Comprehensive and Detailed Explanation (Based on NREMT standards):

Upon arrival, EMTs must immediately perform a scene size-up, which focuses on safety and incident management rather than patient treatment.

Option A (Identifying hazards) is correct because recognizing dangers such as traffic, fire, violence, or hazardous materials is essential to prevent responder injury.

Option E (Requesting additional resources) is correct because early recognition of the need for more personnel, ALS support, fire services, or law enforcement improves patient outcomes and scene control.

Option B is incorrect because ruling out life threats occurs during the primary assessment, not immediately upon arrival.

Option C is incorrect because patient treatment must wait until scene safety is confirmed.

Option D is incorrect because PPE use is a personal responsibility, not a primary scene-arrival task.

NREMT stresses that effective EMS operations begin with safety, situational awareness, and resource management.