The containment is a modular gas-tight room system that includes a self-supporting substructure, on which stainless steel panels are bolted, either on one or on both sides. The panels are sealed together with a chemical-resistant, nonageing dry sealant. The panels can be dismantled from inside the containment. The standard grid dimension is 1.200 mm, but any other grid dimension up to 1.400 mm are available. The elements can also be used to construct a floor or ceiling. In this case, the ceiling substructure is detached from the main body, so that a room-in-a-room system is formed. The substructure grid is made in accordance with the static requirements. The system makes it possible for fittings to be mounted using the same chemical-resistant, non-ageing dry sealant as used on the wall panels.