Which step is crucial during scene size-up for hazardous material incidents?

During a hazardous materials incident, ensuring personal safety is the most crucial step during the scene size-up. This involves identifying and mitigating any immediate dangers to yourself and others before taking further actions at the scene. Personal safety measures include wearing appropriate personal protective equipment (PPE), maintaining a safe distance from the hazard, and assessing the potential risks present in the environment.

By prioritizing personal safety, responders can effectively gather information about the scene without becoming victims themselves, thus preserving their ability to assist others. Once safety is confirmed, responders can focus on other important aspects, like assessing the environment or coordinating with authorities. This foundational step is critical since any lapse in personal safety could lead to additional injuries or complications during the response effort.