Dynamic fire emission of smoldering peat under water suppression

Abstract

The persistent smoldering peat fires are most difficult to extinguish because of their hidden nature and resurgence from underground. This study experimentally investigated the effects of water spray (fixed at 0.4 L/min or 600 mm/h) on the smoldering peat sample (20 cm × 20 cm × 10 cm) and associated gas emissions. The spray duration varied from 10 to 150 s, equivalent to water depths up to 25 mm. The dynamic emissions of CH4, CO, CO2, NH3, and C6H14 were measured during the burning and suppression. After water spray, three distinct outcomes were observed: failed, partial, or complete fire suppression. Notably, an accumulated water depth below 25 mm failed to achieve complete fire suppression. In cases of failed suppression, the smoldering fire resurged and ultimately consumed all peat. With increasing water volume, both the time to resurgence and the subsequent emission peak were delayed. The peak mass fluxes and emission factors (EF) of CO2 and CO, along with the modified combustion efficiency (MCE) and CO/CO2 ratio, exhibited weak dependence on water volume. In contrast, at the threshold water depth of 25 mm, the peak mass flux and EF of CH4, as well as the CH4/CO2 ratio, decreased by approximately 50%. This work advances the scientific understanding of transient gaseous emissions from hidden underground peat fires subjected to water suppression.