IEC 61285:2015 describes the physical requirements for the safe operation of the process analyser measuring system installed in an analyser house (AH) in order to ensure its protection against fire, explosion and health hazards. This standard applies for analyser houses with inner and/or external potential explosive atmospheres and it applies to hazards caused by toxic substances or asphyxiant gases. This third edition cancels and replaces the second edition published in 2004 and constitutes a technical revision. The main changes are: - incorporation of previously issued corrigendum and - minor updates to several sections and references.