The Ohio State University rate of heat release apparatus was calibrated with two measurement systems, the standard compensated thermopile and an instrumentation for oxygen comsumption measurements. Based on the calibration results the oxygen consumtion technique was chosen when testing 13 different materials including woodbased materials, wallcoverings and plastics. The same set of materials has also been tested in a full scale room corner test and in a number of small scale reaction to fire tests at different Scandinavian laboratories. These results are reported separately. Results for the 13 materials are presented as RHR and THR at three radiation exposure levels 2, 3 and 5 W/cm2.