To clarify the influence of unevenness of chemical amount in fire-retardant-treated wood, cone calorimeter and model box tests were carried out. The cone calorimeter tests demonstrated there is a critical content of chemicals whether flaming combustion occurs, and above this amount, heat release and flaming are hardly influenced by unevenness. Flame spread in model box agrees with this tendency, yet eventual heat release rate significantly decreases as the average chemical content increases. The result implied that efflorescence inside present products do not lack fire safety, owing to the margin between their average and the critical amount for suppressing flaming combustion.
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