Determination of Notional Char Rates for Protected and Unprotected Timber When Subjected to Variations in Heating Regimes, Test Duration and Thermocouple Configurations

There has been much discussion in technical literature regarding the best method of installing thermocouples to minimise interference with the specimen, ensure accurate thermocouple positioning, minimise errors if the thermocouple cables are not run continuously along isotherms as well as the selection of the construction of thermocouples. Consensus is difficult to achieve given the best method will tend to vary depending upon the application and a broad range of fixing techniques, configurations and thermocouple types that have been used in standard and enclosure fires which complicates the application of data from multiple sources. To investigate these variations, a test program to systematically quantify the performance of timber construction under a range of simulated fire conditions has been undertaken to provide a better understanding to the sensitivity of timbers to variations in heating regimes. The test series compared a proposed alternative configuration using ceramic fibre insulation and screwing adjacent timber sections together without the use of adhesives, to that of the proposed European configuration requiring rebating of the timber sections to run thermocouple leads and bonding of timber members together. The tests were performed using the standard and hydrocarbon heating regimes and different thermocouple configurations were evaluated to quantify potential variations that can occur. The tests also quantified variations in the measured char rates with different heating regimes, different exposure times for protected and unprotected timber, and enable char rate modifications to be derived to account for these variables.