In an initial incident, a size-up is done to set the immediate incident objectives. The first responder to arrive must assume command and size-up the situation by determining:

• Nature and magnitude of the incident
• Hazards and safety concerns
• Hazards facing response personnel and the public
• Evacuation and warnings
• Injuries and casualties
• Need to secure and isolate the area
• Initial priorities and immediate resource requirements
• Location of Incident Command Post and Staging Area
• Entrance and exit routes for responders