for respirable crystalline silica of 0.05 mg/m3. We are now working towards that goal.