OCCUPANCY TYPES 7

7.1 OVERVIEW 
The previous chapters have focused on the protective design of office buildings 
because this occupancy is one that has been of most concern within the public and 
private sectors to date. The concepts discussed, however, are largely applicable to any 
type of civilian building serving large numbers of people on a daily basis. This 
chapter considers the unique challenges associated with three other high-occupancy 
building types: multi-family residential buildings, commercial retail buildings, and 
light-industrial buildings. Protection of schools and hospitals is addressed in other 
FEMA reports and is not explicitly addressed here. 
The uniqueness of these other occupancy types from the perspective of protective 
design is a function of many factors, including hours of peak usage, dominant 
population, size of building, and construction type. 
For dual-use facilities such as those that incorporate both retail and commercial 
office uses, two important recommendations for the HVAC are: 
. _	to provide separate HVAC zones; and 
. _	to strictly adhere to isolation principles (that is, to treat any public area 
as equivalent to an entrance lobby in a single-use building). 


7.2 MULTI-FAMILY RESIDENTIAL OCCUPANCY 
Multi-family residential buildings are unique because they tend to house more 
elderly, handicapped, and children than do office buildings, which tend to have 
more able-bodied occupants within working age (18-65). Office buildings of course 
can have a certain percentage of less-able-bodied populations, depending on the 
tenancy (e.g., medical offices, social services, or child care centers), and such 
populations need to be accounted for in the design of these buildings as well. In any 
case, the occupancy will have a major effect on the evacuation and rescue efforts. 
For multi-family residential buildings, it becomes more imperative that primary 
egress routes, including hallways leading to stairwells, remain as clear of debris and 
smoke as possible during the evacuation period. This criterion demands a higher 
level of protection than has been discussed for office buildings. Some 
recommendations for providing 
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enhanced protection to facilitate evacuation and rescue of distressed populations 
are listed below. 
. _	Place hallways in a protected location away from the building exterior. 
. _	Do not use glass in the hallways used for primary egress. 
. _	Egress routes should lead to exits that are as far as possible from high-
risk areas such as the lobby, mail room, and delivery entrance. 
. _	Create pressurized safe havens in elevator vestibules and stairwells 
using tightly constructed, air-tight enclosures placed in a protected core area of the 
building. 
. _	Emergency exits should be easily accessible by emergency vehicles and 
should be spacious enough to accommodate rescue workers entering the building as 
well as injured persons exiting the building. 
. _	The side(s) of the building with emergency exits should be free of any 
canopies, overhanging balconies, or other ornamentation that may fall and block the 
exits. 
. _	Emergency power should provide sufficient lighting and or phos-
phorescence to lead persons safely out of the building.

. _	Avoid using false ceilings in hallways. These can become falling 
debris that interferes with evacuation.

. _	Attach light fixtures to the floor system above to avoid hazardous 

debris in the exit path and to provide emergency lighting. Multi-family residential 
construction is more likely than office building construction to incorporate flat 
plate/slab or pre-fabricated components and therefore tends to be more structurally 
vulnerable. To improve performance, robust connection detailing becomes 
paramount to ensure that the connections are not weaker than the members to 
which they are attached. Also, balconies are more common in multifamily residential 
buildings. These present a debris hazard due to their inherent instability and 
connection weakness.


