The function of an egress system is to conduct occupants of a building to a safe place in case of fire or other emergency.
A safe place is usually a public way or other large open space at ground level.
For the occupants of the upper floors of a tall building, or for people who are incapacitated or physically restrained, the safe place may be a fire-protected area of refuge within a building.
M E A C N O S M P O O F N E E N G T R S E S S
Means of Egress
Components of an Egress System
Exit Access – a corridor, an aisle, a path across a room, or a short stair or ramp that conducts the occupants of a building to an exit.
Exit – a protected means of evacuation (door opening, an enclosed and protected exit passageway leading to a door, or an enclosed exit stair or ramp) from an exit access to a safe discharge point, must be of 2 hour construction with self closing doors rated at 1 1/2 hrs.
Exit Discharge – a means (door, protected exit corridor, path across a ground floor vestibule or lobby) of moving from an exit to a safe discharge point (public way or other large open area.)
Two Remote Exits
Most buildings require at least two separate exits. These must be as remote from each other as possible and arranged to minimize the possibility that a single fire or other emergency condition could simultaneously render both exits unsafe or inaccessible. With only minor exceptions, the access path to an exit may not pass through kitchens, restrooms, storerooms, workrooms, bedrooms, hazardous areas, or rooms subject to being locked.
Distance Between Exits
The minimum distance between exits is one-half the diagonal measurement of the building or the space served by the exits. On an open floor, this is measured as a straight-line distance between exits. Where the exits are joined by an exit access corridor that is protected from fire as specified by the building code, this distance is measured along the path through the corridor.
Dead-end pockets in exit access corridors are undesirable, but they are tolerated for most building occupancies within the length restrictions listed in each model code.
General Rule is that a dead-end corridor must be 20’ or less in length.
Maximum Travel Distance
Maximum travel distance to the nearest exit is specified by the code. Travel distance is always measured along the actual path occupants must take to reach an exit. There are two way to measure as shown on the diagram. The code will dictate which way you must measure it.
Doors should always swing in the direction of egress travel in all buildings except single family dwellings and in all rooms except those with fewer than 50 occupants.
Obstructions of the required egress width are allowed as follows:
Half of required width when door is open 90 degrees
7” into the required width of a corridor or aisle when door is fully open
3 ½” into the required width of a stair or stair landing
Even locked, doors along an exit path must be easily openable in the direction of egress travel
Exit access corridors must be enclosed in fire-resistant walls and accessed via fire-resistant doors. One-hour walls with 20-minute doors are required in most buildings.
The simplest exit is a door opening directly from an interior room to a public way, as it might from an exhibition hall, theater or classroom
The most common type of exit is an enclosed stairway. The enclosure must be of 2-hour construction with 1 ½ hour self-closing doors that swing in the direction of egress travel. (In other words, doors must swing into the stairway enclosure except at the level of exit discharge, where they must swing out.) Stairway and landing widths are determined in accordance with the occupant load they serve and are calculated according the guidelines in the prevailing codes.
An exit passageway is a horizontal means of exit travel that is protected from fire in the same manner as an enclosed interior exit stair (2-hour walls, 1 1/2-hour self-closing doors). An exit passageway has several uses: It may be used to preserve the continuity of enclosure for an exit stair whose location shifts laterally as it descends through the building. It may be used to eliminate excessive travel distance to an exit. And it may be used as part of an exit discharge, to connect an enclosed stair to an exterior door.
The widths of passages, doors, landings, and stairs used as exits must be determined in accordance with values given by the various codes.
Misc. Means of Egress Concepts
Smokeproof Enclosure – designed to limit the penetration of smoke and heat from a fire into an exit stairway to such an extent that the stairway is likely to remain usable throughout the course of a fire in a building. It is a place of safe refuge for people unable to use stairs.
Outside Stairways and Fire Escapes – exterior means of egress with either solid treads (outside stairway) or open treads (fire escape), they must meet all the requirements of inside fire stairs
Misc. Means of Egress Concepts
Horizontal Exits – a way of passage through a fire-resistant wall to an area of refuge on the same level in the same building, must have tight fitting, self-closing 1 ½ hour doors
Stair Proportions – Maximum riser height is 7”, minimum tread depth – 11”
Ramp Proportions – 1:8 for general exit ramps, 1:12 for handicapped exit ramps (1:20 is better for handicapped exit ramps)
Means of Egress Problems
Problem #1: Design an exit for a department store basement, sprinklered, dimensions 105’-0” x 292’-6”.
Problem #2: Design the exits for a lecture hall, sprinklered, dimensions 84’-0” x 80’-0”.
Problem #3: Design the exits for a night club, not sprinklered, dimensions 162’-0” x 100’-0”.
Problem #4: Design the exits for a lecture hall, sprinklered, dimensions 63’-0” x 80’-0”.