- Gas zones 0, 1 and 2 are defined in IEC 60079-10-1 and dust zones 20, 21 and 22 in IEC 60079-10-2, by likelihood and duration.
- Division 1 covers both Zone 0 and Zone 1, while Zone 2 corresponds to Division 2, so the two systems cannot be mapped mechanically in both directions.
- Area classification is the plant operator's duty, not the supplier's; a device vendor can state what its equipment suits but cannot tell you your zone.
- A portable device must be selected for the most onerous zone it will enter, and any Zone 21 area on the route requires a dust marking too.
Every specification for equipment that will be carried into a plant begins in the same place, and it is not the datasheet. It begins with a drawing: the hazardous area classification drawing, which divides the site into regions according to how likely a flammable atmosphere is to be present, and for how long. Get that reference right and the device question answers itself. Get it wrong and you can buy an entirely genuine certified product that is not permitted where your people actually work.
There are two systems in use worldwide for describing hazardous area zones and their North American cousin, divisions. They overlap, they are not identical, and most large operators end up dealing with both. This guide explains what each one says, who decides, and what the answer means when you are buying a device rather than a motor.
Zones: the IEC and European system
The zone system splits by the medium and then by likelihood. For gases, vapours and mists there are three zones, defined in IEC 60079-10-1. For combustible dusts there are three more, defined in IEC 60079-10-2.
| Zone | Medium | An explosive atmosphere is |
|---|---|---|
| Zone 0 | Gas, vapour, mist | Present continuously, or for long periods, or frequently |
| Zone 1 | Gas, vapour, mist | Likely to occur occasionally in normal operation |
| Zone 2 | Gas, vapour, mist | Not likely in normal operation, and only for a short period if it does |
| Zone 20 | Combustible dust | Present continuously, or for long periods, or frequently |
| Zone 21 | Combustible dust | Likely to occur occasionally in normal operation |
| Zone 22 | Combustible dust | Not likely in normal operation, and only for a short period if it does |
Guidance documents often attach indicative hour counts to those descriptions, along the lines of more than a thousand hours a year for Zone 0, between ten and a thousand for Zone 1 and under ten for Zone 2. Those figures are a planning aid used by some codes of practice. The definitions in the standard are written in terms of likelihood and duration in normal operation, not in hours, and a classification study should be argued on the process rather than on arithmetic.
Two things about the dust zones are routinely missed. The first is that dust and gas are classified independently, so a site can be Zone 2 for gas and Zone 21 for dust in the same physical location, and equipment has to satisfy both. The second is that dust zones are driven as much by layers and housekeeping as by clouds, which is why a fertiliser bagging hall or a mineral handling plant can carry a more onerous dust classification than the visible dust suggests.
Divisions: the North American system
The National Electrical Code, NFPA 70, uses a different cut. Article 500 splits by class, according to what the combustible material is, and then by division, according to likelihood.
- Class I covers flammable gases, flammable liquid-produced vapours and combustible liquid-produced vapours.
- Class II covers combustible dusts.
- Class III covers ignitable fibres and flyings.
- Division 1 means the hazard is present under normal operating conditions, or frequently because of repair, maintenance or leakage.
- Division 2 means the hazard is present only under abnormal conditions, such as the failure of a container or a ventilation system.
The important structural difference is that the division system has two categories where the zone system has three. Zone 0 and Zone 1 both fall inside Division 1. Zone 2 corresponds to Division 2. That asymmetry is why the two systems cannot be mapped mechanically in both directions, and it is the root of most of the cross-acceptance rules in the code.
North America also groups its materials differently. Class I is subdivided into Groups A, B, C and D, characterised by acetylene, hydrogen, ethylene and propane respectively, against the IEC gas groups IIC, IIB and IIA. Class II dusts are subdivided into Groups E, F and G, covering metal dusts, carbonaceous dusts and dusts such as grain, flour and plastics, against the IEC dust groups IIIC, IIIB and IIIA.
How an area actually gets classified
Classification is an engineering study, not a judgement call. It works from sources of release outwards.
- Identify the dangerous substances present and their properties: flash point, vapour density, lower explosive limit, auto-ignition temperature, and for dusts the minimum ignition temperature of a cloud and a layer.
- Identify every source of release: flanges, valve stems, sample points, pump seals, vents, drains, open handling operations, loading arms, and so on.
- Grade each release as continuous, primary or secondary, according to whether it happens continuously, occasionally in normal operation, or only abnormally. The grade of release maps closely onto the resulting zone.
- Assess ventilation, its availability and its effectiveness, which can promote or demote the resulting zone.
- Determine the extent of each zone in three dimensions and record it on drawings, with a supporting schedule listing every source of release and the reasoning.
