Comprehensive and Detailed Explanation (Based on NREMT standards):

This scenario strongly suggests a hazardous environment involving chemical crowd-control agents such as tear gas or pepper spray. During the scene survey, NREMT prioritizes scene safety, hazard recognition, and incident size-up before any patient contact.

Option D (Determine the control agent being used) is correct because identifying the chemical agent helps determine the level of risk, appropriate personal protective equipment, and whether EMS can safely operate in the area.

Option E (Identify the number of patients) is correct because determining the number of patients is essential for assessing the scope of the incident and requesting additional resources if needed.

Option A is incorrect because removing restraints is not part of the initial scene survey and must be coordinated with law enforcement.

Option B is incorrect because patient decontamination occurs only after scene safety is ensured.

Option C is not a priority until hazards are identified and the scene is safe.

NREMT teaches that EMTs must never compromise their own safety and must fully assess hazards before providing care.