Complex buildings often require fire-engineered solutions that go beyond prescriptive guidance. We explore when and how performance-based design delivers better outcomes.. Beyond Prescriptive Codes Approved Document B and BS 9999 provide prescriptive fire safety guidance suitable for most conventional buildings. But what happens when a building doesn't fit the standard templates? Atria spanning multiple storeys Open plan designs exceeding compartment size limits Extended travel distances Innovative structural systems Heritage buildings where prescriptive compliance is impractical The BS 7974 Framework BS 7974 provides the methodology for performance based fire engineering in the UK. It uses a systematic approach: Qualitative Design Review (QDR) Define fire safety objectives Identify fire hazards and scenarios Establish trial designs Select appropriate analysis methods Quantitative Analysis Fire dynamics modelling Smoke movement analysis Structural response calculations Evacuation modelling Risk assessment Computational Tools CFD Modelling (e.g., FDS) Computational Fluid Dynamics simulates fire growth, smoke production, and temperature distribution in 3D: Smoke layer depth and temperature predictions Visibility analysis along escape routes Tenability assessment (temperature, toxicity, visibility) Smoke exhaust system design validation Zone Models Simpler two layer models suitable for: Single compartment analysis Preliminary design Parametric studies Rapid assessment of multiple scenarios Evacuation Modelling Agent based models simulate occupant behaviour: Pre movement times based on cue reception and decision making Movement speeds on stairs, corridors, and through doorways Queuing at exits Mobility impaired occupant egress Behavioural responses to fire cues Structural Fire Engineering Finite element analysis of structural behaviour in fire Temperature dependent material properties Load redistribution and alternative load paths Connection behaviour at elevated temperatures Case Study: Multi Storey Atrium Design A 12 storey commercial building with a full height atrium required fire engineered solutions because: Atrium volume exceeded ADB compartment limits Open connections between floors Glazed atrium walls with limited fire rating Solution CFD modelling of design fires at each floor level Smoke exhaust system sized to maintain 2.5m clear layer above highest occupied level Sprinkler protection throughout with enhanced coverage around atrium Smoke curtains at atrium openings Phased evacuation strategy with voice alarm Outcome The fire engineered approach delivered: Open, flexible workspace design (client priority) Equivalent or better safety compared to prescriptive compliance Reduced overall cost compared to full compartmentation approach When to Use Fire Engineering Situation Prescriptive Fire Engineered Standard office ✅ Not needed Large atrium ❌ Cannot comply ✅ Required Heritage conversion Difficult ✅ Recommended Extended travel distance ❌ ✅ Can justify Complex mixed use Challenging ✅ Optimal Regulatory Acceptance Fire engineered solutions require acceptance by: Building Control (local authority or Approved Inspector) Fire and Rescue Service (consulted during design) Building Safety Regulator (for higher risk buildings) Early engagement is essential. A well documented fire engineering report following BS 7974 methodology provides the evidence base for approval. For fire engineered design solutions, contact Magnus Opifex.