Silica Dust In Control

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

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.

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, tells Contractor.

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.

This new research will seek to document the worksite behavioural changes that have taken place since the hazard became known and WorkSafe and the industry began working together to mitigate it.

Donna says the principal tools in getting the silica hazard message out to the industry have been fact sheets and Toolbox Talks.

“We’ve had really good buy-in from industry with that approach.

“Rather than saying ‘This is what you must do,’ we’ve said ‘These are the things that actually work, so let’s try them and see if they work out there in your workplace’.”

Donna saw the effects of the campaign herself on a Christchurch site in early May.

“The guys showed me how they were using water suppression on the demolition work they were doing.

“They were all kitted up and the water was keeping the dust down really well.

“They wouldn’t have been doing that 18 months ago,” she says.

Because industry had taken up the challenge so well, “We haven’t had to regulate to the nth degree and say ‘Thou must do this’ – we haven’t felt the need to do that at this stage.”

As for the workers who might have been exposed to silica dust before the alarm was given, Donna says it’s too early to see if any health problems are emerging.

“We’re working with industry and health professionals to develop the awareness that, if a worker does come in with respiratory problems, to think whether it could be related to work.

“The health professionals don’t always think of that.”

There has been anecdotal evidence of workers being affected by dust, “but nothing robust yet”.

“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.

Meantime, it can safely be assumed that 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.

Andrew Robertson, currently a member of the New Zealand Safety Council, was at the time a mines and quarries inspector 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 the silica dust hazard in the extractives industry.

The inspectorate took samples from quarries all around New Zealand 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”, Andrew tells Contractor.

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,” says Andrew.

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