Part 1 – What is a Horizontal Exit?
By Steven Dannaway, PE, DBIA – The Horizontal Exit can be a useful element in the design of a building’s Means of Egress system; however, the Horizontal Exit seems to be one of the least understood tools by both building designers and by enforcing authorities. Part 1 of this article reviews the basic concept of a Horizontal Exit and how the Horizontal Exit might be used on a project. Code references are to the 2021 Edition of the International Building Code (IBC).
IBC Chapter 2 defines a Horizontal Exit as: “An Exit component consisting of fire-resistance-rated construction and opening protectives intended to compartmentalize portions of a building thereby creating refuge areas that afford safety from the fire and smoke from the area of fire origin.”
Horizontal Exits are regulated by IBC Section 1026. The Horizontal Exit is comprised of a two-hour fire-resistance-rated wall that sub-divides a building into at least two fire compartments, providing an effective barrier against fire/smoke spread between fire compartments. The Horizontal Exit concept allows for occupants to egress out of the compartment of fire origin during a fire emergency, across the two-hour Horizontal Exit barrier, and into the adjoining compartment. The other side of the Horizontal Exit provides a refuge area that allows the occupants to congregate in a safe place while they continue to evacuate the fire floor in an orderly fashion.
Exit, Exit Access, or Exit Discharge?
The Horizontal Exit is defined by the IBC as part of the exit stage of the Means of Egress. This is a crucial point of understanding. The Horizontal Exit is not part of the Exit Access or Exit Discharge portions of the Means of Egress.
- Occupants approaching a Horizontal Exit are in their Exit Access stage of the egress system.
- Occupants pass through the Exit stage of the egress system when they egress through the Horizontal Exit
- Downstream of the Horizontal Exit, occupants are in the Exit Discharge stage of the egress system once they exit through the Horizontal Exit doors and are in the refuge area fire compartment.
This understanding is important because a proper definition of the various stages of the Means of Egress is necessary in order to apply the correct code requirements of IBC Chapter 10.
Example of Horizontal Exit Application
The Horizontal Exit can be applied in all occupancies but can especially serve as a valuable tool in Group I-2 (hospital) and Group I-3 (detention/correctional facilities) occupancies. The Horizontal Exiting concept supports the defend-in-place egress strategy that these institutional occupancies employ, relying on horizontal relocation of occupants out of the fire zone and into an adjacent compartment.
These occupancies already require sub-division of the floor by smoke barriers to form smoke compartments; therefore, one or more horizontal exits can be incorporated into the design to align with the routing of a smoke barrier (increase a one-hour smoke barrier to a two-hour fire/smoke barrier). These occupancies are also subject to stringent exit access travel distance requirements (200 ft. maximum to an exit). A horizontal exit door can serve the same purpose as an exit door to a stairway or an exterior exit door. Exit access travel distance measurements (IBC 1017) can be terminated at the horizontal exit door. The horizontal exit can also increase the exit capacity (IBC 1005) of a story.
In certain projects, it may be advantageous to design a horizontal exit in lieu of introducing additional exit stairways into the building, as the horizontal exit can also satisfy exit access travel distance and contribute to the floor’s exit capacity in the same manner as an exit stairway would. Note: Horizontal Exits may be used in all occupancies; however, there are specific code requirements that need to be incorporated into the design that may lend the horizontal exit to be a better solution in some buildings than others.
The figure below is from a hospital tower in Southern California, depicting a Horizontal Exit that sub-divides a patient floor. The horizontal exit aligns with one of the smoke barriers that was already provided as a smoke compartment separation.