From wood wall assemblies

Heat Release from Wood Wall Assemblies Using Oxygen Consumption Method... 

Our results are comparable to the results of Brenden and Chamberlain (6) and Chamberlain and King (7). In our most comparable assembly having gypsum on the fire-exposed side and no insulation (B-3) (Fig. 7), contribution from the walls started approximately at 30 min and rose to about 200 kW at 50 min. Similar results were obtained despite differences in assembly constructions. The exterior sheathing in our tests was plywood whereas that of Brenden and Chamberlain (6) was gypsum. Moreover, we used untreated wood studs in our assemblies. 

Commercial fire-retardant treatments generally do not add significantly to the fire endurance of assemblies. It is often more advantageous from the cost standpoint, either to use thicker wood members or to select species with lower charring rates, than to add the cost of the fire-retardant treatment. In some assemblies, however, it has been found worthwhile to use some fire-retardant-treated components in order to gain the extra time which will bring the fire endurance time up to the goal desired. For example, treated wood studs in walls and treated rails, stiles, and cross bands in solid wood doors have been used. 

Figure 2.8. (a) Hemicelluloses with long persistence lengths are relatively inflexible and can only snake between microfibrils, (b) Schematic assembly of polydiverse xylans and lignins during secondary wall formation of a hardwood, (c) Microfibrils cluster in arrays surrounded by wider regions of matrix material (schematic from spruce wood). 

Cellulose, the most abundant organic compound found in nature, forms the principal constituent of cell walls in higher plants. It accounts for 91% of cotton fibers and 40-50 of wood. It is a linear chain made of up to 10 (l->4)-linked P-D-glucose molecules. The characteristics of cellulose result from the tendency of the individual chains to form linear, extended ribbons, which assemble to form highly ordered, hydrogen-bonded microfibrils. If the ribbons are laid down in sheets in a parallel manner such that all reducing terminals occur at the same side of the bundle, it is called cellulose I. This is the most common natural material (Fig. 4.2.23). 

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