Battery Electric Vehicles in Underground Mining: Benefits, Challenges, and Safety Considerations

Abstract

This paper explores the implementation of battery electric vehicles (BEVs) in underground mining operations, focusing on their benefits, challenges, and safety considerations. The study examines the shift from traditional diesel-powered machinery to BEVs in response to increasing environmental concerns and stricter emission regulations. It discusses various lithium-ion battery chemistries used in BEVs, particularly lithium–iron–phosphate (LFP) and nickel–manganese–cobalt (NMC), comparing their performance, safety, and suitability for underground mining applications. The research highlights the significant benefits of BEVs, including reduced greenhouse gas emissions, improved air quality in confined spaces, and potential ventilation cost savings. However, it also addresses critical safety concerns, such as fire risks associated with lithium-ion batteries and the emission of toxic gases during thermal runaway events. The manuscript emphasises the importance of comprehensive risk assessment and mitigation strategies when introducing BEVs to underground mining environments. It concludes that while BEVs offer promising solutions for more sustainable and environmentally friendly mining operations, further research is needed to ensure their safe integration into underground mining practices. This study contributes valuable insights to the ongoing discussion on the future of mining technology and its environmental impact.

1. Introduction

It is widely recognised that mining has a considerable impact on the environment. Still, it is essential to understand that mining is necessary to meet our demand for materials and energy. As P.N. Martens and L. Rattmann [1] noted, “Without mining, there would be no future for anybody to look forward to,” as the materials being mined are used in every aspect of our lives. Iron ore is one of the most mined raw materials in the world, and it does not include mineral fuels [2]. In total, 98% of mined iron ore is used in steel production [3], one of the most critical construction materials needed in almost every aspect of our lives if we want to continue upgrading our living standards. Steel is mainly used in buildings, infrastructure, transportation, metal products, mechanical equipment, domestic appliances, and electrical equipment [4]. As all the above-mentioned markets have boomed over the last decades, iron ore production has also grown (Figure 1). One reason for the rapid drop in 2015 was China’s growth strategy reorientation, which led to a substantial supply overhang [5]. Since 2015, there has been a slow but steady growth in iron ore production, which started to decline in 2018.

As mentioned before, mining significantly impacts the environment, and therefore, the industry’s reputation with the majority of stakeholders is broadly neutral or negative [7]. Comparing the reputations of different mining industries, according to the World Gold Council report, the iron ore industry has the highest overall ranking in every stakeholder group analysed (government, civil society, media, and international organisations). As the conversation on climate change and the necessary next step toward a more sustainable future intensifies, the mining industry, including iron ore mining, is under increasing pressure to adopt more sustainable practices in the long run. Gold mining company Anglo American’s CEO [8] thinks that when discussing the future of mining, it is essential to understand and connect it with next-generation societal values, including responsible technological innovation and sustainability. To maintain or regain a social licence to operate, mining companies must take radical steps to ensure sustainability in their operations. Also related to the iron ore industry is the steelmaking process. In addition to the mining industry’s environmental footprint, the steel industry accounts for 7% of global CO₂ emissions [9], making it one of the industries with the highest CO₂ emissions.

The Swedish government has set a goal in Sweden’s Minerals Strategy [10] to secure its leading position in the European mining industry. According to the mineral production statistics compiled by the Geological Survey of Sweden, mineral production levels have increased since 2009, with a slight drop in 2015. Goals set in Sweden’s Minerals Strategy will ensure that mineral production, including iron ore production in Sweden, continues to increase. As the largest iron ore miner and pellet producer in Europe, LKAB has recognised its responsibility as an iron ore company to its stakeholders and has initiated projects such as Sustainable Underground Mining and HYBRIT to explore ways to make iron ore production more sustainable. The company’s goal is to achieve a CO₂-free value chain. In both projects, changing the energy source used in the processes is vital—in the pelleting process, replacing fossil fuels with hydrogen [11] and switching from diesel to electricity in mining operations. In July 2021, the first patch of sponge iron was produced using 100% fossil-free hydrogen with the HYBRIT technology [12]. The Minerals Strategy supports both mentioned projects initiated by LKAB and highlights the importance of research and innovation in the mining industry.

