Abstract: In order to pass a duct across a wall between two spaces in which different pressures prevail, there is formed in said wall a passage which is temporarily closed off by means of a panel applied in position by the pressure, whereafter, at the time at which the duct is to be passed across the wall, the pressures in the two spaces are equalized making it possible to remove the temporary closure, the duct is introduced through the passage, a temporary seal between the passage and the exterior of the duct is formed by inflating a pair of inflatable seals, the pressure difference between the two spaces is restored, and a final seal between the passage and the exterior of the duct is created by injecting an adhesive cement between and into the inflatable seals.