Can peat soil support a flaming wildfire?

Abstract

Smouldering wildfire in peatlands is one of the largest and longest-lasting fire phenomena on Earth, but whether peat can support a flaming fire like other surface fuels is still unclear. Our experiments demonstrate the successful piloted flaming ignition of peat soil with moisture up to 100 wt-% under external radiation, indicating that flames may rapidly spread on peatland before transitioning to a conventional smouldering peat fire. Compared with smouldering ignition, flaming ignition of peat is more difficult, requiring a higher minimum heat flux and tripling the ignition energy. The propensity for flaming increases with a drier peat and greater external heating. We also found that the flaming ignition temperature increases from 290 to 690°C as the peat moisture increases to 100 wt-%. Flames from peat soil are much weaker than those of pine needles and wood, and they eventually transition to smouldering. The heat of flaming is estimated to be 13 MJ kg−1, close to the heat of smouldering. The measured CO/CO2 ratio of flaming peat fires is less than 0.02, much smaller than 0.2 for smouldering peat fires. This research helps understand the development of peat fire and the interaction between flaming and smouldering wildland fires.