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Undetected firespread: Wildfires

Hazard Knowledge

Undetected firespread is a significant hazard because it may lead to fires burning into areas that were not anticipated. It may compromise some or all of the following:

  • Access, egress and escape routes
  • Vehicles and equipment
  • Personnel working at the incident
  • Members of the public
  • Effective implementation of the LACES safety protocol
  • Other elements of the tactical plan

Three specific types of undetected firespread that are particularly challenging to identify are ground fires, spot fires and crown fires, and they should be given due consideration.

Ground fires

Ground fires are fires that burn in the fuels present below the ground surface. Ground fires usually burn in organic matter where oxygen is available, for example, burning within the roots of vegetation, buried branches, twigs or needles. In some situations, ground fires may burn in the soil itself, such as peat fires.

Peat is an extremely valuable, natural resource that plays an important role in carbon storage. It takes thousands of years to develop and is very susceptible to damage that is directly or indirectly caused by fire. Refer to the hazard 'Environmental impact' for specific control measures to minimise the environmental damage caused by peat fires, and fires in other sensitive environments.

Ground fuel fires usually burn with low intensity through smouldering combustion. They can smoulder for a significant amount of time, and travel undetected for considerable distances. They can also burn through ground fuels and then reappear at the surface and become surface fires. The unpredictability of where and when ground fires will return to the surface is a significant hazard to personnel, vehicles and members of the public. For example, ground fires may burn beneath, and subsequently breach, control lines.

Ground fires can be very difficult to locate and extinguish without access to large volumes of water and/or a means to excavate and expose the burning material. Specialist knowledge and equipment may be required to safely and effectively identify and suppress ground fires.

One of the most significant hazards posed by ground fires is that they can affect the stability of the ground that personnel may be working on. The burning of soil layers can lead to structural collapse of the ground, particularly if personnel or vehicles move onto ground where a ground fire has been burning. Also, overhangs, holes on the ground and pan-shaped voids around tree bases are commonly produced during smouldering fires. These can lead to local subsidence of the soil and damage to roots, which can threaten the stability of trees, increasing the likelihood that they may fall. Personnel should take additional care when walking through conifer woodlands on peat soils as the lattice of shallow roots overlying burnt peat can leave dangerous trip hazards. Refer to hazard 'Working environment: Terrain' for further information.

The smoke from ground fuel fires is produced abundantly day and night and can also represent a hazard. During periods of stable atmospheric conditions, ground fire smoke can accumulate in low lying areas. This may significantly reduce visibility for personnel working at the incident, vehicles at the incident and for members of the public in the vicinity of the fire using, for instance, roadways and other transport routes. The hazard is further amplified when ground fire smoke accumulates at night, further reducing visibility.

Spot fires

Spot fires occur when sparks and embers are transported by the wind or convection column and land to ignite new fires outside the main fire perimeter. During this process, burning material (sometimes referred to as flying brands or firebrands) can be carried considerable distances. Spot fires can breach control lines and threaten access, egress and escape routes for personnel and vehicles. Spot fires can represent a significant hazard to personnel, particularly if undetected for a period of time.

Crown fires

Crown fires are fires that burn in the upper canopy of vegetation. Crown fires can occur in shrubs or trees and their intensity is usually dependent on the amount and condition of the fuel. For crown fires to occur, there usually needs to be sufficient and continuous fine fuels.