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Occupant load

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Contents
  1. 1Definition and related terms
  2. 2How the occupant load is calculated
  3. 3Typical occupant load factors
  4. 4Worked examples
  5. 5Use in egress design
  6. 6Use in evacuation time calculations
  7. 7Design values and actual populations
  8. 8Occupant load and crowd density
  9. 9See also
  10. 10Notes
  11. 11References

The occupant load is the greatest number of people likely to occupy a particular space within a building.[1] It is usually found by dividing the floor area by a fixed area per person for the activity in the space, or by counting the beds or fixed seats.[1] The number is the starting point for the design of the means of escape, because building codes size exits and stairs to the number of people they must serve.[2] In a fire engineering analysis it is also an input for the required safe egress time. A hand calculation of the evacuation time begins by establishing how many people are present in each space.[3][4]

Most building regulations express the design values as occupant load factors in square metres of floor area per person. In New Zealand, C/VM2 (second edition, 2025) lists factors from 0.4 m² per person for standing space to 10 m² per person for offices and 100 m² per person for bulk storage.[5] These factors are design values rather than predictions. Field studies in Canadian office buildings found about 25 m² of gross rentable area per actual occupant, against the 9.3 m² per occupant assumed in traditional code rules.[6]

Definition and related terms

C/VM2 (second edition, 2025) gives three ways to determine the occupant load of a space. The floor area can be divided by the area per person for the activity, the sleeping or care spaces can be counted, or the fixed seats can be counted.[1] In care and detention, a "bed" is any place where a person stays for treatment, including recliners, dentist chairs and treatment tables.[7] The first edition of C/VM2 used the term "occupant densities" for the same table of values.[8]

In crowd movement research, density is the number of persons per unit area of walkway, such as 2.0 persons/m².[9] It is often expressed by its inverse, the area per person, which for the same crowd is 0.5 m² per person.[9] An occupant load factor in m² per person is therefore an inverse density for a whole space. Nelson and Mowrer use density in a different sense, as the degree of crowding in an evacuation route at a given moment.[10] The two ideas are linked but not the same, as the section on crowd density below explains.

In Australia, the data sheets for the Fire Safety Verification Method speak of "occupant numbers and densities".[11] They take the values from Table D1.13 of the National Construction Code (NCC) Volume One, which gives the area required per person for each use.[11] Where that table does not cover a use, the authority, the fire engineer and other stakeholders agree a value that is consistent with it.[11]

The use of a space matters a great deal. In the building codes discussed in the NIST report on the World Trade Center, office space was designed for 100 ft² (about 9.3 m²) per occupant.[12] Restaurants, bars and function rooms were assembly space at 15 ft² (about 1.4 m²) per occupant.[12] A typical office floor in the towers therefore had a design load of 365 to 390 people, while the restaurant floors had more than 1,000 each.[12]

How the occupant load is calculated

For a space with one activity, the occupant load follows from the floor area and the occupant load factor for that activity.[7] The factor is the floor area allowed for each person. Dividing the area by this factor gives the number of people: N=Af

Symbol Description Unit
N occupant load persons
A floor area of the part of the building containing the activity m²
f occupant load factor for the activity m²/person

The relation applies to one activity at a time. A floor with offices and a conference room, for example, is split into parts with different factors.[13] It does not apply to fixed seating, beds or sleeping spaces, which are counted directly.[1] The area used is the total enclosure floor area, including the area taken up by internal partitions and permanent fixtures.[14] The factors already allow for the part of the floor occupied by furniture, partitions, fixtures and equipment.[7]

C/VM2 adds several rules for applying the factors. If a space may be used for different activities, the activity with the greatest occupant load governs.[7] If an activity is not listed, the nearest reasonable description is used.[7] People involved in more than one activity are counted once. No load is assigned to exitways, lift lobbies or sanitary facilities, because the people using them are already counted elsewhere.[7] For fixed seating, extra standing occupants may be added on adjoining floor area, provided the escape route is not obstructed.[7]

Codes also differ in which floor area they use. The New York City Building Code calculates the occupant load on a net basis, subtracting shafts, storage rooms and stairs from the gross floor area.[15] The logic is that no egress capacity is needed for floor area where nobody will be.[2] The International Building Code and NFPA 101 use the gross floor area.[15] For a tower floor of the World Trade Center, the net basis gave a design load of 390 people, the gross basis 428.[15]

Two identical square office floor plans; left the whole floor is shaded as gross area, right the core shafts and stairs are left white as excluded area.
Gross and net floor area of the same office floor: a net basis leaves out shafts, storage rooms and stairs, so the design occupant load is lower. Based on Averill et al. (2005), pp. 44 and 47.

