Final answer:
In an emergency, first responders must prioritize preserving life and then secure the scene for investigation. Safety of individuals comes first, followed by securing the scene to facilitate a thorough investigation and prevent evidence contamination.
Step-by-step explanation:
When responding to an initial call for service, the priorities for a first responder are well established. As outlined in your question, the first thing to do is to always preserve life first, and then work to secure the scene for investigation. Preserving life entails attending to individuals who may be injured or at risk, ensuring that they receive immediate medical attention. Once the safety of all individuals is assured, securing the scene becomes the focus to prevent contamination of evidence or further harm and to ensure a thorough investigation can take place.
In the scenario of a building fire, for example, firefighters will prioritize rescuing any victims and ensuring everyone's safety before they turn to investigating the cause of the fire and preventing its spread. Similarly, if an ambulance arrives at the scene, bystanders should stop moving and become stationary until it passes by, which is much safer than attempting to run toward or alongside the ambulance, which can create additional risks and chaos. Understanding the timelines of such emergencies is crucial for effective response and investigation.