An inflatable pressure vessel (1), which may be a decompression chamber for treating divers, has a flexible elongate casing (2) made of a silicone elastomer material reinforced with windings of reinforcing filaments and one or more removable end members (7, 8) to provide access. An end member may be a rigid plate which seals against a frame (3, 4) defining the entrance under internal vessel pressure. A transparent plastics plate gives illumination and allows inspection of a diver under treatment in a decompression chamber. Two pressure vessels (31, 32) may be connected by a linking element (24) comprising a male part (25) which seals within a female part (33, 34) under internal pressure and which has inter-engaging projections (29, 35) and depressions (30, 36) to prevent the parts from sliding apart axially under that pressure.