Download florida building code bct 1760

FLORIDA BUILDING CODE
BCT 1760
CHAPTER 4
MEANS OF EGRESS
MICHAEL KNOTEK
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MEANS OF EGRESS
ACCESSIBLE MEANS OF EGRESS
A continuous and unobstructed way of egress travel from any point in a building or facility that
provides an accessible route to an area of refuge, a horizontal exit or a public way.
GENERAL
Perhaps the best way to analyze a means of egress system in a building is to travel or trace it,
component by component, from the farthest point in the building to safety.
And that’s what means of egress is all about: a continuous and untrammeled path of safety from any
and all points in a building to the street or public way.
The means of egress must have continuity; exit access to exit to the exit discharge for example.
And it must be without obstruction in the minimum permitted configuration.
By obstruction, we not only mean projections into the required size but also other obstructing
pitfalls such as too steep ramps or stairs, door swinging into the exit path, dead end corridors,
head-bashing stairway soffits, etc.
If you, as a designer, have difficulty following a means of egress path, you may be uneasily
assured that a typical occupant in the building would be overwhelmingly at a loss in tense
situations.
EXAMPLE #1
TWO STORY OFFICE BUILDING
EXAMPLE #1 TRACING THE MEANS OF EGRESS - COMPONENT BY
COMPONENT
Every building level is required to have a means of egress
Multiple means of egress may also be required, depending on the occupant load, height, and other
factors.
Let’s examine a two-story office building of a regular 50 feet wide by 30 feet deep for a total of 3,000
square feet, 1,500 square feet per floor
In computing the occupant load, we may consider it to be the area of the building divided by the
square feet per occupant factor found in Chapter 10.
Floor area/sq.ft. per occupant = Occupant load
3,000/100 = 30 occupants calculated for the entire building, 15 per floor
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50 ft.
2 STORY OFFICE
BUILDING - 30’ x 50’
(3,000 SQ.FT. OR
1,500 SQ.FT. PER
FLOOR
30 ft.
MAXIMUM FLOR AREA ALLOWANCES PER OCCUPANTS
DEFINITIONS
FLOOR AREA, GROSS: The floor area within the inside perimeter of the exterior walls of the building
under consideration, exclusive of vent shafts and courts, without deduction for corridors, stairways,
closets, the thickness of interior walls, columns or other features.
The gross floor area shall not include shafts with no openings or interior courts
FLOOR AREA, NET: The actual occupied area not including unoccupied accessory areas such as
corridors, stairways, toilet rooms, mechanical rooms and closets
EXAMPLE #1
To determine the number of exits from each level, the Table in Chapter 10 must be used.
Because this is a Group B occupancy, we find that two exits are required when the occupant loads
exceeds 50 or if the common path of egress travel exceeds the limits found in the code.
The common path of egress travel limit is 75 feet for an office. Since our building is only 30’ x
50’, it is unlikely that our building would exceed the travel limits.
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BUILDINGS WITH ONE EXIT
EXAMPLE #1
To determine if an office building with one exit only is permissible, we would turn to Section “Buildings
with one exit”
Our two-story office building has an occupant load per floor of 15 and does not exceed the travel limit
of 75 feet.
Using the Table, we find that a Group B occupancy can have up to two stories above the grade
plane, a maximum of 30 occupants per floor, and a travel distance that cannot exceed 75 feet
We comply therefore; we can use just one exit from the first and from the second floors
Now what about some of the elements of the means of egress system?
These are typically doors, stairways, ramps, and corridors to name a few.
Every door in the means of egress in our office must comply with Chapter 10, excluding doors in
small closets.
They are not part of the means of egress system
Doorway size is the first consideration.
The real concern is the passage through the opening once the door is opened
The code requires a minimum clear opening of 32” of the doorway itself. This will allow a nominal
passage through the opening
The height per code is 80” minimum or 6’8”.
The type of door required is a side-hinged, swinging door.
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This is the type most familiar to people in general, although a few other types of doors can be
used
Most of these doors should swing in the direction of egress travel
However, the code does not require this until the occupant load served reaches 50 or more
In our case, it is not a requirement, because we have 15 occupants per floor.
Nevertheless, it remains a good idea
A landing must be provided on each side of the doors
Chapter 10 states that a landing must be level on the interior side and can have a nominal slope on
the exterior side, to promote runoff of storm water
There size must equal the width of the door and not less than 44 inches in length.
Thresholds cannot exceed ½ of an inch in our building with beveled edges
One of the most important considerations is whether or not our doors can have a lock or latch.
