ISO 24678-3:2022

Overview

ISO 24678-3:2022 - "Fire safety engineering - Requirements governing algebraic formulae - Part 3: Ceiling jet flows" specifies requirements for applying explicit algebraic formulae to calculate key characteristics of ceiling jet flows. It is part of the ISO 24678 series for performance‑based fire safety engineering and is intended for competent practitioners performing rapid engineering calculations (screening, comparison of trial designs, or preliminary design checks) rather than detailed numerical simulation.

Key topics and requirements

• Scope and purpose: Defines the use of algebraic formulae for estimating ceiling jet velocity, ceiling jet temperature, characteristic depth of velocity/temperature profiles, and associated convective heat transfer quantities.
• Assumptions and limitations: Emphasises the need to declare assumptions (e.g., quasi‑steady state, axisymmetric flows, circular or near‑circular fire sources, unobstructed ceilings) and to identify the domain of applicability for each formula.
• Calculation process requirements: Requires clear description of the calculation procedure, input parameters, and the physical regions (plume turning region, source influence zones) where each formula applies.
• Input and documentation: Specifies required input parameters (e.g., heat release rate, fire source diameter, flame height, convective fraction) and an example documentation format. Annex A provides a formula set for quasi‑steady, axisymmetric ceiling jet flows and includes a newly added formula for time‑mean temperature rise in a smoke layer and experimental comparisons.
• Conformance and cross references: Requires consistency with ISO 24678-1 (general requirements for algebraic formulae) and uses terminology from ISO 13943 (fire safety vocabulary).

Practical applications and users

Who uses ISO 24678-3:2022:

• Fire safety engineers and consultants performing performance‑based design
• Building and safety code officials reviewing model assumptions and rapid calculations
• Smoke-control and detection system designers estimating detector response times and smoke layer properties
• Fire protection researchers and manufacturers validating simplified models against experiments

Typical applications:

• Quick estimation of ceiling jet temperatures and velocities for detector placement and response analysis
• Screening-level evaluations during early design to compare alternative fire safety strategies
• Input to compartment fire hazard assessments (smoke filling, radiant and convective heat to ceilings)
• Complementary use with CFD or zone models: algebraic results used for verification, sensitivity studies, or when computational resources are limited

Related standards

• ISO 24678-1 - General requirements for algebraic formulae in fire safety engineering
• ISO 23932-1 - Principles for performance‑based fire safety engineering
• ISO 13943 - Fire safety - Vocabulary
• Other parts of the ISO 24678 series for additional formulae and guidance

ISO 24678-3:2022 is a practical, standards‑based resource for reliably applying algebraic ceiling‑jet models in performance‑based fire safety workflows while ensuring documented assumptions, input clarity, and awareness of model limitations.