ReviewAirborne respirable dust in fully mechanised underground metalliferous mines – Generation, health impacts and control measures for cleaner production
Graphical abstract
Introduction
Generation of dust is invariably associated with mining, as most mining operations cause size reduction of rocks and minerals due to drilling, cutting, crushing, grinding, etc. In recent years, heavy mechanisation of the mines due to increased demand for minerals has resulted in a sharp increase in dust generation and the miners’ health risk (Biffi and Belle, 2003). The principle of underground metalliferous mining and dust generating sources are shown in Fig. 1 (Hamrin, 2001). Nowadays, diesel operated mobile equipment, such as LPDTs (low profile dump trucks) and LHDs (load haul dumpers), are extensively used in trackless fully mechanised underground metalliferous mines (FMUMM) (i.e., a mine with no rails, where tyre mounted vehicles are used for haulage and transportation) because of their flexibility in operation and productivity. These equipment, which frequently operate in the declines or ramps serving as intake airways and transportation of men and material in FMUMM, constitute a major source of DPM and significantly contribute to mineral dust aerosolization.
In declines, the reduction or stagnation of airflow due to leakage in the upper sections of mine creates more dust problems (van den Berg et al., 2019). Due to inadequate ventilation in declines and other working areas in FMUMM, miners are exposed to a high level of mineral dust, heat, and other contaminants such as DPM, radon progeny, etc. (Cecala et al., 2012; Sahu et al., 2014b; Panigrahi et al., 2015; Wallace et al., 2015). Consequently, depending upon the type of dust and their combinations, they suffer from various respiratory diseases, such as chronic bronchitis, silicosis, asbestosis, talcosis, siderosis, lung cancer, etc. (Fermor, 1975; Banerjee, 2003; AIOH, 2009; Cullinan et al., 2017; ICRP, 2017).
Apart from adverse health effects, the corrosive effect of dust particles reduces the life of lubricants used in heavy earth moving machineries (HEMM) and in turn, increases their maintenance cost due to excessive wear and premature failure of the machine components (Pandey, 2012). Moreover, the dusty underground mine environment affects the laser-based navigation and electrical systems used in autonomous mining operations (Ghodrati et al., 2015; Gustafson et al., 2017). Hence, it is important to dilute and suppress the mine dusts to a safer level for maintaining a safe and productive workplace environment in FMUMM.
The dust problems in underground mines can be solved by proper ventilation through a well-designed ventilation system. The critical contaminants of mine environment, such as dust particulates and heat, should be considered while designing the ventilation system for FMUMM (Biffi and Belle, 2003; Gonen, 2018). In the past, studies related to mine dust mainly focused on the dust exposure of miners, dust dispersion and control measures in mechanised underground coal mines (Toraño et al., 2011; Kurnia et al., 2014; Mishra et al., 2019; Ren and Wang, 2019). Some studies have also reported the generation and estimation of mine dust in surface mining operations (Chakraborty et al., 2002; Ghose, 2004; Gautam and Patra, 2015; Patra et al., 2015). However, studies on mine dust and their control measures in FMUMM are limited (Biffi and Belle, 2003; Bugarski et al., 2012; Saarikoski et al., 2018). Hence, there is a necessity to conduct more studies on dust related issues for improving the workplace environment in FMUMM.
This comprehensive review focused on the issues concerning all kinds of airborne respirable dusts (ARD), including two important aerosols, viz. diesel particulate matter (DPM) and radon progeny, found in FMUMM. It covered a gamut of topics, such as generation, classification, characteristics, health and safety concerns, legislative guidelines, monitoring, and mitigation and control measures of ARD in major mining operations in underground metalliferous mines. Moreover, it highlighted the current research activities, knowledge gaps and explored ideas for future research on dust dispersion, monitoring and control to maintain a safe, healthy, clean and productive workplace environment in FMUMM. Overall, the knowledge disseminated through this review can greatly benefit the mining industry.
