The date of expiry is intended to ensure that the cylinders contain oxygen at any time. Irrespective of the type of gas that has been compressed, valve systems will always have a rate of leakage, and the date of expiry is intended to account for this. Though it is found at the quarterly inspection that the cylinders contain oxygen, they must be replaced in accordance with the date of expiry. The requirement for ships and shipowners has been introduced in addition to the requirements for suppliers of the medical oxygen.
Read more about the requirements made by the Danish Medicines Agency in order no. 1318 of 27 November 2007 (only available in Danish).