Student Name: Isabel Kotzee
Student Number: 46472306
Course Code: OHSS7102 Occupational Hygiene Research Project
Supervisor details: Brett Jones (GCG) & Dustin Bennett (GCG)(brett@gcg.net.au)(0732164897) (dustin@gcg.net.au)(0416193842)
Submitted: 8th November 2024
This report was completed by Isabel Kotzee, a Dual Masters of Occupational Hygiene and Occupational Health and Safety Science student. This project was conducted under the supervision and guidance from GCG Health, Safety & Hygiene. The overall aim of this research was to determine the difference in sampling techniques when measuring respirable elemental carbon (REC) and submicron elemental carbon (SEC) as a surrogate for DPM concentrations in an underground coal mine. This project was conducted between 22nd July and 8th November 2024. The current recommended workplace exposure standard (WES) in Queensland for DPM is 0.1mg/m3, based on the submicron size fraction (<1 μm). However, Safe Work Australia has proposed a new WES for DPM measured in terms of REC (5μg REC/m3).
Therefore, the main research questions were as follows:
1. Does using a GS-3 Respirable Dust Cyclone with respirable elemental carbon (REC) analysis lead to higher concentrations of REC as a surrogate for measuring DPM concentrations?
2. Does using a DPM Plastic Cyclone with submicron elemental carbon (SEC) analysis, as a surrogate for measuring DPM concentrations, impact the amount of interference from coal mine dust on the inferred concentration of DPM?
3. How do the sampling methods differ in the proportion of visual coal articles and DPM particles when using Scanning Electron Microscopy (SEM). Note: This research question was taken out of the scope of this project due to time restraints)
4. What insights do these findings provide for the Queensland Mining Inspector (QMI) with regards to the proposed new REC WES for DPM?
Area sampling was conducted in an underground coal mine located in the Central Queensland Bowen Basin region of Australia on the 27th and 28th of September 2024. Sampling consisted of utilising a GS-3 Respirable Dust Cyclone with REC analysis and sampling using a DPM Plastic Cyclone with SEC analysis, as a surrogate for measuring DPM concentrations Sampling was undertaken on two development panels (Panel 601 and 602). Three different locations were sampled at each panel: Panel Roadway, Shuttle Car Circuit and at the Boot End. Overall, the results demonstrated that SEC concentrations were consistently lower than REC concentrations, irrespective of the location Potential interference from coal dust and other carbonates was identified, as the presence of coal dust can artificially elevate the carbon measurement that is attributed to DPM. Therefore, the proposed new REC WES for DPM would present significant limitations in measuring and regulating DPM in underground coal mines, where interferences can occur. This suggests that the submicron sampling method using an impactor should be utilised in an underground coal mine environment to avoid this. However, DPM and dust have been found to agglomerate together, meaning that this method may miss supra-micron DPM, therefore, additional research is required. This should include multiple mines, thus increasing the sample size to enhance the reliability of the results due to potential variations that exist between mines.
I would like to express my gratitude and acknowledge those who supported me throughout this Occupational Hygiene Research Project. Thank you to the mine that generously participated in this research – the mine’s support was essential to the success of this study.
I am especially grateful to the support received from GCG Health, Safety & Hygiene, who provided their supervision and assistance with data analysis and sampling. Special thanks to my supervisors, Dustin Bennett and Brett Jones, for providing support and guidance throughout this project.
Lastly, I would like to acknowledge and thank Dylan Hempel, who provided me with invaluable support and assisted me with the static sampling on site.
Table 1 – DPM Tag Board Showing Vehicles in the Area and Vehicles on Standby to Enter on the Second Day of Sampling......................................................................................
Table 2 - Paired REC/SEC and SEM REC/SEC Locations and Number Samples Collected....... 15
Table 3 – Descriptive Statistics of Ambient Elemental Carbon, Organic Carbon and Total Carbon Measurements.............................................................................................
Table 4 – Linearized Ratios for Comparative Analysis of Carbon Fractions
Table 5 - Linear Regression Outcome for SEC and REC
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Figure 1 – Diagram Showing the Approximate Location of Static Sampling on Panel 601 and Panel 602 ...............................................................................................................
Figure 2 – Schematic Representation of the Three Approximate Locations for the Static Sampling Conducted on each Panel 17
Figure 3 – Representative Figure Showing the Placement of Samples Hanging on the Coal Seam Bolts from Protective Pouch .............................................................................
Figure 4 – Graph Showing the Ten Pairs of SEC and REC Concentrations (mg/m3) ..............
Figure 5 – Plot of Linear Relationship between REC and SEC Concentrations (mg/m3) with
Abbreviation Definition
ALARP
As low as reasonably practicable.
DEE Diesel Engine Exhaust.
DPM
Diesel Particulate Matter.
DPM refers to the component of diesel exhaust that includes soot particles made up of very small carbon, ash, metallic abrasion particles, sulphates and silicates.
EC Elemental Carbon.
DPM has a solid core, which consist of EC and other substances attached to the surface, including organic carbon compounds.
OC Organic Carbon
PAH
Polycyclic Aromatic Hydrocarbons.
DPM contains a large amount of PAHS, which is emitted from engine exhaust. PAHS are a type of chemical that can be found in coal, crude oil and gasoline.
REC Respirable Elemental Carbon.
REC refers to the respirable fraction of inhaled EC that penetrates the gasexchange region of the lung.
SEC Submicron Elemental Carbon
The submicron particles of DPM are made up of a carbonaceous core, which is defined as EC.
SEM Scanning Electron Microscopy.
This type of microscopy creates an image of a sample by scanning the surface with a focused beam of electrons.
TC Total Carbon.
Organic Carbon and Elemental Carbon combined.
TWA
Eight-hour Time-Weighted Average.
A TWA refers to the maximum average airborne concentration of a substance when calculated over an 8-hour working day.
Workplace Exposure Standard.
