This International Standard 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. (Refer to national guidelines on toxic hazards.) This standard does not address facilities where solids (dust, powder, fibres) are the hazard. This standard does not seek to address all functional safety issues related to analyser houses. Clause 4 addresses the location of the AH and connection within the process plant areas. Clause 5 addresses the design, construction and layout of the AH. It does not address parts of the analyser measuring system installed in other locations such as sample conditioning rooms (SCR) or switchgear rooms. Clause 6 addresses measures for reducing the danger of explosion for AHs while permitting maintenance of equipment with the power on and the case open. For most fluids, the major constraint is that the concentration of vapours, which are toxic for personnel, is lower than the lower explosive (flammable) limit (LEL) (see Clause 7). Using n-Pentane as an example, the LEL is 1,4 % or 14 000 × 10–6, the level immediately dangerous to life or health (which is the maximum level from which a worker could escape within 30 min without any escape-impairing symptoms or any irreversible health effects) is only 0,5 % or 5 000 × 10–6. Clause 7 addresses those measures for protecting personnel from materials in the atmosphere of AHs that are hazardous to health