A tank and method for containing a cryogenic liquid in which a purge gas is introduced into an insulation space defined between an outer vessel and an inner vessel to contain insulation material. The inner vessel is used to contain the cryogenic liquid. The purge gas can be cryogenic vapor evolved from the liquid and routed into the insulation space. Control of the purge gas within the insulation space can be provided by a programmable logic controller in which purge gas is vented from the insulation space should the pressure be indicative of a leak within the inner vessel and purge gas is introduced into the insulation space should the pressure be below the ambient to maintain a positive purge gas pressure. An adsorbent bed can also be located within the insulation space to adsorb any moisture.