A WES refers to the regulatory limit to which workers can be exposed to a particular hazard. Under the WHS laws in Australia, a PCBU must ensure that no person in the workplace is exposed to an airborne contaminant at a concentration exceeding the WES.
This study was conducted as part of the completion of the Dual Masters of Occupational Hygiene and Occupational Health and Safety Science by student Isabel Kotzee, under the guidance of Dustin Bennett, Certified Occupational Hygienist from GCG Health, Safety and Hygiene in Brisbane, Queensland. Sampling was conducted at an underground coal mine located in the Central Queensland Bowen Basin region of Australia on the 27th and 28th of September 2024.
Coal has played an essential role in Australia since the industrial revolution (Morla & Karekal, 2017). At the end of 2021, Australia was the fifth largest producer of coal and the second largest exporter of coal in the world (Geoscience Australia, 2023). The vast majority of these mines use diesel-powered equipment for the transportation of workers and materials (Morla & Karekal, 2017). Diesel-powered vehicles are often used as they can travel vast distances and are depended upon to travel between sections of a mine (Morla & Karekal, 2017). However, the principal issue with diesel equipment is that it releases exhaust fumes, which contains a mixture of diesel particulate matter (DPM) and other gases such as nitrogen oxides, hydrocarbons, carbon monoxide and substances (Morla & Karekal, 2017). DPM is the byproduct of incomplete combustion of diesel fuel in the diesel engine (Morla & Karekal, 2017) Concerningly, DPM is recognized as one of the most hazardous substances released from diesel engines and can also function as a carrier for other environmental dust or chemicals associated with diesel emissions (Azam et al., 2024)
The primary aim of this research was to determine the difference in sampling techniques when measuring respirable elemental carbon (REC) and submicron elemental carbon (SEC) as surrogate DPM concentrations. This research investigated how these sampling techniques can be used as a surrogate for DPM measurement in an underground coal mine environment with potential interference from carbonaceous materials (i.e. coal dust).
This research aimed to answer the following research questions:
1. Does using a GS-3 Respirable Dust Cyclone with respirable elemental carbon (REC) analysis lead to higher concentrations of REC as a surrogate for measuring DPM concentrations?
2. Does using a DPM Plastic Cyclone with submicron elemental carbon (SEC) analysis, as a surrogate for measuring DPM concentrations, impact the amount of interference from coal mine dust on the inferred concentration of DPM?
3. How do the sampling methods differ in the proportion of visual coal articles and DPM particles?
5. What insights do these findings provide for the Queensland Mining Inspector (QMI) with regards to the proposed REC WES for DPM?
2.1. What is DPM and what are the associated health effects?
In the underground mining industry, diesel engines are often used as the primary power source, particularly where high horsepower output is necessary (Azam et al., 2024). Particulate matter, and other complex substances, are produced due to the incomplete combustion of the diesel fuel (Azam et al., 2024). The formation and make-up of exhaust emissions is determined by several factors such as fuel injection technology, the type of fuel used, compression ratio, exhaust gas recirculation and after-treatment technologies (Azam et al., 2024). The contaminants produced by diesel engines are known to be environmental and human health hazards (Azam et al., 2024). In particular, the ultrafine particulate matter released from diesel engines, have been shown to be a serious concern for public health (Azam et al., 2024). DPM is a complicated mixture that contains both gas-phase and particlephase emissions (Gren et al., 2022). It consists of an elemental carbon (EC) core, with a high surface area that other substances, such as metals and organics, can be absorbed onto (Gren et al., 2022). The EC core occupies around 70-80% of the total composition, with other organic carbon (OC) compounds such as hydrocarbons, PAHs, metals, sulphur and nitrogen carbons and other compounds (Azam et al., 2024).
Exposure to DPM primarily occurs via equipment or vehicles that are powered with diesel fuels (Gren et al., 2022). Moreover, underground workers are often exposed to higher concentrations of DPM due to working in restricted spaces with poor ventilation conditions (Ping & Guang, 2017). DPM particles can be suspended in the air, where it can easily be inhaled by workers (Parks et al., 2021). Moreover, underground mine workers have been found to be exposed to approximately twice the measured EC levels than surface workers (Coble et al., 2010). The size distribution of DPM varies, with a range of 5nm to 10μm, however, more than 90% of the particles are less than 1μm (Chang & Xu, 2019). Particles with aerodynamic diameters >2.5μm tend to collect in the upper portions of the respiratory tract, whereas, particles with diameters <2.5μm are deposited in all areas, specifically in the lower part of the respiratory tract such as the alveolar area and trachea-bronchial regions (Rumchev et al., 2020). These ultrafine particles have a very large surface area per gram mass, meaning that they can absorb and transport inorganic and organic compounds into the lungs (Rumchev et al., 2020).
Short-term exposure to DPM can cause acute irritation, a cough, light-headedness, eye irritation and sensitivity amongst patients with asthma (Ping & Guang, 2017). A comprehensive review by Ping and Guang (2017) was conducted to establish the health effects of DPM on underground mining workers (Ping & Guang, 2017). Researchers reported that
epidemiological studies have shown strong evidence for the association between long-term DPM exposure and an increased risk of lung cancer (Ping & Guang, 2017). Moreover, Silverman et al. (2012) investigated lung cancer risk related to DEE exposure among a cohort of 12,315 workers across eight non-metal mining facilities (Silverman et al., 2012). The study found a three times greater risk of lung cancer in heavily exposed workers compared to those who are exposed at lower levels of DPM (Silverman et al., 2012). Therefore, based on the proven genotoxicity of its constituents, DEE has been classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC, 2014). Other long-term impacts include adverse effects on cardiovascular functions and neurophysiological symptoms (Ping & Guang, 2017).
