While dispersed populations may be affected through contamination of water or the food chain resulting from a chemical accident, those exposed are frequently inside an industrial site. In an urban area, a community may be exposed to hazardous substances escaping from a breached tanker vehicle that has been transporting them. In rarer cases, the exposed population may be at some distance from the accident site, including beyond national borders. Potentially affected areas in neighbouring countries could include those with limited chemical emergency response plans or capabilities.
The identification of potential risks and the geographical zones where effects are likely to occur in the event of an accident is a part of the emergency planning process. It should include general zoning and mapping of hazardous industrial activities, taking into account all aspects of protecting health and the environment (including property) and case-by-case decision-making concerning the siting of a new facility or proposed development near an existing facility.