Bethel process is a standard procedure to treat timbers with creosote oil using the full-cell process to protect the timbers from marine borers. Creosote oil is prepared by the distillation of tar. It is black or brown in colour.
    Working process of Creosote Oil
    Firstly, the timber is well seasoned and dried.
    Then, it is placed in airtight chamber and inside air is pumped out.
    Finally creosote oil is pumped into the chamber with high pressure about 0.7 to 1 N/mm2 at a temperature of 50°C.
    After allowing it for 2 hours, the timber absorbs creosote oil sufficiently and taken out from the chamber.
    Creosote oil is flammable so, it is not used for timber works in fire places. It is generally used for wood piles, poles, railway sleepers etc.