ISO 6184-2:1985

Overview

ISO 6184-2:1985, "Explosion protection systems - Part 2: Determination of explosion indices of combustible gases in air," specifies a reference test method for measuring the explosion indices of gas/air mixtures in a confined volume. The standard defines how to obtain the two primary explosion metrics - Pmax (maximum explosion overpressure) and K (index related to the maximum rate of pressure rise) - under controlled “at rest” and turbulent conditions, and gives criteria for correlating results from other test methods to this reference procedure.

Key Topics and Requirements

• Reference test apparatus: a cylindrical 1 m3 test chamber (nominal 1:1 geometry) equipped with a pressure transducer and recorder.
• Ignition system: electrical spark source (example: induction spark train, 0.5 s duration) with electrodes spaced 3–5 mm; a high-voltage transformer (approx. 15 kV output) is described as an example.
• Turbulence generation: a ~5 L pressurized reservoir (up to 20 bar) connected by a 19 mm rapid-opening valve and a perforated semi‑annular spray ring (hole diameters 4–6 mm, total cross-sectional area ~300 mm²) to inject a turbulent charge; valve opens within 10 ms.
• Test procedure:
  • Prepare homogeneous gas/air mixtures (partial-pressure or other accepted methods) at atmospheric pressure.
  • Record pressure-time traces for a wide concentration range to plot Pmax and K versus concentration.
  • For turbulent tests, inject compressed charge and ignite after a defined ignition delay (turbulence index t_i).
• Definitions and indices: Pmax (maximum overpressure), K (relates to maximum dP/dt for volume V), Kmax at rest and turbulent, turbulence indices (t_i and Tu).
• Performance and uncertainty: typical precision on Pmax is ±4%; precision for Kmax depends on turbulence conditions.
• Correlation allowance: other apparatus/methods may be used provided they can be proven equivalent to the 1 m3 reference over a broad range of gases.

Applications and Users

ISO 6184-2 is directly applicable to:

• Explosion hazard assessment and risk analysis for combustible gases.
• Design and verification of explosion protection systems: venting, suppression, isolation.
• Testing laboratories reporting standardized explosion indices (Pmax, Kmax).
• Safety engineers, plant designers, equipment manufacturers, and regulators who need reliable input data for sizing protective devices and assessing explosion severity.
• Use cases include chemical, petrochemical, gas processing, and other industries handling flammable gases.

Related Standards

• ISO 6184-1: Determination of explosion indices of combustible dusts in air (Part 1).
• ISO 6184-3: Explosion indices for other fuel/air mixtures (Part 3).
• ISO 6184-4: Determination of effectiveness of explosion suppression systems (Part 4).

Keywords: ISO 6184-2:1985, explosion protection, explosion indices, Pmax, Kmax, combustible gases, gas explosion testing, turbulence index, test method.