Guidance about explosion hazards

An explosion is a sudden and rapid increase in volume and release of energy in an extreme manner. This is usually accompanied by the generation of high temperatures and release of gases caused by changes in pressure, temperature and phase.

In mining, explosives are the most obvious form of explosion hazard. Blasts and shots are controlled releases of chemical energy. However, the potential for the uncontrolled release of (stored) energy is also present and can be unrecognised. Unwanted events can damage equipment and infrastructure, release shrapnel and cause injury or, in the worst case scenario, be fatal.

Explosions can be:

• chemical - high explosives, gas ignition, and fine particulate or dust sulphide dust ignition (SDI)
• electrical or magnetic - high current arc flashes or excessive magnetic pressure in an ultra-strong electromagnet
• through mechanical failure - change to the safe operating conditions of a classified plant, or a tyre failure.

Examples of the hazard types are provided below.

Explosives and dangerous goods

Sulphide dust ignition and gas outbursts

The presence of combustible dusts and gases can result in explosions and fires. For example, the dust produced during the mining of some metalliferous sulphidic orebodies can ignite under certain conditions. During drilling activities in particular geological settings, pockets of methane and other hazardous gases can be intersected.

When present in the underground environment, the risk is greater because of restricted access and the potential for dust or gas to accumulate. The most common ignition method is through the blasting process.

An explosion produces:

• heat which sets fire to combustible material in its path
• air blast that can move equipment and damage ventilation systems
• toxic gases
• an oxygen deficiency.

Electrical arcing

Mechanical changes

Much of the plant on a mining operation has the potential for an uncontrolled explosion. This includes:

• classified plant (e.g. pressure vessels, boiler, air compressors)
• processing plant using chemicals with temperature and pressurisation components
• tools or equipment with pressurised gas or fluid
• vessels that contain flammable or combustible vapour or pressurised gas (e.g. tyres).

An uncontrolled explosion may result from:

• mechanical failure of components
• incorrect design of work area e.g. poor ventilation
• where there is no or incorrect isolation of  hazardous energies
• removal or bypassing of safe work processes
• incorrect use of equipment and non-standard maintenance techniques
• modifications, demolition or scrapping (e.g. hot work on empty flammable liquid containers).

Tyre explosions

When a tyre explodes the force of the escaping compressed air and the potential shrapnel generated (from the tyre, wheel and nearby material) can have fatal consequences.

Tyre explosions can be caused by:

• a brake or wheel-motor overheating (or fire)
• a heat source, such as a tyre fire
• welding or heating on rims or hubs
• electrification of the vehicle
• combustible materials, including introduced materials in the tyre, particularly those with low auto-ignition temperatures.

A risk management approach is required to identify explosion hazards and identify and implement the appropriate control measures.