Comparison of a Standard Fire-Resistance Test of a Combustible Wall Assembly with Experiments Employing Pre-defined Heat Release Curves

Abstract

To improve the perceived equivalency of fire testing of combustible and non-combustible members we have proposed a simple modification in the fire resistance test procedure by introducing a lower limit of the heat release rate of the furnace. With this approach the combustion of the sample adds to the heat of the furnace, which is in contrary to current approach and does increase the severity of the test. To quantify the consequences, three wall assemblies were tested with pre-defined heat release curves and modified furnace conditions. The assemblies were timber walls built from two layers of Oriented Strain Boards (OSB, 25 mm thick) on a timber frame with an air cavity (100 mm). A reference experiment with a well-insulated wall was performed to determine the furnace’s minimum heat release rate (HRR) required to maintain the standard (ISO 834) temperature/time curve. The first wall was tested with a standard fire resistance test, and in the 2nd and 3rd wall experiment, the furnace followed the minimum HRR value determined in a reference experiment. In experiment 2, the furnace ventilation matched the air requirements of the burners, and in experiment 3, the furnace was over ventilated. Peak temperatures measured in experiments 2 and 3 exceeded the standard temperature/time relation by 420°C and 600°C, respectively. The assembly’s failure (integrity criterion) was observed after 27 min, 23 min and 14 min of experiments 1, 2 and 3, respectively. The limitations of the approach used related to reproducibility and validity are discussed.