Presented by Dr Martin Stirling
When managing the issue of dust generated during concrete shaping operations in construction, the full hierarchy of controls needs to be considered, from design all the way through to protective personal equipment.
In this presentation, recorded at the Healthy Lungs Forum in November 2019, Martin provides practical examples of engineering controls and describes how their effectiveness was assessed, relative to current and future working exposure standards.
Note: From 1 July 2020 in Queensland the new national workplace exposure standard for respirable crystalline silica was revised from a time weighted average of 0.1 milligrams per cubic metre (mg/m3) down to 0.05mg/m3. This means that, from 1 July 2020, the reference to the workplace exposure standard for respirable crystalline silica in this presentation should be understood as a reference to the new standard of 0.05mg/m3.
Dr Martin Stirling is an experienced engineering and marketing professional with a history of working in power generation, manufacturing and the construction industry in Australia, Ireland and South Africa.
He has an extensive catalogue of skills in mechanical engineering, materials science, construction technology, marketing and is a graduate of the Australian Graduate School of Management (MBA) and University of Cape Town (BSc / PhD).
Martin's interest in dust came about from his post-graduate research work into wear caused by fly ash in coal fired power generation. This was followed by industrial research work in diamond cutting tools.
Since 2004 Martin has worked in construction, introducing new technologies for drilling, cutting, grinding and breaking applications. As all these applications are dust generating, Martin has developed a passion for occupational health.
Run time: 24 minutes 34 seconds
View presentation slides (PDF, 3.62 MB)
Download a copy of this film (ZIP/MP4, 817MB)
Dr Martin Stirling: The presentation that I'll be delivering today really focuses on looking at some of the practical solutions that are available in the industry, both from us as a supplier, but just generally making some wider comments about what is available to control silica dust in the industry when it comes to on-tool extraction.
And really, I suppose, as an engineer where my passion comes from is, is I'm in the kind of position where I need to bridge between the occupational health and the engineering and then the trades person at the end of the day. And often it's pretty difficult to make that link, but through some of the trainings that we've developed over the last few years, we're starting, I think, to make some traction. And it's particularly gratifying when I visit Queensland to see the huge strides that have been made within the industry over the last few years.
I remember coming up here 10 years ago and walking onto construction sites, and you'd literally be breathing in dust, seeing dust billowing out of open windows. And it was a really messy place to be. Now, all these years later, it's a very, very different environment. And quite honestly, particularly if you walking on to a tier one building site in the CBD, you'd be hard pressed to see any evidence of dust. So there's been massive strides made in there. So it's evidence of the good work that's been done by the government is very, very clear.
But I just want to indulge the science geek within myself and just show you a few slides of what exactly are we talking about when we look at silica dust.
The scanning electron micrograph that you see, let's see if I can find the laser, this is a crystalline silica particle in Sydney sandstone, undisturbed. And this is a crystalline silica particle in concrete, again, undisturbed. Now really those measure about 400 microns across, but what you'll notice about them, they're pretty angular. And what I'd like to stress about them is that they are very hard and they are very insoluble. And really this is the issue with crystalline silica. If you disturb them and you break them down and you're unfortunate to breathe them in, your body just simply can't break them down. And when those macrophages within your lungs come along to try and destroy them, they die eventually and release those enzymes that cause the scarring within the lung and leading to the eventual health problems we've seen.
So what happens when the silica particles do actually get disturbed? So we did a series of experiments where we recovered silica particles from P2 dust masks, post grinding and drilling. And what you see over here is an example of a silica particle embedded in a P2 dust mask. Look, it's pretty much the same thing, it's still extremely hard, it's still insoluble, but you'll notice it's a little bit more angular. And one thing important to notice, or to note with crystalline silica is when it's freshly disturbed, it is more reactive. So the kind of toxicity studies that have been developed, that have been performed will indicate that freshly cut silica or freshly disturbed silica is a little bit more hazardous than silica that's been lying around for some time.
Now where we find silica dust in construction, a lot of the focus in the last few years has really been on the presence of silica in engineered stone, but really we find it in varying proportions across a wide range of construction materials. You're just always going to see that. It's just simply because silica is, forms a considerable part of all of our earths crust, I think about 55% as an element.
