In the event of a fire alarm, a security guard's first action should be to:

In the event of a fire alarm, the primary focus should be on ensuring the safety of individuals within the premises and facilitating their evacuation. This action prioritizes human safety, which is of utmost importance during any emergency situation, especially a potential fire. The guard's role includes directing people to exit routes and making sure no one remains in danger.

While it is important to investigate the source of the alarm, that should not come before ensuring that everyone is evacuated safely. Calling security management and accessing fire extinguishers are secondary actions that may take place after confirming that people are safe and out of harm's way. Therefore, the correct action is to ensure safety and assist in evacuations first, reflecting the fundamental duty of a security guard during emergencies.