Fire Performance of Heritage Hardwood: Conservation and Adaption of Existing Timber Structures

In Canada, there currently is a drive to rehabilitate existing buildings for new uses. This practice offers a way to reduce the environmental impact of construction by avoiding demolition and new construction while addressing the occupancy needs of today. One challenge of rehabilitating historic Canadian structures is to preserve the heritage value of their timber construction while also addressing concerns of fire safety. While contemporary timber construction only uses softwood, heritage structures often used hardwoods as well. The purpose of this study is to better understand the fire performance of these historic hardwoods for when they are encountered in practice. Historic hardwoods and softwoods were tested in a cone calorimeter following a modified ASTM 1354 procedure. The result of the testing found that the hardwood samples had a faster charring rate than the softwoods. This would suggest extra precautions are needed when working with historic hardwoods. This paper also evaluates the potential of using a numerical model for historic timber as a viable tool for evaluating the fire performance of heritage timber when suitable samples cannot be acquired for testing. The finite element analysis software, LS DYNA, was used. The hardwood tests were replicated, however, timber presents unique challenges as it is a combustible material, with complications regarding moisture and changing thermal properties with temperature. Results of the model indicate high char rates, nearly double the experimental results. One of the main challenges with the model is its inability to change the material from timber to char during pyrolysis. Therefore, the insulating char layer that would slow the rapid charring is not being accounted.