Charring behaviour of tropical hardwoods under standard fire exposure

This study investigates the charring behaviour of Malaysian tropical hardwoods under ISO 834 (1999) standard fire exposure. Four species, Keranji, Keruing, Kedondong, and Light Red Meranti were selected to represent a density range of 350 to 950 kg/m3. Full-scale timber specimens measuring 100 × 300 × 1400 mm were exposed to three-sided fire conditions for 45 and 60 minutes in a vertical furnace. Charring behaviour was evaluated using two complementary approaches: the direct residual section method and the indirect 300°C isotherm method based on embedded thermocouple measurements. The results confirm that density primarily governs the charring behaviour, while moisture content has a minor effect. Keranji, with the highest density, exhibited the lowest charring rates, while Light Red Meranti showed the highest charring progression. Charring depths were consistently greater at the bottom surface than at the side surfaces due to exposure orientation and corner effects under three-sided fire conditions. Charring rates obtained using the 300°C isotherm method were generally lower than those measured using the residual section method, reflecting differences between tracking the pyrolysis front during heating and measuring final material loss after cooling. Compared with Eurocode 5 (2004), thermocouple-based results were largely conservative, whereas residual section measurements often exceeded the code values.