The difference between upper and lower tier establishments, in terms of Directive 96/82/EC, is based on the levels of dangerous substances held at that establishment. The relevant quantities of dangerous substances that determine an establishment to be upper tier — the most hazardous — or lower tier are listed in Annex 1 to Council Directive 96/82/EC.
All establishments, subject to the directive, are subject to general requirements including that they must be notified to the Health and Safety Authority. A major accident prevention policy document, MAPP, must also be prepared and held by the establishment. All are subject to the land use planning provisions of the directive.
Upper tier establishments, in addition to the general requirements, must produce and submit to the authority a detailed safety report and must notify the public within a specified area of safety measures to be taken in the event of an emergency. The relevant local competent authorities must prepare an external emergency plan to deal with potential major accidents at each upper tier establishment.