At this time, there is no published Workplace Exposure Standard (WES) for DPM in any Queensland legislation. However, the Queensland Mines Inspectorate (QMI) proposed implementing a guideline limit that is used in the New South Wales Machine Design Guideline MDG29, which is an 8-hour Time-Weighted Average (TWA) of 0.1mg/m3, measured as SEC (Resources Safety & Health Queensland, 2012). As part of a recent WES review, Safe Work Australia found that there was sufficient evidence to recommend a WES for DPM based on measuring REC (Safe Work Australia, 2022). The review recommended an 8-hour TWA of 15μg REC/m3 for DPM from any type of diesel engine (Safe Work Australia, 2022). The new DPM WES is set to become adopted by Safe Work Australia on the 1st December 2026 (Safe Work Australia, 2022). Moreover, the suggested TWA would be employed in combination with the WES for other components of Diesel Engine Exhaust (DEE), such as nitrogen dioxide, to ensure that the health effects from the mixture are sufficiently managed (Safe Work Australia, 2022)
However, measuring DPM in terms of REC, rather than SEC, may introduce several issues in underground mines. This is because DPM is within the aerodynamic particle size range of the samplers used for respirable and inhalable dust measurements, meaning that both DPM and other interferences, such as coal dust, can accumulate on the sample filter (Noll et al., 2005). In carbonaceous mines, the carbon attributed to DPM would be artificially high from the coal dust interference (Noll et al., 2005). To avoid analytical interference from coal or mineral dust, a submicron impactor was developed (Noll et al., 2005). This impactor effectively separates larger particles, such as coal dust, from the airflow and enables smaller particles, such as DPM, to be collected (Noll et al., 2005). It takes advantage of the aerodynamic diameters of these particles, where respirable dusts generally exceed 0.8μm, while most DPM typically has an aerodynamic diameter of less than 0.8μm (Cantrell & Rubow, 1991). DPM cassettes with builtin impactors have been shown to be 90% effective at separating coal dust from DPM (Noll & Birch, 2004).
Consequently, if the WES is changed from being measured in terms of SEC to REC, this could cause coal dust interferences with the final determination of REC (Noll & Birch, 2004). This means that the proposed WES would present significant limitations in measuring and
regulating DPM in underground coal mines, where interferences can occur (Noll et al., 2005). This offers a clear and urgent problem as there is insufficient research specifically focussing on the differences between these sampling methods in underground coal mines and what this means in terms of regulation of DPM. Although similar studies have been conducted to evaluate DPM sampling methods, these studies are often focused on the non-coal mining industry or do not specifically compare REC and SEC sampling methods (Birch & Noll, 2004; Fleck et al., 2019; Gaillard et al., 2021; Haney, 2008; Pretorius & Grove, 2011). Therefore, further research on this topic is crucial to influence the current recommendations by Safe Work Australia in relation to a DPM WES.
2.3. What are the relevant WES for DPM exposure in Australia and internationally?
Although there is no WES for DPM in Australia currently, the Australian Institute for Occupational Hygienists (AIOH) has recommended a WES (measured as SEC) as low as reasonably practicable (ALARP) below an 8-hour TWA guidance exposure value of 0.1mg/m3 , with an action level TWA of 0.05mg/m3 (AIOH, 2017). This guideline WES has been implemented by most Australian mines and workplaces.
In the United States, The Mine Safety and Health Administration (MSHA) recommends a WES of 160μg/m3 in terms of Total Carbon (TC) for underground metal/nonmental mines (MSHA, 2006). In Canada, the government of the Province Ontario introduced a new WES for DPM of 0.12mg/m3 (measured as EC) in underground mines on the 1st September 2023, replacing the old TWA of 0.4mg/m3 (measured as TC) (Occupational Health and Safety Act, 1990). However, most provinces in Canada follow 0.75mg/m3 (measured as TC) set by The Canada Centre for Mineral and Energy Technology (Ngele, 2017). In Germany, the DPM WES for underground non-coal mines is 0.3mg/m3 and 0.1mg/m3 for all other activities (measured as whole diesel particulate) (Ping & Guang, 2017)
2.4. How can exposure to DPM be evaluated?
Due to the complex make-up of DPM, measurements of DPM are prone to interferences (Noll et al., 2006). An alternative was needed to establish DPM exposure due to these interferences (Noll et al., 2006). At first, Total Carbon (TC) was studied by MSHA to be the best substitute for DPM as it makes up over 80% of DPM (Noll et al., 2006). However, the Elemental Carbon (EC) and Organic Carbon (OC) particles from mineral dust and OC aerosols from other sources are frequently found in underground mines, which can affect the TC analysis (Noll et al., 2006). Although size selective samplers have been shown to effectively separate the coarse mineral dust from the submicron DPM, they are not effective in removing OC aerosols (Noll et al., 2006). Selecting extractable organic compounds as a reliable surrogate of exposure is challenging, with the organic fraction associated with diesel exhaust aerosol being highly variable in composition (Cantrell & Watts Jr, 1997).
Uncertainties exist about the role the organic fraction associated with diesel exhaust aerosol compounds play in mutagenic and carcinogenic activity (Cantrell & Watts Jr, 1997) Therefore, the use of EC instead of OC was determined to be feasible as no other sources of SEC are known to occur in the metal/non-metal mining environment (Noll et al., 2006). Furthermore, EC is the superior measure of exposure to DPM as EC represents a large portion of the particulate mass, it can be measured at low levels and its only major source in many workplaces are diesel engines (Birch & Cary, 1996). Importantly, artifacts do not affect EC and coal dust also has less of an effect on EC findings than TC or DPM mass, due to a smaller portion of coal dust being EC (Noll & Birch, 2004).
