Analysis of wood fuel moisture content on enclosure fire through small scale experiments

Abstract

Norway is a country where there are many dense residential areas consisting of wooden houses. Many of these areas consist of old buildings with historical value and mapping shows that there are 167 areas of this type. Areas as these are quite vulnerable if a fire occurs as shown in Lærdalsøyri in 2014, where 40 buildings, including 4 historic building was lost. Wood is a hygroscopic material, meaning it will absorb or release moisture depending on the air relative humidity and temperature. Low humidity prior to the Lærdal-fire resulted in low wood fuel moisture content which caused a rapid fire development. The purpose of this master thesis is to investigate how the fuel moisture content (FMC) in the compartment linings affects the different stages in an enclosure fire. This has been examined by doing experiments of rooms which were scale down to 1/8 and 1/16 scale of the ISO-room from ISO 9705-1. The reason for this is to assess the possibility of doing small-scale experiments and see if they give sensible results compared to more costly and time-consuming large-scale experiments. I addition, it was an interest to find a scale and method which makes it easy to demonstrate these experiments in educational purpose. Based on this, it was conducted 17 experiments to get a good understanding of the effect of FMC and doing small scale experiments. Ten rooms in 1/8 scale and seven rooms in 1/16 scale were tested with FMC ranging from 6,5 % to 16 %. The start fire was placed in the left back corner and was scaled down from the start fire in ISO 9705-1 using the Froude-scaling technique to assure correct scaling. This resulted in the start fire having a heat release rate of 0,85 kW for the 1/8 scale and 0,2 kW for 1/16 scale. Mass loss rate, temperature and observation was collected during the experiments to evaluated the fire development and to determine time to flashover. The results shows that the impact of the FMC is greater in the pre-flashover period but also influences the post-flashover fire. By increasing the FMC from 6,5 % to 11,6% the time to flashover increases from 4 min to 7 min. A further increase to 14,5 % FMC, the time to flashover increases to 9 minutes. Results shows that scaling down to 1/8th scale using Froude-scaling and ISO 9705-1 provides a good representation of the full-scale fire phenomenon. Scaling further down to 1/16 scale has shown to be difficult and doesn’t give any reasonable results.