Final answer:
A chief officer may assume a role other than Incident Commander (IC) on-scene when the original IC has made reasonable progress toward stabilization.
Step-by-step explanation:
When a chief officer may assume a role other than Incident Commander (IC) on-scene is when the original IC has made reasonable progress toward stabilization. This means that if the original IC has successfully addressed the immediate needs of the incident and has made significant progress towards controlling the situation, they may hand over the role to another chief officer to continue managing the incident. However, it is important for the original IC to ensure that the new IC is capable and qualified to take on the role.