Microwave Heating as an Experimental Model for Spontaneous Combustion in Organic Materials
Carrick, Ian T.
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Microwave Heating as an Experimental Model for Spontaneous Combustion in Organic Materials Ian T. Carrick and Robert Rynk Hypothesis: Heating organic materials in a microwave oven mimics the heating mechanisms of spontaneous combustion as observed in materials like mulch, composting feedstocks and hay. Spontaneous combustion primarily occurs in moderately moist organic materials, in the range of 20% to 40% moisture content. The moderate moisture supports initial biological heating, which raises the temperature enough for chemical reactions to take over. Dry materials inhibit the biological starting point while very wet materials limit the temperature rise by evaporating the abundant water. Similarly, microwave ovens rely on the presence of some moisture to create heat within the material. Because of this similarity, a microwave oven might serve as a model to conveniently study the mechanisms and factors of spontaneous combustion at a laboratory scale. On-going experiments are seeking to verify this hypothesis by demonstrating a predisposition towards spontaneous combustion in moderately moist feedstocks and the ability to generate heat from the nucleus of moist material. The research has been conducted using the dairy manure as a feedstock. The manure was dried in order to control the moisture content of the feedstock by adding a prescribed amount of water after drying. Samples with 10%, 20%, 40% and 60% moisture are microwaved for short intervals of time until smoke, embers, charring or flame are observed. This procedure has been conducted was done at a variety of power settings to both get a wider range of data and to allow for ignition time differences in the samples to be observed. At this current stage, the majority of the trials resulted in the 20% and 40% moisture samples showing signs of combustion first, which is consistent with observed moisture contents in the mulch, compost and hay piles that spontaneously combustion. While more trials are necessary, so far the results suggest that microwave heating does mimic the heating mechanisms of spontaneous combustion.