What should a Protective Security Officer (PSO) establish immediately during an active shooter incident?

Establishing a perimeter and controlling access to the area is crucial during an active shooter incident. This action helps to contain the situation, preventing the entry of unauthorized personnel who might hinder law enforcement's response or escalate the chaos. A secured perimeter allows for an organized and effective operation by emergency responders, ensuring that only emergency personnel can enter the scene. It also helps to keep civilians away from danger, providing a safer environment for both those present and responding units.

The other options, while important in their own contexts, are secondary to the immediate need for containment and safety. Creating a medical station or a media briefing area are necessary actions but should follow after the scene is secured and the immediate threat is addressed. Organizing a clean-up crew, although necessary for post-incident recovery, is the least urgent during an active shooter situation, as the focus must remain on protection and response rather than cleanup.