In nuclear facilities, where unacceptable quantities of radioactive aerosols could be spread in the event of a fire, the ventilation system must he designed so that an underpressure is maintained under such circumstances. This is the reason why the extracting ventilation of the room in which the fire has broken out has generally to be kept going as long as possible. This prevents smoke and radioactive aerosols from spreading to accessways and adjacent rooms. Consequently, the various devices of the ventilation network need to have high fire resistance.

Fire dampers can be applied to exhaust air to delay the heat buildup of a major fire. Specialized qualification testing is required for these dampers.

The criteria we have used as a basis for specifying the required qualities of installations are defined. The tests that have been performed, or are now in progress, are described. The results obtained so far are given. Devices and arrangements are suggested