This fact sheet aims to clarify the concept of the safety perimeter used during an emergency response involving hazardous substances and that of the emergency measures planning zones established in the environmental emergency plans required by the Regulation respecting Environmental Emergencies 2019. It illustrates the link between the results of scenario modeling resulting from a risk analysis and the planning of emergency measures. The concepts and recommendations presented in this document apply mainly to fixed installations and are generally not applicable to incidents involving the transport of dangerous substances.