Battery electric vehicles (BEVs) are becoming more common in underground mines, and with that adoption, the mining industry must also adapt its safety protocols to evolve in step with the technology. 

This focus was front and centre at the Battery Electric Vehicle Safety in Mines Symposium, hosted on Sept. 11 by Workplace Safety North in Sudbury and virtually through live streaming. Experts at the one-day event emphasized that managing fire risk is one of the most critical aspects of BEV safety underground. 

“A fire is a fire underground—it doesn’t matter if it’s diesel and/or battery [vehicle],” said Mike Mayhew, founder of consulting firm Mayhew Performance, during his session entitled ‘Case Study: Planning and Implementation of an Electrified Fleet.’  

“Understanding the training policies, understanding the process for your fire emergency response plan [is critical], but most importantly is educating your mine rescue people so they know what they’re dealing with, either if it’s a diesel fire and or a battery fire.”  

Central to BEV fire risks is thermal runaway, which is a chain reaction created inside a battery that increases temperatures and leads to fire.  

According to Ayden Robertson, senior health and safety consultant at Workplace Safety & Prevention Services, thermal runaways can be triggered by several different factors.  

This can range from mechanical abuse, where damage is sustained during transport, handling or operation in rough mining conditions; to electrical abuse, where short circuits or cascading failures result from earlier mechanical damage; to thermal abuse, where extreme heat or cold causes failure or malfunctions in the battery management system; and finally, to quality control issues, which can be errors during manufacturing or assembly.  

“The problem here becomes these minor failures that we may not be able to readily view or identify—whether it’s seconds or minutes or days—become a very self-sustaining, positive feedback cycle,” said Robertson during his presentation titled ‘Plugged into Safety’. 

That is why early warning signs of battery fires are critical to catch. Some indicators could include smoke and vapour leaks to sparking, discoloration or even an unusual burning smell. 

“Things that you can be on the lookout for: before we use a battery electric loader or forklift, do the same as we expect people to do with commercial vehicles,” Robertson advised. “Do your pre-use inspection. Can you notice anything outside of the norm in that environment?” 

Responding to fires 

How to respond when a fire does occur underground remains an area of active discussion for the industry. In some cases, specialized in-house fire extinguishing systems may be effective. In others, evacuation and reliance on third-party firefighting support may be the safer choice. 

“Either approach is fine,” said Robertson. “But doing that soul searching in the context of the work you do with these systems is critical—and not treating it like a guessing game.” 

That uncertainty reflects a larger gap in research, noted Adrian Halim, senior lecturer in mining engineering at Luleå University of Technology in Sweden, during his presentation on ‘Managing Fire Safety of Battery Electric Vehicles in Underground Mines.’  

“The majority of studies around underground BEV fires are based on lab-scale tests,” Halim explained. However, a real BEV fire is the result not only of thermal runaway in the battery, but also other combustibles in the vehicle—plastics, cables, hydraulic oil, wiring—that can fuel the fire. 

While some lab studies have trialled firefighting techniques, Halim stressed that these experiments are too limited in scale. “An actual BEV fire is much larger than that,” he said. “The only way to test manual firefighting techniques is through full-scale fire tests.” 

So far, no such full-scale tests have been carried out on underground BEVs, largely due to cost. “One underground mine BEV costs more than $1 million,” Halim noted. “Understandably, no one is willing to donate a brand-new vehicle to be burned. But I’m hoping that someone or some companies will be willing to do so in the foreseeable future.” 

In the meantime, researchers are turning to on-road BEV fire studies for some insights. Tests in Austria, Sweden and Denmark have shed light on fire growth, gas and soot emissions, and suppression methods. 

Halim highlighted an Austrian tunnel fire test that trialled a manual firefighting tool using an extinguishing lance device developed by Germany-based fire protection equipment supplier, Murer Feuerschutz. The device is a lance with a water nozzle at the end that can pierce into a battery pack. 

“The team found that the best way to stop thermal runaway or ignition is by flooding the battery with water. That’s exactly what this tool does,” said Halim. 

Some equipment manufacturers are building on that insight. Epiroc, for example, has introduced quenching ports in its battery packs that enable firefighters to inject water directly into the pack. 

However, Halim cautioned that practicality is still a concern underground. “The main issue I see is whether firefighters can get close enough to hammer the extinguishing lance into place or connect a water hose to the quenching port. An underground BEV fire is likely larger than that of [above ground] road BEV [fire],” he said. 

Prevention is key 

Ultimately, while insights from road BEV studies are valuable, Halim stressed “preventing the fire from happening in the first place is always the best option.” 

For Mayhew, regular audits and risk assessments are critical. He recommended companies bring in outside expertise if needed and lean on OEMs for system data and monitoring tools. 

“Every fire, in my opinion, could be eliminated from the ones that I’ve seen. There was a root cause, either by a component, by people or by manufacturing,” said Mayhew. “If we’re doing everything—managing risk, doing risk assessments, proper pre-ops, due diligence—we should be able to eliminate any of those risks when it comes to battery fires.” 

Mayhew emphasized using battery management systems to monitor the battery at the cell, module and pack level is at the heart of battery fire prevention. Working closely with manufacturers to interpret battery management system data can allow mines to identify early warning signs, shut down compromised equipment and lock it out before an incident occurs. 

“From the investigations that I’ve done, these mitigation strategies could have eliminated a lot of the incidents we talk about,” Mayhew said.