The biochemical reactions described below all take place within the feed stuff before a haystack bursts into flame due to spontaneous combustion:
A part of the plant cells remains alive, even after the hay has dried out. The respiration process continues in these cells, but at a limited metabolic rate which releases heat. The excellent insulation properties of hay increases its temperature.
Im Heu vorhandene Pilze und Bakterien vermehren sich sehr stark in der durch die Zellatmung und den Stoffwechsel entstandenen Wärme. Besonders an Stellen mit höherer Restfeuchte entwickeln sich bestimmte Arten von Bakterien besonders schnell. Durch deren Stoffwechsel erhöht sich die Temperatur im Heu nochmals sehr stark.
A chemical process of decomposition takes place between the cells and between the active ingredients within the cells themselves (the pectins). This also releases a great deal of heat. The temperature continues to rise.
As hay cannot dissipate heat effectively, heat builds up in particular places. The temperatures increase to the extent that the hay ignites. The risk of spontaneous combustion in haystacks has risen over the past few decades and continues to do so. The increased use of fertilisers on meadows and mechanical harvesting methods mean that clumps of damp soil and grasses that have not dried sufficiently are being gathered and stored. The use of modern machinery to bring in harvests quickly, and blowers and hay spreading machines to greatly compress the hay in the storage barns, also increase the risks described above. Storing the hay in bales also creates „hot spots“ and the accompanying danger of spontaneous combustion.
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