Why is smoke in the stairs considered a major threat during a fire?

Smoke in the stairs during a fire is considered a major threat primarily because it reduces visibility and causes disorientation. In emergency situations, clear escape routes are critical for ensuring the safe evacuation of occupants. When smoke fills the stairwells, it significantly diminishes visibility, making it difficult for individuals to see where they are going. This lack of visibility can lead to confusion, increased anxiety, and poor decision-making as people attempt to navigate their escape routes.

Moreover, disorientation from smoke can result in individuals becoming lost or trapped, preventing them from reaching safety. The combination of smoke obscuring vision and the chaotic environment can escalate the dangers associated with a fire emergency. Thus, the presence of smoke in the stairs poses an immediate risk to life by obstructing safe egress routes for building occupants, which emphasizes the critical nature of fire and evacuation planning in structures.