SR42 Charring rates of timber (1992)

This report describes an investigation into parameters that influence charring rate of timber.

Firstly, from an international perspective, the investigation sought to determine how internal properties of different timber products (solid and glulam) influenced charring and also attempted to show how two New Zealand grown timbers differed from overseas grown timber and why any differences existed.

Secondly, the different charring rates produced by exposure to test and real fires are considered. Two tests were performed, the first to demonstrate a model's ability to predict charring rate of various samples prepared with different physical parameters. The second test attempted to relate comparative results from the first test to a heavy section beam or column.

Results from this study indicate that revision of methods used to design timber structures for fire resistance is warranted. The present practice of assuming the charring rate of radiata pine is 0.6 mm/min is found to be valid only for higher-density timber. Selection of a charring rate based on the timber density is much more reliable, especially for timber of lower densities.