The flash carbonization process quickly and efficiently produces biocarbon (i.e., charcoal) from biomass. This process involves the ignition of a flash fire at elevated pressure in a packed bed of biomass. The fire moves upward through the bed, against the downward flow of air, triggering the transformation of biomass into gas at elevated pressure and charcoal with fixed-carbon yields that can reach the thermochemical equilibrium "limit" within 20 min of reaction time. Research described in this paper had two foci. The first concerned the propagation of the flaming pyrolysis reaction. The spatial distribution of the products' properties confirmed that the carbonization reaction propagated upward from the bottom of the bed to its top, and revealed that the charcoal products were further carbonized and combusted from the top downward after the entire bed was converted to charcoal. In addition, we found that higher pressures increased the upward speed of the flame through the bed. The second focus concerned the use of an afterburner that operated at elevated pressures, and used a commercially available catalytic monolith to reduce emissions. When the afterburner was supplied with sufficient secondary air, virtually all carbon monoxide emissions were eliminated.