Which protection concepts can be used in Zone 0?

Zone 0 needs equipment with equipment protection level (EPL) Ga, which corresponds to ATEX category 1G. The concepts that reach Ga are intrinsic safety level ia, encapsulation level ma, inherently safe optical radiation op is certified for Ga, non-electrical equipment (Ex h) assessed to Ga, and equipment that combines two independent Gb types of protection under IEC 60079-26. Flameproof da exists but only for catalytic sensors of portable gas detectors, so db, eb, pxb and similar Zone 1 concepts are not acceptable in Zone 0 on their own.

Short answer

• Required level: EPL Ga (category 1G). Zone 0 has an explosive atmosphere continuously, for long periods or frequently, so equipment must stay safe even with rare malfunctions.
• Single concepts that reach Ga: Ex ia (with the whole loop at level ia), Ex ma, Ex op is where certified Ga, Ex h with a Ga assessment, and Ex da only in its narrow scope.
• Combined concepts: two independent types of protection, each giving Gb, combined to give Ga (IEC 60079-26:2021, edition 4).
• Boundary devices: sensors mounted in a tank wall between Zone 0 inside and Zone 1 outside use a separation element and are typically marked Ga/Gb.
• Not Ga on their own: flameproof db, increased safety eb, pressurisation pxb/pyb, oil immersion ob, powder filling q, and all Zone 2 levels.
• Read the EPL, not the letter: the marking must end in Ga (or show category 1G); the concept letter alone does not tell you.

Why Zone 0 needs a higher level of protection

In Zone 0 the explosive atmosphere is present most of the time. A fault that is unlikely on any given day will, sooner or later, coincide with the gas. The ATEX product directive (2014/34/EU, Annex II, 2.1.1.1) therefore requires category 1 equipment for gases to keep its ignition sources inactive even in rare incidents. It must either have a second, independent means of protection that still works if the first fails, or stay safe with two faults occurring independently of each other.

The IEC EPL system says the same thing in different words: Ga equipment is not an ignition source in normal operation, in expected malfunctions or in rare malfunctions. The workplace directive 1999/92/EC and IEC 60079-14 make category 1 / EPL Ga the default for Zone 0. IEC 60079-14 also allows the required EPL to be set by a documented risk assessment, but any departure from Ga in Zone 0 must then be justified and recorded in that assessment.

Concepts that achieve EPL Ga

For dust Zone 20 the equivalent is EPL Da: ia, ma and dust protection by enclosure ta.

Applying it: a tank level sensor

A storage tank holds toluene (IIA, T1). The area classification shows Zone 0 in the vapour space and Zone 1 around the roof nozzles.

• A radar or float level transmitter whose antenna sits in the vapour space and whose electronics sit on the roof can be marked Ga/Gb: the part inside is Ga, the head outside is Gb, and a separation element (the process connection) divides them under IEC 60079-26.
• A temperature sensor fully inside the tank must be Ga, typically Ex ia IIC T4 Ga, connected to associated apparatus marked [Ex ia]. If the barrier is only [Ex ib], the loop is ib (Gb) and not acceptable in Zone 0.
• A flameproof Ex db junction box cannot be mounted inside the tank, even though it is "explosion-proof".

Common mistakes

• Assuming an "ia" field device makes the loop Ga. The associated apparatus, cable parameters and any simple apparatus must all be at level ia. See can Ex ib be used in Zone 0.
• Treating Ex d as the strongest concept. Flameproof db is EPL Gb; it is a Zone 1 concept.
• Ignoring the inside of equipment. Pumps and vapour recovery systems can have a Zone 0 interior; parts in contact with it need category 1 even if the outside is Zone 1.
• Reading old markings wrongly. Older equipment shows only the category (II 1 G) or EEx ia; check the certificate for the level.

Related on excodex

• Ex protection concepts at a glance: d, e, i, p, m, o, q, n and t
• Intrinsic safety (Ex i): ia, ib and ic and the energy limitation principle
• Equipment Protection Levels (EPL): Ga, Gb, Gc, Da, Db, Dc and how they match zones
• Which Ex protection concepts are allowed in Zone 1 and which only in Zone 2?
• Tools: Ex marking check, standards space IEC 60079-26

Standards and further reading

• Directive 2014/34/EU, Annex II, 2.1.1 (category 1 equipment for gases, two independent means of protection or two independent faults): legislation.gov.uk
• IEC 60079-26:2021 (edition 4), equipment with separation elements or combined levels of protection, abstract: webstore.iec.ch
• US Coast Guard OCS National Center of Expertise, Drill Down 28 (equipment protection levels, definition of EPL Ga): dco.uscg.mil
• IEC 60079-28, protection of equipment and transmission systems using optical radiation; 2006 edition with the table of op is, op pr and op sh by EPL and marking examples: law.resource.org; current 2025 edition preview: standards.iteh.ai
• Directive 1999/92/EC, Annex II Part B (equipment categories for each zone): legislation.gov.uk
• IEC 60079-11 (intrinsic safety), IEC 60079-18 (encapsulation), IEC 60079-1 (flameproof), IEC 60079-14 (selection and installation), ISO 80079-36 and ISO 80079-37 (non-electrical equipment).

This article is general technical information prepared by the excodex editorial team. It does not replace the applicable standards, the equipment certificates and instructions, national regulations or the assessment of a competent person.