Overview
ISO/PAS 24499:2024 - Method of test for burning velocity measurement of A2L flammable gases - is a Publicly Available Specification from ISO (first edition, May 2024) that defines a laboratory method to measure the burning velocity (BV) of slow-burning refrigerants (A2L class) for safety classification and engineering use. The method targets refrigerants with BV below 10 cm/s and documents practical limits (lower measurable BV approximately 3–4 cm/s). The standard describes a vertical open-ended glass tube technique with optical imaging to quantify flame propagation through a quiescent, well-mixed refrigerant–air column.
Key topics
- Test principle: Vertical tube method - flame propagates upward through a prepared refrigerant–air mixture while optical systems record flame front motion.
- Measurement parameters: Flame propagation velocity, flame front area, and cross-sectional area of the flame base; methods to separate local burning velocity from bulk flame speed.
- Apparatus requirements: Test tube design and dimensions, tube positioning, interchangeable damping orifices, quenching considerations, glass type, tube etching and purging procedures.
- Gas handling: Mixture preparation (including partial-pressure technique), purge/exhaust and gas treatment requirements to ensure repeatable concentrations.
- Ignition & visualization: Ignition types and placement, electrode and power-supply considerations; high-speed photography, exposure, scaling/optical distortion, spectral considerations, and camera resolution.
- Experimental protocol: Step-by-step test method, test temperature setting, and protocol for mixtures prepared using partial-pressure techniques.
- Data evaluation: Result expression, uncertainty estimation (BV and concentration uncertainty), and recommended reporting practices.
- Safety & flame behavior: Safety precautions, flame shapes, propagation regimes, stability in tubes, quenching effects, and relation between tube diameter and burning velocity.
Applications
- Refrigerant classification and safety assessment: Provides BV data to support classifications in standards such as ISO 817 and to inform safety requirements in standards like ISO 5149.
- Regulatory compliance & risk analysis: Used by regulators and testing laboratories to quantify relative flammability of A2L refrigerants for codes and equipment approvals.
- Product development & selection: Valuable for HVAC&R manufacturers, refrigerant producers, and system designers assessing alternative, lower-global-warming refrigerants.
- Research & reproducibility: Useful for academic and industrial researchers comparing slow-burning refrigerants; the document notes reproducibility experience (e.g., R-32 ~ 6.7 ± 0.7 cm/s).
Related standards
- ISO 817 (refrigerant safety classification) - referenced for context and use of BV data.
- ISO 5149 (safety requirements for refrigeration systems) - potential consumers of BV-derived limits.
- Research literature and ASHRAE notes are referenced for background on the vertical tube technique and limitations.
Keywords: ISO/PAS 24499:2024, burning velocity, BV measurement, A2L flammable gases, slow burning refrigerants, vertical tube method, refrigerant safety, ISO 817, ISO 5149.