Battery electric vehicles (BEVs) represent a significant shift in the mining industry, emerging as a promising alternative to traditional diesel-powered machinery. As the demand for more sustainable and environmentally friendly technologies grows, BEVs have gained attention due to their potential to address key challenges in underground mining operations. This development trend raises important questions regarding the technical, economic, and environmental implications of its implementation. Understanding the foundational theories and research surrounding BEVs, as well as the associated benefits and challenges, is crucial for assessing their role in the future of mining.

2. Regulations on Diesel Vehicles

So far, the mining industry has mainly relied on equipment powered by internal combustion engines (ICEs) that run on diesel. While diesel-powered vehicles have many advantages, such as reliability, efficiency, durability, ease of maintenance, and necessary mobility for mining operations [13], they also have considerable disadvantages, including the emission of diesel exhaust gases, diesel particulate matter (DPM), and heat.

Stricter regulations on heavy-duty diesel engine emissions were adopted in the 1990s in Europe, North America, and Japan. At first, the primary emissions targeted with the regulations in all regions were CO, HC, NOx, NMHC + NOx (in North American regulations), and DPM. Later, additional regulations followed regarding greenhouse gas (GHG) emissions and fuel consumption. According to Jääskeläinen and Majewski [14], regulations targeting emissions and fuel economy have been the main factors for improvements in engine technology. Market demand for lower fuel consumption and high engine performance has also played an important part. The companies using diesel machines have acknowledged the need for change towards more sustainable production. European standards for nonroad heavy-duty vehicles have been divided into five stages (Stages I to V). The first EU standard on nonroad emissions was passed in 1997 [15], which aimed to approximate the laws of the Member States relating to emission standards and type approval procedures for engines to be installed in nonroad mobile machinery. It aimed to contribute to the smooth functioning of the internal market while protecting human health and the environment. From 2004, Stage III and IV emission standards were adopted [16], with Stage III phased in from 2006 to 2013 and Stage IV entering into force in 2014. Stage V [17] was phased in 2018 for new engine types and in 2019 for all sales. For machines used in mining, usually, the net power of the vehicle is between 130 and 560 kW, which means that allowed CO emissions have decreased from 5.0 g/kWh under Stage I regulations to 3.5 g/kWh under Stage V regulations, HC from 1.3 to 0.19 g/kWh, NOx from 9.2 to 0.4 g/kWh, and DPM from 0.54 to 0.015 g/kWh [15,16,17]. Specific changes from Stages I to V are presented in Figure 2.

Regulations on diesel heavy-duty vehicles have been divided into four stages in the USA and Canada. In 1994, the first regulations were structured as a three-tiered process, with Tier 1 taking effect in 1996 [18], Tier 2 in 2001, and Tier 3 in 2006 [19]. Tier 4 was phased in from 2008 to 2015, with stricter regulations on NOx and DPM emissions [20]. Specific changes in different regulatory stages in North America are presented in Figure 3.

Examining the standards adopted over the years, it appears that CO emissions have remained constant from Stage 2 to Tier 2, suggesting that there may be limited room for improvement. Like CO emissions, HC regulations have remained unchanged in European standards, and other emission reduction steps have also decreased over time. Considering options to lower or eliminate emissions from vehicles used in mines, the next logical step would be to explore alternative energy solutions. Most commonly, electric machines that do not generate emissions are targeted with regulations. When considering electric vehicles for cleaner energy in the mining industry, it is essential to examine the entire production cycle, not just the processes within mines, as the electricity used for charging the vehicles must also be clean to have a meaningful impact on operations.

3. Battery Chemistries Used in BEVs

Electric vehicles have been tested and used in the mining industry since the 1920s, becoming one of the significant topics in industry development over the last decades. Most commonly, electric vehicles are powered by three solutions: vehicles with cables, vehicles with overhead catenary lines, and battery electric vehicles. Looking more closely at LKAB, they have used tethered Sandvik loaders in the Kiruna mine since the mid-1980s [21], and the results have been very successful. The only problem with electric loaders has been the vehicles’ mobility. That is why LKAB is exploring battery electric vehicles, which combine the best features of electric and diesel cars—productivity and mobility—in one vehicle.

