Final answer:
The step in an arson investigation that entails setting up a command post and safeguarding the crime scene's evidence integrity is known as preservation.
Step-by-step explanation:
The correct step of an arson investigation which involves establishing a command post and ensuring access to a crime scene without disturbing evidence is preservation.
During an arson investigation, it's crucial to preserve the integrity of the crime scene, which includes preventing the contamination of potential evidence. The step known as preservation focuses on protecting the site. It is during this phase that a command post is established to oversee operations and restrict access to authorized personnel only.
This systematic control is essential to maintain a clear record of people who enter and leave the scene, thus ensuring that the evidentiary value is not compromised. Investigators work meticulously to document the scene with photographs and sketches, also collecting any physical evidence that may assist in determining the fire's origin and cause. The overarching goal is to prevent any alterations, removals, or other disturbances to what the fire has left behind before a thorough analysis is conducted.