There are three methods by which airborne DPM samples can be gathered: total dust samples, respirable dust and submicron dust (Haney, 2008). To ensure there are no interferences with the analysis method, the sampling media (filter) must be a pre-fired quartz fibre filter (Haney, 2008). This filter is able to withstand temperatures from the analytical method and is pre-fired to eliminate residual carbon that is attached to the filter during production (Haney, 2008) For total dust sampling, a filter cassette that permits the whole face of the filter to be uncovered during collection of the sample is used (Haney, 2008). However, this represents all the particulate matter in the environment, meaning that there is the capacity for inference from mineral contaminants containing EC and OC (Haney, 2008) These interferences can be sizable and can often not be removed from the analytical procedure, leading to inaccuracies in determining DPM concentrations (Haney, 2008) The sources of these interferences can include oil mist and environmental tobacco smoke (Fleck et al., 2019) Therefore, MSHA determined that it is not an appropriate sampling method for the mining industry when sampling for DPM (Haney, 2008)
The second method that can be used to sample for DPM is respirable dust sampling (Haney, 2008). This method is often used when the dust being collected represents the fraction of dust deposited in the lungs (Haney, 2008). For this method, a respirable dust cyclone can be used to separate the respirable fraction of the aerosol from the total aerosol (Haney, 2008). This method is appropriate when there is not much interference from carbonaceous mineral dusts, as this can cause interferences in either EC or OC measurements (Haney, 2008). This is further highlighted by Vermeulen et al. (2010), which conducted a study to describe the interrelationships between REC and CO as well as other components of DEE (Vermeulen et al., 2010). Researchers found that particulates and most OC measurements only correlate moderately with REC measurements, which suggests likely contributions from non-diesel exhaust sources within underground activities, such as mine dust and lubricating oil (Vermeulen et al., 2010). Therefore, respirable dust sampling is not a universally applicable sampling method to sample for DPM in the coal mining industry (Haney, 2008).
A more suitable sampling method, especially in a coal mine environment, is submicron dust sampling (Haney, 2008). The submicron DPM sampling method was created to eliminate interference from coal mine dust when sampling for DPM in coal mines (Haney, 2008). The DPM Cassette is commercially accessible from SKC, where the built-in impactor screens out
respirable particles ≥1μm and particles that are <1μm are collected on the filter (Noll & Birch, 2004). A study conducted by Noll and Birch (2004) aimed to determine the SKC DPM Cassette’s ability to exclude coal dust and found that it is as effective as the US Bureau of Mines sizeselective sampler (Noll & Birch, 2004). Additionally, the submicron impactor was shown to be effective in collecting DPM, while allowing less than 10% of mineral and coal dust to enter in both laboratory and field studies (Noll et al., 2005).
2.5. How can exposure to DPM be controlled in the underground coal mine industry?
A review was conducted by Chang and Xu (2019) to present a summary of the operational capacity of various control methods of DPM exposure in underground mines. Researchers determined that there are two main approaches to control DPM emission: source controls and exposure controls (Chang & Xu, 2019). Source controls restrict DPM before it is emitted from the diesel engine, whereas, exposure controls reduce DPM levels after it is discharged into the working area (Chang & Xu, 2019). Source controls should be the first consideration when controlling DPM levels in a mining environment (Chang & Xu, 2019). A main source control for DPM exposure is engine maintenance and design improvements (Chang & Xu, 2019). According to Haney et al. (1997), engine design improvements can reduce DPM emissions by as much as 90% (Haney et al., 1997). Additionally, engine maintenance is another effective control to reduce DPM emissions, where poor engine conditions can generate much more DPM (Chang & Xu, 2019). Moreover, a report conducted by NIOSH revealed that the use of low sulphur diesel fuel reduces the sulphate fraction of DPM, which allows oxidation catalysts to perform properly, which generates less DPM (Bagley et al., 2001).
Exposure controls to reduce DPM exposure includes ventilation and the use of aftertreatment devices (Chang & Xu, 2019). Ventilation is the most commonly used control for DPM in underground mines, as it carries fresh air to the working area and dilutes the DPM concentration (Chang & Xu, 2019). Aftertreatment devices are also vital in controlling DPM levels in underground mines, as these devices have the ability to remove pollutants from the exhaust gases before they are released into the environment (Chang & Xu, 2019). There are a wide variety of different aftertreatment devices, with Diesel Oxidation Catalytic Converters (DOCC) shown to reduce DPM emissions by 50% (Haney et al., 1997). Other exposure controls include environmental cabs and respirators, which are vital methods to prevent miners from DPM exposure (Chang & Xu, 2019). According to research conducted by Noll et al. (2011), cab filtration systems of a loader and haul truck were found to be over 90% effective in removing DPM, except when a window is kept open (Noll et al., 2011)
The workplace of interest for this study was an underground coal mine located in the rural Central Queensland Bowen Basin region, approximately 90 kilometres north-west of Emerald and 46 kilometres south-west of Middlemont. This underground mine produces metallurgical
coal for export, with the total area of land being roughly 22,000 hectares. There are approximately 838 people employed across this site, with coal mine workers typically working 10-12 hour shifts, occurring during the day or night. The mine operates 24/7, except for Christmas or Boxing day. Shifts can last up to 10 days in a row, with many workers undertaking a ‘fly-in-fly-out’ (FIFO) work schedule.
Static sampling for DPM exposure was conducted at three locations on two development panels (Panel 601 and Panel 602) on the 27th September and 28th September (Figure 1). Paired samples of different sampling techniques were taken i.e. REC and SEC and co-located. Normally, the mine runs three development panels, but at this time, only two were in full operation (Panel 601 and 602).
Figure 1 – Diagram Showing the Approximate Location of Static Sampling on Panel 601 and Panel 602
The activities conducted on the two panels each day were recorded. On the first day, Panel 601 did not have normal production, instead, strata support was undertaken. On Panel 602, a conveyor belt move occurred. On the second day of sampling, both Panel 601 and Panel 602 resumed normal production activities. The DPM board was noted on the second day (as seen in Table 1). It shows that at Panel 601, three vehicles were in the area and three were on standby to enter the area. At Panel 602, four vehicles were in the area, with two on stand-by to enter.
