Victoria’s Hazelwood coal mine is still burning, nearly three weeks after it started from a grassfire during severe fire conditions. Police are currently investigating the original fire for arson. Meanwhile health concerns continue for firefighters and residents in the nearby town of Morwell, with air quality very poor due to particulates produced in the fire.
Although rare, coal fires can burn for decades — though the Hazelwood fire will probably not last that long, especially given the current firefighting effort. (The latest Country Fire Authority updates are here.)
But what does the current fire tell us about our preparation for potential future fires?Coal fires: rare, but dangerous
The Hazelwood coal mine is a large, open-cut brown coal mine, close to homes and a major power station that depends on the mine for supply. These factors mean that the Hazelwood fire poses a threat to safety of the community and energy supplies.
It is rare for a coal mine fire to pose such a significant threat. The Jharia coal fire in India has been burning since at least 1916 and has caused serious health problems and subsidence in nearby villages and slums.
Another fire in 2006 at the Hazelwood mine did cause loss of generating capacity to the nearby power station.
The risk of a fire in an open-cut coal mine depends on several factors.
Fire is caused by the combination of three elements: a fuel that can burn, an air supply, and the heat generated by the combustion process. Coal is, of course, the fuel, while the atmosphere supplies the air, and any coal reacting with air will generate heat.
Most coal mined in Australia is black coal, which is geologically older and much less reactive than brown coal.
In the Hazelwood situation the coal fire was started by the grass fire. The coal seam at this mine is very close to the surface, so the heat from the grass fire would easily transfer to the coal seam.
If the seam is fractured and porous, the air would get into the coal and the coal would quickly dry out to a point where it will react with the air, until the coal temperature could increase to flame point and burn. The thickness of the coal seam also meant that there was a large mass of coal available to combust.
It is very rare to get a coal fire of the scale found at Morwell. Most open-cut coal fires in Australia have been caused by unusual circumstance, such as the intersection of the open cut mine with old underground coal mine roadways, which facilitate air paths into the coal seam. At these mines, the fire is controlled through prevention by isolating the underground areas, covering the exposed tunnels to prevent air getting in and only exposing small amounts of coal at a time for mining.
Fighting fire with more than water
Treatment of a fire at a coal mine depends upon the size and location of the fire and the available resources. If the fires are small they can be quenched with water, covered in foam and the offending area dug out and removed.
Large underground fires are often sealed in and the area is filled with inert gas. If possible, and the topography of the coal seam suits it, the area may be flooded.
Open-cut fires similarly depend upon size, location and access.
Often the fire consists of relatively small amounts of smouldering coal under the surface (such as Burning Mountain in New South Wales, 6,000 years old and considered the oldest coal fire in the world). This can be treated by drilling into the areas and injecting with water, foams or other wetting and suppression agents. They can also be treated by compacting the surface above the coal seam and covering the surface with an impervious layer to prevent air entering the seam.
Why is Morwell’s blaze so hard to put out?
Large scale open-cut fires such as at Morwell are far more difficult to manage. The scale of the fire precludes the use of many high-tech solutions due to the lack of bulk materials.
Water is usually the first resort to quench the active fire. Additives can be used in the water to enhance its capacity to quench the fire.
The location of the fire at Morwell makes close access problematic as the smoke and fumes pose a significant health risk to the firefighters (not to mention other emergency workers like parademics, along with local residents). The logistics of dealing with this size of fire are quite staggering in terms of people, machinery, water and length of time.
The danger is that the visible fire will be extinguished but the underlying coal will remain hot. If this is the case and air can get into the seam, the fire can rekindle, days, months or even years into the future. This has been observed here and overseas on many occasions. Brown coal has to be kept moist to prevent it spontaneously combusting.
Better risk management
Now, there needs to be a review of fire management plans at the Hazelwood mine. Clearly the mine can’t prevent arson, but it should be able to prevent the coal igniting and spreading through the coal seam.
Where the fire is currently burning has not been mined for many years. Theoretically, this could have been rehabilitated and capped, although this is not without difficulties.
Perhaps the simplest solution is to have water supplies in the abandoned areas. While we can’t control where the coal is or what starts a fire, the mine can ensure precautions are in place to prevent future fires.
How do we stop this happening again?
It would be reasonable of the regulator to ask the mine to demonstrate that a fire like the current one cannot recur.
The previous fire in 2006 should have triggered a review of the safety management system in accordance with the requirements of Australian Standard AS4804 and the OHS regulations. The controls before 2006 and implemented as a result of that event are clearly not adequate.
Adequate controls may well be very expensive. Consideration could be given to reshaping the batters and capping with an inert material before revegetation occurs.
Controls need to be effective. Access to the grassland could be restricted with better security and inspections. Improved fire detection systems could be installed, such as are used to detect bushfires. Improved water reticulation systems could be installed.
A thorough investigation should also look at the issue of the initial response. When was the fire first detected? What was the early response? When was it realised that the mine was under threat?
Any argument about the cost of controls must recognise the direct and indirect costs of the current incident to Victorians – and particularly the locals living in and around Morwell.
David Cliff receives funding from Australian Coal Association Research Program on projects related to the prevention and control of coal mine fires.