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Exposure to silica dust

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It can safely be assumed that exposure to silica dust does not pose a serious threat to underground and surface miners – it’s largely unique to the construction industry – because a study carried out nationwide in the mid-1990s allayed such fears. HUGH DE LACY explains.

Silica dust is carcinogenic, leading to lung diseases like silicosis, and from there to chronic obstructive pulmonary disease, lung cancer, tuberculosis and kidney disease.

Alarm bells rang in the Christchurch rebuild industry when a pilot study carried out by WorkSafe NZ and published in July last year revealed high levels of silica dust at 39 construction sites.

However, past studies in quarry sites put a different picture on the problem. Silica dust is not a problem in the extractive industries, though it might conceivably occur in some goldmines, but it is otherwise confined to construction sites where it’s mostly generated by breaking, cutting, grinding and smoothing concrete.

Andrew Robertson, currently a member of the New Zealand Safety Council, was a mines and quarries inspector in the 1990s employed by the then Ministry of Energy.

He was appointed to an inspectorate created under the auspices of that ministry and the state-owned research body Environmental and Scientific Research (ESR) to evaluate silica dust risk in the extractives industry.

The inspectorate took samples from quarries all around the country, which were then tested by ESR.

“In the whole country we could only find one quarry that exceeded either the respirable dust exposure limits or the free silica levels,” Andrew says.

The single exception was an Auckland quarry, and that occurred, “only because they had a dry dust collection system above screens and all sorts of things, and when they blew it into a bin they had an Archimedes screw with a water jet on it that blended with the water to produce a slurry they could dump in the over-burden”.

Because the dust kept bridging at the bin, a worker – properly kitted in respiratory gear – was designated to clear it, and it was at that point that the dust might have been a hazard.

“I can well understand how silica dust might be a problem on Christchurch construction sites, but it’s certainly not a major for the extractives industries,” Andrew says.

Meantime, the civil construction industry’s response to the silica dust risk in the Christchurch rebuild has been such that it’s unlikely that asbestos-type regulations will have to be introduced to control it.

The demolition stage of the Christchurch rebuild in particular generated huge amounts of the dust, and that has continued into the reconstruction phase.

The industry at large was generally unaware of the hazard that silica dust poses, and WorkSafe responded when its pilot study identified a lack of efficient dust suppression, and the failure of many workers to use respiratory protection.

“There was a real lack of awareness among people – they seemed to be a bit surprised about it,” Donna Burt, WorkSafe’s occupational health project manager for the rebuild, told Q&M.

There was plenty of international data to show the extent of the hazard, but little to tell whether it was a problem in Christchurch.

“What we did [after the publication of the pilot study] was we engaged with industry directly to get them to take ownership of it as well, and we’ve worked with them since then,” Donna says.

And the industry’s response has been such that WorkSafe has no plans to introduce regulations for silica dust such as those about to be unveiled for the better-known and more widespread hazard of asbestos.

“[The industry] have really taken it on board: there’s still room for improvement but there are a lot of really good things that the sector’s doing – in fact we’re just about to do an evaluation of it,” she says.

“We’ve just got a project underway looking at some of that [evidence], and there’ll be some data looking at health monitoring results and the lung function that’s been going on for five years here in Christchurch.”

Once that data arrives in a few months, WorkSafe will be able to judge how effective its response to the silica dust hazard has been.

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