Abstract: A jacket (1) is shaped to enclose at least partially a liquid storage vessel (2; 200), the jacket comprising a skin (5) arranged as a plurality of folds (20) which are capable of opening out to permit expansion of the jacket in the event of liquid escaping from the storage vessel, securing means (9a, 9b, 10a, 10b, 13a, 13b, 14a, 14b; 35) are provided to secure the upper part (32) of the jacket in position with respect to the vessel and to maintain the upper part of the jacket in position in the event of liquid escaping from the vessel. The jacket may be fitted to existing oil tank or new oil tank installations, or may be used with cold or hot water tanks.