Table 1 – DPM Tag Board Showing Vehicles in the Area and Vehicles on Standby to Enter on the Second Day of Sampling
Panel 601
Vehicles in the area
1. 2P333 → Taxi Vehicle
2. TP33 → Drift Runner (Transport Personnel)
3. LH35 → Loader
Vehicles on standby to enter the area
1. LH38 → Loader
2. HFM74 → Drift Runner (Transport Personnel)
3. TP24 → Drift Runner (Transport Personnel)
Panel 602
1. LG16 → Loader
2. TP230 → Drift Runner (Transport Personnel)
3. LH36 → Loader
4. 2P333 → Taxi Vehicle
1. TP11 → Drift Runner (Transport Personnel)
2. TP60 → Drift Runner (Transport Personnel)
As aforementioned, there is no WES for DPM in Queensland. However, The Coal Mining Safety and Health Regulation 2017 requires underground mine’s Safety Health Management Systems to provide measures to control workers’ exposure to an atmosphere at the mine containing internal combustion pollutants (Queensland Government, 2017). Additionally, the exposure of pollutants must be below specified concentrations to achieve an exposure as low as reasonably achievable (Queensland Government, 2017). DPM is classified as a respirable particle, meaning that Recognised Standard 15 (RS15) can be applied (Department of Natural Resources, 2017). This standard states approaches for the site senior executive (SSE) to meet health and safety responsibilities and to develop the mine’s safety and health management system to control respirable dust in an underground coal mine (Department of Natural Resources, 2017).
This project used an in-field experimental design to test two different sampling methods representative of DPM concentrations (REC and SEC). Static sampling was conducted over two
days on the 28th and 29th September 2024. All equipment used meets NMAM5040 and AS2985 (NIOSH, 2003; Standards Australia, 2009)
5.1. Equipment for the measurement of SEC DPM Analysis
For the SEC sampling, SKC DPM Plastic Cyclones 37mm (225-68) with a flow rate of 2L/minute were fitted with SKC DPM Cassettes with built-in 0.8µm impactors (225-317). This was used to screen out respirable particles, allowing submicron particles to be deposited onto the filter. SKC AirCheck 3000s (210-3311AZ) air sampling pumps were utilised with SKC Protective Nylon Pump Pouches (224-95A) (for calibration certificates see Appendix 2) The SKC AirCheck 3000s hold intrinsic safety accreditation to ANZex. Calibration was completed using a Porter rotameter (Model F150). Additional equipment used included flexible tygon tubing, three transport bags and a field record sheet for each day. Information recorded on the field data sheet on the days of sampling included pump numbers, sample heads, filter IDs and corresponding locations Moreover, two field blanks per set were used in accordance with NMAM5040 (NIOSH, 2003)
5.2. Equipment for the measurement of REC DPM Analysis
For the REC sampling method, SKC GS-3 Respirable Dust Cyclones with a flow rate of 2.75L/minute with bowl adaptors, cassette adaptors and grit pots 37mm (225-100) were fitted with Three-Piece Clear Plastic Cassettes 37mm (225-401). The SKC GS-3 Respirable Dust Cyclone conforms to ISO 7708:1995 for respirable fractions (ISO, 1995). See further aforementioned equipment that was also used for REC sampling (calibrator, air sampling pumps, rotameter, tygon tubing, transport bags and a field data record sheet).
5.3. Sample Size
Overall, 10 paired samples (a total of 20 samples) of REC and SEC sampling methods were collected. Additionally, 8 pairs of SEC Scanning Electron Microscopy (SEM) and REC SEM were collected over the two sampling days. Each sample was co-located with its relevant analysis type (i.e. one SEC and one REC, one SEC SEM and one REC SEM) with the relevant location, as seen in Table 2.
Table 2 - Paired REC/SEC and SEM REC/SEC Locations and Number Samples Collected
Day 1: Friday 27/09/24
Panel 601 Location and Number of Samples Collected
Panel 602 Location and Number of Samples Collected
1. Panel roadway1st c/t from face 2. Shuttle car circuit (wheeling road) 3. Boot end 1. Panel roadway1st c/t from face 2. Shuttle car circuit (wheeling road) 3. Boot end
Total Number of Samples SEC and REC = 10, Total Paired SEM = 10. Overall = 20
Day 2: Saturday 28/09/24
Panel 601 Location and Number of Samples Collected
1. Panel roadway1st c/t from face
2. Shuttle car circuit (wheeling road)
3. Boot end
Panel 602 Location and Number of Samples Collected
1. Panel roadway1st c/t from face
2. Shuttle car circuit (wheeling road)
3. Boot end
Total Number of Samples SEC and REC = 10, Single SEC SEM = 5, Single REC SEM = 3. Overall = 18
*Only 1 SEM SEC was able to be collected due to faulty filter or sample head
On both days, an underground taxi was used to travel to Panel 601 and Panel 602. The sample run times were preset to 360 minutes for all sampling pumps (6 hours). On the first day, the samples were taken underground via an underground taxi to the first panel at approximately 10:30am. The relevant times that each sampling pump was switched on was recorded on a data entry sheet. Additionally, an observation activity record book was kept to document workplace activities that occurred during the work-day. Informal interviews were also conducted with workers to establish regular workday activities.
Due to a delay whereby the second panel was only reached at approximately 3:30pm, the run times on the pumps on Panel 602 had to be adjusted to 300 minutes instead of 360 minutes in order for the workers at the end of their shift to bring them back up to the surface on time. This is because workers arrive back up at the surface at approximately 9:30pm but start travelling back up to the surface at 8:45pm. On the second day, all run times were changed to
300 minutes to avoid time delays. The first panel was reached at approximately 12:30pm and the second panel was reached at approximately 2pm. Similar to the first day, workers brought the sampling pumps back up to the surface at the completion of their shift in order to be collected.
The general area within the underground coal mine was on two development panels (Panel 601 and Panel 602) in order to obtain the highest potential concentration elemental carbon (Figure 2). The location was determined in to achieve a two times Limit of Reporting (LOR) to 20 times LOR to allow for a greater chance that the results were above the Limit of Quantification (LOQ).
