14 pipeline 16 and a plurality of spraybars 18 situated towards the roof 20 of the container 10 the container may be divided into a number of compartments 10a 10b by movable partitions in which case at least one spraybar 18 is provided per compartment a control system 22 comprising a plurality of heat sensors 24 thermostats 26 and liquid cryogen flow control means 28 is provided to ensure the interior of the container 10 remains within desired temperature limitations thusfar the refrigeration system 12 is conventional the present invention however makes use of further non standard components including an atmosphere composition analyser 30 for monitoring and analysing at least the oxygen content within the container the analyser 30 may be linked to the control system to facilitate the automatic closedown of the refrigeration process should the oxygen content of the container rise above a predetermined safe limit alternatively the analyser 30 may be linked to a simple warning device so as to warn the operator of the necessity to close the system down the cryogenic storage tank 14 shown in cross section in fig2 comprises an inner and an outer skin 32 34 spaced from one another by a vacuum insulating region 36 an outlet 38 communicates with pipeline 16 for the passage of liquid cryogen thereto in operation tank 14 is filled with a mixture of liquid oxygen and liquid nitrogen the initial proportions of which are selected so as to produce a gas having an oxygen content of between above 18 and 22 when fully vaporised whilst the actual ratio of the mixture required will very much depend on the magnitude of any enrichment during storage transfer and transportation it has been found that a mixture containing approximately 15 by.