ATEX discussions often start with the explosion protection document, but one of its key technical inputs is area classification. Classification defines where an explosive atmosphere may occur and assigns a zone based on how likely and how long that atmosphere is present. It underpins equipment selection, installations, ventilation assessment, marking and work procedures. This article explains how zoning is built, what zones 0–2 and 20–22 mean, and how they connect to equipment categories, explosion groups and ignition-source control.
What is area classification based on?
Area classification is part of the explosion hazard assessment. The assessment identifies substances and conditions that can form an explosive atmosphere: a mixture of flammable gas, vapour, mist or dust with air that can ignite. It covers normal operation, foreseeable disturbances and fault conditions.
Key sources in Finland and the EU include:
- Government Decree 576/2003 on protection of workers from the risks of explosive atmospheres
- ATEX workplace directive 1999/92/EC
- ATEX equipment directive 2014/34/EU
- Act on the Safety of Hazardous Chemicals and Explosives (390/2005)
- IEC 60079-10-1:2020 for classification of areas with gas and vapour explosion hazards
- SFS-EN 60079-10-2 for classification of areas with dust explosion hazards
- SFS Handbook 59 as practical guidance, especially for flammable liquids and gases
Zoning is not an opinion or a box-ticking annex. It is a documented assessment used to choose equipment, installations and operating practices.
A three-step assessment process
Explosion hazard assessment usually follows the hierarchy of controls: first prevent an explosive atmosphere from forming, then control ignition sources, and if needed limit the effects of an explosion. In practice the steps overlap, and the measures you need depend on the overall risk.
1. Identify and reduce the explosion hazard
First, assess whether substances or conditions on site can form an explosive atmosphere. Ask, for example:
- are flammable vapours, gases or dust present
- can they mix sufficiently with air
- can a mixture form in normal operation or during disturbances
If the formation of an explosive atmosphere can be reliably prevented by design and operating measures, the need for hazardous-area classification may be eliminated for that particular hazard. This conclusion must be supported by the explosion hazard assessment. Other chemical, fire and occupational safety risks must still be assessed separately. If formation is possible, move on to zoning and protection design.
2. Prevent ignition
Where a mixture can form, identify and control ignition sources. Typical sources include hot surfaces, mechanical sparks, static electricity, electrical equipment, open flames and hot work. If ignition can be reliably prevented, risk drops significantly. The protection measures you still need depend on the overall risk assessment.
3. Limit the effects of an explosion
If you cannot fully rule out mixture formation or ignition, plan technical and organisational measures to limit the consequences. These may include explosion pressure relief, flame arresters, explosion suppression, structural strengthening and procedures that reduce harm to people.
Explosion triangle and pentagon: In the basic model an explosion needs fuel, an oxidiser and an ignition source. Remove one and there is no explosion. For dust explosions the model expands to a pentagon: you also need dust dispersed in air and a confining space. An exception is where oxygen is replaced by another oxidiser, such as a nitrate or peroxide: the principle stays the same.
Gas, vapour and mist zones: 0, 1 and 2
Where the hazard involves flammable gas, vapour or mist, use zones 0–2. The distinction is based on how likely an explosive atmosphere is to occur and how long it may persist.
| Zone | Presence | Meaning |
|---|---|---|
| 0 | Continuously, for long periods or frequently | An explosive mixture is an inherent part of the process, or forms for a long time, for example during open handling. |
| 1 | Occasionally or periodically in normal operation | Mixture formation is part of the process, but it is neither continuous nor long-lasting. |
| 2 | Unlikely in normal operation | An explosive mixture is not expected in normal operation; if it does form, it usually lasts only a short time. |
Practical sources include fuel vapours, solvents, LPG and places where pressurised gases are used or changed. Also assess the extent of the effect: a zone does not always cover an entire hall, often only a limited area around the source.
Dust zones: 20, 21 and 22
For combustible dust, use zones 20–22. The classification concerns explosive dust clouds, while dust layers, deposits and accumulations must also be considered as potential sources of explosive dust atmospheres.
| Zone | Presence | Meaning |
|---|---|---|
| 20 | Continuously, for long periods or frequently | The area is permanently or repeatedly a dust explosion hazard, often inside closed processes. |
| 21 | Occasionally in normal operation | A dust mixture may form periodically in normal work steps such as filling, emptying or transfer. |
| 22 | Unlikely in normal operation | An explosive dust mixture is not expected in normal operation; if it does form, it usually lasts only a short time. |
Dust zoning is typically needed where fine organic or other combustible dust is handled. Assess both airborne dust and layers that can later lift into a cloud.
Matching zones to equipment categories
Zoning describes how often an explosive atmosphere may be present and sets the minimum protection level for equipment. Final suitability also depends on EPL, gas or dust grouping, temperature requirements, environmental conditions and intended use. Under the ATEX equipment directive, products fall into two main groups: Group I for mining and Group II for other explosive atmospheres. Industry and workshops usually deal with Group II.
Ex equipment also uses Equipment Protection Levels (EPL). For gases and vapours, zones 0, 1 and 2 typically correspond to EPL Ga, Gb and Gc; for dusts, zones 20, 21 and 22 correspond to EPL Da, Db and Dc.
Group II equipment is divided into three categories:
- Category 1: very high protection level, two independent means of protection, safe even in fault conditions
- Category 2: high protection level, safe in normal operation and during frequent disturbances
- Category 3: normal protection level, for situations where a mixture appears rarely and briefly
In the marking, G means gases and vapours, D means dusts. For example, II 2D is Group II, Category 2 equipment for dusty explosive atmospheres.