Replacing vehicles with ICE powered by diesel working in a mine with electric ones comes with many benefits associated with workers’ health and safety, work environment, lower energy consumption, reductions to mine ventilation requirements, smaller heat generation, lower maintenance costs, etc. [22]. Using electric vehicles in mines can be achieved through tethered equipment, vehicles with overhead catenary lines, or battery electric vehicles. All three have their challenges: tethered vehicles have limited mobility and still rely on diesel fuel for commuting to the workplace, the use of cars with catenary lines is mainly limited by cost and mobility, and BEVs developed with current knowledge lack suitable batteries that can last for an entire shift.

Most BEVs run on lithium-ion batteries, but the exact battery chemistry varies between original equipment manufacturers (OEMs). Lithium-ion batteries (LIBs) are currently the most suitable energy storage devices for powering BEVs, owing to their attractive properties, including high energy efficiency, a lack of memory effect, long cycle life, and high energy density. These advantages allow them to be smaller and lighter than conventional rechargeable batteries such as lead–acid batteries, nickel–cadmium batteries (Ni-Cd), and nickel–metal hydride batteries (Ni–MH). The importance of LIBs in future technologies is acknowledged by the fact that in 2019, the Nobel Prize in Chemistry was awarded to Akira Yoshino, John B. Goodenough, and M. Stanley Whittingham for their development of lithium-ion batteries.

The most common LIB chemistries used for underground BEVs are lithium–iron–phosphate (LFP, used in Sandvik’s BEV batteries) and nickel–manganese–cobalt (NMC, used in Epiroc’s BEV batteries), both of which have advantages and challenges when employed. Another alternative is lithium–titanate chemistry, which is not currently in commercial usage in BEVs due to its being more than three times more expensive than LFP [23]. As a LIB chemistry with the most kWh per volume of the cells, lithium–cobalt batteries are not used for underground mining BEVs due to being fire-hazardous [24].

One LIB chemistry widely used for underground mining BEVs is lithium–iron–phosphate, the most common and well-tested LIB chemistry. As a result of higher production rates, LFP batteries have a lower cost than the other LIB chemistries. According to OEMs, the main reason for using LFP chemistry is that it is the safest chemistry for BEVs used in underground mining, as the batteries do not catch fire or burn when punctured; they only produce smoke [23]. However, they lack the energy density of NMC batteries. LFP chemistry may face a balancing issue with ageing as it has a higher self-discharge rate than other LIBs [25], which can be mitigated by purchasing high-quality cells or using control electronics. Still, the solutions will increase the cost of the battery pack.

According to OEMs using nickel–manganese–cobalt chemistry in their LIBs, the chemistry is controllable and easily steerable. It is designed for energy density, allowing the batteries to be more compact and lighter [26]. Another benefit of NMC chemistry is its lowest self-heating rate compared to other lithium-ion chemistries [27]. NMC has also demonstrated a higher cycle life than other cathode materials. In a study conducted by Popp et al. [28], it was determined that NMC batteries, compared to LFP batteries, can operate longer before reaching the same retention rate as their initial capacity. According to the study, NMC reaches 80% of its initial capacity with 455 cycles, while LFP reaches it with 377 cycles. Due to the high price of cobalt, many battery manufacturers are moving away from cobalt-based cathode chemistries toward nickel cathodes [29]. Nickel-based systems have a higher energy density, lower cost, and longer cycle life than cobalt-based cells but have a slightly lower voltage. For example, Northvolt, whose batteries are used in Epiroc’s BEVs, has reduced its cobalt content from 30% to 10% and, according to the company, continues to develop this chemistry to achieve the best results [30].

An important aspect to consider while comparing different lithium-ion battery chemistries is the safety of the batteries. Some OEMs say NMC batteries could be more fire-hazardous than LFP batteries [23]. However, according to Christina Lampe-Onnerud [31], CEO and founder of Cadenza Innovation, neither the LFP nor the NMC cathode is what burns due to thermal runaway, but rather the organic electrolyte. The results of a study [32] where the safety of different lithium-ion cells was compared indicated that LFP cells indeed have higher thermal stability, but, at the same time, when overcharged, they are damaged earlier, and LFP cells also showed some electrolyte leakage when short-circuited. The study also stated that apart from the chemistry, the design of each cell is key to its safety.

The safety of batteries used in Epiroc’s BEVs is divided into various levels, ranging from cell chemistry to mechanical crash protection. Figure 4 shows the different levels of the safety onion for Epiroc’s batteries.

