The threat of health-related class action suits due to the impacts on the health of underground mine workers

Mining corporations face the threat of health-related class action suits due to the impacts on the health of underground mine workers, in particular, due to persistent exposure over time to diesel engine exhaust emissions (DEE).

Author's note: sincere thanks to Martin Ralph of DMIRS for reviewing the article’s regulatory and technical content.

Introduction

This issue was raised in a very recent article in The Weekend Australian business section (September 18-19, 2021). It stated that a global survey of more than 800 executives revealed that more than 70 per cent of the 205 Australian-based respondents believe the industry faces a major health-related class action within the next 15 years. Indeed, the newly appointed CEO of Gold Fields, which has four major gold mines in Australia, who was one of the respondents, stated that a major respiratory health issue facing the industry was diesel particulates from underground machinery.

The article states that the risk of such actions in Australia is significant because it has so many very deep underground mines. Hence the reason for the initiatives towards electrifying mine sites. Gold Fields is trialling electric vehicles underground and above ground at most of its sites, including those in Australia. By this means mining companies will remove the threat of diesel particulates completely from their operations, notwithstanding, however, the possible introduction of other risks, such as fire, from the lithium-ion batteries themselves.

The real challenge

The general public became aware of the health risk to miners exposed to diesel engine exhaust (DEE) fumes when the National Institute for Occupational Safety and Health (NIOSH) and the National Cancer Institute’s (NCI) 20-Year Diesel Exhaust in Miners Study was published in the USA in 2012. It reported that underground miners most heavily exposed to diesel engine exhaust fumes were three times more likely to develop lung cancer than those exposed to the lowest levels (Attfield et al, 2012).

Shortly thereafter the International Agency for Research on Cancer (IARC) re-categorised diesel engine exhaust fumes as ‘Carcinogenic to Humans – Group 1’, based on evidence from several studies carried out during the previous decade (WHO/IARC, 2012), and (Benbrahim-Tallae et al, 2012).

Subsequently, a multitude of scientific review papers and research reports have been published on the occupational health hazard to workers exposed on a regular basis to diesel engine exhaust (DEE) fumes, eg (Jones, 2015; Jones, 2016; Jones and Davis, 2017; and Landwehr, 2021). The most hazardous component of such fumes is the ultra-fine (i.e. <100 nm) and in particular its nano-sized carbon particulates (i.e. <50 nm).

Whereas the increasingly demanding standards set by regulatory authorities, notably in the USA and Europe, have led to reductions in the total carbon mass emissions, it has done little to reduce the number of ultra-fine and nano-sized particulates emitted. It is also worth noting that whilst recent improvements in the effectiveness of diesel particulate filters and oxidation catalysts have been reported, the implementation of the improved units is far from universal, and the claims made in relation to reduction of the number of particulates below 100 nm need to be verified over extended periods of use.

These ultra-fine and nano-sized carbon particles, with their capacity to adsorb onto their surfaces a host of toxic hydrocarbon compounds, some of which are carcinogenic, pose the most serious health hazard to workers, because they bypass the body’s epithelial clearance mechanism and readily penetrate the lung’s deeper alveolar sacs and pass through the alveolar membrane, thereby entering the bloodstream and lymph system. Thereafter they can readily reach such sensitive targets as the lymph nodes, spleen, heart and central nervous system.

Apart from the ultra-fine and nano-sized carbon particulates, other nano-sized volatile nucleation mode particles (NUP) can also occur as the exhaust products cool and dilute in the atmosphere beyond the tailpipe. These semi-volatile vapours can condense and/or adsorb onto the carbonatious soot agglomerates or exist as nano-sized nucleate droplets, thereby adding to the complexity of the health hazard to underground mine workers in particular.

To further add to the complexity of the challenge we must consider the 40 or so toxic compounds in the gaseous fumes such as benzene and formaldehyde as well as some 15 of the polycyclic aromatic hydrocarbons (PAHs) also considered carcinogenic, not to mention the toxic gases such as carbon monoxide (CO) and nitrogen oxides (NOx). Hence the problem of relying solely on a single metric to assess the health hazard of diesel engine exhaust (DEE) fumes at work sites.

Monitoring standards and exposure metrics – their influence on diesel disease class action suits

Whereas there is no perfectly ideal surrogate for use in assessing the health hazard of occupational exposure to Diesel Engine Exhaust (DEE) fumes, elemental carbon (EC) is still the most widely used by most regulatory regimes. This is, because, amongst other reasons, the proportion of EC in diesel exhaust is reported to vary with engine operating conditions.

A recent NHMRC sponsored research program in WA (Peters et al, 2017) examined the Department of Mines and Petroleum’s CONTAM data from 2003 to 2017, as well as available medical records, which included all incident cancers as mandatorily notified in WA, and thereafter modelled the findings for various occupations in order to ascertain the number of certified lung cancer deaths caused by various levels of EC.

