A review of recent updates in the guidelines for management of respirable dust in mineral mines and quarries in Queensland

Queensland has a rich and seasoned mineral mine and quarry industry. Continuous improvement of occupational safety and health-related requirements creates opportunities for embracing more innovative techniques to ameliorate dust-related hazards. Bearing testament to the progressive approach to reducing risks associated with respirable dust particles the Queensland Government recently updated guidelines for mineral mines and quarries under the Mining and Quarry Safety Health Act of 1999. The article seeks to evaluate the past, present and future of dust suppression based on the recent updates to the QGL02 guideline. Whilst we can learn from the past, the present now accommodates other dust control products other than water. The future is even more exciting with the prospect for specific product development of highly efficient dust suppressants. 

Reviewing Previous Guidelines and Practices

Versions one and two of the guidelines for the management of respirable dust in Queensland mineral mines and quarries focused strictly on dust in the form of respirable crystalline silica. Although it causes mine dust lung disease, exposure to other omitted respirable dust can significantly contribute to the disease as well. The most common form of crystalline silica is quartz, which accounts for about 12% by volume of the earth’s crust and is present in many rocks, waste materials and products from operations in mineral mines and quarries. The majority of mining activities potentially involve direct exposure with overburden and ore containing quartz. Inhalable and respirable silica dust particles penetrate the respiratory system and settle in the alveolar region of the lungs and stimulate inflammation and toxic responses that eventually lead to clinical silicosis. The severity of silicosis ranges from acute, accelerated and chronic depending on the concentration and duration of exposure. 

Water has been the predominant dust suppressant with some successes based on achieving water droplet size comparable to that of the dust particle for optimal agglomeration. However, this is not always the case in practice as the resuspension of respirable silica dust ultra-fine particles on impact increases the risk of exposure. The limited residual effect due to evaporation of water also means more reapplication is required and the balance between over-application and under-application also creates moisture dependency to maintain its effective use. Although the focus on respirable crystalline silica has yielded fruitful industry legislation in the past the complexity and chemistries of other respirable dust have created the necessity for a third and current version of the respirable dust management guidelines. 

The new guideline

The new guideline emphasises and strengthens the need to have effective and reliable respirable dust mitigatory measures. The quantitative and qualitative approach to risk management associated with respirable dust involves determining the level of risk and measuring dust levels if ever there is any potential that they exceed the exposure limit. Acceptable, uncertain and unacceptable are the risk criteria that have been suggested for use in the risk management process. Classification of reliability and effectiveness of controls is performed through a hierarchy of control. The transition from the base to the pinnacle of the hierarchy of control equates to an increase in the effectiveness of the respirable dust control measure implemented. The hierarchy of implemented measures in a precise order from least to most effective include:

• PPE – Workers to wear personal protective equipment including respirators
• Administrative and work practice controls for employer and employee
• Physical change in the workplace through engineering controls
• Isolation or separation through maintaining safe distances away from exposure
• Substitution achieved by the use of a process or activity that generates less dust
• Elimination of exposure before it can occur

Responsible authorities for managing risk associated with respirable dust have an obligation as far as reasonably practicable to apply hazard controls implementing the hierarchy of control. Considering other respirable dust particles, it is important to target the chemistry of interaction between the dust suppressant and the particle of concern. 

An integrated approach

Integrating the right software, hardware and chemistry are critical in preventing or stripping out airborne dust. Complete elimination of exposure before it occurs can only be attained through the use of alternative and supplementary dust control solutions to water. Liquid polymers, ionic surfactants and highly refined fluids from green feedstocks, when used intelligently and to needs of a specific site, can achieve complete elimination of exposure prior occurrence. 

Making water work on hydrophobic dust particles of any sizes can be attained through its super-activation using a surface-active agent that through the amphiphilic nature can reduce the interfacial energy and allow for binding and immobilising of fugitive respirable dust particles. The dilution factors depend on the type of surfactant used and the quantities required to perform the dust control. Liquid polymers can either be hydrophilic or amphiphilic with the latter achieving excellent dust control. Surface activity of dust control agents is key to the efficacy of dust control. The ability to environmentally friendly feedstock can yield self-healing and biocompatible dust suppressants whilst harnessing their abundance to further develop sustainable solutions to all kinds of respirable dust. 

Looking to the future

Selectivity that leads to the total elimination of dust is the future of managing dust generated from mineral mines and quarries. The broadness of respirable dust particles as a result of different mining and quarrying activities will even be more prevalent in Queensland over time. Fields such as nanotechnology and atomic force microscopy will be at the frontiers of supporting more technological advancement in the product development of dust suppressants. The merging of chemistry, engineering and wellness will stir more conversations about occupational health and safety not just from a control point of view but also the need for collective decision making for the good of all stakeholders in the industry. The needs of the industry will keep evolving and the progression of those inevitable changes need to be supported with affirmative action from the Queensland Government through immediate response and zero tolerance to any form of exposure of workers to respirable dust in any form.  The solutions to the challenges will rely on a frequent and consistent revision of guidelines. 

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REFERENCES 

Cecala, A.B., O’Brien, A.D., Schall, J., Colinet, J.F., Fox, W.R., Franta, R.J., Joy, J., Reed, Wm,R., Reeser, P.W., Rounds, J.R., Schultz, M.J. 2012. Dust Control Handbook for Industrial Minerals Mining and Processing. Report of Investigations 9689. 

Department of Natural Resources, Mines. 2020. QGL02 Guideline for management of respirable dust in Queensland mineral mines and quarries. Mining and Quarrying Safety and Health Act 1999. 

Occupational Safety and Health Administration. 2009. Controlling Silica Exposure in Construction. U.S. Department of Labor OSHA 3362-05. 1-72.