Typical occupant load factors

The table lists a selection of the occupant load factors in C/VM2 (second edition, 2025), from the most crowded uses to the least crowded.[5]

Activity Occupant load factor (m²/person)
Standing space 0.4
Bar standing areas 0.5
Dance floors; stadiums and grandstands 0.6
Space with loose seating 0.8
Bar sitting areas; lobbies and foyers 1
Space with loose seating and tables 1.1
Dining, restaurant and cafeteria spaces 1.25
Exhibition areas and trade fairs 1.4
Classrooms 2
Meeting rooms 2.5
Retail spaces and malls 3.5
Art galleries and museums 4
Office spaces 10
Parking buildings and garages 50
Bulk storage including racks and shelves 100

The range covers more than two orders of magnitude. Standing space at 0.4 m² per person corresponds to 2.5 persons per square metre, while a parking building is assumed to hold one person per 50 m².[5] Bleachers, pews and bench seating are not given an area but a length of 0.45 m of bench per person.[5] For assembly occupancies, Proulx regards seat counts and an area of 0.3 to 0.6 m² per person in waiting spaces as a reasonable basis for the maximum population.[6]

Horizontal bar chart of occupant load factors on a log scale, from 0.4 m² per person for standing space to 100 m² per person for bulk storage.
Selected occupant load factors in C/VM2 (second edition, 2025): the design floor area per person ranges from 0.4 m² for standing space to 100 m² for bulk storage. Based on Ministry of Business, Innovation and Employment (2025b), pp. 11–12.

Worked examples

The commentary to the first edition of C/VM2 works through a function centre and hotel. The occupant loads are based on the floor area of each space and the occupant densities of C/VM2.[16] The grand ballroom measures 50 m by 20 m, so its floor area is 1,000 m². With 1 m² per person, the ballroom holds 1,000 people, for whom four exits are provided where two are required.[17] N=1000 m21 m2/person=1000 persons The restaurant of 420 m² is assessed at 1.1 m² per person. The division gives 381.8, and the commentary uses 382 people.[17] The meeting rooms, 564 m² at 2.5 m² per person, give 225.6 and are taken as 226 people.[17] Hallways and corridors count as spaces of intermittent use, so their occupants are included in the loads of the rooms they serve.[17]

Plan of a ballroom, meeting rooms and a restaurant, each with its floor area, area per person and resulting number of occupants.
Occupant loads in the commentary example: floor area divided by the area per person for each room. Based on Ministry of Business, Innovation and Employment (2013), p. 190.

These numbers then set requirements for the escape routes. The example separates the exits by at least 8 m when up to 250 occupants use the escape routes, and by at least 20 m above that number.[17] The second edition keeps a similar rule for spaces with more than 250 people that escape through only two routes.[18] Where a primary entrance can be identified, C/VM2 (2025) assigns half of the occupant load of a space to that entrance.[19] For the restaurant this is 191 people. A self-closing door leaf is limited to 50 people per minute, so one leaf would need about 3.8 min to pass them.[20]

A second example shows the effect of the factor itself. An office floor of 1,400 m² at the C/VM2 office factor of 10 m² per person gives a design load of 140 people.[5] Proulx describes 70 able-bodied persons on a floor of about 1,400 m² as a fairly high population for an office building.[6] At the observed 25 m² per occupant, the same floor would hold 56 people.[6] The design value is thus two to two and a half times the population found in the Canadian studies.

Column chart for a 1,400 m² office floor: 151 people at 9.3 m² per person, 140 at 10 m², 70 in a busy floor and 56 at 25 m² per person.
Number of people on a 1,400 m² office floor for different areas per person: design values give two to two and a half times the observed populations. Based on Ministry of Business, Innovation and Employment (2025b), p. 12, and Proulx (2002), p. 3-355.