4. Benefits of Using BEVs in Underground Mines

Many of the benefits of BEVs mentioned above are related to the fact that they do not generate diesel exhaust gases, diesel particulate matter, or greenhouse gases while in operation, as they do not use fossil fuels for energy. When comparing two different types of vehicles and their emissions, it is essential to consider the broader perspective—the entire life cycle of the vehicles, from production to the end of their useful life.

Examining the GHG emissions of diesel cars and BEVs, studies have yielded opposing results. Buchal et al. [33] claim that while driving, BEVs generate approximately 50% less GHGs than diesel cars (73 g/km for BEVs and 143 g/km for diesel cars). Calculations were performed based on an energy mix used in Germany, which consists of fossil fuels and nuclear and renewable energy sources. But manufacturing a BEV generates up to five times more GHG than the manufacturing of a diesel car (100–125 g/km for BEV, with battery manufacturing accounting for 75%, and 27 g/km for a diesel car), making the whole life cycle of a BEV generate more GHG than a diesel vehicle. However, Hoekstra [34] stated that earlier comparisons between GHG emissions from diesel vehicles and BEVs have overestimated different parameters of BEVs like battery manufacturing, battery lifetime, etc., and concluded in his study that BEVs generate 60% fewer GHGs over their life cycle than diesel vehicles (95 g/km for BEVs and 244 g/km for diesel cars). GHG emissions from BEVs can be even more reduced by running them on electricity generated from renewable energy sources. One great benefit while talking about replacing diesel vehicles with BEVs in LKAB is the fact that about 97% of electrical energy in Norrbotten is generated from renewable sources (hydro, solar, and wind power) [35], which, according to Hoekstra, [34] would lower GHG emissions while driving BEVs by about 90% (from 55 g/km to 6 g/km).

In many cases, Diesel vehicles are significant contributors to diesel exhaust, which can be categorised into gaseous and particulate matter phases. Diesel exhaust, including both gases (NOx, CO, CO₂, SO₂, and HC) and diesel particulate matter, is classified as carcinogenic to humans (Group 1) [36]. As discussed earlier, due to strict regulations, diesel vehicles used in underground mines have undergone significant development in terms of reducing diesel exhaust gas emissions. Lower emission levels have been achieved through in-cylinder technologies, such as exhaust gas recirculation, which improves the efficiency of the combustion process, as well as various after-treatment technologies [37]. Short-term exposure limits and threshold limit values, as well as time-weighted averages of diesel exhaust gases such as NO₂, CO, and NO, are parameters that dictate ventilation requirements in Sweden [38]. Lowering or eliminating diesel exhaust gases from mining processes, in addition to a safer and healthier work environment, will make it possible to implement considerable reductions in the ventilation system [39]. The study [40] on the ventilation on demand (VOD) concept in the Konsuln test mine showed that with battery electric vehicles, cost savings can be up to 86.7% compared to using diesel vehicles.

DPM mainly consists of organic carbon and elemental carbon [41], with the addition of particles from unburnt fuel, metallic additives, and other components [42]. Results of a study based on the Australian mining industry [43] indicate that, on average, miners working in underground conditions are exposed to 18–44 μg/m³ of elemental carbon for a 12 h shift. Tests carried out in deep mines in Canada [42] reported elemental carbon exposure for miners that exceeded Australian results by three times (elemental carbon exposure ranging from 31 μg/m³ to 150 μg/m³). Studies in [44,45,46,47] have found that long-term exposure to diesel particulate matter in high concentrations increases the risk of lung cancer. Silverman et al. [46] concluded that mineworkers who are exposed to over 1005 μg/m³ of respirable elemental carbon a year have a three times higher risk of lung cancer than workers with lower exposure.

Using different treatment technologies for diesel engines helps lower the emissions, but in conventional diesel combustion, it might not be possible to reduce all emissions simultaneously [37]. By using in-cylinder methods to lower NOx emissions, DPM emissions will increase because NOx emissions typically rise with higher combustion temperatures and leaner conditions. Still, lower combustion temperatures and rich conditions will increase the formation of elemental carbon. One option is to combine various after-treatment and in-cylinder methods, but this will only lower the emissions. In addition to engine control technologies, Rojas-Mendoza et al. [48] tested the possibility of using fog treatment to eliminate DPM from the airflow, with results indicating that DPM removal using fog treatment ranged from 39.6% to 54.6%.

