DENSITY EFFECTS AND ITS RELATIONSHIP WITH MAJOR FLAME CHARACTERISTICS OF SELECTED FIRE TOLERANT TREES IN SOUTH-EAST NIGERIA: A LOOK AT OVEN AND SUN DRIED TIMBERS

Abstract

Physical and flame characteristics of fifteen tree species in South-East Nigeria were investigated. The tree species Daniellia oliveri, Anacadium occidentale, Vitex doniana, Lonchocarpus griffonianus, Gmelina arborea, Nauclea latifolia, Tectona grandis, Mangifera indica, Delonix regia, Newbouldia laevis, Azadirachta indica, Dialium guineense, Terminalia superba, Manilkara obovata and Irvingia gabonensis were identified and named by taxonomists. The aim was to investigate the effects of oven and sun dried densities of timbers on major flame characteristics (ignition time, flame propagation rate, after glow time, flame duration and ash formation) and to establish timber density relationship with the flame properties. Physical properties (density and moisture content) and flame characteristics of all the timbers were carried out using their respective standard methods. Oven and sun dried densities of timbers ranged from 0.39 to 0.97 and 0.45 to 1.16 g/cm3 respectively. Moisture content of oven and sun dried timbers ranged from 8.02 to 11.56% and 8.15 to 11.65 % respectively. The range of values for ignition time were (3.00-10.00) seconds for oven dried timbers and (5.00-10.00) seconds for sun dried timbers. Flame propagation rate ranged between 0.15 and 0.27 cm/s and from 0.09 to 0.25 cm/s for oven and sun dried timbers respectively. The values for flame duration ranged from 12.00 to 56.00 seconds for oven dried timbers and 7.00 to 45.00 seconds for sun dried timbers. Afterglow times of oven and sun dried timbers ranged from 70.00 to 267.00 and 19.00 to 188.00 seconds respectively. Ash formation values ranged from 0.19 to 2.38 and 0.25 to 2.46 % for oven and sun dried timbers respectively. Combustion/pyrolysis pattern of oven and sun dried timbers on exposure to fire was similar. Density related to flame propagation rate, although, for the denser hard woods above 0.60g/cm3 and 0.70g/cm3 for oven and sun dried timbers respectively, this dependence was less straight forward. The flame characteristics of the oven dried timbers compared favourably with sun dried timbers and showed that ignition time, flame duration, afterglow time and ash formation have no clear relationship with timber density.