We are concern with the egress of the occupants, so this only applies to the interior side of our doors.
The egress side of our doors must be operable without the use of a key or special knowledge
or effort.
Many designers use panic hardware, but in our case this is not necessarily required
The last exit element of our building will be stairway from the second floor.
This is an important element because of the potential for serious accidents.
Chapter 10 of the code contains the first aspect: the width of the stairs.
The minimum width is 44 inches to begin with.
However, there are exceptions
The first exception applies to our building. That is, where stairways serve an occupant
load of 50 or less, the width can be reduced to 36 inches
Our building has an occupant load of 15 that will be served by the stairway, so this
exception can be used
The next aspect is the headroom over the stairway.
There have been cases of people who have been severely injured because of projecting
elements such as beams over stairways.
The minimum height is 80 inches or 6’8”
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A controversial item is the rise and run of the stairs.
The rise of the stairs tread can be between 4 inches and 7 inches with the run, or horizontal
portion, required to be 11 inches minimum.
This item has seen considerable debate over the years in the code development hearings, with these
dimensions being the continuing outcome
At a minimum, a stairway needs two landings: one at the top and one at the bottom.
This is dependent on the space allotted to the stairway itself and the vertical distance that the
stairway rises
If the stairway rises greater than 12 feet from bottom to top, then an intermediate
landing would be required
This is to allow the occupants using the stairs to rest and get back into the rhythm of
climbing the stairway
Stairways need to be constructed of materials consistent with the type of construction of the building
they serve
Also, the walking surface of the stairways needs to be relatively level with only a nominal slope to
allow proper drainage of water
The last element of a stairway is the handrail assembly
The handrail assembly serves two functions:
One is to prevent the occupants from falling to the level below and;
The other is to assist in the climbing of the stairway itself
There is no way to prevent all falls; however, keeping children from easily passing through the
handrail and providing enough height to keep them on the stairs is a concern
The maximum spacing allowed for the verticals in a handrail or guardrail is 4”
The height of a handrail is between 34 to 38 inches in an intended safeguard to keep the user
from falling over the guard in the event of a trip
The grasp ability of the top of the handrail is vital, especially for occupants who trip while progressing
down the stairway.
It allows them to get a “power” grip to prevent them from falling farther down the stairway
The outside cross-sectional diameter of the handrail is required to be between 1 ¼ and 2 inches
The handrail can have other than a simple circular shape but must meet a perimeter dimension of
between 4 and 6 ¼ inches
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EXAMPLE #2
THREE-STORY APARTMENT BUILDING
EXAMPLE #2
Let us consider a three-story apartment building.
Each story is identical
There is a central corridor running the length of the building, and each dwelling unit’s “front door”
opens onto the corridor
There is a stairway at each end of the corridor
There are eight dwelling units per floor, for a total of 24 dwelling units for the building
Each dwelling unit has a floor area of 750 square feet and each floor has 6,000 sq.ft. (8 x 750 sq.ft.)
in dwelling units plus 1,000 square feet in corridors, etc.
Thus, each story has 7,000 sq.ft. of area (6,000 + 1,000), and the total area for the building is 21,000
sq.ft. (3 X 7,000)
Apartments – 750 sq.ft. each
8 Units per Floor
1
Corridor – 1,000 sq.ft.
5
2
6
3
4
7
8
stairway
3 STORY APARTMENT BUILDING
EXAMPLE #2
We will assume that the location on property, occupancy, type of construction and other standard
requirements are met.
First, compute the occupant load of each story
area
Sq.ft. per occupant = Occupant load
The area per occupant is 200 sq.ft.
7,000
200 = 35 persons per floor
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MAXIMUM FLOR AREA ALLOWANCES PER OCCUPANTS
EXAMPLE #2
If we were to trace the path of egress from the third story we would find the following:
1. Dwelling units through exit door to exit corridor
2. Exit corridor to exit stairway (either end of corridor)
3. Exit stairway to exit door
4. Exit door to exterior of building
5. Exterior of building to street or public way
The following is a step by step analysis:
The occupant load of an individual dwelling unit is 3.74 (750/200) or four persons.
With the occupant load being less than 10, the means of egress from any dwelling unit to the
common corridor need be only one.
Thus, the front door into the corridor is sufficient
However, secondary emergency escape from bedrooms to the out of doors still must be provided
The occupant load` of any story is 35, and being in excess of 10, the corridor (walls and ceiling) must
be of one hour fire-resistive construction.
Penetrations through the fire resistive construction must have opening protection.
