The calculation of maximum occupancy of a building has a significant place in the hazard management. The idea is increasingly influencing new construction methods.
The maximum occupancy of a building is calculated primarily based on two factors. One is the number of available exits in the building and the other is the use of space. The International Building Code has laid down some rules regarding the maximum occupancy of an area. IBC is a model building code developed by the International Code Council (ICC).
As per the definition given by IBC, an exit is a continuous and unobstructed path of vertical or horizontal egress travel from any occupied portion of the building or structure to a public way. Usually, the doors from kitchen and unused rooms are not considered exits.
When calculating the occupancy figure for a building, the two following calculations are used.
1. Floor space factor – The number of persons who can safely reside in the premises. Number of people = Floor area (m²) / Occupant density
2. Exit factor – The width and capacity of the exit routes to allow people to escape safely.
Whichever the less between these figures is the maximum occupancy of a building.
According to the building regulations, the occupant density varies depending on the nature of a building. As per the IBC recommendations, a standing/bar area should have an occupant density of 0.3 M²/person while a shop area could have 2 M²/person and an office area must have 6 M²/person.
Thus, for a bar with an area of 300 M², the maximum occupancy will be 1000. At the same time, an office space with the same area would have a maximum occupancy of 50 as per the floor space factor.
Now we consider the exit factor. As per the recommendations, the ideal width of an escape route or exit is 1050 mm. In any case, it should not be less than 750 mm. An exit with a width of 1050 mm can accommodate 200 Persons in normal conditions. An additional 15 Persons can be accommodated per every 75 mm. If the premises have multiple exits, the wider one is considered to be unavailable. Suppose the above mentioned bar has an exit of 1200 mm width and three exits 1050 mm wide. The total number of persons the exits can accommodate will be 600. Since it is the smaller figure, the maximum occupancy of the premises will be 600.
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