Final answer:
A secure fire scene requires a recognizable perimeter with someone assigned to maintain it, ensuring the area is safe and evidence is preserved.
Step-by-step explanation:
For a fire scene to be secure, it crucially requires: a recognizable perimeter with someone assigned to maintain the perimeter. While it may involve a specialized team or law enforcement personnel, and perimeters may be marked differently for various levels of access, what is essential is the establishment and maintenance of a clearly defined perimeter. This ensures that the area is secure and safe for both the first responders and the public, reducing the risk of contamination or destruction of potential evidence and keeping untrained individuals at a safe distance from hazards. In contrast, the need for perimeter markings every ten feet is more a matter of practicality and does not inherently determine the security of the scene.