Example: The dwelling unit exit doors must be at least 20-minute tight fitting, smoke and draft control
labeled assemblies and are required to have automatic or self-closing devices and be gasket
Two exits are required from the second and third floor
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When two exits or exit access doorways are needed, they must be located in such a manner that an
occupant may go in either direction in the corridor to an exit
Thus, in this example, one exit at one end of the corridor and the other exit at the other end of the
corridor comply
These exits at the corridor ends are the stairways.
Therefore in this example, the exit corridors are` continuous until egress is provided from the building
without interruption from intervening rooms
BUILDINGS WITH ONE EXIT
EXAMPLE #2
The occupant load does exceed nine persons but is less than 50; hence, the corridor is required to be
at least 36 inches wide, and fully opened doors or other projections may not reduce the width to less
than 29 inches (36” – 7” = 29”)
A door in any position may not reduce the required corridor width by less than half. This may be
handled in at least one of three ways
Where the occupant load of space is less than 50, the door may hinged to swing into the exited space
rather than into the corridor
The door may be recessed into an alcove of the space a distance such that its swing path does not
extend beyond one half of the required corridor width and that when fully opened it does not project
more than 7” into the required width
The corridor may be widened to accommodate door swing with one-half width clearance.
Required width
36 inches
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One-half required width
Assumed door width
Adjusted corridor width
18 inches
36 inches
54 inches
When an interior stairway serves less than 4 stories, it is required to be an exit enclosure.
In our example the stairway shaft must be isolated from the rest of the building with one-hour fireresistance rated construction
The shaft may have no communicating openings with the rest of the building except the exit doors
leading from the corridor, and these must be rated one-hour fire-resistive opening protection with
smoke-activated automatic or self-closing hardware
The door must have a special label that shows the maximum transmitted temperature end point is not
to exceed 45050F above ambient at the end of 30 minute of fire exposure
This is to prevent the occupants from becoming exposed to serve heat as` they flee the building using
the exit enclosures
Based upon an occupant load of 35 for each story, the minimum width of the stairs is determined from
Chapter 10, and it is assumed that the second story exits to grade on dependently of the stair
enclosures.
This assumption is valid, as most multistory buildings provide for grade-level existing directly to grade
without reliance upon the stair enclosure
Thus, the maximum occupant load served by the stair enclosure is 35, and as this is less than 50, the
stairs width may be 36”.
The pitch of the stairs must not be greater than 7 inch riser height or less than 11 inch tread width
The minimum rise is 4”
Handrails must be provided on both sides of the stairway with the height and projection restrictions
per example 1
A long rise of stairs, without interruption, can be rhythmically hypnotizing and therefore hazardous,
causing the pedestrian to tumble.
It is significant that where the vertical dimension (height) exceed 12’, a landing must be provided at
least 12 foot vertical intervals
Because of limited horizontal space available, you would expect to find a landing at midpoint between
floors as well as at each floor level
The width of the landing is required to be no less than the required width of the stairway or the width
of the door.
In our example that is 36”
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The length of the landing at the door, in the direction of travel, should not be less than the width of the
stairway served.
The landing also need not exceed 48”
At the main entrance (exit) of the building you would have a foyer or lobby
This space is no less a part of the egress system and must also comply with the requirements for
width, fire isolation, and opening protection as a corridor
If an exit terminates in the rear yard, for example, the escape responsibility does not end there,
because this is not a public way but more nearly resembles an exit court
One side yard of the building of the building could be a continuation of the exit court to the public way,
provided
The capacity of the exits being served is maintained
The yard is unobstructed to a height of 7’; and
If the yard is less than 10’ wide, wall openings with 10’ vertically of the yard grade are provided with
three-fourths-hour fire protection and the wall is one-hour fire-resistive construction
The exit access (the corridor and the stairway) must be illuminated to show the way to a safe means
of egress.
These lights may be on the “house” circuit because the stories required two or more exits
Because two exits are required from top and bottom, exit signs are required.
The graphics, illumination, and the alternate power source shall meet the minimums.
EXAMPLE #3
FOOD MARKET
EXAMPLE #3
A food market, whether it’s Mom & Pop’s Neighborhood Greengrocer or the A & P’s Regional
Shopping Center, has certain features in common:
A retail sales area consisting of display cases and aisles in between
A stock storage and service area
A check-out or cash register counter location
For a typical one-story example:
Sales area
Storage area
50,000 square feet
5,000 square feet
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Total area
55,000 square feet
Based on 30 square feet per occupant, the sales (mercantile) area has an occupant load of:
50,000 = 1,667 persons
30
Based on 500 square feet available per person the storage area has an occupant load of:
5,000 = 10 persons
500
The total occupant load for the market is:
Sales
Storage
1,667
10
1,677 persons
Considering the storage area first, only one exit is required because the occupant load does not
exceed 30 persons
The exit would probably be a door to the exterior
The occupant load is less than 50 persons, and therefore the door may be hinged to swing in or out.
