Calibration procedure for fire resistance furnaces

On behalf of CEN/TC 127 "Fire Safety in Buildings", a series of tests has been carried out to evaluate and complete the draft calibration procedure for fire resistance furnaces [4]. Fourteen laboratories in nine European countries participated in the test series, each carrying out one calibration test. The results show that when the furnaces are controlled using 1 mm diameter sheathed thermocouples, the thermal exposure of a test specimen differs greatly over the various furnaces. By a simple mathematical procedure, a prediction was made of the results that would have been observed, had the furnaces been controlled using Plate Thermometer readings. In the predicted results, the above differences in thermal exposure are substantially reduced. This suggests that replacing thermocouples by Plate Thermometer as the controlling sensor can prove a significant step towards harmonised fire resistance testing. On the other hand, the tests have revealed problems with the design of the calibration elements, and with the control over the temperature development at the unexposed surface of the test specimen. As a follow-up to the test series, an additional test series is currently under progress. The test procedure in this series is identical to the previous one, except that furnace control is by Plate Thermometer. Preliminary results confirm the above suggestion that Plate Thermometer control improves the comparability of furnaces. The article puts the test series in the perspective of the overall problem of calibration for fire resistance testing. The test results are discussed, and the subsequent activities within CEN are presente