Water- based dust suppression: pre, during and post characterisation of respirable coal dust at a power station in South Africa

Abstract

Background Exposure to coal dust may lead to serious health risks such as coal workers’ pneumoconiosis (CWP), lung cancer and premature death (Han et al., 2017; Pollock et al., 2010). Therefore, the negative impacts of coal exposure on human health necessitated control strategies to prevent or minimize exposure. Literatures indicated that, despite the availability of various dust control strategies, occupational diseases from coal dust exposure still exists in large numbers particularly among the coal related employees (Almberg et al., 2018; Joy & Colinet, 2012; Perret et al., 2017; Shekarian et al., 2021). Coal workers pneumoconiosis (CWP) remains an important occupational lung disease in many parts of the developing world (Hulshof et al., 2019). “Based on International Labour Organisation (ILO) on global occupational health and safety (OHS), more that more than 2 million deaths occur in the workplace worldwide due to several occupational incidents”(Hulshof et al., 2019). This report further states that about 6 300 workers die daily due to exposure to dangerous occupations (Hulshof et al., 2019). To date, despite the inherent health burden associated with hazardous exposure to coal dust there is paucity of studies focusing on the efficacy of engineering controls in reducing dust emissions(Qi & Echt, 2016).

Aim of the study The study aim was to evaluate the efficacy of the water based dust suppression method in reducing airborne coal dust exposure at the coal stockyard at a Power station. This study hypothesised that water suppression methods do not reduce concentrations of coal dust submicron and nanoparticles at coal stockyard scenario.

Methods This study is a quasi experimental study design whereby measuring results from various locations in the Coal stockyard was taken to determine dust concentration before, during and after water dust suppression. The measuring was based on three possible exposure scenarios (pre or before, during and post or after). Three measuring points (point A –C) within the coal stockyard were identified for the efficacy determination. The measuring was carried out for 30 minutes in each of the exposure scenario. To qualify the scientific validity and reduce uncertainty/ increase data quality, triplicates measuring were conducted in each point. A direct reading instrument for area dust measuring, Nanozen (DustCount 9000-Z1) was used to obtain respirable coal dust particle of (PM1) before, during and after water dust suppression method.

Results The study evaluated the efficacy of water suppression as a control measure used at the coal stockyard area. The dust concentrations recorded were 8, µm 6, 9 micrometre (µm) and 13, 1 µm for the pre, during and post treatment, respectively. After evaluating and comparing results, it was observed that during the application of water dust suppression method, 80 to 90% dust particle of the size ranging between 1, 1 -5, 5 µm were effectively reduced and 40 -60% dust particles of smallest size between 375 nm to 732 nanometre (nm) were reduced.

Conclusion The findings indicated that the efficacy of water dust suppression method increases where there are an increase in number of larger dust particle diameter in size. When comparing the three exposure scenarios namely pre, during and post treatment, it was found out that high concentration of fine and course particles were emitted during water suppression scenario, which was more than any other scenarios. Through observation activities leading to the emissions of coal dust particles included tipping of coal in the stockyard, coal stockpiling using bull-dozers while resuspension of dust particles was due to high wind speeds, workers movements and truck/ vehicles movement. This finding was expected since there are several activities which influences dust resuspension prior or after water suppression treatment. Therefore, it may be necessary to utilise the water sprinklers around a coal stock yard area due to the frequent entry and exits of the heavy vehicular movement for larger particles. However, as for submicron particles it is recommended that the use of fogging be considered as a long-term intervention. On the road surface design, the use of tarred road may assist in reducing the resuspension potential due to increase in the particle binding force.

The hypothesis of this study confirmed that dust water suppression methods do not reduce concentrations of coal dust submicron and nanoparticles. The efficacy of coal dust water suppression method depend on the size of particles released. The bigger the particle, the more the effectiveness and the smaller the particle, the less effective. In this study it was found out that water dust suppression at coal stockyard have led to a 90% reduction of particles above 1 micron while a reduction percentage of about 40% was found for submicron particles. This dissertation laid the groundwork both for improvement in the design of existing coal dust suppression methods and the development of improved dust control interventions such the use of fogging to suppress submicron particles. The insights gained from this study may assist in the selection of appropriate strategies and technologies to mitigate hazardous exposures in coal storage facilities.