ISO 24678-4:2023

Overview

ISO 24678-4:2023 - "Fire safety engineering - Requirements governing algebraic formulae - Part 4: Smoke layers" specifies requirements for the application of explicit algebraic formulae used to calculate key characteristics of smoke layers in enclosures. It is part of the ISO 24678 series for fire safety engineering and is intended for qualified fire safety practitioners who use algebraic models (quick analytical methods) to estimate smoke layer behavior during fires in buildings, ships and vehicles.

This standard defines the scope, terminology and required treatment of physical phenomena and the calculation process. Annex A provides practical formulae based on mass, species and energy conservation for predicting smoke layer interface position, average temperatures and species mass fractions. The 2023 edition replaces ISO 16735:2006 and introduces improvements such as inclusion of plume arrival time in smoke filling calculations and comparisons with experimental data.

Key topics and technical requirements

• Applicable phenomena and terminology: Defines smoke layer, interface position (smoke layer height), plume, vent flow, thermal inertia, heat release rate and related terms (references ISO 13943).
• Description of physical phenomena: Requirements for how buoyant smoke layers and influences (buoyancy, wind, mechanical fans) are described and limited in algebraic models.
• Calculation process: Conformance with the general requirements in ISO 24678-1 for calculation methodology, documentation and validation.
• Input parameters and limitations: Specifies what input data must be declared (e.g., heat release rate, vent geometry, material thermal properties) and the domain of applicability for each formula.
• Annex A formulae: Four sets of algebraic formulae for
  • initial-stage smoke filling in a single enclosure,
  • steady-state smoke control by mechanical exhaust,
  • steady-state smoke control by natural vents (multiple cases),
  • methods to estimate interface position, average smoke temperature and species mass fractions.
• Documentation: Example documentation that meets the requirements for transparency and traceability of assumptions and limitations.

Practical applications

• Rapid estimation of smoke filling time and smoke layer height for performance-based design.
• Preliminary assessment of detector response, occupant tenability and visibility in fire scenarios.
• Comparison of alternative smoke control strategies (natural vents vs mechanical exhaust).
• Screening-level analysis to guide more detailed CFD or experimental studies.

Who should use this standard

• Fire safety engineers and consultants
• Building designers and architects involved in performance-based fire design
• Safety assessors for buildings, ships and transport vehicles
• Regulatory bodies and code developers evaluating analytical smoke models

Related standards

• ISO 24678-1 (General requirements for algebraic formulae)
• ISO 13943 (Fire safety - Vocabulary)
• ISO 23932-1 (General principles of fire safety engineering)

Keywords: ISO 24678-4, fire safety engineering, smoke layers, algebraic formulae, smoke interface height, smoke filling, heat release rate, vent flow, smoke control.