Final answer:
Narrow and small fire plumes initially produce an upward flow that is laminar, meaning it is smooth and displays less resistance, but may become turbulent as the plume rises and conditions change.
Step-by-step explanation:
When considering fire plumes where the heated region is small and the plume is narrow, the upward flow of the smoke starts as laminar, which is a smooth and orderly flow. As the heated gases rise and cool, they may become unstable, leading to the formation of swirls and eddies, which is characteristic of turbulent flow. Observations show that smoke rises more rapidly when the flow is laminar because turbulent flow creates more resistance to motion. In the specific conditions of a small and narrow heated region, the flow is more likely to start as laminar due to the smaller scale of the objects involved and the lower velocity as compared to turbulent requirements. However, as the plume rises and if the conditions permit in terms of velocity and scale, the flow may transition to turbulent flow.