Wood is a corrosive substance by nature, and can be made more corrosive by treatment given to it. Unlike most other corrosive substances, one of the corrosive chemicals in it, acetic acid, is volatile, and in an ill-ventilated space, wood can cause corrosion of metal nearby but not actually in contact. Where there is contact in atmospheric conditions, corrosion can occur by the usual micro-electrolytic mechanisms, and in immersed conditions, large-sized electrolytic cells can form. Corrosion problems caused by wood can therefore arise in three areas: a) inside wooden containers, by vapour corrosion without contact; b) at contacts in land-based structures, through attack by wood acids and wood treatment chemicals; c) at contacts in immersed structures, where macro-galvanic mechanisms predominate.