An apparatus and method for the testing of materials by thermal oxidation is provided. The apparatus comprises a housing having at least one optic-isolated chamber. A photon counting photomultiplier and a heat source, for each optic-isolated chamber, are also provided within the housing. A cell, having a plurality of gas inputs and gas outlets, for holding a sample to be tested, is provided within the housing for each chamber. The gas inputs and outputs are distributed about the cell so as to disperse gas evenly about the material to be tested. The apparatus is used to count the number of photons which escape from a test sample as various oxidation conditions are employed.