The main factors that affect fire spread in peat are moisture content, oxygen supply, and the type and density of the fuel. This article covers some suppression options for shallow peat fires burning to a depth of 1 metre.
Logistics of peat fires
The amount of personnel, equipment, water, and other consumable items required can strain logistic systems. Adequate and continual water supply will always be a significant challenge for peat fires.
Some machinery used for peat fires may need to be smaller and have much lower ground pressure with different attachments than what may typically be used in a forest environment. Machinery may still require roll-over protective structures (ROPS) and falling-object protective structures (FOPS) and because of the environment, enclosed cabins with adequate cabin particulate filtration systems.
Stopping the lateral and downward spread of the fire
Burning may be influenced by the upper dry peat layers and newer organic materials (grass, plants and tree roots). In some cases, fuels or soils may also become hydrophobic, repelling water. The depth of burning may be affected by the fuel, the drying effect of the fire, higher fuel moisture at deeper levels or inert minerals underneath the peat layers until a maximum depth is reached. The burning activity is usually close to the fire’s perimeter. Within the fire’s perimeter after a maximum depth has been reached, any remaining smouldering material will be mostly unburnt islands of peat that may slowly continuing to burn out.
Methods for containing and extinguishing peat fires
Several methods can be used during containment and eventual extinguishment of peat fires, these can include, but are not limited to, the following:
Removing surface vegetation to slow or prevent fire spread
Surface and newer near-surface organic material can promote and sustain the spread of peat fire. Removing this vegetation can provide access, reduce fire spread, allow penetration of extinguishing mediums, and may be necessary for any of the strategies and tactics used.
Direct attack with water
The effectiveness of water and water with additives is dependent on sufficient quantity and penetration deep enough into the fuels to extinguish them. These can be used on shallow burning material with direct water application to the fire’s edge using a straight jet/spray, or the use of a lancing probe for deeper penetration of burning material from a handline. This can cool the ash, char and fuel and can be done in conjunction with machinery or hand tools.
Other methods of wetting down the fire edge also include the use of sprays, sprinklers and ground monitors. These can be set in place and left for as long as required, then redeployed as needed.
Returning moisture to the ground/flooding the site –
Large volumes of water can be applied indirectly to the fire-affected area. This can return moisture levels to drought-affected or drained peat areas and prevent and stop fire spread, as well as extinguishing the fire. This can be done by ongoing and long-term soaking with hose line sprays, ground monitors, sprinklers and lancing on a smaller scale.
Additional work may be needed to retain ground moisture. This may include blocking drains or damming areas as well as ongoing ‘top-ups’ and monitoring of water run-off or loss.
Reducing the supply of oxygen to the fire –
This can be achieved in the short term with class A foam or Compressed Air Foam System (CAFS). This can also be used in conjunction with other methods and has the benefit of providing a safer working environment by reducing smoke and dust emissions for other methods to be used.
Hot spots can also be capped by applying enough water and working it into the ash, char and peat to form a mud slurry, increasing the density of the fuel and has the benefit of adding moisture and cooling. Using inert material such as clay for the capping of small areas or ‘hot spots’ can be problematic long term unless moisture levels are returned.
Cutting a clean edge to the lateral margins of the fire
Containing the fire can be done with low ground pressure machinery or with hand tools by separating the burning peat from adjacent unburnt material by digging at the fire’s edge, just below the depth of the burning material.
As its dug, the burnt material and ‘spoil’ can be placed back inside the burnt area to reduce the risk of fire spread. This method should be done in conjunction with the application of water to dampen down the material, reduce dust and extinguish the burning peat as it is removed. The damp fuel removed from under the burning peat and the outer edges can also assist in raising the overall moisture of the fuel and assist extinguishment. After extinguishment, the spoil can then be pulled back into position while being dampened down again if required with ongoing monitoring as needed.
Ripping a narrow line
This may reduce soil disturbance to preventing unnecessary oxidisation of exposed unburnt peat. This method can be done to the depth of the burning peat at the very edge of the burning material with a ripping attachment on an excavator or similar machine. Water should then be able to penetrate to the depth of the burning peat material to extinguish the fire and retain moisture on the fire’s edge. The main disadvantage with this method is that the extinguished line will be narrow and not all hidden material will be extinguished and may require long-term monitoring and potentially some follow-up with ether further water application and/or a machine. Once complete the spoil can be spread back into place and monitored.
Utilising machinery to rip or rake through burning material
This method may speed up the suppression by breaking up the burning material to allow water penetration and may be effective for shallow burning material on the fire’s edge or small isolated areas. In those circumstances a small tracked loader with a toothed bucket, rake or ripping attachment could also be used.
Trenches can be problematic. If filled with water they will require a significant water supply and may have to be regularly maintained by re-filling. If left dry they can drain water from the surrounding area, further reducing fuel moisture levels and promote fire intensity. Material exposed to the air in the trench and spoil piles may dry by evaporation and oxidisation, causing dust and the peat to become acidic. Trenches and spoil piles may restrict access to the fire and create a safety hazard, which can require an exclusion zone – works should comply with regulatory codes of practice for excavation work.
Depending on the distance from the fire a significant amount of peat may be lost to fire spread before the trench is effective, other methods of direct work on the fire edge may be far more effective.
Allow the fire to continue burning until it reaches damp fuel or inert materials
The downward or lateral spread of fire may also stop when it either runs out of the peat and organic material into mineral layers, or the lower-level peat fuel is too wet to sustain combustion. This will require an assessment of the burning material and underlying moisture levels or inert minerals to establish the burning potential.
Any planning to allow fuels to simply burn themselves out should consider short- and long-term environment impact and potential for further fire spread.
Peat fires can present some unique challenges. The safe, effective and efficient response to a peat fire will depend on a detailed size-up and appreciation of what is mostly unseen. A survey and investigation need to be conducted to determine the fire’s current behaviour and potential.
Emergency soil stabilisation and a rehabilitation plan may need to be considered as part of work undertaken by machinery and following suppression and the environmental impact of firefighting operations.
For more information, email G.Parker@cfa.vic.gov.au
- Coal and Peat Fires: A Global Perspective, Volume 4: Peat – Geology, Combustion, and Case Studies, Glenn B. Stracher, Anupma Prakash and Guillermo Rein, 2015.
- Hydrophilic and hydrophobic characteristics of dry peat, L R Perdana, N G Ratnasari, M L Ramadhan, P Palamba, Nasruddin, Y S Nugroho, 2018.
- WorkSafe Victoria, Compliance code, Excavation, Edition 2. December 2019, Victorian WorkCover Authority.