Clearing the air on dust emissions
Dust emission regulations are changing, both in Australia and internationally.
Parliamentary enquiries in both Queensland and NSW over the past 12 months looking into dust from extractive industries and the management of impacts on workers, have identified failures and inefficiencies of the regulatory framework under which dust diseases are managed.
Add to this the review of exposure standards and their development currently being undertaken by Worksafe Australia, and it is reasonable to expect the interest in occupational exposure to dusts will continue for the foreseeable future and with that will come an onus on businesses to adapt their processes accordingly.
In addition to this, at the environmental level, a review of the air quality objectives provided in the Ambient Air Quality National Environment Protection Measure (NEPM) was also recently completed.
At the community level, improvements in technology and the availability of low cost sensors is leading to an increased interest in the quality of air in and around people’s homes.
For extractive industries, this increased focus on dust and the change to the regulatory framework likely as a result, is a source of uncertainty.
Not all dusts are equal
The composition, size and concentration of dust varies with the sources of emissions, atmospheric conditions and local topography.
While there is potential to treat all dust in the same way, not all dust is equal with some sources presenting a greater risk in terms of potential health and nuisance impacts.
For most atmospheric contaminants, an exposure limit is a single number – a concentration is established where the risk of adverse impacts, whether on a worker or nearby resident is understood and considered acceptable.
The operator can then monitor or review emissions of that compound to gain comfort that the impacts on both workers and the surrounding environment are acceptable.
For dust or particulate matter, this process becomes more complicated.
While all dust can be harmful, the potential for health or nuisance impacts associated with particulate emissions is dependent not only on the duration and level of exposure, but also on the size, type and chemical composition of the particles involved.
The size of particles in a plume of dust determine how far into the respiratory system the particles are able to penetrate, with larger particles captured in the nasal and oral cavities and smaller particles able to reach the bronchi.
In addition to size, research has identified that in many cases the chemical composition of the particulates comprising the dust have a larger impact on the potential for health impacts than size alone.
While much of this research is ongoing, specific health impacts necessitating stricter controls and exposure limits have been identified for many metallic compounds, diesel particulate matter, crystalline silica and coal dust.
What you can’t see can hurt you
As consultants, we regularly speak with site staff involved with the management of dust on construction and extractive industry sites.
We’re often told they use visibility of dust as a measure of the effectiveness of their controls – that is, if you can’t see it, it’s not there. Or alternatively, if you can’t see it, it can’t hurt us.
While it’s usually fair to assume a visible dust cloud may represent a hazard, it should not be assumed that the absence of a visible cloud represents ‘safe’ conditions as in reality, a respirable particle is too small to be seen with the unaided eye.
It ‘s important to realise there is no concentration which represents a safe level of dust.
Managing dust to minimise emissions can be complicated and may take considerable financial outlay and effort, however significant improvements can be made with relatively simple infrastructure in many cases.
Like most decisions, the ultimate solution needs to balance the economic cost against the potential for adverse health impacts on both workers and the community.
Making an informed decision requires:
- a clear understanding of the risks of uncontrolled (or status quo) emissions for both workers and nearby residents;
- what reductions are achievable at what costs;
- and what is the impact of those reductions likely to be.
There is no safe level of dust, and this combined with the overall provisions placed on operators by workplace health and safety legislation and environmental legislation, means it’s important to consider whether improvements beyond the limits could be achieved without significant cost or operational impacts.
Options for dust emission improvement
Low cost particulate sensors are becoming increasingly available.
In Australia and overseas, regulators are experimenting with a large array of low cost sensors to provide continuous information about air quality.
For a relatively low cost, numerous sensors can be established to monitor dust continuously around site and provide continuous feedback about what dust levels are present and when additional controls may be required.
2. On-site audits
The on-site audit represents an effective way of identifying key sources of dust, activities requiring further attention or the effectiveness of on-site controls.
Typically, this would be undertaken by an experienced consultant and would utilise a real-time monitoring device to determine where dust emissions are being generated. The monitoring equipment can be used by an experienced operator to gain an understanding of where dust could be coming from and whether the current controls in place are achieving measurable reductions.
While useful, this information is unable to provide information to assess exposure of workers to dust across a work day in accordance with the occupational exposure limits, although it can provide information about exposure in individual work areas.
3. Predictive dispersion modelling
Another useful tool is the use of predictive air dispersion modelling.
While not suited to assessment of worker exposure, predictive modelling is able to provide information on the potential for impacts on nearby residents. In addition, the model can be used to assess the effectiveness of controls on overall dust emissions from a site.
4. Advanced Management Systems
There is an increasing number of real-time management systems available, and these systems can include both monitoring and modelling capabilities.
In the simplest form, the system could involve a real-time weather station to provide information about wind speed and direction which allows the operator to determine whether emissions from the site could lead to an impact at off-site locations.
In this case, even a relatively cheap weather station is able to provide a means of effectively managing dust emissions with limited water resources (for suppression).
Beyond this, the system could include collection of real-time data from one or more locations around the site to provide continuously updated information about either on or off-site dust concentrations.
More complex systems couple real-time monitoring information with predictive modelling capabilities. These systems take information about operations at the site such as production rate and predict off-site dust impacts based on actual meteorological data.
Of course, increasing sophistication comes at a cost, however the cost of this increasing sophistication is often out-weighed by the operational efficiencies and limitation of time lost to dealing with dust complaints and regulatory processes.