[en] The behaviour of three types of HEPA filters both in static conditions and when operated at nominal flowrate, was examined under rapid overpressure transients, with the aim of obtaining data on their mechanical resistance. Whatever the configuration of the duct and where ever filters were placed, no important difference was noted in their failure mode. Where some improvement in resistance was noted this was related to a new design of some filter part (eg. in the minipleat type). An attempt to measure the filter efficiency during the transient was made. First results show it is possible to obtain an approximate evaluation of the efficiency, which falls down to abnormally low values when the shock wave reaches the filter. (author)