Flammability testing: Flammable gas and vapour jargon buster

Understanding the flammability properties of gases and vapours is crucial for preventing fires and explosions in an industrial setting. To ensure the safety of workers and facilities, various tests — based upon national and international standards — have been developed to help categorise the flammability properties of gases and vapours.

The following list provides a brief overview of the various jargon, tests, and measurements used to assess flammable gases and vapours. It should serve as a valuable resource for professionals involved in flammable gas and vapour hazard management and fire and explosion mitigation.

Flashpoint temperature

Flashpoint is an important parameter when considering the safe handling of flammable liquids. At temperatures below the flashpoint, insufficient vapour is generated to form a flammable concentration in air. The closed-cup method of this test tends to derive lower, or worse, case results because of the confined arrangement.

Upper and lower flammable limits (UFL and LFL)

Understanding the flammable range of a gas or vapour can be useful for determining if a process is operating within its flammable range. The limit values for the vapours and gases are quoted in volume percent. Flammability limits are usually determined at ambient temperature, but widen with increasing temperature.

Minimum ignition energy (MIE)

The MIE is a measure of the sensitivity of a gas or vapour to electrostatic discharges. MIE values are obtained when the gas or vapour concentration is at (or near) the optimum (or stoichiometric) mixture with air. For electrostatic spark assessment, the results obtained by trickle charge and capacitor discharge are relevant.

Auto ignition temperature (AIT)

AIT data is important, when operating in the vicinity of flammable gases and vapours, for selecting the correct maximum surface temperature of electrical equipment in hazardous areas.

Explosion severity

Similar to combustible dusts, the parameters of an explosion severity test are used for the design of new and verification of existing explosion protection systems. P_max and (dP/dt)_max values are determined using a 5L spherical, pressure shock resistant vessel. The explosion severity constant for gases and vapours (K_G), is determined by:

Kg = (dP/dt)max ⁡* V^1/3

Limiting oxygen concentration (LOC)

An LOC assessment determines the minimum concentration of oxygen required to support combustion of a flammable vapour/gas. The test can be completed using several different inert gases — including nitrogen, carbon dioxide, or water vapour. As per combustible dusts, LOC is used to determine the maximum permissible oxygen concentration (MPOC) within inerted or partially inerted vessels.

Minimum igniting current (MIC) and maximum experimental safe gap (MESG)

The MIC is used to determine a flammable gas’ or vapour’s gas group, which can help when selecting electrical equipment to be used in the gas or vapour atmosphere. For most gases or vapours, it is sufficient to make only the determination of the MIC to classify the gas or vapour. However, if the gas or vapour falls on the borderline of two gas groups, it is necessary to undertake the MESG to decide the result.

Gas group data can be used for the selection of electrical equipment and, among other things, the maximum size of insulating plastics (that can cause the occurrence of incendive ‘brush discharges’) for use or presence in hazardous areas.

Liquid conductivity

Conductivity data determines whether liquids are electrically insulating and could accumulate electrostatic charge, or conducting and would likely not accumulate hazardous electrostatic charge in earthed all-metal plant items and equipment.

For further information on assessing gas and vapour flammability — or interpreting test data — reach out to your usual Marsh contact.

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Jargon buster: Flammable gas and vapour testing

Flashpoint temperature

Upper and lower flammable limits (UFL and LFL)

Minimum ignition energy (MIE)

Auto ignition temperature (AIT)

Explosion severity

Limiting oxygen concentration (LOC)

Minimum igniting current (MIC) and maximum experimental safe gap (MESG)

Liquid conductivity

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Jargon buster: Flammable gas and vapour testing

Flashpoint temperature

Upper and lower flammable limits (UFL and LFL)

Minimum ignition energy (MIE)

Auto ignition temperature (AIT)

Explosion severity

Limiting oxygen concentration (LOC)

Minimum igniting current (MIC) and maximum experimental safe gap (MESG)

Liquid conductivity

Related insights

The importance of selecting credible over generic flammability test data

Jargon buster – combustible dust testing

Letters of Credit: Challenges to insurer collateral requirements

Managing risk in a volatile business environment: The role of integrated risk quantification

Related insights

The importance of selecting credible over generic flammability test data

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