A security guard's primary responsibility in a medical emergency is to ensure the safety and well-being of the individual involved. By calling 911, the guard ensures that professional medical assistance is on the way, which is critical in emergencies where timely intervention can save lives. Providing first aid, when qualified, is essential because it can help stabilize the person until help arrives. This proactive approach not only aids the individual in distress but also aligns with the duty of care that security personnel are trained to uphold.
In the context of the other options, attempting to handle the situation independently could lead to inadequate responses or exacerbate the situation, particularly if the guard lacks the necessary training or resources. Ignoring the emergency until a supervisor is present neglects the urgency of medical situations, as every second counts in emergencies. Documenting the incident can be important for legal or administrative processes afterward, but it should not be prioritized over immediate action to assist the person in need. Therefore, the correct course of action combines calling for professional help while providing any necessary assistance.