Correlation between charring rate and oxygen permeability for 12 different wood species

Abstract

The charring rates of 12 different wood species originating from Europe and the tropics with densities ranging from 350 to 750 kg/m 3 were investigated to obtain clues on their fire resistance behavior. This was done by measuring the thickness of the charred layer after a 30-min exposure to the standard fire ISO 834-1. No correlation was observed between charring rate and density. In search of another physical property that could be used as an indicator of fire resistance, the oxygen permeabilities of the selected wood types were measured. A strong correlation between oxygen permeability perpendicular to the wood fiber direction and charring rate was found, which is quite straightforward given that oxygen is the necessary component to enable smoldering and ignition, both affecting the charring rate. It seems that oxygen permeability is potentially more suitable as a parameter to evaluate the fire resistance of char-sensitive wooden constructions, rather than density. No general preference of the tree ring orientation from 0° (tangential) to 45° and 90° (radial) was found for these measurements.

Material properties and external factors influencing the charring rate of solid wood and glue‐laminated timber

“…White [31] compared his results with test results from the literature, and did not find any correlation between density and charring rate for densities varying between 400 and 700 kg/m 3 . Hugi et al [40] also did not find any correlation between the charring rate and the density of the wood for a density range of 350-750 kg/m 3 . The lack of connection between the density and charring rate in these experiments might be due to variations in the density within one cross-section or along the length of a sample that may occur in wood, or it might be due to the small span in density for the sample ranges they tested.…”

“…Hugi et al [40] found a strong correlation between the charring rate and the oxygen permeability of the wood; as the oxygen permeability decreased the charring rate also decreased.…”

“…Charring involves the thermal degradation of wood mass, and the charring rate is therefore slower when there is greater mass to degrade. A few experiments showed only a small or no correlation between density and charring rate [31,34,[38][39][40][41]43], but this might be due to small ranges of wood density in their studies. However, according to Suuberg [24] low density samples might work as insulators because of their lower thermal conductivity, and therefore the low density samples can pyrolyse slower than the high density samples.…”

“…Hugi et al [40] tested 12 different wood species in a small horizontal furnace; abachi, abura, maple, beech, oak, ash, spruce, koto, Meranti dark red, Meranti light red, sipo, and fir, with densities varying from 350 to 750 kg/m 3 . For each species, three specimens of 1000 mm length× 90 mm width×45 mm thickness were cut into different directions to the tree ring orientation.…”

Fire Behaviour of Tropical and European Wood and Fire Resistance of Fire Doors Made of this Wood

“…Accordingly, a high curvature corresponds to a large deflection. The permeability of wood was measured at room temperature using a technique which was originally developed for concrete [20] and later adapted to wood [21]. By considering the common wood fibre orientation in perimeter elements of door frames and door leaves, only the permeability for oxygen perpendicular to the wood fibre direction was measured.…”