How to calculate occupancy load and egress capacity?

Occupational health and safety have become top priority of many prestige organizations around the world because it is proven that an employee can perform more efficiently in a safe working environment designed on the principles of occupational health and safety principals.
Occupational health and safety leads us not only in normal or routine operations but also guides us on
how to deal with emergencies in multiple ways that include emergency planning, preparedness, and
response. Here we will learn two important parameters of occupational health and safety at the workplace which are the backbone of emergency planning with reference to NFPA 101 Life Safety Codes.

1. Occupancy load calculation
2. Egress Capacity calculation

Occupancy Load Calculation

It is a method to calculate the number of people occupied in a specific area or sittings in a specific time period. The calculated value can be greater than the maximum expected number of people in a given space. The calculation composed of a few steps needs to be stated with physical measurements of the space under discussion, then divide the total possible seating area by 15ft2. The result will be the total number of occupants possibly occupied in a given space. For example, if the total occupiable space is 100ft x 100ft the total area will be 1000ft2 to calculate a number of people in 1000ft2 below simple calculation will be done. Total Number of Person in 1000ft2 Area = 1000ft2/15ft2=67 Person.It means we can accommodate 67 persons in a 1000ft2 space as per NFPA 101 Life Safety Codes these figures can be used in emergency planning and other safety-related activities.

Egress capacity Calculation

Another important parameter in workplace safety is egress capacity calculation as it is very crucial to
design egress and exit door size. The calculation of egress capacity is varying from place to place, for
instance, it is very in three different ways. Firstly, the place is equipped with non-sprinkler healthcare
facilities the egress capacity factor is 0.5 inches per occupant. Second, for the occupancies with high
hazards and no sprinkler system, the egress capacity factor is 0.4 inches per occupant. Third, for all other occupancies, the egress capacity factor is 0.2 inches per occupant. Now we will understand
calculations with examples in all three occupancies one by one as under.
The calculation for health care facility which has no sprinkler system, here the egress capacity factor is 0.5 inches per occupant. For example, a hospital facility is composed of two floors (1 st floor & 2 nd Floor) having 2 exit doors on each floor having dimensions of a height of 7ft and a width is 5ft. These doors are connected with an internal stair having dimensions of a height of 9ft and a width of 7 ft. Now calculate the egress capacity for stairs opening on the ground floor, 1 st floor, and second floor. The maximum occupancy load in the hospital facility is 1500 people including all sectors.

• Total occupancy load = 1500 People
• Number of doors on ground floor = 01 Door dimension heigh = 9 ft Width = 7ft
• Number of doors on 1 st floor = 02, Each door dimension heigh = 7 ft Width = 5ft
• Number of doors on 2 nd floor = 02 Each door dimension heigh = 7 ft Width = 5ft

Now calculating egress capacity use egress capacity factor 05 inches per person = 0.042 ft/person
Egress capacity for the ground floor = 1500x0.042 = 63 ft while the door size at the ground floor stairs opening is 5ft which is not compliant with the standard.
Egress capacity for 1 st floor = 750x0.042 = 31.5 ft while the door size at 1 st floor doors opening is 10 ft which is not compliant with the standard.
Egress capacity for 2 nd floor = 750x0.042 = 3.15 ft while the door size at 1 st floor doors opening is 10ft which is not compliant with the standard.
Now another consideration that needs to consider here is the number of exit doors versus occupants
load with compliance of emergency exit door requirements below are the minimum number of
emergency exits.

1. Number of emergency exit doors 1- 500 = 2
2. Number of emergency exit doors 501 - 1000 = 3
3. Number of emergency exit doors More than 1000 = 3

Also, with compliance of the above two requirements, the third requirement is the compliance of below travel distances to the exit door from the furthest point in the occupancy as under;

1. 100 ft without sprinklered
2. 200 ft without sprinklered

We can do the same calculation from egress capacity with occupancy with high hazards and all other
occupancies with factors 0.4 and 0.2 respectively as per NFPA 101.
There are also other standards especially International Building Codes (IBC). OSHAS and Authority having jurisdiction tell us more specific requirements.

Conclusion

It is concluded that occupancy load and egress capacity calculation are two very important parameters to plan occupational health and safety at the workplace to provide a safe working environment and emergency response plan. Both parameters are interlinked and equally important, this article gives you a brief idea about both parameters you can further explore the details of occupancy load and egress capacity calculation in NFPA 101 life safety codes and in international building codes chapter 7.