Charcoal

Description

Charcoal is a highly porous form of carbon burnt at a high temperature with minimum exposure to air. It is shipped in lumps, shells or briquettes, normally in bags but also in bulk.

Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen. The resulting soft, brittle, lightweight, black, porous material resembles coal.

Used amongst others as a decolorizing and filtering medium, in the purification of oils and in the chemical industry. Is a fire risk when in briquette form or when wet, and may ignite spontaneously in air. According to type and quality, charcoal can absorb moisture, 20% by weight being an average maximum figure. Under normal circumstances, charcoal after production will absorb up to 5% of moisture unless actually subjected to soaking or standing out in rainy weather when it can absorb up to 20%. Simple drying of the material at a low temperature will remove the water. May also be subject to loss in weight, probably by loss of moisture. Charcoal, being absorbent, can be contaminated by any material carried in the water, such material possibly staying in the charcoal permanently. Ideally, charcoal should be kept in sacks or similar containers raised from the floor on pallets or duckboards and sheeted over. Paper bags are subject to the normal problems when they are wet or torn.

Commercial charcoal is found in either lump, briquette, or extruded forms:

• Lump charcoal is made directly from hardwood material and usually produces far less ash than briquettes.
• Briquettes are made by compressing charcoal, typically made from sawdust and other wood by-products, with a binder and other additives. The binder is usually starch. Some briquettes may also include brown coal (heat source), mineral carbon (heat source), borax, sodium nitrate (ignition aid), limestone (ash-whitening agent), raw sawdust (ignition aid), and other additives like paraffin or petroleum solvents to aid in ignition.
• Extruded charcoal is made by extruding either raw ground wood or carbonized wood into logs without the use of a binder. The heat and pressure of the extruding process hold the charcoal together. If the extrusion is made from raw wood material, the extruded logs are then subsequently carbonized.

The characteristics of charcoal products (lump, briquette, or extruded forms) vary widely from product to product. Thus it is a common misconception to stereotype any kind of charcoal, saying which burns hotter, etc.

Charcoal is sometimes used to power commercial road vehicles—usually buses—in countries where oil is scarce or completely unavailable. In the years immediately after the Second World War, charcoal buses were in regular use in Japan and are still used today in North Korea.

Hazard: IMDG Class 4.2 Spontaneously combustible.