BR18 Fire Safety Guidance: Chapter 8 – Verification of Fire Safety
The Bygningsreglementet 2018 (BR18) guidance for Chapter 5 - Fire, specifically Chapter 8: Eftervisning (Verification), is the official document issued by the Danish Authority Bolig- og Planstyrelsen. It establishes the technical framework for documenting and verifying that building projects meet functional fire safety requirements in Denmark. This guidance is primarily applicable to buildings categorized in Fire Class 3 and Fire Class 4, where standardized or pre-accepted solutions are not fully utilized, requiring specific engineering justifications.
The document details four primary methods for fire safety verification: Brandteknisk begrundet vurdering (Technically reasoned fire assessment), Komparativ analyse (Comparative analysis), Brandteknisk dimensionering (Fire safety engineering design), and Brandprøvning (Fire testing). It provides explicit acceptance criteria for life safety, including specific thresholds for smoke layer height, visibility, temperature, and radiation levels. The scope covers the analysis of evacuation times, the determination of design fire scenarios, and the fire-resistance verification of structural building components using Eurocodes and other deterministic models.
This guidance includes comprehensive technical appendices featuring formulas for hand calculations, smoke filling models, and system failure analysis procedures to ensure a high level of safety even in the event of technical malfunctions.
Verification Methods and Legal Framework
The document defines the formal procedures for proving that a building design fulfills the fire safety objectives of BR18 § 492. Verification must be conducted through one or a combination of the following methods:
- Brandteknisk begrundet vurdering (BBV): A qualitative assessment for simple deviations where the solution provides the same safety level as pre-accepted solutions.
- Komparativ analyse: A comparative study against a pre-accepted reference building, often used when deviations are limited in scope.
- Brandteknisk dimensionering: Quantitative and deterministic analyses using scenarios, safety margins, and sensitivity studies, suitable for major deviations.
- Brandprøvning: Physical fire testing used as a supplement to verify specific products or materials that lack standard classification.
Acceptance Criteria for Life Safety
To evaluate critical conditions during evacuation, the guidance sets specific quantitative acceptance criteria that must not be exceeded before evacuation is complete:
- Smoke Layer Height (z): Must not be lower than 1.6 m + 0.1 * h (where h is ceiling height), and never lower than 2.0 m.
- Visibility: Minimum 5 m in rooms up to 150 m² and 10 m in larger rooms and escape routes, measured at a height of 2.0 m.
- Temperature: Smoke and air temperatures must not exceed 80 °C at 2.0 m above the floor.
- Thermal Radiation: Long-term exposure must not exceed 2.5 kW/m², while short-term exposure is capped at 10.0 kW/m² for up to 4 seconds.
Fire Engineering Design and Modeling
Advanced verification often involves CFD (Computational Fluid Dynamics) or 2-zone models. The document provides strict requirements for modeling parameters to ensure consistency:
- Design Fire: Fire growth is categorized into Slow, Medium, Fast, and Very Fast, defined by the fire growth factor alpha.
- Soot Yield: A minimum soot production value of 0.06 g/g is generally required for design fires, increasing to 0.1 g/g for sprinkler-controlled scenarios.
- System Failure Analysis: Projects in Fire Class 3 and 4 must include an analysis of potential failures in active systems like ABA (Automatic Fire Alarm), AVS (Automatic Sprinkler), and ABV (Fire Ventilation).
- Natural Flow: A supplementary criterion of 8 minutes is set for the time it takes occupants to pass the final bottleneck in the evacuation route.
Verification of Building Components
Building components must be verified for their separating and insulating functions (EI classification). Verification is typically based on Eurocode 5 for timber structures or standard fire curves (ISO 834):
- Insulation (I): Average temperature rise on the unexposed side must not exceed 140 K, with a maximum peak of 180 K at any point.
- Integrity (E): The component must prevent the passage of flames and hot gases for the duration of the required fire resistance period (e.g., EI 30 or EI 60).
- Material Classification: The total assembly is classified based on the material with the lowest fire rating within the component.
Frequently Asked Questions
What is the required smoke-free height for escape routes in Denmark?
The smoke layer height (z) must be at least 1.6 m + 10% of the ceiling height, but it can never be less than 2.0 m above the floor.
When must a system failure analysis be performed?
A systemsvigtsanalyse is mandatory for all building sections in Fire Class 3 and 4 that rely on fire safety engineering design to document safety.
What are the visibility requirements for large rooms during a fire?
In rooms larger than 150 m² and in all escape routes, visibility must be at least 10 meters at a height of 2.0 meters above the floor.
How is a design fire growth rate determined in BR18?
Growth rates are selected based on the building use; for example, offices are typically 'Medium' (0.012 kW/s²), while shops in malls are 'Very Fast' (0.190 kW/s²).
What is the maximum allowed temperature for persons during evacuation?
The temperature in smoke and air must not exceed 80 °C when measured 2.0 meters above the floor.
What is the 'Time to Natural Flow' criterion in Danish fire regulations?
It is a supplementary acceptance criterion set at 8 minutes, representing the time from when evacuation starts until the last bottleneck is passed.