So no matter what you quarry, no matter what you put together as a construction material, except for organic wood, of course, you probably going to find it. So in terms of content, right at the top, the highest amount of silica that you're going to see within construction is the engineered stone. But then we also going to see a lot of it in a fiber cement board and then decreasing concentrations through concrete all the way down to almost close to zero in just plasterboard.
So read the message that I'm trying to put forward in the slide is, it's really important to look at all construction materials, look at everything you're dealing with when you're looking at developing risk assessments for dealing with silica, it's not just a matter of focusing on stone bench tops or even just concrete. There are quite a few watch outs there.
Just another point regarding a silica dust generation onsite, really, we see two main sources. The primary source being the silica dust that's generated when you actually do the machine operation. And then once that dust settles, it can be re disturbed with people just walking through it or machinery moving over that part of the area where dust has been deposited. So you generate the hazard once again.
The kind of rough size range of silica particles generated on site, it varies between 0.1 micron and up to over a hundred micron, but the size range of particles that are generated from these machining applications, they range between one micron and about a hundred micron. But they also very slightly, depending on the kind of machining operation that you're using. So say for example, you are doing diamond cutting or diamond grinding. We typically find that the size fraction of the silica particles, about 50% of it lays between 10 micron and 0.1 micron. Then when you get to other kind of operations like drilling, which is more of a percussion based material removal process, then the particle size that is generated is much higher. So it's slightly less hazardous. So really we have to be very careful, not only just with the material itself that we cutting, but the cutting operation itself.
Now the big question, how much dust is actually generated in these different applications, if I wasn't to recover it. And we just look at a wide range of applications, you typically see here on site, ranging from drilling, cutting, dry coring, grinding, they all generate dust, but we don't really have a great feel for how much dust these applications generate. And I put this forward just so we can start to think about what do we need to have in our SWMS when we start to look at controlling these kinds of situations.
And this gives you a rough idea of the amount of dust that is generated per application. So say for example, slitting or chasing, in suburbs where double brick masonry is very prevalent, where a lot of chasing gets done, that's a real watch out. Slitting, unprotected generates an enormous amount of crystalline silica dust, and particularly residential areas or mom and dad kind of operations, this is a particular area that holds a lot of concern, certainly with us, when we see it being done and protected.
Then when we get to a light drilling that we see when you go into site, when plumbers and electricians are installing screws, overhead, to hang pipes et cetera, it's not as much of a dust generating exercise. But there again, we have to be pretty careful because those kinds of operations are very hazardous. If you think about doing it overhead, the operators right in the breathing zone of the dust, gently flooding down into their mouths. So it's not just a matter of the amount of dust that's generated, but also where it's being generated and how close is the operator.
So now we get to the point of what kind of engineering controls are available to take care of dust when we involve these various machining applications. And the good news really is, it is a very easy process to control, but it has to be done in concert with RPE. So although RPE is a low order control, it's not a control by itself. It needs to be used in conjunction with an engineering control, quite often.
So let's just get a visual impression of what it looks like when we don't control dust. Now, yes, it's true that when you see this kind of dust, that's probably in the greater than 20 micron size range. Most operators are tempted that once the dust disappears, that they then safe, but that isn't the case because these particles hang around for quite some time. But if you walk into site and you see dust billowing out, like this, it's a very strong indicator that that person is at risk.
So here's some just rough examples of what these engineering controls can look like. So you can fit dust hoods onto grinders, connected with a vacuum cleaner, and you can fit dust hoods onto large electric cutters, again, fitted to a vacuum cleaner. Very similar thing with slitting, it's very easy to control with a dedicated slitting machine. And then an alternative is the wet cutting. Now wet cutting, and will be covered in some of the presentations later, wet cutting is not a silver bullet for cutting of any silica dust containing materials. And that's really due to the battle between the aerodynamics of a water droplets and aerodynamics of very small silica particle, but I won't go into too much detail there, but wet cutting is a very good start to try and create a barrier between the operator and the dust particle.
Concrete grinding is a very easy process to control as well, with a customized hood connected to a vacuum cleaner. It's very effective to remove dust as we grinding. And then we get the good old rotary combihammer, with the rotary hammer. In times gone by, I'm sure we've all got horror stories of when working on construction site at the end of the day, feeling dust between our teeth. It's not very pretty, particularly if you're working overhead. This is probably the simplest issue to control on site, because it's very easy to turn just your humble rotary hammer into a combination of a vacuum cleaner and a rotary hammer.
