CFD (computer simulation) By using CFD-modelling it is possible to reproduce, based on a scientific calculation model, evacuation as well as smoke movement in a comprehensive and visual manner. For the elaboration of our computer simulations we work in close collaboration with the well-known Building Research Establishment (BRE) / Fire & Risk Sciences (FRS), UK. "Full scale" fire tests in buildings Contrary to most other fire safety systems installed in a building it is difficult to test a SHEVS system which is completely dependant of the natural flow convection of hot smoke generated from a fire. It is only possible to control the mechanical functioning of its components. Furthermore, during the design of SHEVS systems the calculations are based on simple geometric principles, which is not the case for other fire safety systems. For more complex buildings the design will require to appeal to the common sense and estimates will be often used. The possibility of an unexpected event in a building must always be considered; at that moment the safety margins would no longer be respected. Whatever safety system is used, an error in the design or a construction fault is always possible. The installation then no longer complies with the exigencies. A smoke control system can all of a sudden affect other systems. The efficiency of the smoke ventilation system is checked during a fire test considering 3 criteria: