The Swedish Parliament decided 1991 that ventilation systems in all non-industrial buildingsshould be regularly inspected in intervals from 2 to 9 years, shortest for schools, hospitals etcand longest for natural ventilated flats. The systems are checked to fulfil the requirementsgiven when installed.The goals of the evaluation were to give estimated rates for how many systems that wereapproved at the end of 1997 and the cause of the faults that made the system either not to beapproved or to be remedied before next inspection.The evaluation was made in three steps:1.
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