Section snippets
Review methodology
For this review, relevant research papers were collected from online databases and offline library collections. Various conference proceedings of international repute and reports of reputed agencies, e.g., International Labour Organization (ILO), World Health Organization (WHO), National Institute for Occupational Safety and Health (NIOSH), USA, Directorate General of Mines Safety (DGMS), India, etc., were also consulted to address the prevailing dust issues in FMUMM. The main databases
Classification of mine dusts
Mine dusts may be classified based on their environmental impacts, occupational health, physiological and combustible effects, and source of generation (Fig. 2). Various mine dusts have a respective degree of hazard, and it largely varies. The chemical composition and size of dust particles are the important factors that determine the harmful effects of dust on human beings. Apart from posing a health hazard, some dusts, such as the dusts generated in coal and sulphide ore mines, have the
Characteristics of mine dusts
Mine dusts are solid particulate matters ranging in size from below 2 μm and up to 100 μm (WHO, 1999; DGMS, 2010). Dust is also defined as small solid particles of less than 75 μm diameter that settle down under their weight but sometimes remain suspended in air (ISO, 1995; Hartman et al., 1997). The dust type varies depending upon the nature of the mineral extracted from the mine (Table 1). While mining of iron ores, manganese, lead, zinc, copper, asbestos, etc. produce siliceous fibrogenic
Sources of mine dust
Mine dusts are mostly generated due to the breaking down of parent rocks during the process of various mining activities, and the quantity of potential airborne dust is proportional to the amount of rock broken (Sengupta, 1990). The significant dust generating sources in FMUMM include mechanical rock cutting (e.g. drilling, raise boring, etc.), blasting (both primary and secondary), blast hole cleaning using compressed air, rock bolting, mucking, driving ore passes, movement of rock in stopes,
Health impacts
Occupational exposure remains a significant contributor to the health hazard of the miners. The workplace environment in FMUMM is associated with various health hazards due to different types of dusts and hazardous fumes, poor illumination, high temperature and humidity, noise and vibration (WHO, 1999; Dhatrak and Nandi, 2009). ARD is identified as an important component responsible for causing respiratory diseases, such as silicosis, a prominent occupational health hazard in mines (IARC, 1997;
Exposure limits of airborne respirable dust in FMUMM
Different countries formulated different guidelines regarding exposure limits of airborne respirable dust. In India, specific provisions on airborne dust in metalliferous mines have been provided under regulation 124 of the Metalliferous Mines Regulations (MMR), 1961. According to the regulation, the permissible time-weighted average (TWA) concentration of ARD in an 8-h shift is 3 mg/m3 if the free silica content in the dust is less than 5%, and 5 mg/m3 in the case of manganese ore. In other
Airborne dust monitoring in FMUMM
Airborne dust monitoring is an essential step for eliminating lung diseases caused by over-exposure to mine dust (Volkwein et al., 2006). Periodic, precautionary, and investigation kinds of measurements are generally conducted to address the airborne dust issues in FMUMM. Two kinds of dust measuring instruments, viz. gravimetric sampler and direct-reading instruments, are widely used to monitor the ARD concentration in mine atmosphere. Gravimetric dust samplers are widely used for statutory
Dust suppression and control measures in FMUMM
Most mining operations necessitate both prevention and suppression methods for effective dust control in mines. Table 4 summarises the various dust control methods adopted in FMUMM, which mostly based on dust generation issues. These measures are not only difficult to implement but also costly as the normal ongoing mining production has to be halted for corrective actions. Capturing airborne respirable dust in mines using water sprays is not very effective. Wet spraying is mostly used in dust
Current research practices on dust dispersion and control in underground mines
It is pertinent to recognize the significant advancements made in dust control in mining by researchers over a period of time. However, the dust issues persist and sometimes become complicated due to the increased level of production and mechanisation in FMUMM. The fugitive nature of mine dust, movement of mobile equipment, and change of airflow direction due to diffusion complicate the dust dispersion in FMUMM. Moreover, the airborne dust concentration downwind of a dust source depends on
General discussion
Airborne respirable dust generated in highly mechanised underground metalliferous mines is a real threat to the health and safety of the miners. A study by NIOSH, USA, indicated that health issues associated with airborne respirable dust need highest attention and ranking (NRC, 2007). The dust and gases produced during blasting are not rapidly cleared away from the stopes and interfere with subsequent mining operations due to poor ventilation (Pejcinovic, 1984). Various techniques, such as
Concluding remarks
Dust generated in underground metalliferous mines raises a major concern, as it impacts the production, productivity, health, and safety of the miners. Diluting the airborne dust generated in FMUMM through auxiliary ventilation is a challenge because of the damage caused to ventilation ducts during blasting and movement of mining machinery, such as LPDTs, LHDs, drill jumbos, explosive charging equipment, etc. These challenges need to be resolved by adopting new technologies and customized
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors express their sincere thanks to the editor and anonymous reviewers for their valuable comments, which greatly improved the quality of the paper.
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