Interior exit stairways serving floors over how many feet above the lowest level of fire department access must be smokeproof enclosures?

The requirement for interior exit stairways to be designed as smokeproof enclosures when serving floors above a specified height is primarily driven by the need to enhance safety during emergencies, particularly in terms of fire protection and evacuation routes. In many building codes, including those governed by the International Building Code (IBC), the threshold for smokeproof enclosures is set at 75 feet above the lowest level of fire department access.

When the height reaches 75 feet or more, the potential for smoke and heat to accumulate in stairwells increases significantly, thereby compromising the safety of occupants who may need to use these exits during a fire. Smokeproof enclosures help to maintain clearer evacuation routes by preventing smoke from infiltrating the stairwell, allowing for a safer descent to the ground level.

While there are additional measures for buildings exceeding greater heights, the 75-foot criterion serves as a key threshold in ensuring adequate protection for occupants. This standard reflects the concern for occupant safety and the need for effective evacuation solutions in taller structures.