Use in egress design

Building codes largely relate the required egress capacity to the size and use of the area served.[2] The width and number of stairs are specified so that they equal or exceed the number of occupants on a floor. Generally the floor with the largest occupant load dictates the design of the whole egress system.[2] Under the 1968 New York City Building Code, 365 people on a World Trade Center floor needed six and a half units of exit width at 60 people per unit of 22 in.[21] That gave an allowable floor load of 390 people.[21]

The number of stairs also depends on the occupant load. The same code required at least two stairs for fewer than 500 people and four stairs for more than 1,000.[21] The International Building Code of 2000 requires 0.005 m of stair width per occupant in a sprinklered building, which gives 2.2 m for a floor of 429 people.[22] NFPA 101 (2003) requires 0.0076 m per occupant, or 3.3 m in total for the same floor.[22] The occupant load is thus the quantity that turns a code's exit capacity per person into a required width in metres.

Several thresholds in C/VM2 (second edition, 2025) are expressed directly as occupant loads. A manual alarm instead of automatic detection is only permitted in high spaces where fewer than 50 occupants are awake and familiar with their surroundings.[23] Doors on escape routes must open in the direction of escape unless no more than 50 occupants use them.[19] The design scenario in which a fire blocks an exit applies to escape routes serving more than 50 people, and single escape routes may serve up to 50 people.[18]

Use in evacuation time calculations

C/VM2 requires the occupant loads in a calculation of the required safe egress time to be determined with its occupant load factors.[4] In the Introduction to Fire Safety Engineering, the first of eight steps in a hand calculation is to establish the number of people in each relevant space.[3] The next steps assign these people to the exits and find the exit that takes longest to clear. In the book's example, 300 people are divided equally over four stairs, so each stair serves 75 people.[3] A stair of 1.6 m passes 1.2 persons per second, and the 75 people need about 63 s to pass it.[3]

The Australian data sheets for the Fire Safety Verification Method list occupant numbers and densities as the first occupant characteristic in an evacuation analysis.[24] Maximum numbers are typically assumed in deterministic analyses. Variations with time of day and season can be included in probabilistic analyses.[24] The fire safety strategy must state the maximum number of occupants assumed for the building and its enclosures.[11]

In evacuation modelling with computer software, the geometry of the building is built first and then filled with people, often with several occupant profiles.[25] The NIST study of the World Trade Center towers used such models to test the effect of the population. In the simulations, each additional 1,000 occupants added about 5.2 min to the total evacuation time of a tower.[26]

Design values and actual populations

Code values and real populations can differ widely. In Canadian office buildings, Proulx found about 25 m² of gross rentable area per actual occupant, compared with the 9.3 m² per occupant of traditional codes and standards.[6] Codes can therefore misjudge the actual number of occupants by a factor of more than 2.[6] Counts of workspaces also tend to overestimate office populations, sometimes by 15 percent.[6]

For the World Trade Center towers, NIST counted offices, cubicles and other workstations on typical floor plans.[27] This gave an average of 14 m² per person and 19,800 people per tower, or 11 m² per person and 25,500 people when visitors were included.[27] The Port Authority later estimated that the population of a tower would not have exceeded 20,000.[27] About 8,800 people were present in each tower on 11 September 2001.[28] Without building damage, the simulated evacuation of 8,800 people took at least 52 to 71 min, and that of 19,800 people 92 to 112 min.[28]

C/VM2 allows a lower occupant load than its table gives, but the basis must be substantiated to the building consent authority.[7] The document warns that designing for a reduced load can severely restrict future uses of the building and make later upgrades of the means of escape expensive.[7] Conversely, if the maximum number of people will be higher than the table gives, the higher number must be used and justified.[7]

Occupant load and crowd density

A common misunderstanding is to treat the occupant load factor as the crowd density in the escape routes. The factor describes how many people a whole space may hold, averaged over its area. Crowd density describes how closely people stand while they move or queue.[10] Nelson and Mowrer base the density of the first exit element, such as an aisle or corridor, on all the occupants it serves, unless their dispersion is known.[10]

Crowd density controls walking speed. Below about 0.54 persons/m², people move at their own pace, and above about 3.8 persons/m² movement stops until the crowd thins out.[29] The Introduction to Fire Safety Engineering gives about 1.25 m/s for unhindered walking on a level floor at fewer than 1 person/m².[30] For flow through doors, C/VM2 assumes a density of 1.9 persons/m² near the constriction.[31] In crowd disasters, densities approach a critical value of about 8 persons/m², at which no space remains between people.[9]

