The airtight doors by BUCHELE are certified in accordance with DIN 1026 and are classified in accordance with DIN EN 12207 in different so called air permeability classifications. The test is to determine how many m³ of air gets into a room within an hour starting from a low breeze up to a hurricane. Special four-sided seals reduce penetrating air masses. For special high demands the contact pressure may be increased with additional locking mechanisms.