7.3 COMMERCIAL RETAIL SPACE OCCUPANCY 
Commercial retail space such as malls, movie theatres, hotels, night clubs, casinos, 
and other spaces that house large public populations gathering for shopping or 
entertainment have their own unique features that increase their vulnerability 
compared with that of office buildings. Often, these spaces are low-rise buildings that 
have large interior spaces with high, laterally unsupported walls, long-span roofs, and 
interior columns spaced relatively far apart. They are generally constructed 
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using lightweight construction and may be prefabricated. This type of construction 
has little if any redundancy, which increases the structural vulnerability significantly. 
The primary goal for this type of construction is to prevent progressive collapse of the 
building in response to a large-scale attack. Where possible, floor-to-floor height and 
bay spacing should be reduced, and lateral bracing of the columns and roof joists 
should be provided. Connections should be designed to be at least as strong as the 
members. Secondary structural framing systems further enhance protection. To limit 
laceration injuries, lamination of glass is recommended. Consider structural 
partition walls or shelving units placed within the space that will stop the roof system 
from falling directly on the occupants in the event of collapse. If this approach is 
used, take care that the partitions have sufficient lateral support so that they do not 
topple over. 
In these large spaces, it is virtually impossible to isolate HVAC to protect against CBR-
type threats. In this case, negative zone pressurization or smoke-evacuation methods 
become critically important. Also, mechanical areas should be protected with 
restricted access and a hardened shell (walls, ceiling and floor). It is also 
recommended to have centralized redundant control stations, easily accessible by 
appropriate personnel. Consideration should be given to providing additional, 
clearly marked, easily located egress routes to facilitate mass evacuation. If there are 
business offices serving these buildings with a sizable workforce, consider relocating 
these and other mixed-use functions to a separate, offsite location.


7.4 LIGHT INDUSTRIAL BUILDINGS 
Light industrial buildings are used through out the United States for offices, light 
manufacturing, laboratories, warehouses, and other commercial purposes. Typically, 
these buildings are low-rise buildings three to five stories high, often using tilt-up 
concrete construction.  Typically, they are located in industrial or commercial 
complexes and may have significant setbacks from public streets. They are serviced by 
surface parking lots or parking structures outside the building.  Security may vary 
widely depending on the use of the building.  For a building used for laboratories or 
manufacturing, there may be already be significant security measures at the perimeter 
and inside the building.  For office buildings, security may be light to negligible. 
The main focus of this section is on light industrial buildings that house office 
space, because these are the buildings with potentially high popu-
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lations, and therefore, life safety is a primary concern.  For warehouses and 
manufacturing plants, the primary objective is more likely to be protection of the 
contents and processes.  For laboratories, the primary objectives are to prevent release 
or deflagration of hazardous materials and to protect processes. 
Office parks inherently have an open character with medium-to-large setbacks from 
the street and public parking.  In this environment, the most effective way to protect 
the building from moving vehicle threats is to use landscaping methods between 
public streets and parking to prevent the intrusion of vehicles. Devices such as ponds, 
fountains, berms, and ditches can be very effective in reducing the accessibility of the 
building exterior to high-speed vehicles. 
Parking should be placed as far as practical from the building. Driveways leading 
directly to the building entrance should have a meandering path from the public 
streets that does not permit high velocities to be achieved. Separation between the 
driveway and building may be achieved through a number of devices such as a pond 
with a bridge leading to the entrance, a knee wall with foliage in front, or other 
landscape features. 
The design of parking structures servicing these buildings should fulfill two main 
objectives to prevent explosions in the parking structure from seriously damaging the 
main office building. The first is to control the lines of sight between the parking 
structure and the building to limit air-blast effects on the building. One solution is to 
use a solid wall that is bermed and landscaped on the side of the parking structure 
facing the building.  Second, design the parking structure to withstand the design-
level explosion without structural failure in order to reduce the potential for debris 
from a parking structure failure damaging the office building. This second objective 
can be achieved while still allowing the parking structure to sustain significant levels 
of damage. 
For the tilt-up walls, use continuous vertical reinforcement with staggered splices, 
preferably on both sides of the wall to resist large lateral loads. It may be 
advantageous to consider designs that permit the wall to bear against floor 
diaphragms to resist loads.  Connections between the walls and structural frame 
should be able to accept large rebound forces to prevent the wall from being pulled 
off the exterior. Care should be taken to prevent the wall from bearing directly 
against exterior columns to limit the opportunity for progressive collapse. Using 
laminated glass on the exterior reduces the potential for laceration inju-
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ries. For the roof, a concrete slab with or without decking is preferred over a solution 
using metal decking only.


7.5 FURTHER READING 
FEMA, 1988, Seismic Considerations: Office Buildings, FEMA 153, Earthquake Hazards 
Reduction Series 38, Federal Emergency Management Agency, Washington, D.C. 
FEMA, 1988, Seismic Considerations: Apartment Buildings, FEMA 152, Earthquake Hazards 
Reduction Series 37. Federal Emergency Management Agency, Washington, D.C. 
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