Overview - ISO 24678-5:2023 (Vent flows)
ISO 24678-5:2023 is part of the ISO 24678 series for fire safety engineering and sets out requirements for the use of explicit algebraic formulae to calculate characteristics of vent flows. The standard targets buoyant and thermally driven flows through openings (vents) and provides a documented, repeatable approach for estimating mass flow rate, including cases with equal temperatures, uniform but different temperatures, and two-layer temperature profiles. Annex A contains the formula set (based on orifice flow theory) and Annex B gives example flow coefficient values.
Key topics and technical requirements
- Scope and references: Links to ISO 24678-1 (general requirements) and ISO 13943 (terminology).
- Terms & definitions: Neutral plane height, effective flow area, flow coefficient, smoke layer height, hydrostatic pressure, quasi-steady state, etc.
- Physical phenomena description: Buoyant vent flow behavior, limitations of simple algebraic models, and identification of applicable physical scenarios (natural vent flow, mechanical exhaust, pressurization).
- Calculation process requirements: Procedures for applying algebraic formulae to compute vent mass flows and mass fluxes between enclosures.
- Input parameter controls: Requirements for specifying temperatures, densities, effective areas, and flow coefficients.
- Domain of applicability and limitations: Clear statement of when the formulae are valid; effects such as wind or mechanical forces are acknowledged but not modelled by this part.
- Documentation example: Annex A provides sample documentation that satisfies Clauses 4–8; Annex B lists representative flow coefficient values for practical use.
Practical applications and users
ISO 24678-5 is intended for fire safety engineering and performance-based design where rapid, defensible estimates of vent and smoke flows are needed. Typical applications include:
- Estimating smoke movement and mass flow rates through vents in compartment fire scenarios
- Early-stage design and comparison of smoke control strategies (natural vs mechanical)
- Calculating inputs for detector response, smoke filling, and smoke extraction designs
- Supporting performance-based compliance documentation and engineering reports
Primary users: fire safety engineers, smoke control/HVAC consultants, building designers, risk assessors, and code officials performing or reviewing engineering calculations.
Related standards
- ISO 24678-1 - General requirements for algebraic formulae in fire safety engineering
- ISO 13943 - Fire safety vocabulary
- ISO 23932-1 - Performance-based fire safety engineering methodology
- ISO 16737 (replaced) - earlier related guidance
Keywords: ISO 24678-5:2023, vent flows, fire safety engineering, algebraic formulae, mass flow rate, smoke control, flow coefficient, neutral plane, performance-based design.