When an exit serves multiple stories, what specifies the required egress capacity?

The required egress capacity when an exit serves multiple stories is specified by the capacity of the story with the highest occupant load. This is crucial for ensuring that in the event of an emergency, the exit can accommodate the maximum number of occupants it would need to serve at any point in time.

Buildings are designed with life safety in mind, and during an evacuation, the flow of people into the exit must not exceed its capacity. If the egress capacity were based on the combined total of all stories or simply the level of exit discharge, it could lead to situations where the exit is overwhelmed by occupants from the story that has the highest number of people at that time, resulting in dangerous bottlenecks.

By focusing on the story with the highest occupant load, fire safety codes ensure that the design of the exit healthily supports the worst-case scenario for egress during emergencies. This principle helps reinforce safety protocols to minimize risks during evacuations, aiming to prevent injuries or fatalities due to overcrowded exits.