Spontaneous ignition hazards in stockpiles of cellulosic materials: Criteria for safe storage

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Abstract
The ambient temperature at which ignition is brought about in various sizes, shapes and masses of sieved bagasse pith was investigated on a laboratory scale. ΔT‐time and ΔT‐position profiles were obtained, and critical temperatures are determined to closer than 0.5 K; this is the highest precision for location of the sub‐critical/super‐critical margin so far reported for any thermal ignition system. Such quality is a pre‐requisite for quantitative extrapolation in order to predict the critical sizes for field stock‐piles in normal climatic conditions. Scaling rules based on stationary‐state, thermal ignition theory are used and comparisons of the results are made with real piles. The predictions are shown to grossly over‐estimate the safe size of stock‐piles, and the reasons for this discrepancy are discussed. Distinctions between the reactivity in perfectly dry substrates (as is inevitable at the temperatures prevailing in laboratory experiments) and that of natural, wet piles, and the part played by water are important features. A need for supplementary measurements of heat‐release rates at temperatures close to those prevailing in stock‐piles is stressed. The results are found to be consistent with similar measurements in woodflour and the conclusions are, therefore, applicable to all cellulosic materials at high temperatures.

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