What are the three phases involved in an incident size-up?

The correct choice highlights the three essential phases involved in the incident size-up process, which are crucial for an effective response.

Preincident information refers to the data and knowledge gathered before arriving on the scene. This includes understanding the location, building layouts, potential hazards, and available resources. This phase sets the groundwork for what responders can anticipate upon arriving at the incident.

Arrival on-scene is the point where responders begin to assess the situation firsthand. This phase is critical as it allows the incident commander to observe the incident's dynamics, evaluate the severity of the situation, and determine the safety of operations for both the public and the responders.

Ongoing assessment involves continuous evaluation throughout the incident. As conditions can change rapidly, maintaining situational awareness allows the incident commander to adapt their strategies, allocate resources effectively, and ensure that the response is appropriate for the evolving circumstances.

This combination of phases ensures that a comprehensive and informed size-up is conducted, which is vital for making effective incident management decisions.