And I might just touch on another point. Really the success of an engineering control depends on the ergonomics of that engineering control. So if it's easy to fit, the worker is definitely going to use it. And this is really how simple it can be.
That's normally when it goes wrong, isn't it, trying to do it on stage. But this is how simple it is just to attach an onboard extraction device onto a drill. If it's designed to do that. So there's really in terms of getting subcontractors on board, that's often a challenge for principal contractors. As soon as you can demonstrate that the controls are very easy to use and very ergonomic and not that expensive, it becomes a lot easier.
Another way of controlling dust is controlling at its source. So there's a number of suppliers in the industry that supply these types of products. So instead of using conventional drill bits, one can use a hollow drill bits, which actually suck the dust out through the center of the drill bit. And we got a few examples of this on our desk outside, if you want to have a look during lunch.
An alternative to dry drilling, of course, is wet coring, but then there's a watch out with wet coring. One has to be careful to suck up slurry, post coring, because that dried slurry, if it's disturbed, post coring, also presents a hazard. So it's good to either recover during coring or post coring by vacuuming it up.
Exhausting dust during braking. That's also entirely possible just simply by fitting a jacket to the breaker and then sucking it up to the vacuum cleaner. And we saw some pictures from painter from Townsville, where we saw not one of the commercially available jackets, but certainly one that did exactly the same job.
But now the big question, and this is really the crux of this presentation is how effective are these controls?
Now the kind of testing that we do, clearly we can't test every single last application. And there are a number of variables at hand when you're testing these kinds of applications. Just listening to some of the questions earlier, a big variable is whether you working in an enclosed space, a semi enclosed space, or even outdoors, because that has a huge impact on the overall dust concentrations you might pick up in dust monitoring.
So what we try and do is just really aim for the worst case scenario. So the testing is done in a dedicated lab and it's done in a fully enclosed space, 200 cubic meter space with no air exchange. And then a set [inaudible 00:14:05] type test is done where we machine a certain number of meters, where it's cutting or drilling a certain number of holes, when it's drilling.
So the fact that it's in this enclosed space means that dust builds up over time and presents the kind of the worst situation. So these kinds of test results, you really need to just look at and then extrapolate to your kind of a situation to give an indication of whether you need to do this in conjunction with RPE, whether you need to do this kind of operation in conjunction with an air scrubber to keep the passes by safe.
So looking at these kinds of test results, machining about 13 meters worth of cuts, which generates four kilos of dust. After that one hour period, within that closed space, the silica dust concentration is about 0.3 milligrams per cubic meters, which is way over the existing limits. So in that particular case, that operator really should be wearing RPE. And very importantly, in this kind of situation, we need to make sure that the passes by or the people working in that kind of environment, where there's concrete cutting, they also need to be protected.
Then we need to get to a dust control during grinding, as long as the surface is flat, dust control during grinding is quite an easy problem to manage. So again, using those same test conditions in our enclosed space of 200 cubic meters, you see the dust concentration about 0.04 milligrams per cubic meters. So using the appropriate RPE, it really means that the worker can be well underneath the current and the future exposure levels. But again, with a watch out that these kinds of test results need to be looked at as a single data point, not as a promise that the system will keep a worker completely under the limit for an entire working day.
Then this example of the rotary hammer, because you generate a courser dust, when drilling with a tungsten carbide bit, again, it's quite a simple problem to manage. And the silica dust concentrations that we've seen after drilling quite a few holes, sort of 75 ml holes with quite a large diameter for this machine. We see the silica dust concentration being quite low after that one hour period. And the plumbers and electricians that I've presented this kind of data to tell me that they'd be pretty thrilled, if they could get a worker doing this number of holes a day, let alone in one hour.
But then I'm just really to finish off this presentation, I would just want to speak a little bit about some of the methodologies that we've seen principle contractors use with subcontractors and proving to them and getting them to buy into why controlling dust is important, not just for workers' health.
And this is really because controlling dust on a construction site is really a win win situation for two reasons mainly. The most important reason is that it almost completely obliterates your cleaning bill, right? And that's simply because if any of you, like myself, are the household cleaner, it is so much faster to vacuum up mess compared to sweeping it. So we get huge productivity gains just by switching to vacuum cleaning, to clean, but then the productivity gain is also huge if you've controlled dust in the first instance.
