Evacuation modelling has evolved from simple calculations to sophisticated agent-based simulations. This guide covers ASET/RSET analysis, software tools, and validation of evacuation designs.. The Science of Safe Escape Evacuation modelling is the quantitative analysis of how people move through buildings during fire emergencies. At its core is the fundamental principle: the Available Safe Egress Time (ASET) must exceed the Required Safe Egress Time (RSET) with an appropriate margin of safety. ASET/RSET Framework ASET (Available Safe Egress Time) Determined by fire modelling (CFD): Detection time — time from fire ignition to alarm activation Tenability criteria — visibility 10m, temperature <60°C, CO <1400ppm ASET = time from ignition until conditions become untenable in escape routes RSET (Required Safe Egress Time) Determined by evacuation modelling: Detection time (t det) Alarm time (t alarm) — fire alarm system response Pre movement time (t pre) — recognition, decision making, preparation Travel time (t travel) — physical movement to a place of safety RSET = t det + t alarm + t pre + t travel Safety criterion: ASET RSET × Safety Factor (typically 1.5 2.0) Pre Movement Time Data Pre movement time is the most uncertain variable: Occupancy Awake/Asleep Familiarity Pre Movement Time Office Awake Familiar 30 120 seconds Retail Awake Unfamiliar 60 180 seconds Hotel Asleep Unfamiliar 120 600 seconds Residential Asleep Familiar 120 300 seconds Hospital (ambulant) Mixed Familiar 60 180 seconds Hospital (non ambulant) Mixed N/A 300 1200 seconds School Awake Familiar 15 60 seconds Modelling Software Software Type Developer Key Features Pathfinder Agent based Thunderhead 3D, BIM integration, steering mode STEPS Agent based Mott MacDonald Multi floor, escalators, lifts MassMotion Agent based Oasys Large venues, transport hubs FDS+Evac Coupled fire evac NIST/VTT Integrated with FDS fire model Exodus Agent based Univ. Greenwich Research grade, behavioural model PedSim Flow based Various Simple geometries, quick results Agent Based Modelling How It Works 1. Population definition — age distribution, mobility, pre movement times 2. Geometry import — 3D building model from BIM or CAD 3. Route assignment — agents choose routes based on familiarity, signage, visibility 4. Movement simulation — agents navigate using steering algorithms 5. Results analysis — evacuation time, flow rates, congestion points, residual populations Key Parameters Walking speeds — 1.2 m/s (average adult), reduced for elderly/disabled Door flow rates — 1.33 persons/second per metre of door width Stair speeds — 0.6 0.8 m/s downward, 0.4 0.5 m/s upward Density limits — maximum 4 persons/m² in queuing areas Merge ratios — floor to staircase merging typically 50:50 Validation and Verification V&V Process (BS 7974 Part 6) 1. Code verification — is the software solving the equations correctly? 2. Model validation — does the model represent reality? 3. Sensitivity analysis — how do results change with input variation? 4. Scenario analysis — multiple fire/evacuation scenarios tested 5. Peer review — independent review of methodology and results Acceptance Criteria No trapped agents in any scenario ASET 1.5 × RSET minimum (BS 7974 recommendation) Congestion — no queue density exceeding 4 persons/m² Flow rates — no exit exceeding 80% of theoretical capacity Sensitivity — results robust across ±20% parameter variation Real World Applications Stadium Evacuation (50,000 capacity) 8 minute total clearance target (FIFA requirement) Multi scenario analysis: normal exit, restricted exits, adverse weather Agent based modelling with 50,000 individual agents Validated against actual evacuation drill data High Rise Residential (50 storeys) Progressive horizontal evacuation from fire floor Simultaneous evacuation as worst case scenario Dual staircase capacity analysis with contraflow (firefighters ascending) Lift assisted evacuation for mobility impaired residents Magnus Opifex SEVEN LTD — UK's Leading Fire Safety & Fire Engineering Consultancy 🌐 magnus opifex.co.uk 📞 +44 7486 691724 ✉️ office@magnus opifex.co.uk Founders: Nicoleta Vasile, Baroness of Brattleby — CEO, Lawyer and Barrister, Legal & Administrative Director Alina — Technical Director & Expert Fire Engineer (BEng) Head Office: Ealing Cross, 85 Uxbridge Road, London W5 5BW Magnus Opifex SEVEN LTD delivers engineering led fire engineering, fire risk assessments, CFD modelling, and building safety consultancy across the United Kingdom and internationally. With over 20 years of combined experience and a UK portfolio spanning healthcare, residential and infrastructure, we bring truly engineered solutions with a personal touch. © 2026 Magnus Opifex SEVEN LTD. All rights reserved.