Tall buildings exceed the scope of standard prescriptive guidance. Fire engineering approaches using BS 9991 and BS 7974 are essential for buildings over 30m.. When Prescriptive Guidance Falls Short Approved Document B provides prescriptive guidance for buildings up to 30m. Beyond this height, the complexity of fire safety design increases exponentially. BS 9991: Code of Practice for Fire Safety in Residential Buildings This code provides recommendations for: Evacuation strategy — stay put, simultaneous, or phased evacuation Common corridor ventilation — smoke shafts, mechanical ventilation Firefighting access — firefighting shafts, wet risers, fire service lifts Sprinkler provision — recommended above 30m Structural fire resistance — 120 minutes above 30m The 30m+ Challenges 1. Evacuation time — evacuating a 40 storey building via stairs can take 90+ minutes 2. Stack effect — wind driven fires and stack driven smoke spread intensify with height 3. Firefighting — fire service aerial appliances limited to 30m; above this, internal firefighting is required 4. Water supply — booster pumps needed for wet risers; gravity fed systems insufficient 5. Wind effects — wind pressures affect smoke movement and evacuation routes at height Fire Engineering Framework (BS 7974) The fire engineering approach follows: 1. Qualitative Design Review (QDR) — identify fire hazards, scenarios, design objectives 2. Quantitative Analysis — fire modelling (CFD), evacuation modelling, structural analysis 3. Assessment — compare results against acceptance criteria (tenability limits) 4. Reporting — fire engineering report with clear design parameters and ongoing management requirements Tenability Criteria Parameter Limit Visibility 10m in large spaces, 5m in small rooms Temperature <60°C at head height Radiation <2.5 kW/m² CO concentration <1,400 ppm (30 min exposure) O₂ concentration 15% Key Design Decisions Single vs dual stair — BS 9991 recommends dual stairs above 30m; single stair possible with compensatory measures but increasingly challenged Sprinklers — virtually essential above 30m for insurance, structural efficiency, and evacuation strategy Evacuation lifts — becoming standard for tall residential buildings to assist mobility impaired residents For tall building fire engineering, contact us. 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.