To identify a problem and assess the potential consequences. Initially, a size-up is the responsibility of the first officer to arrive at the scene of an emergency. Size-ups continue throughout the response phase and continuously update the status of the incident, evaluate the hazards present, determine the size of the affected area as well as whether the area can be isolated. A size-up also determined if a staging area will be needed and where it should be located to allow for the best flow of personnel and equipment. See also Incident Command System.

The verbal appraisal via radio of conditions at the scene of an incident by the first-in company or officer. May be updated as command officers arrive on the scene.

To evaluate a fire to determine a course of action for fire suppression.