Annex I (Oil) came into force on 02.10.1983 and contains conditions for discharge of mixtures containing oil and also requirements applicable to the construction and equipment of tankers larger than 150GRT and other ships larger than 400GRT. This Annex is based on the principle that oil and water do not mix and are therefore easily separated. It contains requirements regarding the operation, construction and equipment of ships. The operational requirements stipulate the conditions under which ships may discharge water/oil mixtures into the sea. Overboard discharges are to be above the waterline so that discharges can be visible. The construction and equipment requirements are such as to enable the ship personnel to comply with the discharge conditions. Other construction requirements are such to minimise the chances of oil cargo tank penetration in the event of damage, i.e. double hull construction and protective location of segregated ballast tanks. Requirements for minimising oil pollution from oil tankers in the event of side and/ or bottom damages penetrating the cargo oil tanks are also included.