The table below shows the minimum Group II category driven by the zone. That alone does not decide suitability: also check the full Ex marking, EPL, gas or dust group, temperature class or maximum surface temperature, and the operating environment.
| Zone | Minimum requirement | Note |
|---|---|---|
| 0 (G) | II 1G | Highest protection; can also be used in lower zones |
| 1 (G) | II 2G (or 1G) | Suitable for intermittent exposure |
| 2 (G) | II 3G (or 1G/2G) | Basic protection for rare, short events |
| 20 (D) | II 1D | Highest dust protection |
| 21 (D) | II 2D (or 1D) | Suitable for intermittent dust exposure |
| 22 (D) | II 3D (or 1D/2D) | Basic protection for occasional dust exposure |
Higher-protection equipment can usually be used in a lower-demand zone if the other suitability requirements are met.
Equipment must meet the minimum category required for the zone and must also be suitable for the specific substance, environment and conditions of use.
Electrical protection concepts by zone
An Ex marking also states the protection concept. A single concept letter does not automatically decide which zone the equipment suits. Common electrical concepts include:
| Marking | Protection principle | Note |
|---|---|---|
| Ex i | Intrinsic safety | Protection level depends on ia, ib or ic |
| Ex d | Flameproof enclosure | Suitability depends on the full Ex marking |
| Ex e | Increased safety | Suitability depends on protection level and the full Ex marking |
| Ex p | Pressurisation | Protection level and design affect suitability |
| Ex m | Encapsulation | Protection level depends on, among other things, ma, mb or mc |
| Ex t | Enclosure for dust atmospheres | Used in dusty explosive atmospheres |
So a single Ex protection concept does not by itself say which zone the equipment suits. Check suitability from the full Ex marking and the manufacturer’s stated conditions of use.
For mechanical equipment, ISO 80079-36 and ISO 80079-37 apply. The protection concepts include constructional safety (c), control of ignition sources (b) and liquid immersion (k).
Explosion groups and temperature classes
Zoning alone is not enough for equipment selection. Substance properties also define the explosion group and temperature class.
Gas groups:
- IIA: less demanding gas group, for example propane
- IIB: more demanding gas group, for example ethylene
- IIC: most demanding gas group, for example hydrogen and acetylene
The explosion group is part of equipment suitability: do not read it as ignition energy alone.
Dust groups:
- IIIA: combustible fibres
- IIIB: non-conductive dust
- IIIC: conductive dust
For gases and vapours, the temperature class limits the equipment’s maximum surface temperature relative to the ignition temperature of the substance. In dust atmospheres, assessment uses the maximum permitted surface temperature and considers ignition properties of both the cloud and the layer. If a surface exceeds the ignition limit, it can ignite without a spark.
Ignition sources that zoning alone does not solve
Zoning defines the area, but safety also depends on how ignition sources are controlled inside it. In practice, assess among other things:
- hot surfaces and hot gases
- open flames and hot work
- mechanical sparks and frictional heat
- faults in electrical and electronic equipment
- static electricity in piping, filters and transfers
- charge built up by people on insulating floors or in synthetic clothing
Static control typically relies on equipotential bonding and earthing, managing charge-generating materials and processes, and where needed using antistatic or conductive materials. Environmental conditions such as humidity can also affect charging. Ventilation is critical: it can prevent a mixture from forming at all, or, if it fails, increase the need for zoning.
Installation, inspection and maintenance
ATEX installations follow the manufacturer’s instructions and the relevant standards. For electrical installations the key standard is IEC 60079-14 (latest applicable edition). After installation, carry out the appropriate inspections; inspection and maintenance of Ex electrical installations are covered by IEC 60079-17 (latest applicable edition). Inspection confirms that category, protection concept, surface temperature, cabling, penetrations and earthing match the zoning.
Organisationally, zoning also shows up in day-to-day work:
- marking and warning signs for Ex areas
- staff induction on zones and substances
- hot-work permits and area checks before hot work
- access to safety data sheets
- housekeeping and dust removal
- reporting and handling of deviations
What should good zoning documentation include?
Good area classification is more than one sentence. In practice the documentation usually includes:
- identification of flammable substances and their properties
- source assessment: where a mixture can form
- zones by area, not only for the whole property
- zone drawings that show the boundaries
- justification for each zone (normal operation / disturbance / fault)
- conclusions for equipment, installations, ventilation and work procedures
These form the technical core of the explosion protection document. Without zoning, the document easily stays generic and of little practical use.
When should zoning be updated?
Review area classification whenever operations, processes, workplaces, equipment or ventilation change in a way that affects safety. Update is needed, for example, when:
- new chemicals, gases or dust-generating processes are introduced
- a new workstation, store, silo, paint shop or charging area is built
- ventilation, local extraction or dust extraction is changed
- equipment or its layout is renewed
- gaps are found in a risk assessment or authority inspection
Up-to-date zoning is what keeps equipment choices, marking and staff guidance correct.
Summary
Area classification defines where an explosive atmosphere may occur and assigns a zone based on likelihood and duration. For gases use zones 0–2; for dusts 20–22. Zoning underpins equipment and protection-level choices as well as installation, ventilation and work procedures. Final equipment selection must also consider EPL, gas or dust group, temperature requirements and the operating environment. Assessment follows the hierarchy of controls: first prevent mixture formation, then control ignition, and if needed limit the effects. Good zoning is bounded, justified and documented: neither oversized nor undersized.
If you need help with area classification, zone drawings or a full explosion protection document, RISKRAMI specialists carry out the assessment in line with the standards and legislation.