Egress is defined as “the action of going out of or leaving a place”.
Egress is a major component of safety features in the building, and has an entire chapter devoted to it in the IBC (International Building Code).
This post will cover some of the main concepts that the code uses to ensure a safe way for occupants to exit a building in case of an emergency, fire, etc…
Occupant Loads
You’ve probably seen a sign posted in some rooms/ buildings saying something like ” no more than 155 persons in the space”. This isn’t an arbitrary number. The code has calculated “occupant load factors” (OLF) for different uses of spaces. Table 1004.1.2 is the place this is found.
For instance, if a space is used as an office, that is calculated at a rate of 100 sf per person. So If you have 1,000 sf office room, the occupant load would be 10 people (1,000/100=10).
A 1,000 sf room used for a concert type setting with standing room only would be calculated at a different rate of 5 sf per person. That would result in a much higher occupant load of 200 people (1,000/5=200)
Egress Sizing
We use the number of occupants serving a stair or hall to size how wide it needs to be. Stairs use the multiplier or .3 inches per occupant. All other egress components, such as halls and doorways use the multiplier .2 inches per occupant.
So, for instance, if you have 300 occupants, a total door width of 60″ (300x.2=60) would be required. A space serving this many occupants would certainly need to have at least 2 doors, so (2) 36″ doors would meet the requirement.
In most cases, a 36″ wide door minimum is required. A 36″ wide stair is the code minimum in most cases. A 36″ wide corridor is the code minimum, but 42″ is more often required for various reasons.
Number of exits & exiting configuration
The column in the above chart called “maximum occupant load of space” tells use the number of occupants that trigger the need to have more than 1 exit to a space. So, for instance, if you have 48 occupants in an office room, 1 exit is ok. If there’s 52 occupants, you must have 2 separate exits.
When 2 exits are required from a space, room, or building, they must be separated by 1/3 the diagonal distance of the space, room, or building being served (in a sprinklered building). In an unsprinklered building, they must be separated by 1/2 the diagonal distance of the space, room or building being served. Please see the diagram below.
The Maximum Common Path Of Egress Travel (CPET) is another complex yet important concept. The CPET is the distance that one must travel before reaching a point that they have 2 separate options of paths to take to egress the building.
So, even if an office room is 40 occupants, but from the most remote corner of the room to the door is over 100′, this one door will not suffice, and a second separate exit must be provided.
Doors & Everything Else
The code has egress requirements for doors. In many cases, doors must swing in the direction of travel, but in some cases (usually under 50 occupants & depending on occpancy) the doors may swing in. You will usually see inswinging doors into smaller rooms within buildings, but main exterior doors or doors into stairwells will often swing out.
Emergency egress lighting that turns on during a power loss must be provided along the egress path. These are often attached to exit signs, or also separate.
Exit signs are an important feature to building egress. They are required in may situations, but there are several exceptions, the main one being that they are not required for rooms or areas needing only 1 exit.
Theres several other concepts of egress that may apply to your building. Accessibility within the IBC & ADA should also be considered. If there are differences between the 2, the more stringent rule will prevail. If you’d like to know more, please consult chapter 10 of the IBC, or seek help from a design professional.
Thanks!
