This is by FAR the most misunderstood element of all!
The ERP must define the types of releases that could potentially require an emergency response and should define what types of releases would not be an emergency, or, in other words, what may be handled as an “incidental release.”
The ERP should include an inventory of the hazardous substances found on site, the manner in which they are stored, and the consequences of an uncontrolled release.
Scenarios or circumstances that trigger activation of the ERP should be described for the various hazardous substances stored on site that have the potential to cause an emergency.
Reasonably predictable worst-case scenarios must be identified in the planning phase.