General Rationale

The temperatures required to form charcoal are in excess of 270°C. Fully carbonised products are of no concern to quarantine. During carbonisation, wood or agricultural waste is heated in a closed vessel, without oxygen to force the wood substance to decompose and form charcoal, a black porous solid consisting mainly of elemental carbon.

As the wood is heated in the retort it passes through definite stages on its way to conversion into charcoal. The formation of charcoal from wood under laboratory conditions has been studied and is summarised below:

At less than 110°C the wood absorbs head and water evaporates. Once the wood is completely dry, temperatures begin to rise. Between 110 to 270°C the wood starts to decompose. The temperature continues to rise as breakdown of the wood structure continues. At 400°C the transformation of the wood to charcoal is practically complete. To drive off tar the charcoal is subject to further heat inputs to raise its temperature to about 500°C, thus completing the carbonisation stage.