This apparatus, developed at EL, determines gasification rate (mass loss rate) of a horizontally oriented specimen exposed in a nitrogen environment to a controlled radiant heat flux from a cone-shaped heater. These non-flaming conditions allow the condensed-phase gasification processes to be de-coupled from complicating gas-phase processes; permit a better estimate of the actual incident heat flux that is producing the fuel gas; and provide a much better view of surface phenomena (e.g., bubbling, charring) during degradation. The cylindrical chamber is 0.61 m in diameter and 1.70 m in height. Two windows provide optical access. The chamber's interior walls are blackened and water cooled to 25 EC to minimize indirect heating of the specimen. The cone-heater temperature is usually fixed at 809 EC to maintain a constant emission spectrum. Changing the distance between the sample and heater can vary incident heat flux to the sample between approximately 25 kW/m2 and 70 kW/m2. A water-cooled shutter is extended to protect the sample from the incident heat flux prior to testing: it also can be used to quickly halt the exposure at any time to "freeze" the remaining sample for subsequent chemical/physical analysis. Flux levels vary approximately 8-10% across a 0.1 m diameter specimen. Product and ambient gases are removed via an exhaust duct by a constant nitrogen flow of 7.7 l/s at 25 EC. Degradation products can be collected above the specimen's surface and condensed in a cold trap for further chemical analysis. Load cell data are taken every 0.5 s with an uncertainty less than 1% over a 100 g range. Specimens instrumented with thermocouples also can be accommodated.