The three locations were defined as follows:
1. Panel Roadway – The first cut-through from the face of the coal seam. Placed approximately on the 60m mark for consistency.
2. Shuttle Car Circuit – Placed directly across from the crib hut room area on the wheeling road.
3. Boot End – Refers to the end of the conveyor belt, which accepts coal from the shuttle car.
5.4.2. Sample Set-Up
Prior to taking the air sampling pumps underground, each filter ID for the corresponding type of elemental carbon (SEC, REC and SEM REC, SEM SEC samples) were co-located and documented. Sample pumps were attached together via the protective cover by buckling them together and placing them into different bags according to which panel they were being placed on, as seen in Figure 3 Samples were hung at a height of approximately 1.5metres (by toggling with the black straps) on the side of the coal mine walls on a coal seam bolts and switched on (Figure 3).
Figure 3 – Representative Figure Showing the Placement of Samples Hanging on the Coal Seam Bolts from Protective Pouch
5.4.3. Calibration and Procedure Followed
Calibration was completed using a Porter rotameter (Model F150) (see Appendix 3 for calibration certificate). Calibration was conducted the night before the first sampling day and post-calibration was completed on the morning of the second day in a clean office on site. For the post-calibration process, if the flow rate differed by -+5% from the original flow rate, then it was not included in analysis (no samples were excluded in this study). Calibration for the second load of samples was also completed on the morning of the second day and postcalibration was completed once the samples were collected from underground. The SKC DPM Plastic Cyclones 37mm (225-68) were calibrated to a flow rate of 2L/minute and the SKC GS-3
Respirable Dust Cyclones were calibrated to a flow rate of 2.75L/minute. This is in accordance with NIOSH5040 and the SKC Operating Manual (NIOSH, 2003; SKC).
5.5.
From the mine site, samples were transported in travel bags and flown from Emerald to Brisbane on Sunday 29th September. There was a time delay due to unforeseen circumstances. The samples were sent to be analysed by NQ Lab (Townsville) NATA accredited laboratory on the 10th of October. The laboratory analysis method used was NMAM5040, which uses thermal-optical analysis and flame ionization detection (NIOSH, 2003). The limit of detection (LOD) according to NIOSH3040 was 3µg per filter portion (NIOSH, 2003).
5.5.1. SEM Samples Not Analysed
Due to time restraints, the SEM samples were not able to be analysed and will not be included in this research.
5.6.
The raw results were received from the laboratory on the 21st of October and entered into Microsoft Excel (version 2410) in a table format (Appendix 1). From there, Strata (version 18) was used to undertake non-parametric descriptive tests, linear regression models and to create a scatterplot graph. Additionally, Microsoft Excel was also used to create a bar graph. Where results were lower than the detection limit, NDExpo was used to transform the result. Only one SEC concentration at Panel 601 on the Panel Roadway was below the LOD.
Table 3 presents the results from a descriptive statistical analysis of the 20 samples collected. The geometric mean (GM) for REC was 0.036mg/m3, with a geometric standard deviation (GSD) of 1.414. This can be compared to the GM for SEC, which was smaller at 0.008mg/m3, with a GSD of 1.477. For OC, the GM for the respirable fraction was 0.062 mg/m3, with a GSD of 1.278 and for the submicron fraction, the GM was 0.044mg/m3, with a GSD of 1.129. Additionally, the GM for the respirable fraction of TC was 0.100mg/m3, with a GSD of 1.329 and for the submicron fraction, the GM was 0.052mg/m3 with a GSD of 1.159.
Table 3 – Descriptive Statistics of Ambient Elemental Carbon, Organic Carbon and Total Carbon Measurements
Fraction
The maximum REC value recorded was 0.055 mg/m3 and the minimum was 0.022mg/m3 . For SEC, the maximum value was 0.012mg/m3 and the minimum value was 0.00159mg/m3 (below the LOD)(as referred to in Figure 4). Although this data cannot directly be compared to the WES as it is not personal sampling, it can serve as a useful marker of potential exposure concentrations. All of the samples for SEC were below the guideline WES for SEC (8-hour TWA 0.1mg/m3), as seen in Figure 3 (Resources Safety & Health Queensland, 2012). For REC, the proposed new WES for DPM is an 8-hour TWA of 15μg REC/m3 (0.015mg/m3) (Safe Work Australia, 2023) All of the samples for REC were above this proposed new WES (15μg REC/m3).
Linearized ratios to compare carbon fractions was conducted. Table 4 indicates that there is no significant difference between the two panels samples (Panel 601 and 602). This can be deduced by observing the bootstrap standard error (BSE). For SEC Panel 601, the BSE was 0.010, which is only marginally different from the BSE for REC Panel 602 (0.019). This is further demonstrated by analysing the observed ratio 95% confidence interval, with Panel 601 SEC being 0.132-0.171 and the observed ratio 95% confidence interval for Panel 602 REC being 0.140-0.213. For submicron OC, the BSE at Panel 601 was 0.066 and the BSE for respirable OC was 0.044, which is only slightly different. Additionally, this is also shown for submicron TC and respirable TC, with the BSE being 0.043 and 0.036 respectively. Overall, the results presented in Table 4 indicate that the difference between REC and SEC is not due to variation among the two sampling panels.
Table 4 – Linearized Ratios for Comparative Analysis of Carbon Fractions
As seen in Table 5, the current model suggests that SEC accounts for 21% of REC. The Standard Error (0.047) implies that the estimated coefficient is accurate and that the true relationship between REC and SEC is close to the estimated coefficient (0.210). Additionally, the p-value is 0.002, which suggests strong statistical significance and that the null hypothesis can be rejected (Submicron EC = Respirable EC). Furthermore, the R-Squared value is 0.714, indicating that approximately 71.4% of variation in SEC concentrations can be explained by the REC. The F-test is a regression analysis statistic that, in this case, further supports the understanding that the null hypothesis can be rejected (19.932). The small Prob > F number (0.002) indicates strong evidence against the null hypothesis, meaning that REC has a strong effect on SEC. Moreover, the T-value of 4.46 further corroborates this as it suggests a strong relationship between REC and SEC.
