Driverless Vehicles in Mining: The Hidden Fire Risk Inside the Tyre

Driverless vehicles are changing the way mines operate. Autonomous haul trucks and other driverless mobile plant can improve productivity, reduce human exposure to hazardous operating environments and allow mine sites to move material for longer periods with fewer interruptions.

But removing the driver from the cab does not remove the fire risk.

In some cases, it changes the way that risk is identified, monitored and responded to. One of the more serious hazards in mining and heavy equipment operations is tyre pyrolysis: a dangerous process where heat builds inside a tyre, causing the rubber and internal tyre components to chemically decompose. This can generate flammable gases and pressure within the tyre assembly, creating the potential for sudden tyre rupture, fire or explosion.

This is particularly relevant in mining, where heavy vehicles operate under extreme loads, long duty cycles, rough ground conditions and high ambient temperatures. NFPA 921 recognises mining equipment within the category of heavy equipment and notes that these vehicles are subject to ordinary vehicle failure modes as well as failures associated with overloading, hydraulics, bearings and the material being handled. It also highlights that the investigation of heavy equipment fires requires knowledge of the specific systems involved in that vehicle.

What is tyre pyrolysis?

Pyrolysis is the thermal decomposition of material in the absence of sufficient oxygen for normal flaming combustion. In the context of large mining tyres, the rubber and internal tyre structure can be exposed to heat from several sources, including under-inflation, overloading, braking systems, wheel-end failures, bearing failures, external fire exposure, or prolonged operation under abnormal conditions.

As the tyre heats, the internal material can begin to break down. This may generate combustible gases inside the tyre. Because mining tyres are large, pressurised assemblies, the build-up of heat and gas can create a serious pressure hazard.

Importantly, the danger is not always visible from the outside. Resources Safety & Health Queensland has warned that tyres on trucks, cranes and heavy vehicles may catch fire, but that a lesser-known danger occurs when combustion takes place inside the tyre with no external signs.

That is what makes tyre pyrolysis so dangerous. By the time smoke, flame or visible damage is observed, the tyre may already be unstable.

Why driverless mine vehicles need a different fire risk approach

In a conventional haul truck, an operator may notice changes that are difficult to capture through standard telemetry alone: vibration, odour, smoke, noise, braking abnormalities or handling issues. In a driverless vehicle, those human observations are removed from the immediate operating environment.

This does not mean autonomous vehicles are inherently more dangerous. In fact, they can reduce exposure by keeping personnel away from hazardous operating zones. However, it does mean the vehicle’s monitoring, maintenance and emergency response systems become even more important.

Autonomous mine vehicles rely heavily on sensor data, control systems, dispatch systems and remote monitoring. If tyre temperature, pressure, wheel-end condition or braking abnormalities are not properly monitored, a developing pyrolysis event may not be identified early enough.

Modern tyre pressure and temperature monitoring systems can provide real-time data to fleet management systems, helping operators detect abnormal tyre conditions before they escalate. But monitoring is only effective if the data is acted upon, alarm thresholds are appropriate, and escalation procedures are clear.

The role of heat, pressure and operating conditions

It is important to be precise: pressure alone does not cause pyrolysis. Heat is the critical factor that causes the tyre material to decompose. Pressure becomes a major hazard because gases produced during internal heating can accumulate inside an already pressurised tyre.

In mining operations, heat can build up in several ways:

• under-inflated tyres flexing excessively under load

• Overloaded vehicles increase tyre stress

• extended downhill braking or retarder use

• seized bearings or wheel-end mechanical failure

• dragging brakes

• proximity to external fire or hot surfaces

• poor maintenance or incorrect tyre repair practices

• operation outside tyre manufacturer's specifications
  

NFPA 921 identifies ignition as the process of initiating self-sustained combustion and defines autoignition as combustion initiated by heat without a spark or flame. These concepts are important in tyre-related fire investigations because the ignition pathway may not involve a deliberate flame or obvious external ignition source. It may instead involve a combination of heat generation, material degradation and delayed ignition of combustible gases or tyre material.

The consequence: sudden and severe failure

Large mining tyres store enormous energy. When a tyre affected by fire or pyrolysis fails, the result can be catastrophic. NSW Resources has warned that when heavy earthmoving machinery tyres are exposed to heat and fire, tyre explosions can propel debris several hundred metres and pose a risk of severe injury or death. It also notes tyres can remain an explosion risk for up to 24 hours.

This has significant implications for mine emergency response. A tyre that appears externally intact may still be unsafe. Approaching, cooling, inspecting or moving the vehicle too early can expose workers, emergency responders and investigators to significant risk.

Fire investigation considerations

From a forensic fire investigation perspective, tyre pyrolysis and tyre-related fires require a careful and systematic approach. The investigator should not assume the tyre was merely a fuel package consumed by a broader vehicle fire. It may have been part of the origin-and-cause sequence.

Key areas to consider include:

• tyre pressure and temperature data before the incident

• fleet management and autonomous system logs

• braking, retarder and wheel-end data

• vehicle payload and operating conditions

• road grade, haul profile and duty cycle

• maintenance history

• tyre age, repair history and manufacturer specifications

• evidence of bearing failure, brake drag or mechanical overheating

• fire suppression activation data

• witness observations from remote operators or nearby personnel

• whether the vehicle continued operating after abnormal alerts
  

The 2024 edition of NFPA 921 emphasises systematic fire and explosion investigation, including origin, cause, fire spread, responsibility and prevention. It also notes that the scientific method should be applied in every instance. This is particularly important in autonomous mining vehicle fires, where the cause may involve the interaction between mechanical systems, tyre behaviour, operating data and remote decision-making.

Why this matters for mine operators and insurers

For mine operators, tyre pyrolysis is not just a maintenance issue. It is a fire, explosion and business interruption risk. A single haul truck fire can result in loss of equipment, production delays, emergency response costs, investigation costs and potential injury exposure.

For insurers, autonomous mine vehicles introduce new questions around causation, maintenance, monitoring and response. Was the vehicle operating within specifications? Were tyre pressure and temperature alerts present? Were they escalated appropriately? Was the vehicle stopped in time? Were exclusion zones implemented? Was there a delay because there was no driver physically present to observe the developing event?

These questions matter because the presence of autonomous technology does not remove the need for proper risk controls. It increases the importance of data review, maintenance records, fire suppression systems, tyre management plans and post-incident preservation of evidence.

Reducing the risk

Mine operators should consider tyre pyrolysis within their broader fire and explosion risk management framework. Practical controls may include:

• real-time tyre pressure and temperature monitoring

• clear alarm thresholds and escalation procedures

• routine inspection of brakes, bearings and wheel-end components

• strict tyre inflation, loading and speed controls

• haul road design and maintenance to reduce abnormal tyre stress

• automated shutdown or park-up protocols for critical tyre alerts

• exclusion zones for suspected tyre fire or pyrolysis events

• emergency response training specific to tyre explosions

• preservation of vehicle data after a fire or thermal event

• independent fire investigation following serious incidents
  

Driverless vehicles are part of the future of mining. But as the industry adopts more autonomous systems, fire risk management needs to evolve with them.

The hidden danger with tyre pyrolysis is that the most serious part of the event may occur before anyone sees flames. In a driverless mining environment, the first warning may not come from a person in the cab. It may come from the data.

The question is whether the system, the site and the response plan are ready to act on it.