Citation

Back EL. Fire Safety J. 1981; 4(3): 185-196.

Copyright

(Copyright © 1981, Elsevier Publishing)

DOI

unavailable

PMID

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Abstract

This paper summarizes and quantifies experience concerning self-heating and the risk of auto-ignition, due to the absorption of moisture from the surrounding air by low-density bales of hygroscopic cellulosic material such as textiles, waste-paper, and insulating boards during storage. Such risks do exist, especially after a drying operation, and they have apparently led to a number of fires.

As a starting-point, the equilibrium moisture content of ligno-cellulosic material over a range of relative humidities and temperatures is presented as well as the heat release accompanying the absorption of water and the condensation of water vapour from ambient air. Using data on the specific heat of cellulosic material, the possible adiabatic temperature rise is calculated. The kinetics of moisture absorption into the bale and the rate of heat transport out of the bale are discussed as a function of the density of the material.

It is shown that the heat released by an increase of a few percent in the moisture content can raise the temperature of low-density hygroscopic material into a range where oxidation rates are sufficient to lead to the onset of carbonization in the centre of the bale. Thereafter, smouldering may lead to auto-ignition. Bales which are not yet ignited often show this carbonization zone in the centre.Preventive measures -- such as a controlled remoistening after drying -- are summarized.