Health & Safety including Dust Control
Control quarry dust
Careful design of dust control measures for quarry and mineral processes
will enhance operator safety, says Dantherm Filtration’s Gus Bishop
Quarrying and mineral processing are inherently dusty and noisy operations. Indeed, short term emissions from operations such as blasting are virtually impossible to contain. Nonetheless, quarries and processing plants are designated workplaces, subject to the provisions of DSEAR and Control of Noise at Work Regulations 2005. Furthermore, external environmental standards must also be addressed. However, dust and noise from static machinery and other continuous sources of noise and dust can be treated successfully. The challenge is to design and install efficient, long-lasting low capital cost abatement that operates with minimum energy and maintenance costs without inconveniencing the process or operators.
It can be clearly beneficial to make use of available materials and site features at the outset to minimise emissions particularly in sensitive directions; for example overburden that must be removed initially may be used to form a baffle at the site perimeter. Crushing, screening and grading plant should be located so as to minimise nuisance noise. Of course, established quarries with a floor well below the surrounding ground level will cause fewer problems, at least with noise. Among the range of sounds emitted by static and mobile machinery, one could be forgiven for dismissing as insignificant the relatively low grade noise from dust extraction fans and discharge systems. However, continuous tonal noise from fans and ducting, particularly during extended shift working, can give rise to complaints from neighbouring properties and in many cases from quite distant neighbours.
Dealing with dust
As part of general accident reduction targets set by the Health & Safety Executive (HSE), abatement of dust and in particular silica dust have been identified as important factors. Maximum
ABOVE: Aggregate silo with filtered inlet, for vehicle loading bays
exposure limits (workplace exposure limit, or WEL) for crystalline silica are set very low, at 0.3mg/m3
(8 hour time weighted
average TWA). Most other undefined mineral dusts have TWAs of 10mg/m3
for inhalable and 4mg/m3 for respirable dusts. These
ABOVE: Filter unit with skimmer pre-separator – asphalt mixing
www.solidsandbulk.co.uk
limits are published in the regularly updated HSE handbook EH40/ – Workplace Exposure Limits. Whilst personal protective equipment (PPE) may be employed, it should not be the first defence against potentially harmful emissions. Under CoSHH legislation regular inspections at intervals of 14 months must also be made and accurate records kept to monitor the environmental and physical condition of dust control equipment (Local Exhaust Ventilation – LEV – in HSE parlance). Careful loading of crushers, with minimal drop heights will assist the dust collection at these machines, particularly as quite low site wind speeds, even as low as Force 1 - wind speeds up to 1.5m/s, described merely as “light air”on the Beaufort scale - can adversely effect extraction from partial enclosure hoods. Adjacent conveyors should be enclosed where possible, with dust extraction hoods at their loading and delivery points. Belt conveyors should be fitted with effective and accessible scraper bars to prevent spillage from the return belt and these should be fitted with dust extraction hoods. A conventional reverse jet pulse-cleaned bag filter could serve the crusher and adjacent conveyors as part of a centralised dust extraction plant.
May 2010 • Solids & Bulk Handling 39
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