To eliminate diesel exhaust gases and DPM emissions from the production cycle, it is necessary to overhaul the entire technology used in mining. Based on current knowledge, many mining companies have begun testing electric equipment and, more specifically, battery- electric equipment [49,50,51].

5. Temperature Limitations of BEVs

Low temperatures in mines significantly reduce battery performance, particularly for lithium-ion batteries. Cold conditions slow down electrochemical reactions, reducing ion mobility and causing battery capacity to decrease by 20–30% at 0 °C and up to 80% at −20 °C. Internal resistance rises, resulting in lower power output and increased heat during discharge. Extended cold exposure also accelerates battery degradation and reduces lifespan. Charging batteries at temperatures below 0 °C may lead to lithium plating, which increases safety risks, including short circuits. To lessen these effects, thermal management—such as insulation or preheating—is crucial, and using low-temperature-optimised chemistries like LiFePO₄ can help sustain performance. Proper storage and operational protocols further minimise risks and prolong battery life in cold mining environments [52].

6. Risks Associated with Introducing BEVs to Underground Mining

Underground mines have limited entrances and exits, and the ventilation system’s design limits the supply of oxygen; therefore, they can be listed as confined spaces. Although some undeniable benefits can be achieved by using BEVs in underground mining, research on battery electric vehicles and LIB packs suggests a potential for safety hazards when using BEVs in confined spaces.

Regardless of their exact composition, LIBs used to power battery electric vehicles contain high-energy and combustible materials, which can pose a fire hazard in the event of a critical failure [53]. A failure within the car or in a battery pack could, in the worst case, lead to a fire and the emission of toxic gases from the battery. A considerable amount of research has been conducted on the issues related to those risks. It has been concluded that even though ICE vehicles pose a fire hazard as well, fires related to BEVs have a different nature and require different handling from ICE fires—they need significantly more fire suppressant to fight the fire, and extinguishing the fire takes considerably more time [54]. With a fire incident involving LIBs, there is a risk of the fire reigniting after it has been extinguished, sometimes even several days after the initial fire [55]. That means, with the introduction of battery electric vehicles into an underground mine, risks associated with battery technology must be analysed to evaluate whether it is safe to use the cars and what measures should be taken to make the risk level acceptable for the mining environment.

As mentioned above; to extinguish a fire involving a lithium-ion battery, a significant amount of suppressant is required. Fire tests on batteries have shown that using water as a suppressant has a cooling effect on the battery [56,57,58]. Fire tests performed by RISE (Research Institutes of Sweden) [58] found that having a fire suppression system inside a battery pack could lower the risk of thermal runaway propagation (which is the leading cause of fire within the battery) compared to the outside suppression system, which, in the tests performed, did not have a cooling effect on the battery. However, an external suppression system is necessary to prevent the fire from spreading from the battery to other parts of the vehicle (such as tyres and hydraulics) and the surroundings, especially in confined spaces. It is essential to note that runoff water from extinguishing a fire can pose a distinct hazard—the pH of the runoff water has been measured to be between pH 6 and pH 11, indicating that it can range from slightly acidic to alkaline. Tests conducted in Switzerland [59] also confirm that the water used for battery cooling is highly alkaline (pH 12). Therefore, when using BEVs in a mine, there must be preparedness to treat the runoff water used in firefighting before it is disposed of.

Lithium-ion battery fires mainly emit toxic gases from the combustion of the electrolyte [60]. RISE’s test in 2020 [60] measured the gas compounds emitted during a battery pack fire, including CO₂, CO, hydrocarbons, HF, HCl, HBr, HCN, SO₂, NO, NO₂, and polycyclic aromatic hydrocarbons. ICEV and BEV fires were measured during the tests, and the differences in amounts of anions sampled from ICE vehicles and BEVs were compared. The results show that measured HCl levels are similar (1720 g for ICE vehicles and 2080–2240 g for BEVs), and measured levels of HF and HBr for BEVs were considerably higher (HF was measured at 651–818 g from BEVs and 24 g from ICE vehicles). In addition to gases, various metal compounds were measured during the tests, with BEVs having higher concentrations than ICE vehicles. One concern that might arise from the toxic gas emission during a BEV fire is that HF, when inhaled or contacted, can cause severe injuries, which must be considered when evaluating risks associated with BEVs, especially in a mine. In a study analysing the risks of HF, it was determined that, for example, a combination of base layers and firefighting clothing provides relatively good protection to prevent skin exposure to HF in gaseous form when protecting firefighters during the extinguishing of BEV fires. This means that when introducing BEVs to mines, the suitability of existing personal protective equipment (PPE) must be evaluated and, if necessary, upgraded.

