Posted By Roger K. Bentley David, The threshold quantities of dangerous chemicals even for lower tier COMAH sites are sufficiently high to put people at risk even inside buildings. For example, 10 tonnes of chlorine leaking can hardly be disregarded. Also there is might be the possibility of an explosion affecting a building structurally. If you don't consider a risk assessment is required in the establishment you have in mind, then you must at least justify your argument in the major accident prevention policy which is a specific requirement of COMAH for lower tier sites.