On the 9th of February 2014, Morwell residents grew concerned by the rising smoke and ash of what they presumed were several disastrous fires in nearby regions. Firefighters eventually brought blazes in Gisborne, Craigieburn and Warrandyte under control, although many homes were lost. Neither officials nor residents realised that something was amiss much closer to home. The Hazelwood mine fire was not discovered until well after it had started. The fire would last a staggering 45 days before it was finally declared to be extinguished fully.
Mine fires are a constant risk for not only closed mines, but active mining operations. By nature, coal mines especially are home to a range of flammable liquids, combustible materials, and heavy machinery which is working at high temperatures. In fact, some coals can self-ignite in as little as 40 degrees Celsius. These conditions make it easy for fires to break out, and rage on for days, if not weeks, without the proper precautions. Not only are fires dangerous, but the cost in lost productivity, loss of assets and clean-up can quickly reach the millions.
Identifying possible hazards and areas of risk for mine fires is the first step in preventing such disasters. Legislation requires mines to have a hazard reduction and risk management strategy in place to mitigate the potential for unexpected fires to break out. Steps in this process involve identifying flammable materials that are in use in mining operations, and either replacing with less hazardous materials where possible, or protecting these materials against ignition by proper storage and use.
Hazardous materials might include fuels, which are classified into the following categories:
- Class A: Carbonaceous solids which may be at risk of burning, such as coal dust, non-metallic materials (textiles, rubber, plastic), rags, paper and timber.
- Class B: Flammable and combustible liquids such as diesel, petrol, solvents degreasers and alcohol.
- Class C: Combustible gases such as methane, LPG, acetylene.
- Class D: Combustible metals such as magnesium, aluminium, lithium, potassium and their alloys.
- Class E: Electrically energised equipment, such as fuels of any class.
Ignition sources must also be identified. Sources of energy or heat such as:
- Heat energy: diesel engines, exhaust systems, turbochargers, pumps etc.
- Electrical energy: Electrical arching, static electric discharge, cables overheating, lightning etc.
- Mechanical energy: Frictional heating, frictional sparking, strata failure.
- Chemical energy: Spontaneous combustion of coal, contraband, chemical reactions.
- Pressure energy: Shotfiring
- Radiant energy: Welding, overheating of motors etc.
Hazardous materials and areas of the plant or surrounds which are at risk from hazardous materials or equipment should be identified, and appropriately contained.
As the diagram below shows, the prevention strategy should also include measure such a fire shields, emergency stops and escape routes.
Despite best efforts to contain hazardous materials and avoid fires breaking out, working in a mine is an inherently dangerous undertaking. Fires may occur in spite of best practice, and an early detection system is vital to containing fires before they spread into other areas, threaten plant equipment and lives, and put mine operations at risk.
Coal seam gas mines can experience underground fires which reach into the hundreds of degrees Celsius, and yet only affect the surface temperate by a few degrees, if at all. By the time a fire reaches these kinds of temperatures, it is very difficult to control. Early detection can be the difference between catastrophe and minor inconvenience.
Thermal imaging cameras such as those produced by Bestech Australia measure temperatures between -20 and 1500°C, and their high degree of sensitivity can pick up even the slightest changes in temperate. Alerting staff to changes in conditions, and also triggering automatic sprinklers at predetermined levels, these kinds of systems can stop fires before they’ve had a chance to spread. These and other similar systems can also measure pressure, airflow and gas composition and can withstand extreme conditions such as high pressures, temperatures and collisions; making them ideal for the challenging conditions of mining, and of mine fires.
As well as the obvious—fire extinguishers—there should be a number of measures available to extinguish fires, if they do happen to occur. Automated sprinklers, like those triggered by advanced sensor systems are important, however manual solutions should also be available in case of a systems failure of some sort.
Foams and fire-reduction chemicals should be on hand and within easy reach of safety officers onsite, as well as fire blankets and protection materials in case of risk to people at the site of the fire. Fire hydrants must be properly equipped and stationed at intervals within the mine site. Hoses must be long enough to reach beyond the next hydrant, so as to give complete coverage of the site.
Clearly marked fire stations and substations should be free of obstructions, and accessible at all times. These measures, and others mentioned in the Guideline for Prevention, Early Detection and Suppression of Fires in Coal Mines produced by the Mine Safety Operations branch, Investment & Industry NSW are best practice in the prevention and fighting of mine fires. Consult your relevant state bodies for updates to these guidelines.