In the maintenance of (petro-)chemical installations, substances present in non-core production installations such as storage facilities as well as in the production installations to be cleaned or maintained may constitute a risk. During shutdowns, regularly used tanks and warehouses that have to be maintained will still contain feedstock, intermediates or final products. However, temporary storage facilities may be used as well during shutdowns. It has been observed that in those cases accidents may arise from the fact that incompatible chemicals are stored close to each other, in particular when maintenance work is subcontracted. In the following paper you will see many incidents have occurred in the storage tanks as they are fragile and easily damaged by slight overpressure or vacuum.