Abstract: An exchanger having an enclosure with a bottom (5), a cover (4) and a peripheral casing (6), at least one block (1-3) disposed between the bottom and the cover, each block comprising a body, longitudinal channels (10) and transverse channels (12). At least one of the interfaces (112, 114, 123, 135) between two opposite front faces belonging to the cover and to the block adjacent thereto, to the bottom and to the block adjacent thereto, or optionally to two contiguous blocks, a so-called radially inner peripheral seal (J1, J?1) is provided, extending radially outside the area (14) of the openings of the longitudinal channels, and a so-called radially outer peripheral seal (J2, J?2) defining, with the inner peripheral seal and the opposite front faces, an annular space (E, E?) for containing a possible leak of one or the other fluid.