emergency discharge. If both main pumps fail then to remove the cargo, the tank's safety valves are adjusted to lift at 100 kPa (1 bar). Then the filling line which goes to the bottom of the tank is opened along with the filling lines of the other tanks on board. The pressure is then raised in the tank with the defective pumps which pushes the cargo into the other tanks where it can be pumped out. IHI (Prismatic IMO type B LNG tanks) Designed by Ishikawajima-Harima Heavy Industries, the self-supporting prismatic type B (SPB) tank is currently employed in only two vessels. Type B tanks limit sloshing problems, an improvement over Membrane LNG carrier tanks which may break due to sloshing impact, therefore destroying the ship's hull. This is also of prime relevance for FPSO LNG (or FLNG). In addition, IMO type B LNG tanks can sustain internal accidental damage due for example to internal equipment releases. This was incorporated into the design following several incidents that occurred inside membrane LNG tanks. TGZ Mark III Designed by Technigaz, these tanks are of the membrane type. The membrane consists of stainless steel with 'waffles' to absorb the thermal contraction when the tank is cooled down. The primary barrier, made of corrugated stainless steel of about thickness is the one in direct contact with the cargo liquid (or vapour in empty tank condition). This is followed by a primary insulation which in turn is covered by a secondary barrier made of a material called "triplex" which is basically a metal foil sandwiched between glass wool sheets and compressed together. This is again covered by a secondary insulation which in turn is supported by the ship's hull structure from the outside. From the inside of the tank outwards, the layers are: LNG Primary barrier of 1.2 mm thick corrugated/waffled 304L stainless steel Primary insulation (also called the interbarrier space) Secondary barrier within triplex membrane Secondary insulation (also called the insulation space) Ship's hull structure. GT96 Designed by Gaztransport, the tanks consists of a primary and secondary thin membrane made of the material Invar which has almost no thermal contraction. The insulation is made out of plywood boxes filled with perlite and continuously flushed with nitrogen gas. The integrity of both membranes is permanently monitored by detection of hydrocarbon in the nitrogen. An evolution is proposed by NG2, with the replacement of nitrogen by