Silane-modified sealants are widely used for the construction of railway vehicles and have several advantages in the production of elastic structural joints and seals featuring high bond thickness. The use of hydrogen fuel cells to power newly developed rolling stock places further safety constraints on the design of the sealing elements of those technical compartments that contain the storage tanks of the propulsion system. Given the lack of solutions based on the use of silane-modified sealants validated for operating environments in which leaks of gaseous hydrogen may occur, an experimental test was carried out to characterize the permeability of some adhesive products according to the requirements of the BS ISO 15105-2:2003 standard, and a specific test bench was developed for this. Two different sealants were subjected to the hydrogen permeability test. The processing of the results provided by the apparatus designed specifically for the execution of the test made it possible to determine a permeability rate dependent on the thickness of the adhesive in the order of ng/(min × cm2). The results of the test were subsequently contextualized within the technical application to rolling stock, with the ultimate aim of verifying that the permeability rate determined experimentally is compatible with the design safety criteria. The developed test bench allowed the correct execution of the permeability test. In general, the two sealants showed hydrogen permeability values compatible with the application. In particular, the hydrogen permeation rate (Rp) was lower than 0.25 ng/min for both sealants.