Final answer:
The best approach for a security guard when an alarm goes off is to follow the site's specific post order procedures, as these are designed to address the unique needs and potential dangers of the site.
Step-by-step explanation:
The best approach for a security guard to take when an intrusion alarm goes off is to follow whatever procedures for alarm response are set out in the post orders for that site (Option E). This is because each site may have specific protocols tailored to its particular security needs, which might involve assessing the situation with caution, contacting law enforcement, or any combination of measured responses. Proceeding quickly or slowly to investigate, or calling the police immediately are all actions that may or may not be appropriate depending on the context and the established post orders. It is critical that a security guard is trained to handle such situations with the understanding that there could be an uncertainty over whether a serious fire or hazard awaits after an alarm, which could present a potential for extreme physical danger. Making judgment calls informed by experience, observations, and the specific post orders helps ensure the safety of the property, its inhabitants, and the security personnel themselves.