Backup cylinder: This is a cylinder (generally 10 or 20 litres) to be used if there is a power failure when using a stationary concentrator or when your liquid oxygen unit fails. Although OxygenWorldwide does its utmost to have these cylinders provided at no charge we can not guarantee this on a worldwide scale. In case a back-up cylinder is delivered and one should return it with the delivery truck because it e.g. takes up to much space in a holiday apartment OxygenWorldwide can not be held responsible for any problem caused.