7. Costs Associated with Implementation of BEVs

Although not the focus of this paper, a note is needed on the general cost of switching to battery electric mining equipment. It mainly involves high initial costs, with vehicles costing up to twice as much as their diesel equivalents. However, operational savings from reduced ventilation (more than 30% less), energy, and maintenance (a 25% reduction in parts) lead to 56–88% lower lifetime costs. Annual savings exceed GBP 150,000 per unit, offsetting the initial investment [61,62,63].

8. Future Alternatives to BEVs

Hydrogen fuel cells represent a promising alternative to battery electric vehicles (BEVs) for underground mining equipment, offering distinct advantages and challenges. These systems generate electricity through electrochemical reactions between hydrogen and oxygen, emitting only water vapour and heat. This eliminates diesel particulate matter (DPM) and toxic emissions, significantly improving air quality in confined mining environments. Hydrogen’s high energy density allows for longer operational ranges and faster refuelling compared to BEVs [64], addressing limitations like battery weight and charging downtime.

Techno-economic analyses indicate viability, with studies showing a net present value of EUR 12 million and a 7.8-year payback period for hydrogen-powered load-haul-dump (LHD) vehicles, alongside potential annual CO₂ reductions exceeding 16,500 tonnes. Real-world implementations, such as Anglo American’s 2 MW hydrogen fuel cell haul truck and Fortescue’s converted Liebherr excavator, demonstrate the practical deployment of this technology. However, challenges include the development of hydrogen storage infrastructure, redesigning vehicle frames to accommodate fuel cells, and high initial costs [65,66].

9. Conclusions

As analysed above, much research has been performed on battery electric vehicles regarding their battery chemistries, performance, and safety. As the pressure to transition towards CO₂-free mining grows, implementing BEVs in mines is a great way to achieve this goal. It has been studied and analysed to determine its implications for mine design and ventilation requirements. However, conclusive studies on the safety aspects of that change are still largely missing or conducted on a case-by-case basis by companies testing battery electric vehicles. Therefore, it is necessary to provide an in-depth analysis of the risks that implementing BEVs in underground mines might present and what the appropriate mitigation measures are to ensure safe working conditions in the mines.

10. Future Research Areas for BEV Implementation in Underground Mining

Future research must address significant gaps in the deployment of battery electric vehicles (BEVs) for underground mining. A comparative case study of Canada and Australia would clarify regional drivers of adoption: Canada’s regulatory incentives for decarbonisation versus Australia’s emphasis on ventilation cost savings (up to 86.7%) and reduction in diesel particulate exposure. This should examine mine-specific variables such as depth, ore type, and grid connectivity to develop regionally tailored transition frameworks.

Cost and life cycle analysis need refinement using real-world operational data. Current TCO models suggest approximately EUR 150,000 annual savings per BEV unit, but they must include battery replacement cycles and the scalability of charging infrastructure. Research should expand LCA boundaries to cover battery refurbishment for stationary storage, evaluating shared environmental impacts across different applications. The effects of dynamic energy pricing on TCO also require further investigation.

Safety factors require urgent attention, especially thermal runaway risks in confined spaces. Studies need to quantify toxic gas emissions (HF levels up to 818 g per BEV fire) and validate suppression systems for underground-specific conditions. Fire spread between battery units (which occurs within 3–5 min without barriers) calls for standardised emergency protocols and PPE improvements. Additionally, trade-offs in battery chemistry safety—LFP stability versus NMC energy density—necessitate mine-specific risk assessments.

Broader contextual research should examine duty cycle optimisation for heterogeneous BEV fleets and develop predictive models for battery degradation in high-vibration environments. Interoperability standards for charging infrastructure remain essential for multi-OEM operations.