ISO 24678-2:2022

Overview

ISO 24678-2:2022 - Fire safety engineering - Requirements governing algebraic formulae - Part 2: Fire plume specifies requirements for applying explicit algebraic formulae to calculate key characteristics of a fire plume. Intended for fire safety engineering use, the standard constrains how simple, fast-running plume models are documented, validated and applied within a performance-based fire safety design process.

This part of the ISO 24678 series focuses on algebraic methods for plume properties (e.g., temperature rise, vertical velocity, entrained mass flow, mean flame height) and references the general requirements in ISO 24678-1 and the vocabulary in ISO 13943. Informative annexes include a set of formulae for quasi‑steady, axisymmetric plumes from circular or near‑circular fire sources (Annex A) and guidance on fire-source input data (Annex B).

Key topics and technical requirements

• Scope and intended use: Defines application limits for algebraic formulae used to estimate fire plume behavior in design scenarios.
• Description of physical phenomena: Requires clear identification of plume regions (flaming vs. buoyant flow), symmetry assumptions (axisymmetric plumes), and ambient conditions affecting plume behavior.
• Calculation process requirements: Mandates that formula application follows the procedural and documentation expectations set out in ISO 24678-1 (e.g., clear inputs, assumptions and modelling steps).
• Limitations and domain of applicability: Specifies that users must state limitations, validity ranges and scenario constraints (e.g., quiescent environment, circular sources).
• Input parameters and documentation: Requires definition and reporting of required inputs (heat release rate, convective fraction, source diameter, ambient temperature, etc.) and an example documentation format.
• Annex content:
  • Annex A: Formulae for quasi‑steady, axisymmetric fire plumes (circular/near‑circular sources) and comparisons with experimental data.
  • Annex B: Recommended input data for fire-source characterization.

Note: the standard emphasizes that algebraic plume models are simplified and have stringent limitations (e.g., typical plume centreline temperature rise at mean flame height ≈ 500 K; convective fraction typically 0.6–0.7), and should be applied by qualified practitioners.

Practical applications and target users

ISO 24678-2 is useful for:

• Fire safety engineers and consultants performing rapid assessments of plume consequences.
• Designers comparing multiple trial designs or screening design options before detailed CFD.
• Regulators and assessors reviewing documentation of plume calculations in performance‑based designs.
• Those modeling detector activation, ceiling-jet flows, smoke transport through vents, or convective/radiative heat transfer from plumes.

Users should be competent in fire safety engineering and aware that algebraic formulae are best for quick estimates, design sensitivity studies, and early-stage design decisions, with more detailed methods used where necessary.

Related standards

• ISO 24678-1 (General requirements for algebraic formulae)
• ISO 13943 (Fire safety - Vocabulary)
• ISO 23932-1 (Fire safety engineering - performance-based methodology)

Keywords: ISO 24678-2, fire plume, algebraic formulae, fire safety engineering, plume properties, heat release rate, entrained mass flow, mean flame height.