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Two-storey assembly-over-business building: occupant loads, exits and egress widths against the code factors, separation and travel-distance checks, and the evacuation time by the hydraulic model
| Tool | Occupant Load and Egress Capacity |
| Source | U.S. Department of Defense (2016). Fire Protection Engineering for Facilities. UFC 3-600-01 with Change 6 (2021), Section 10-3 and Table 10-1 (occupant-load factors, the 7 ft² net maximum); Averill, J. D., et al. (2005). Occupant Behavior, Egress, and Emergency Communications. NIST NCSTAR 1-7, pages 46 to 47 (the IBC / NFPA 101 egress arithmetic restated: 0.3 and 0.2 in per occupant, two stairs below 500 and four above 1,000 occupants, 32 in doors, one-third of the diagonal) and page 129 (one person per second per door); Peacock, R. D., et al. (2015). Movement on Stairs During Building Evacuations. NIST Technical Note 1839, pages 33 to 35 and 111 (the SFPE hydraulic model: S = k (1 − a D), a = 0.266 m²/person, k = 1.40 m/s level and 1.08 m/s on 7/11 stairs, 0.15 m and 0.09 m boundary layers); Nelson, H. E. (1990). FPETOOL. NISTIR 4380, Section 3.6 equations 16 to 21. |
| Level | Professional |
Problem
A sprinklered two-storey building has an assembly floor (a 3,000 ft² hall with loose chairs and a 900 ft² meeting room) over a business floor (6,000 ft² of offices, a 600 ft² conference room, a 300 ft² waiting lobby), a 100 × 60 ft plan, two 76-in exit stairs with 7/11 steps entered from two 72-in corridors through pairs of 34-in-clear doors, three exit discharge doors (two pairs of 34-in leaves at the stair discharges and a 36-in lobby door) and a 60-in ground-floor corridor. Find the occupant load of every space and floor, the exits and egress widths required at 0.3 in per occupant on stairs and 0.2 in on level components against the widths provided, the loss-of-one-exit check, the exit separation against one-third of the diagonal, the travel-distance, common-path and dead-end checks, and the time to evacuate by the hydraulic model.
Inputs to Enter
- Capacity factors 0.3 / 0.2 in per occupant (base set); sprinklered, separation 1/3 of the diagonal; one exit up to 49, two up to 500, three up to 1,000; minimum stair 44 in, door 32 in clear, corridor 44 in; handrail allowance 4.5 in; discharge floor 1; maximum 7 ft² net per person
- Spaces: Assembly hall 3,000 ft² at 7 net (floor 2), Meeting room 900 ft² at 15 net (floor 2), Offices 6,000 ft² at 150 gross, Conference room 600 ft² at 15 net, Lobby waiting area 300 ft² at 15 net (floor 1)
- Floors: plan 100 × 60 ft; floor 2 separation 70 ft, travel 150 ft (limit 250), common path 15 ft (20), dead end 10 ft (20); floor 1 separation 70 ft, travel 180 ft (300), common path 60 ft (100), dead end 30 ft (50)
- Components: corridors 2A / 2B 72 in; doors to stairs 1 and 2 two leaves × 34 in; stairs 1 and 2 76 in wide, 3.5 in handrails, 7 in risers, 11 in treads, top floor 2; corridor 1 60 in; exit doors D1 / D2 two leaves × 34 in, D3 36 in, all swinging with the travel
- Hydraulic model: k 275 ft/min, a 2.86 ft²/person, D_0 0.05 persons/ft², layers 6 in walls and doors, 3.5 in handrails, 8 in corridors; no pre-movement time; storey 12 ft; 8 ft of landing per storey
Answers
- Occupant loads: hall 3,000/7 = 429, meeting room 60, floor 2 = 489; offices 40, conference room 40, lobby 20, floor 1 = 100; building 589. Posted load of the hall 428 at the 7 ft² maximum (the load rounds up, the maximum rounds down)
- Exits: floor 2 needs 2 (489 ≤ 500), has 2 stairs; floor 1 needs 2 (100 > 49), has 3 exit doors. Widths floor 2: stairs 489 × 0.3 = 146.7 in required, 152 in provided (ratio 1.04, governs; 76 in left with one stair lost ≥ 73.4), stair doors 97.8 required / 136 provided, corridors 97.8 / 144; floor 1: discharge doors 97.8 (largest floor served) / 172, corridor 20 / 60. Every stair and door meets its minimum; every door serving 50 or more swings with the travel
- Diagonal √(100² + 60²) = 116.6 ft, separation required 38.9 ft, measured 70 ft; travel 150 ≤ 250 and 180 ≤ 300 ft, common path 15 ≤ 20 and 60 ≤ 100 ft, dead ends 10 ≤ 20 and 30 ≤ 50 ft: all satisfied
- Hydraulic model: free speed 236 ft/min, maximum specific flow 24.04 persons/min per ft on the level at 0.175 persons/ft² and 18.58 on the 7/11 stairs (k 212.6 ft/min); effective widths 56 in per corridor and double door, 62 in per stair, 24 in for the 36-in door; capacities 112.2 persons/min per corridor and double door, 96.0 per stair, 272.7 for the three discharge doors; descent 30.4 ft per storey at 106 ft/min = 17 s
- Queues: floor 2 arrives at 768 persons/min over 38 s, corridors queue 344 persons (1 to 130 s), stair entry queue 70 (the stairs, 192 persons/min pooled, control), discharge queue 7; first occupant outside at 1 s, last at 170 s = 2.83 min; controlling-component estimate 489 / 3.197 persons/s + 17 s = 169.9 s; FPETOOL estimate 4.04 min (5 door leaves at one person per second: 1.96 min; stairs J 10.67 ft at 18.3: 3.02 min; travel 1.02 min)
Notes
The tool's default inputs are this building; press Submit. The building is illustrative (stated on the page). The arithmetic is checked by test_occupant_load_egress.php (718 checks) against an independent numpy script (References/Occupant-Load-Egress/checks/) on this building and twenty seeded ones, against the NCSTAR 1-7 figures for the World Trade Center floor (429 occupants, 129 in of stair width at 0.3 in, two and four stairs, the one-third diagonal), the TN 1839 statement of the hydraulic model and the FPETOOL equations.