Model: SEC = 0.21 x REC + 0.0005 P-value Significance: *** p<.01, ** p<.05, * p<.1
The results of a Wilcoxon Signed Ranked Test for REC and SEC presented in Table 6 show that SEC is consistently lower than REC, with all 10 observations indicating a sum rank of 55 for negative comparisons. Furthermore, the Z-Statistic is -2.803, meaning that SEC is reliably lower than REC The results in Table 6 further reinforce that the null hypothesis that SEC concentrations are equal to REC concentrations can be rejected due to the outcome of the two-sided p-value from normal approximation (0.005) and the two-sided exact p-value (0.002).
Table 6 - Results of a Wilcoxon Signed Rank Test for REC and SEC
Two-sided p-value from normal approximation (Prob > [Z]) 0.005***
Two-sided exact p-value 0.002***
Null Hypothesis (H0): Submicron EC = Respirable EC P-value Significance: *** p<.01, ** p<.05, * p<.1
The Linear Relationship plot shown in Figure 5 demonstrates that different locations only impacted the results minimally, as indicated by the large variations in concentrations at each
location. Although, compared to the other locations, Boot End did have higher concentrations and less variation (Figure 5) Panel Roadway contained the lowest REC to SEC concentration (0.022mg/m3 REC to 0.00159mg/m3). The highest REC to SEC concentration was recorded in the Boot End (0.055 mg/m3 REC to 0.011 mg/m3 SEC).
Figure 5 – Plot of Linear Relationship between REC and SEC Concentrations (mg/m3) with Different Locations Identified
Overall, this research aimed to determine the differences in sampling techniques when measuring REC and SEC as a surrogate for DPM concentrations in an underground coal mine. The location of sampling was chosen to achieve a concentration two times Limit of Reporting (LOR) to 20 times LOR to allow for a greater chance that the results were above the Limit of Quantification (LOQ). The locations chosen had consistent respirable dust concentrations and similar ventilation flow paths. Additionally, the locations were chosen based on accessibility in order not to disrupt the standard operations of the mine. The operating conditions being undertaken during sampling were considered a representation of normal conditions in an underground coal mine. Sample trains were hung from the walls of the mine on coal seam bolts. Results demonstrated that SEC concentrations were consistently lower than REC concentrations, irrespective of day, location and development panel sampled.
Research by Vermeulen et al. (2010) was conducted in nine non-metal mining facilities and investigated the interrelationships between REC and other measured elements of DEE. Vermeulen et al. (2010) conducted area sampling for total EC, REC, SEC, total OC, respirable OC and submicron OC. Samples were collected over the work shift, for a median run time of 372 minutes (Vermeulen et al., 2010). Results showed that the GM for REC concentrations was
66µg/m3 and SEC 44 µg/m3 , respectively (Vermeulen et al., 2010). This can be compared to the current study, which had a GM for REC of 0.035mg/m3 and 0.008mg/m3 for SEC. Even though the present study had a more significant difference between REC and SEC, Vermeulen et al. (2010) also found that SEC was consistently lower than REC. Additionally, research was carried out by Pretorius and Grove (2011) to evaluate the various DPM sampling methods used in South African mining to compare it to the SEC analysis method for DPM. Researchers collected ambient measurements for underground samples and recorded an average SEC concentration of 0.099 mg/m3 and REC 0.127mg/m3 respectively. These results showed a similar relationship between SEC and REC, although concentrations were higher in samples.
Although the current study found that SEC accounted for 21% of REC, compared to Vermeulen et al. (2010), which found that SEC contributed between 77% and 96% of the REC samples, a consistent linear relationship was still found between EC fractions This linear relationship can further be demonstrated when analysing the R2 value from Table 5 (0.714) which indicated a positive correlation between these EC fractions. Variations from the literature could be due to the variability of using EC as a surrogate for DPM. One of the major issues is that the EC fraction of DPM can vary depending on engine duty cycle, fuel type and variations in day to day mining (Noll et al., 2007). This can further be corroborated by Burtscher (2005), who found that the ratio of EC to total mass for DPM sampled ranged from 45 to 100% depending on the engine load conditions.
The lower overall EC concentrations observed in the present study could be attributed to a variety of reasons. The underground coal mine that was sampled has recently added diesel particulate filters (DPF) in most of their vehicles, which could reduce EC concentrations. DPF has been shown to reduce EC in diesel exhaust and research conducted by NIOSH showed that DPF could reduce DPM mass by 81-87% depending on the type (Bugarski et al., 2012). Moreover, the mine has effective controls in place such as a DPM tag board to control diesel exhaust in panels. This means that vehicles cannot enter the panel unless there is ‘space’ on the tag board or with approval from the deputy in that area. This could lower the amount of DPM in the area, in turn, leading to reduced concentrations of EC. This idea can be corroborated by Peters et al. (2017), who demonstrated that the concentrations of DPM reported in Australia are lower than internationally reported due to the effort of implemented controls for DPM emissions in Australian mines (Peters et al., 2017).