So it's not just numbers that people buy into it, but anecdotal reports that we get back from subcontractors. So they really notice a difference by switching over to like a no broom policy. And by switching over to dust control measures, to engineering controls, to control the dust.
Another major savings for principle contractors and subcontractors is in machine reliability. And we found by really putting both of these arguments in front of subcontractors and contractors, they really buy into the story. And the reason why it is so good for machine reliability is that all of these machines have got cooling ports in them, whether it be small drills or large drills, small cutters or large cutters. And if you don't have an engineering control attached to them, they are quite happy to suck dust through their motors and coat the electronics. And they don't last nearly as long as when you've got an engineering control in place. So with a combination of those two arguments, in addition to the health benefits, it's a really easy discussion to have with a contractor to really convince them that controlling dust is a very easy thing to do.
So really that's it, in terms of my presentation, thanks for your attention. And I'm very happy to take questions. And as I mentioned, we've got a table outside that you can look at some of these products that we've got physically for you to see.
Speaker 2: Hi. I've just got a question, so on all the equipment, it talks about, in a couple of the sessions on how it all sucks it up, but there's nothing really on how, the disposal methods to happen. I've never actually used any of them, but I've been to sites and seen them empty vacuums, like they go to the trouble of vacuuming it up, but then they just put it in the general waste bin that's just outside that the wind is blowing around. So is there, I suppose nothing talked about disposal methods and containment of that.
Dr Martin Stirling: It's an excellent question. And Luke, if you can just start your stop watch, because I might go on a very extended monologue now. Okay, good.
No, it's a really good point because just after you've gone to all of this effort, putting engineering controls in place, you see a worker wander down to the skip and up-end the vacuum cleaner, and they are covered in a billowing cloud of dust.
So we've seen principal contractors when they've done time and motion studies with their workers, where they see spikes in dust exposure, much like the plot that was shown earlier with spikes in exposure, when you get out of a working cab, you see a huge spike in exposure when a person empties a vacuum cleaner, because they automatically become exposed to all of that dust that they've carefully collected.
So it's really important that the vacuum cleaner that's being used, being an N class or be it an H class vacuum cleaner, it simply has to be fitted with a bag. Okay? And now that bag can be a capable bag, which can be capped off and put in a put in a skip or plastic bag that can be tied off and put in a skip. And then you also suggest when putting a SWMS together that if a person is taking off the lid of a vacuum cleaner or changing a bag, regardless if it's capable or not capable, to be wearing a mask, because just the mere action of taking a vacuum cleaner lid off, it does pull out a plume of dust. And then the same goes for exchanging filters. That's a very important thing to be careful with when cleaning a filter or exchanging a filter, is that the person is wearing a mask, but it's also important to bag that filter when it's disposed of in landfill.
Speaker 3: Thank you so much for your presentation. I'm going to go to part two of the questions that are just started with the last speaker, is because we've talked about all these devices that are doing engineering controls to capture the dust whilst the person is doing the drill bits and stuff. And your study is already showed that there are secondary dusts exposure to people that's in the environment or walking in a building construction site, as you can see here, is that there's a lot of people that walk, subcontractors come in, they will not be in full PPE. You may have engineering controls and their dust barriers, plastic sheetings and stuff like that, but still that secondary exposure may still be there. So in this whole forum, I think in the last year, I've been looking, following these trends for, quite seriously and I still haven't seen anything talking about air scrubbing or air filtration systems being used on site. The last presenter had an air scrubber, which was really fantastic. So what's your thought on that?
Dr Martin Stirling: You know, the question of air scrubbers or air cleaners is a very relevant one, but the bigger question is, "Well, how do I control the environment?" So there's two methods. One is the additional engineering control, IE the air scrubber and the other one is the administrative control. So we do observe principal contractors coordinating off areas. Say, for example, if any cutting to be done, they have a cutting area and they either control it fully within that cutting area and then have an air cleaner attached to that cutting area to clean it. Or we see a lot of contractors starting to go to the air cleaner route. And there are a number of products on the marketplace and, and please come up and see me during the break and I can give you some recommendations of potential places to look, but that's an area in development, the air cleaner market, but definitely something we're going to need to consider for the future, when we think about not looking about dust control just with the engineering control, but dust control for my entire environment.