The storage areas of shopping centers frequently have sliding or overhead doors to serve trucks
discharging stock or loading discard.
Doors, when serving an occupant load at 10 or more, other than hinged ones, shall not be considered
to be complying, and the required exit doors would have to be furnished in addition to the specially
mounted doors.
A pedestrian door penetrating such a special door may satisfy exit door requirements, provided it
meets minimum size and hardware requirements and the floor and landing are not more than ½”
lower than the threshold of the doorway
Now the sales area, we considered the floor area for calculating occupant load from wall to wall
without consideration for display cases, shelving, and the rest.
Although it is true that people will not occupy the same space as a display of Frosted Flakes, we have
no way of predicting or projecting the open floor space that may be occupied from day to day, week to
week, and mouth to mouth
Furthermore, on spectacular sales days, you would be hard put to find 30 square feet available to
each occupant in the aisles, let alone the occupied displays
The occupant load of the sales area has been computed to be 1,667 persons and, being in excess of
1,000, four exits are required
The four exits must be reasonable distance apart around the room; for example, one in each of the
four walls.
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The required egress width is derived as follows:
0.15 X occupant load = total width of all exits
Thus,
0.15 X 1,667 = 250”, total width or 20.84’
And,
20.84 = 5.21’
4
Each exit then must have a minimum total opening width of 6’
Two 3’ single doors = 6’ at each exit location would be satisfactory
The market under consideration has an occupant load exceeding 50; therefore, the doors must be
hinged to swing out.
Slide bolts, whether surface mounted or recessed, may not be used to lock the required exit doors,
nor most locking hardware be used that would require special knowledge or a key of any sort to be
open
Provided the doors remain open during business hours, is so identified with a sign, and is approved,
special hardware may be used on the main exit
Panic hardware is not required in our market, because it is not a high hazard, school, or assembly
occupancy
Exit path lighting is required separate sources of power
Exit signs are required and must be illuminated by separate sources of power
The separate source could be either from storage batteries or an on-site generator and must be
hooked to one of the 15-watt lamps
You would expect the market to be a maze of display cases separated by passageway aisles.
In a panic situation, exiting from the aisles can become quite forbidding.
The aisles themselves must be adequate width to provide adequate egress in spite of shopping carts,
children, and shoppers.
Not infrequently, one of the exit doors may be proposed for the wall separating the sales from the
storage area.
In addition to the fire separation requirements of the door, the exit door must have continuity
Such an exit door may not open indiscriminately into the storage area but must clearly lead to safety
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The storage area is of a higher order of hazard than the sales area and requires a separation
between the two; yet each is classified group M occupancy
Therefore, to isolate this exit way from the storage by requiring a corridor leading to the exterior to
intercept the exit access door from the sales area
Of course, as an alternate to the corridor, proper egress from the retail sales area could be provided
by placing an exit door that goes directly to the exterior
Sometimes, a well-defined and maintained aisle from the sales exit access doors through the storage
area to the exterior wall exit door seeks to serve the intent of direct, obvious, and unobstructed
access to an exit.
What determines a well-defined and maintained aisle?
Two lines, painted on the floor, 44” apart
A fence on each side with a 44” open space
Stacked merchandise with 44” aisle between
Exiting is exiting, and storage is storage, and we cannot have it both ways except under the best
conditions of housekeeping
Because our exit will usually serve more than 30 persons, we conclude that if a corridor is used, it will
require that the walls and ceilings be of not less than one-hour fire-resistive construction
It is often observed that the customer walk-through stalls at the checkout counter of our market are
something less than 3’ in width as required for an exit door, or 44” as required for a corridor
The stalls usually consist of short rails and dividing lines of 24” to 30” in width
No special hazard presents itself here because invariably there are more than enough stalls to
facilitate existing.
The transverse distribution of exit lines may make for a more orderly movement of people
SMOKEPROOF ENCLOSURES
In buildings having usable floors 75’ or more above grade or more than 30’ below the lowest level of
exit discharge, a special stairway must be provided.
A smoke tower is such a stairway, and it provides for a stairway isolated from the rest of the building
so that it is not only fire separated but free of smoke.
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