Differences from literature could also be due to the current mine site being an underground coal mine, compared to an underground metalliferous mines. If a dust contains carbonaceous minerals (such as coal dust), then respirable dust sampling can cause an interference in either the elemental carbon or organic carbon concentrations (Haney, 2008) Therefore, the submicrometer impactor reduces possible interferences when sampling for DPM in the presence of a mineral dust containing carbonaceous compounds (Haney, 2008). Moreover, in an underground coal mine, carbonates such as limestone can cause an interference when determining the total carbon content (Haney, 2008) In underground coal mines, limestone is added to the walls of the mine to prevent coal dust explosions spreading (LaBranche, 2024)
Haney (2008) found that using an impactor reduced the amount of carbonate on the sample by up to 90%. Combined with the results that showed higher concentrations of REC compared to SEC, this indicates potential inferences in the result. Therefore, considering that the REC analysis method in an underground coal mine has the potential for interferences from coal dust, the proposed REC WES of 15µg/m3 is not recommended (Safe Work Australia, 2023). Moreover, although area sampling cannot directly be compared to the WES, all of the samples measured for REC exceeded the proposed new WES, with SEC concentrations being well below the current guideline WES (0.1mg/m3 for SEC) (Department of Natural Resources, 2017). This further highlights the unsuitability of the proposed new WES, as the REC concentrations may be artificially inflated due to coal dust interference, signifying that this method should not be used in an underground coal mine. This means that the proposed new WES would present significant limitations in measuring and regulating DPM in underground coal mines, where interferences can occur. Instead, occupational hygiene professionals should utilise the submicrometer method as a surrogate for DPM concentrations in an underground coal mine environment.
Although the submicrometer method is recommended, there are some issues with the size selector approach to sampling DPM. Gaillard et al. (2021) conducted a study to explore the possibility of DPM and dust attachment in an underground stone mine (Gaillard et al., 2021) According to Gaillard et al. (2021), this method can miss some of the DPM if the DPM particles are bigger than the selector’s cut size or if the DPM is larger due to being attached to larger particles (Gaillard et al., 2021). This data indicates that some DPM is omitted by the typical sampling methods (Gaillard et al., 2021) Researchers determined via transmission electron microscopy (TEM) that DPM and dust attachment can occur to a certain extent but that the effect of this has not been investigated yet (Gaillard et al., 2021)
Gaillard et al. (2021) demonstrated that there is potential for the DPM that was produced in this underground coal mine to attach to dust particulates within the mine’s atmosphere, which could result in supra-micron DPM. Due to the variations in total, respirable and submicron EC concentrations that were observed at different sampling locations, this suggests that at this current mine, considerable amount of the DPM may occur in the supramicorn range (Gaillard et al., 2021). These results are similar to what was found by Vermeulen et al. (2010), who found that supra-micron particles can contribute to the total DPM mass. This attachment of DPM to dust would not be able to be quantified by the SEC sampling technique and means that the current technique could be under sampling DPM (LaBranche, 2024). The degree of agglomeration or attachment could be quantified by SEM analysis in future research. It is also not currently known whether this agglomeration is happening in the mine, in the cyclone or on the filter (LaBranche, 2024). Additional research is required to determine the degree of attachment and techniques to account for this (LaBranche, 2024).
Furthermore, there are some other existing gaps in knowledge in terms of the limitations with NIOSH Method 5040 (Noll et al., 2013). Whilst this method precisely measures DPM exposures, it only shows the average concentration over an entire working shift, and it
frequently takes several weeks to obtain the outcomes (Noll et al., 2013). Additionally, it only reveals if an overexposure has occurred, instead of offering the ability to detect the overexposure at its source or to prevent it from occurring (Noll et al., 2013). Consequently, real-time measurements for DPM have been explored to provide instantaneous information regarding overexposures and immediate use of controls (Noll et al., 2013). A recent study conducted by Habibi et al. (2023) utilised a Dekati electrical particle sensor (DePS) which measured concentrations of SEC in real-time (Habibi et al., 2023). The results produced were promising and showed that this methodology is suitable for continuous monitoring of DPM in underground mining operations, however, further research is needed (Habibi et al., 2023).
One of the major limitations of this study was the limited timeline This project was only conducted across one semester at university (approximately 13 weeks), which restricted the in-depth analysis and scope of the research. In turn, this led to the inability to complete SEM analysis of samples, which restricted the conclusions that could be drawn from the research. The SEM analysis would have allowed the results to be visualised, which would have added value to the research. Additionally, area sampling could be vulnerable to spatial variability, which is a recognised issue for the collection of airborne particulate samples in mine environments (Kissell & Sacks, 2002) Another limitation to this study was the run time of the sampling pumps. Although the run time was sufficient to record an EC mass larger than the LOD, longer run times would reduce this risk. If further sampling were to be conducted across multiple days, including multiple mine sites and increased run times, the relationship between fraction sizes could be confirmed This means that higher concentrations of EC would likely be recorded, leading to stronger conclusions to be drawn.
The primary purpose of this research was to determine the differences in sampling techniques when measuring respirable elemental carbon (REC) and submicron elemental carbon (SEC) as surrogate DPM concentrations. Moreover, this research aimed to provide insights for the Queensland Mining Inspector (QMI) with regards to the new proposed REC WES for DPM (8hour TWA of 15μg REC/m3). The results from this study indicated that a positive and statistically significant relationship between REC and SEC concentrations exists. SEC concentrations were determined to be consistently lower than REC concentrations, irrespective of location sampled. It was proposed that potential interferences from coal mine dust could affect EC analysis. To minimize this inference, it was recommended that submicron sampling with an impactor (cutpoint of about 0.8μm) be utilised in an underground coal mine environment to minimize the collection of carbonates and other carbonaceous dusts. Although, super-micron DPM has been suggested to exist within the underground coal mine, which would be excluded in the submicron sampling technique. It is not currently known whether this agglomeration is happening in the mine, in the cyclone or on the filter, indicating
the need for additional research. However, due to the small study size and only sampling from one underground mine, there is a potential for differing results to be observed in other mine environments. In the future, it is recommended to include multiple underground coal mines to further assess the relationship between the different EC fractions. Moreover, a follow-up study should include SEM analysis to provide a visual analysis of EC fractions.
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Appendix 1 – Raw Data Showing DPM as Elemental Carbon, Organic Carbon, Total Carbon and Fraction Types
Appendix 2 – Calibration Certificates for the 20 Air Sampling Pumps
Appendix 3 - Rotameter Calibration Certificate and Flow Rate Chart
