Components of Means of Egress
Components of Means of Egress
What are the components of a Means of Egress?
So far in this series we introduced what a “Means of Egress” system is, and why it’s important to consider in the context of managing or constructing a building.
But what are the components that make up a Means of Egress? What are we really talking about? That’s what we’re going to cover today.
Means of egress are typically broken down into three components: the exit access, the exit, and the exit discharge. It’s usually presented in this order because before an occupant can exit a building, they have to travel to the exit. That travel is called exit access. Once the occupant has reached the exit, they have left the building or are sufficiently protected from the effects of smoke and fire (more on that technicality later). That is the exit. Once the occupant has exited the building, they need to be able to get safely away from the building, that’s the exit discharge.
This is the order that an occupant would take to exit a building: exit access, exit, then exit discharge. However, it may be more intuitive to first start with identifying what is an exit.
WHAT IS AN EXIT?
So, what is an exit?
In a simple, single-story building at grade level, the exits are the doors to the exterior. Often the building entrance also serves as an exit. For most occupancies, windows (even operable ones) are not considered exits. Generally, a building will have two or more exits, so you can expect to see another exit door to the exterior somewhere in the building and these exit doors are available and accessible to all buildings occupants.
Now that we’ve identified where the exits are, we need to analyze how an occupant can get to those exits. This again is the exit access – the path of travel an occupant takes until they reach an exit.
The specific requirements for how to design these exit access paths is discussed in a further video. What’s important to note is there are numerous requirements related to exit access paths, such as the maximum an occupant is permitted to travel until they have reached an exit, minimizing dead ends, and minimizing the distance an occupant has to travel until they have a choice of two separate exit paths.
The basic premise is that occupants don’t have to travel too far to exit the building and that their pathway is arranged such that a fire wouldn’t prevent them from exiting the building.
Finally, the exit discharge.
Once an occupant has exited the building, they must be able to safety get far enough away from the building, which, as you remember is on fire. The basic premise is that occupants are not restricted in being able to continue to get away from the building, until they have reached the public way.
So, what are the different types of exits?
Now, getting back to exits, there are more types of exits than just doors to the exterior.
One of the most prominent examples are stairs. Can a stair be an exit? Yes. Are all stairs exits? Not necessarily.
The most common type of stair that functions as an exit is called an “interior exit stair.” This might also be called an “exit stair,” a fire stair,” a “stair tower,” or a “smokeproof stair.” However, it should be correctly called an interior exit stair because there are other types of stairs within the context of the building code which serve other functions, some of which are not exits or means of egress at all.
One of the key features of an interior exit stair is that it is enclosed in fire-resistance-rated shaft construction and continuous to where it discharges directly to the exterior. Meaning, that once an occupant has entered the stair, they have essentially “exited” the building because they are safe from the effects of fire. Even if they are on the 40th story of a building more than 400 feet above ground, they have “exited.” We will get into more detail later about the specifics of interior exit stairs and what other types of stairs are permitted for a means of egress. [08b]
When we think about designing stairs, we are concerned about critical dimensions that affect occupant movement. Measurements like stair width, stair tread, stair rise, handrails, and size of stair landings all affect how people are able to move through the stair.
Another common type of exit is an exit passageway.
This is sometimes called an “exit corridor.”
These are enclosed in fire-resistance-rated construction and there are severe limitations on what items are permitted to be located within it. You can think of it as a “concrete tunnel” although it does not have to be constructed of concrete, it is protected on all sides with substantial construction.
These essentially “extend” an exit. This could be an exit passageway which extends an exit and brings an exterior door or door to an interior exit stair closer to an occupant. This could also be used in a situation where travel distance to an exit is beyond the allowable limit – by “extending” the exit or bringing it closer to an occupant, this effectively reduces the travel distance to within the allowable limit.
When we design exit passageways, we’re generally concerned about the level of fire-resistance-rating, the width of the exit passageway, its continuity to an exterior door, and preventing piping and HVAC systems from passing through the passageway.
Another type of exit is a horizontal exit.
These are quite common in hospitals.
A horizontal exit essentially subdivides the floor of a building into two halves with a 2-hour rated fire barrier. When a fire occurs on one half of the building, [10b] the occupants on the fire side are able to relocate to the non-fire side.
By relocating, these occupants have “exited” the building, in that they are now safe from the effects of fire. There are limitations on the use of horizontal exits which will be discussed in later videos.
There are numerous other components and terminology which we will introduce in more detail in subsequent videos.
So, what are components of a Means of Egress?
While there are many parts to a means of egress, they generally fall into one of three categories: exit access (how does an occupant get to an exit), exit (how does an occupant leave a building or get to a safe place away from the fire) and exit discharge (once an occupant has left the building, how do they get away from it?).
In our next segment, we’re going to look into the roles behind means of egress. Who is responsible for the evaluation? Who commonly performs and reviews egress? What about design and then the life of building? We’ll cover that next.
I’m Steven Barrett, this is MeyerFire University.
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