Download Determining the Occupant Load

Determining the Occupant Load
 Occupant loads are based upon three factors:
 Occupancy Classification
 Square footage of the floor or area
 Occupant Load Factor
Existing Versus New Buildings
 For existing building compare the calculated occupant load
with the actual occupancy in the building, take whichever
occupancy is higher!
 For new buildings, use the calculated occupant load and
design for that value
Occupant Load Steps
 Classify the Building
 Industrial Occupancy
 Find the Occupant Load Factor
 Table 7.3.1.2 in Chapter 7 of NFPA 101
 Dividing the floor area assigned to that use by the occupant load
factor
 For determining the floor area, use the gross or net square footage as
required in the codes
 Net square footage: Does not include areas such as restrooms, closets,
and mechanical rooms
 The table indicates when to use net versus gross square footage
Determining Capacities of Exits
 With the occupant load calculated, you then need to
determine the widths, number, and placement of exits to
ensure you can accommodate the design occupant load
 For example, if you determined the occupant load to be
1,000 people, you need to provide enough exits of sufficient
widths and placement to serve 1,000 people
 Determine what is the minimum acceptable door width
Calculating Capacities of Exits
 The capacity of an exit is determined by using:
 The exit width
 The exit surface (level versus stairs)
 In some occupancies, if there is a sprinkler system present
 Example: A door has a width of 38” and the occupancy class is
industrial
 Level components have a capacity factor of .2
 Therefore, the one exit can serve up to 190 people (38”/.2)
 If the building has an occupant load of 1,000 people, you will
need at least 6 exits (1,000/190 = 5.26)
Travel Distances to Exits
 Maximum travel distances to exits are determined by
occupancy class
 Different for sprinklered and unsprinklered buildings
 For a sprinklered industrial facility, the maximum travel
distance to an exit is 250 feet
Calculating Travel Distances
 Measurement of Travel Distance to Exits
 The travel distance to an exit shall be measured on the floor
or other walking surface as follows:
 (1) Along the centerline of the natural path of travel, starting
from the most remote point subject to occupancy
 (2) Curving around any corners or obstructions with a 12-in.
clearance therefrom
 (3) Terminating at one of the following:
 Center of the doorway
 Other point at which the exit begins
 Smoke barrier in an existing detention and correctional
occupancy as provided in Chapter 23
Exit Arrangements
 Usually, a floor must have a minimum of 2 exits
 Minimum number increases with occupant load
 Two exits must meet minimum separation requirements
 At least 1/3 the diagonal distance of the floor away from each
other for sprinklered buildings
 At least 1/2 the diagonal distance of the floor away from each
other for unsprinklered buildings
Exit Termination
 Exits shall terminate directly, at a public way or at an
exterior exit discharge, unless otherwise provided
 The exit discharge shall be arranged and marked to make
clear the direction of egress to a public way.
Illumination
 Illumination of means of egress shall be continuous during
the time that the conditions of occupancy require that the
means of egress be available for use.
 Artificial or natural lighting
 The minimum illumination levels
 For example, floors and walking surfaces, other than new stairs, must
provide at least 1 ft-candle measured at the floor
Emergency Lighting
 As required for means of egress in buildings or structures
defined by the codes
 Exit accesses requiring illumination includes only designated
stairs, aisles, corridors, ramps, esc
 Emergency illumination shall be provided for not less than
1½ hours in the event of failure of normal lighting
 Not less than an initial average of 1 ft-candle and, at any
point, not less than 0.1 ft-candle, measured along the path of
egress at floor level
Exit Markings, Exit Access Markings,
and Directional Signage
 Exits, other than main exterior exit doors that obviously and
clearly are identifiable as exits, shall be marked by an
approved sign that is readily visible from any direction of exit
access.
 Access to exits shall be marked by approved, readily visible
signs in all cases where the exit or way to reach the exit is
not readily apparent to the occupants.
 Directional signs with a directional indicator showing the
direction of travel shall be placed in every location where the
direction of travel to reach the nearest exit is not apparent.