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Standard

Ex d

ActivePublished: 28 October 2026Updated: 28 October 2026Published
Key innovation
Instead of keeping flammable gas out of the equipment, a flameproof enclosure permits an internal explosion, withstands its pressure, and uses quenching gaps (flame paths) to stop the ignition from propagating to the surrounding explosive atmosphere.
Category
Standard
Abstraction level
Standard
Operation level
DeploymentRobot control
Use cases
Explosion-protected (Ex) robots and equipment for hazardous zonesMotors, switchgear and control enclosures in the oil & gas industryElectrical equipment in the chemical and petrochemical industryLighting and electrical fittings for Zone 1Mining equipment in methane atmospheres

How it works

The enclosure is designed to withstand the pressure of an explosion of the reference gas mixture inside it (overpressure test). All joints between enclosure parts are made as flameproof joints with a controlled maximum gap and minimum flame-path length. When an explosion occurs inside, the expanding hot gases must pass through these narrow, long gaps, where they lose heat and are cooled below the temperature capable of igniting the external atmosphere. The gap parameters are matched to the gas group (IIA/IIB/IIC) based on the Maximum Experimental Safe Gap (MESG). Cables and conductors enter through certified Ex d cable glands (barrier glands where required) so that the flameproof integrity is not compromised.

Problem solved

How to safely operate electrical and mechanical equipment that may produce sparks, arcs or hot surfaces in an atmosphere containing flammable gases or vapours, without allowing an ignition source inside the equipment to ignite that atmosphere.

Components

Pressure-resistant enclosure bodyContains the internal explosion.

The enclosure body designed to withstand, without permanent deformation or loss of integrity, the pressure of an explosion of a mixture formed inside it.

Flameproof joints (flame paths)Cool and quench the escaping gases, preventing transmission of ignition to the outside.

Flanged, threaded or cylindrical joints with a strictly defined maximum gap and minimum length through which post-explosion gases must pass.

Ex d cable glandsMaintain flameproofness at cabling entry points.

Certified cable and conductor entries (barrier glands where required) that preserve the flameproof integrity of the enclosure.

Hyperparameters (configurable axes)

Gas group (IIA/IIB/IIC)Critical

The gas/vapour class the enclosure is certified for, linked to the MESG. IIC (e.g. hydrogen, acetylene) is the most demanding.

Maximum gap / MESGCritical

The permissible flameproof-joint gap selected for the gas group based on the Maximum Experimental Safe Gap.

Flame-path lengthHigh

The minimum joint length through which post-explosion gases pass; a longer path cools and quenches the flame more effectively.

Reference explosion pressureHigh

The pressure the enclosure is verified against in the overpressure test for the given mixture.