Gas emissions, minerals, and tars associated with three coal fires, Powder River Basin, USA

Ground-based surveys of three coal fires and airborne surveys of two of the fires were conducted near Sheridan, Wyoming. The fires occur in natural outcrops and in abandoned mines, all containing Paleocene-age subbituminous coals. Diffuse (carbon dioxide (CO2) only) and vent (CO2, carbon monoxide (CO), methane, hydrogen sulfide (H2S), and elemental mercury) emission estimates were made for each of the fires. Additionally, gas samples were collected for volatile organic compound (VOC) analysis and showed a large range in variation between vents. The fires produce locally dangerous levels of CO, CO2, H2S, and benzene, among other gases. At one fire in an abandoned coal mine, trends in gas and tar composition followed a change in topography. Total CO2 fluxes for the fires from airborne, ground-based, and rate of fire advancement estimates ranged from 0.9 to 780 mg/s/m2 and are comparable to other coal fires worldwide. Samples of tar and coal-fire minerals collected from the mouth of vents provided insight into the behavior and formation of the coal fires.

► Surveys made of 3 coal fires in May 2009. ► Gas and tar chemistry vary within each fire. ► Variations explained by O2 availability or changes in coal chemistry. ► Data compilation shows CO2 fluxes from coal fires 0.3–780 mg/s/m2.