ISO 11925-3:1997

Overview

ISO 11925-3:1997 - Reaction to fire tests - Ignitability of building products subjected to direct impingement of flame - Part 3: Multi‑source test - defines a laboratory method and a range of ignition sources to determine the ignitability of building materials, composites and assemblies when exposed to direct flame impingement. The standard focuses on evaluating whether a specimen sustains ignition (flame persistence) under different flame sizes and intensities; it is intended for comparative testing and quality control rather than as a full fire‑performance assessment (for example, it does not measure flame spread).

Key topics and technical requirements

• Scope & principle: Expose specimens to specified flame sources and observe ignition behaviour (sustained vs transient ignition, smouldering, flaming debris).
• Definitions: Includes critical terms such as sustained ignition (flame persisting ≥ 4 s after removal of the source) and transient ignition.
• Ignition sources: Specifies a range of burners to simulate different real‑world flame exposures:
  • Diffusion flame source - simulates natural fluctuating flames.
  • Premixed flame source - more directional and generally hotter.
  • Ignition source A example: stainless steel tube bore ~0.5 mm, propane flow 25 ± 2 ml/min (at 25 °C) for a low‑intensity diffusion flame.
• Gas supply and control: Commercial propane supply with a 1 bar absolute regulator; two flowmeters (accuracy ±0.25%) with flow ranges covering 25 ml/min–160 ml/min and 1 L/min–10 L/min; guidance on temperature equilibration of propane.
• Safety & test environment: Ventilation, extraction of toxic gases, and firefighting means are mandatory because specimens can produce hazardous by‑products and intense flaming.
• Test apparatus & procedure: Details on burners, specimen conditioning, flame application times, observations, and reporting. Annexes provide additional burner characteristics and guidance for end‑use products.

Applications and users

• Who uses it: Fire test laboratories, product manufacturers (building materials, finishes, insulation), specifiers, architects, safety engineers, and regulatory bodies.
• Practical uses:
  • Comparative assessment of material ignitability for product development and QA.
  • Informing material selection in building design where direct flame exposure risk exists (e.g., near heaters, appliances).
  • Basis for further testing or regulatory compliance when combined with complementary standards.

Related standards

• ISO 11925-2 (Single flame source test) - other part of the same series.
• ISO 5657 - ignitability assessment by irradiance (addresses secondary ignition by radiative heat).
• ISO/IEC Guide 52 - glossary of fire terms and definitions referenced by the document.

Keywords: ISO 11925-3:1997, reaction to fire tests, ignitability, multi-source test, building products, ignition sources, propane burners, diffusion flame, premixed flame.