Jonathan Ochshorn
Refer to Chapter 10, IBC 2012 and "Egress" chapter of The Architect's Studio Companion, by Allen and Iano (course reserve).
Means of egress is continuous and unobstructed path of travel from any point in a building to a public way. It consists of 3 basic parts:
exit access (including corridors)
exit (basically the enclosed stair)
exit discharge (which leads to the public way)
Review:
Table 1020.1 Corridor Fire-resistance rating
Table 1017.2 Exit access travel distance
There are no maximum distances between exits, except as determined by maximum exit access travel distances (which only require that any space be limited in distance from ANY ONE exit). It's also possible in some cases to measure exit access distance down an unenclosed (exit access) stair!
See: 2012 IBC Hole in Floor Calculator and explanation
Table 1006.2.1 Common path of egress travel (Scroll down to Table 1006.2.1, 2020 NYS Building Code, based on 2018 IBC)
Section 1020.4 Dead-end corridors (Scroll down to Sec. 1020.4, 2020 NYS Building Code, based on the 2018 IBC)
Notes on egress:
continuity: no interruption allowed (check out interrupted stair in Fine Arts Library...)
generally no elevators* or escalators allowed (except as "accessible means of egress" in some circumstances): if unsprinklered, such elevator access must be from "area of refuge" or "horizontal exit."
"The Fire, Buildings and City Planning Departments [in NYC] are writing rules to govern what are called occupant-evacuation elevators — cars that can, in special circumstances, be used to move people down in an emergency."
"That would upend decades of codes and practices based on the notion that elevators are perilous and undependable in fires or other emergencies. Experts who have spent years studying building evacuations believe that approach has become outmoded and is in itself potentially dangerous as extremely tall skyscrapers increasingly pierce the New York skyline."
"Some requirements that the city is expected to impose for evacuation elevators have been anticipated in elevators at 3 and 4 World Trade Center. The floors in front of the elevator doors are raised slightly, to protect the hoist ways from water from sprinklers or firefighters' hoses. The capacity of the emergency generators was increased to provide uninterrupted service to those cars. The cars stop at every floor. Hoist ways are within cores protected by reinforced concrete walls at least 18 inches thick." [NY Times, March 18, 2015]
"common path of travel" (similar to so-called dead-end corridors, but including the distance within a room or space). Dead-end corridors are legal, but limited in length; they should be avoided where possible. The common path of egress travel may or may not include a dead-end corridor.
provide guards where a floor surface is more than 30" above floor below; such guard rails are 42" high (except 36" in R-3 occupancies), and configured so that a 4"-diameter sphere cannot pass through.
need 2 means of egress for most buildings (1 for very low occupancies; 3 for 501-1000 occupants; 4 for more than 1000 occupants). Compute number of occupants by dividing floor area by "design occupant load" in code.
spaces with one means of egress permitted generally have a maximum occupancy of 49, except that number is only 3 for H-1, H-2, H-3; and 10 for H-4, H-5, I-1, I-3, I-4, R; and 29 for S occupancies)
buildings allowed one means of egress have similar occupant limits but also have maximum numbers of stories (generally 1 story maximum, except 2 for R-2 occupancies, 3 if sprinklered); plus maximum travel distances to exits.
so-called horizontal exits are generally permitted for up to 1/2 of required exits; except 100% can be horizontal exits in I-3 occupancies (jails, etc.), presumably to keep occupants both safe and incarcerated. Doors must open in direction of egress. A fire wall or barrier with a minimum 2-hour fire-resistive rating must separate the two spaces or buildings connected by the horizontal exit.
where two exits are required from a space or building floor, the two exits must be separated by a minimum distance determined by multiplying the diagonal dimension of the space (or building) by 1/3 (if sprinklered) or 1/2 (in unsprinklered).
In the example shown above, the 60' diagonal distance requires an exit separation distance of at least 20" (if sprinklered) or 30' (if unsprinklered). Note that, in general, two exits are needed only where the occupancy is 50 or more.
typical minimum width for corridors and exit stairs: The width of stairways shall be determined as specified in Section 1011, but such width shall not be less than 44 inches. Except that accessible means of egress stairways in non-sprinklered buildings, in general, need to be 48 inches wide. An area of refuge also needs to be provided in such a stairway (in a non-sprinklered building).
typical minimum door size is 36" (which is also the most common door size for both egress and accessibility).
doors can swing into corridors, landings, or aisles as long as no more than half of the required width is blocked; when fully open, the door should not block more than 7" of the aisle.
typical egress stairs are proportioned with maximum 7" riser height and minimum 11" tread width.
techniques to keep smoke out of egress stairs: smokeproof enclosures can be exterior "balconies" separating the entrance to the stair from the occupied space and providing a means for smoke to be exhausted to the exterior before entering an enclosed stair; or they can use ventilation ducts provided for that purpose; or, in certain cases; stairs can be mechanically pressurized so that smoke doesn't enter.
Here's a short (2 minute) video showing some egress and guard rail issues in E. Sibley Hall, Cornell Univeristy:
Disclaimer: Students are responsible for material presented in class, and required material described on course outline. These notes are provided as a tentative outline of material intended to be presented in lectures only; they may not cover all material, and they may contain information not actually presented. Notes may be updated each year, and may or may not apply to non-current versions of course.
first posted Sept. 11, 2012 | last updated: Oct. 5, 2021
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