Evacuation Time Calculator

Estimates total building/area evacuation time from occupant load and exit width, using the SFPE (Society of Fire Protection Engineers) hydraulic flow-calculation approach: pre-movement time + travel time + exit queuing/discharge time.

Occupancy & Exits

Total Occupant Load Total number of people to be evacuated from the area/floor/building.

Number of Usable Exits Assumes occupants distribute evenly across all usable exits.

Exit Component Type Sets the specific flow rate and typical boundary layer loss — both remain editable.

Clear Width per Exit (mm) Measured clear/unobstructed width of each exit opening.

Boundary Layer Loss (mm) Width lost to wall/edge effects (people don't use the full physical width).

Specific Flow Rate (persons/min per metre of effective width) Default per IBC/SFPE: ~78.7 for doors/corridors, ~59.1 for stairs.

Timing Factors

Pre-Movement Time (s) Detection + alarm + human response/decision time before movement begins.

Average Travel Distance to Exit (m)

Average Walking Speed (m/s) Typical unimpeded walking speed: 1.0–1.2 m/s; reduce for mobility-impaired occupants or smoke conditions.

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Exit Queuing Time (s)

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Travel Time (s)

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Total Evacuation Time (s)

Formula Reference

Effective Width per Exit = Clear Width − Boundary Layer Loss
Exit Flow Capacity = (Effective Width × Number of Exits) × Specific Flow Rate
Exit Queuing Time = Occupant Load ÷ Flow Capacity
Travel Time = Travel Distance ÷ Walking Speed
Total Evacuation Time = Pre-Movement Time + Travel Time + Exit Queuing Time

Doors / Corridors (IBC/SFPE)	~78.7 persons/min per metre width (24/ft/min)
Stairways (IBC/SFPE)	~59.1 persons/min per metre width (18/ft/min)
Typical boundary layer loss	150–200 mm per exit, per SFPE Handbook

Benchmark Guidance

There is no single universal pass/fail time — acceptable evacuation time depends on occupancy type, building complexity, and applicable code. As a general reference point, BS 9999 (British Standard for fire safety in building design) suggests around 2.5 minutes for low-complexity buildings, up to 5 minutes for more complex ones; many workplace fire risk assessments target under 3 minutes for straightforward office/industrial layouts. Always confirm the applicable target against your local fire code and a qualified fire safety engineer.

Calculations use the SFPE (Society of Fire Protection Engineers) hydraulic flow-calculation method with IBC (International Building Code)-referenced specific flow constants. This is a simplified single-scenario estimate — it does not model queue formation at merge points, phased/staged evacuation, smoke/visibility effects, or occupants with mobility impairments in detail. Always verify against a full fire engineering evacuation analysis and your local Authority Having Jurisdiction (AHJ) requirements before relying on results for life-safety decisions. For customized calculators tailored to your organization, please contact Impact Tech Solutions.