The occupant load therefore answers only the first question of an evacuation analysis: how many people must leave. The time needed to pass an exit follows from this number and the flow capacity of the usable width.[32] The total evacuation time also contains the delay before people start to move, which the occupant load does not describe.[32]

See also

Notes

  1. ↑ 1.0 1.1 1.2 1.3 Ministry of Business, Innovation and Employment (2025b), p. 67.
  2. ↑ 2.0 2.1 2.2 2.3 Averill et al. (2005), p. 44.
  3. ↑ 3.0 3.1 3.2 3.3 Van Rossum (2027), §7.5.
  4. ↑ 4.0 4.1 Ministry of Business, Innovation and Employment (2025b), p. 26.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Ministry of Business, Innovation and Employment (2025b), pp. 11–12.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Proulx (2002), p. 3-355.
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 Ministry of Business, Innovation and Employment (2025b), p. 10.
  8. ↑ Ministry of Business, Innovation and Employment (2013), p. 83.
  9. ↑ 9.0 9.1 9.2 Proulx (2002), p. 3-345.
  10. ↑ 10.0 10.1 10.2 Nelson and Mowrer (2002), p. 3-369.
  11. ↑ 11.0 11.1 11.2 11.3 Australian Building Codes Board (2020a), Data Sheet D1, p. 255.
  12. ↑ 12.0 12.1 12.2 Averill et al. (2005), p. 19.
  13. ↑ Ministry of Business, Innovation and Employment (2013), p. 87.
  14. ↑ Ministry of Business, Innovation and Employment (2013), p. 85.
  15. ↑ 15.0 15.1 15.2 Averill et al. (2005), p. 47.
  16. ↑ Ministry of Business, Innovation and Employment (2013), p. 188.
  17. ↑ 17.0 17.1 17.2 17.3 17.4 Ministry of Business, Innovation and Employment (2013), p. 190.
  18. ↑ 18.0 18.1 Ministry of Business, Innovation and Employment (2025b), p. 37.
  19. ↑ 19.0 19.1 Ministry of Business, Innovation and Employment (2025b), p. 32.
  20. ↑ Ministry of Business, Innovation and Employment (2025b), p. 34.
  21. ↑ 21.0 21.1 21.2 Averill et al. (2005), p. 45.
  22. ↑ 22.0 22.1 Averill et al. (2005), p. 46.
  23. ↑ Ministry of Business, Innovation and Employment (2025b), p. 28.
  24. ↑ 24.0 24.1 Australian Building Codes Board (2020a), Data Sheet D1, p. 252.
  25. ↑ Van Rossum (2027), §10.1.
  26. ↑ Averill et al. (2005), p. 162.
  27. ↑ 27.0 27.1 27.2 Averill et al. (2005), p. 239.
  28. ↑ 28.0 28.1 Averill et al. (2005), p. xxxv.
  29. ↑ Nelson and Mowrer (2002), p. 3-370.
  30. ↑ Van Rossum (2027), §7.4.
  31. ↑ Ministry of Business, Innovation and Employment (2025b), p. 33.
  32. ↑ 32.0 32.1 Proulx (2002), p. 3-347.

References

  • Australian Building Codes Board. (2020a). Data sheets: Fire Safety Verification Method (Handbook annex, Print version 1.1).
  • Averill, J. D., Mileti, D. S., Peacock, R. D., Kuligowski, E. D., Groner, N., Proulx, G., Reneke, P. A., & Nelson, H. E. (2005). Occupant behavior, egress, and emergency communications (NIST NCSTAR 1-7). National Institute of Standards and Technology.
  • Ministry of Business, Innovation and Employment. (2013). Commentary for Building Code clauses C1–C6 and Verification Method C/VM2.
  • Ministry of Business, Innovation and Employment. (2025b). Verification Method C/VM2: Framework for fire safety design (2nd ed.).
  • Nelson, H. E., & Mowrer, F. W. (2002). Emergency movement. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-367–3-380). National Fire Protection Association; Society of Fire Protection Engineers.
  • Proulx, G. (2002). Movement of people: The evacuation timing. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-342–3-366). National Fire Protection Association; Society of Fire Protection Engineers.
  • Van Rossum, E. (2027). Introduction to Fire Safety Engineering. Fire Safety Academy.
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