The researchers modelling found that underground miners who were exposed at work over a period of 45 years to 0.044mg/m3 of EC would have 38 extra lung cancers per 1000 workers compared to that of the general population, whereas the normally accepted risk of occupational disease is 1 in a 1000 workers (note: the data was collected prior to the mine safety regulator’s interventions in 2013-15 which resulted in decreased levels of diesel particulate in Western Australian underground mines).

Consequently, the researchers strongly recommended a reduction in the DMIRS’ current guideline of TWA 8-hour limit of 0.1 mg/m3; a view increasingly shared by researchers at various other international jurisdictions, e.g.

In a letter from the Director, Occupational Cancer Research Centre (OCRC) to Ontario’s Hon. Minister of Labour dated, 4 May 2018, he stated:

• Based on evidence of increased lung cancer risk at very low DEE levels, OCRC recommends moving towards the limit of 20 micrograms/m3 EC for the mining industry and 5 micrograms/m3 for other workers.
• Other groups are recommending similar or even more stringent protective limits, such as the Dutch Expert Committee on Occupational Safety and Health Council recommending a health based OEL for DEE of no higher than background levels (approx 1 microgram/m3).

Inevitably, those jurisdictions that have followed this trajectory of more stringent regulatory levels of EC can claim their willingness to adopt such levels as evidence of their increasing concern for their workers’ health.

Furthermore, a ‘Critical Review of Diesel Exhaust Exposure Health impact Research Relevant to Occupational Settings: Are We Controlling the Wrong Pollutants?’ (Landwehr et al, 2021) suggests that based on published literature, an occupational limit of an average diesel exhaust concentration below 50 micrograms/m3 of diesel particles, 35 micrograms/m3 of elemental carbon, is appropriate to limit health effects. The same researchers also state that an exposure limit of 100 micrograms/m3 is too high and that a limit of 50 micrograms /m3 is more appropriate if lung cancer risk and the effects of exposure on workers with asthma, allergy and respiratory disease are accounted for. Notwithstanding that occupational limits are not designed to protect those workers with allergic responses, an argument can be made that a duty exists to reduce the limit in order to reduce lung cancer risk.

Whilst appreciating the logic underpinning the decision of the WA Government to introduce a new workplace exposure standard (WES) of 100 micrograms/m3 of sub-micron EC - 8 hour standard, into WA’s mine safety legislation on 4 December 2020, in keeping with the Australian Institute of Occupational Hygienists (AIOH) guidelines, the authors respectfully disagree with this ultra-cautious approach. They would much rather see the WA Government following the trajectory of most other international jurisdictions and authorities in adopting a more stringent EC standard, well below the current limit of 0.1 mg/m3 of sub-micron EC.  

Conclusions

Many mining corporations are progressing with some rapidity to electrify their mines, hence eliminating many of the challenges of maintaining healthy environments for underground miners, at mine sites utilising diesel powered equipment. However, whilst diesel powered equipment still exist at numerous mine sites, every effort must be made to minimise the associated health hazards.

In this regard, as stated recently by OCRC ‘measuring elemental carbon is considered the best way to understand the potential carcinogenic effects of diesel exhaust.’ Consequently, Australian regulators should preferably follow the growing groundswell of scientific opinion that urgent action is needed to adopt occupational EC standards well below 0.1 mg/m3.

References

1. Gray ML, “Miners brace for diesel disease class action suits”, The Weekend Australia. September 18-19, 2021
2. Attfield MD., et al, “The diesel exhaust in a miners study: a cohort mortality study with emphasis on lung cancer. J Natl Cancer Inst, 2012.
3. World Health Organisation’s International Agency for Research on Cancer, Press Release No213, June 2012.
4. Benbrahim-Tallaa L., et al., “Carcinogenicity of diesel engine exhaust and some nitroarenes. Lancet Oncology, Vol 13(7):663-664, 2012.
5. Jones IO,” Diesel Exhaust and the Underground Miner in Western Australia”, AusIMM Bulletin Magazine, August 2015.
6. Jones IO, “Underground Miners Lungs and related Occupational Health Issues in Australia”. Australian Mining Journal, Part 1 November 2016, 20-22: Part 2 December 2016, 16-19.
7. Jones IO AND Davis C, “The Occupational Hazard of Inhaling Diesel exhaust Fumes – Future Directions”, Australian Mining Journal, June 2017.
8. Jones IO., et al, “A gateway to healthier environments in WA’s hard-rock mines”. AusIMM Bulletin, December 2019.
9. Landwehr KR, et al., “Critical Review of Diesel Exhaust Exposure Health Impact Research Relevant to Occupational Settings: Are We Controlling the Wrong Pollutants?”, Exposure and Health 13, 2021.
10. Peters S, et al., “Estimation of quantitative levels of diesel exhaust exposure and health impact in the contemporary Australian mining industry”. Environmental Medicine 74. April 2017.
11. Sodhi-Berry N., et al., “Cancer incidence in the Western Australian mining industry (1996-2013)”. International Journal of Cancer Epidemiology, 2017.