The methodology comes from IEC 60079-10-1 and IEC 60079-10-2, and in practice sits alongside industry codes: the Energy Institute model code of safe practice part 15 is widely used for petroleum installations, API RP 505 for zone classification and API RP 500 for division classification in the oil and gas industry, and NFPA 497 and NFPA 499 for chemical process areas and combustible dusts in North America.
Who classifies, and why it is never the supplier
The duty sits with the operator of the plant, not the vendor of the equipment. In Great Britain, DSEAR places the obligation on the employer to assess the risk from dangerous substances, classify places where explosive atmospheres may occur into zones, and record the outcome. The European workplace directive 1999/92/EC does the same through the explosion protection document. In the United States, the classification of areas is expected to be documented and available to those who design, install, inspect, maintain and operate the electrical equipment there.
In practice the study is run by a process safety or loss prevention engineer, reviewed by process, mechanical, electrical and operations representatives, and signed off by the technical authority. The output is a set of drawings plus a schedule, and on a well-run site a hazardous area register that lists the Ex equipment installed in each zone with its certificate references.
The consequence for procurement is simple and worth stating plainly to any supplier who tries to be helpful: a device vendor cannot tell you your zone. They can tell you what their equipment is suitable for. Matching one to the other is your engineering decision, and it needs the classification drawing in front of it.
What changes when a site uses NEC 505 or 506
North American projects are not locked into divisions. Article 505 offers the zone system as an alternative for Class I locations, and Article 506 does the same for combustible dusts and ignitable fibres and flyings using Zones 20, 21 and 22. Many international operators with US assets, and many EPC contractors working to a global standard, choose the zone route so that one classification philosophy covers the whole portfolio.
Three things change when they do. The classification methodology follows the IEC approach, so a European engineer reads the drawings without translation. Equipment marking switches to the AEx form, so a label reads Class I, Zone 1, AEx ib IIC T4 Gb instead of Class I, Division 1, Groups C, D, T4, and the familiar equipment protection level letters appear. And the selection logic follows the zone and EPL relationship rather than the division relationship.
What does not change is that it is still the NEC. Equipment still has to be listed for the location by a nationally recognised testing laboratory, the choice of system is a documented project decision rather than something applied area by area on preference, and the code’s own cross-acceptance rules apply. The most relevant of those for a device buyer: equipment listed and marked for Zone 0, 1 or 2 is permitted in Class I Division 2 locations for the same gas and a suitable temperature class, but a Division 1 location is not covered by that allowance. That is exactly why a Class I Division 1 phone requirement is a separate certification target rather than a paperwork exercise on top of an ATEX file.
From zone to device
Once the classification is settled, selection follows a short chain. The zone determines the required equipment protection level. The EPL determines which protection concepts are acceptable. The gas or dust group and the temperature class then filter what remains, and the certified ambient temperature range filters it again.
| Classified as | Minimum EPL | Typical acceptable concepts | NEC division equivalent |
|---|---|---|---|
| Zone 0 | Ga | Ex ia, Ex ma | Class I, Division 1 |
| Zone 1 | Gb | Ex ia, Ex ib, Ex db, Ex eb, Ex mb, Ex pxb | Class I, Division 1 |
| Zone 2 | Gc | Ex ic, Ex ec, Ex mc, Ex nR, Ex pzc | Class I, Division 2 |
| Zone 20 | Da | Ex ia with dust marking, Ex ta | Class II, Division 1 |
| Zone 21 | Db | Ex ib with dust marking, Ex tb | Class II, Division 1 |
| Zone 22 | Dc | Ex ic with dust marking, Ex tc | Class II, Division 2 |
A higher protection level always satisfies a lower requirement. An Ex ia device carrying EPL Ga may be used in Zone 1 and Zone 2; the reverse is never true. The selection rules themselves live in IEC 60079-14, which also covers the design and erection of the installation, and inspection regimes afterwards are covered in IEC 60079-17.
Why a portable device is a harder case than a fixed one
Fixed equipment is easy to reason about. It lives at one set of coordinates, inside one zone, for its whole life. A phone in a pocket does not. Over a single shift a field operator may cross an unclassified control room, a Zone 2 walkway, a Zone 1 pump area and the immediate surroundings of a sample point, several times.
That has one unavoidable consequence for specification: a portable device must be selected for the most onerous zone it will enter, not the average one. On most process plants that is Zone 1, which is why a serious zone 1 mobile phone requirement is the normal starting point rather than a premium option, and why a Zone 2-only handset creates a procedural control problem instead of solving an equipment problem. Controlling that risk by instruction alone means asking a person carrying a phone to remember a boundary line on a drawing while they are doing something else.
Dust is the second thing portable users get wrong. If any part of the route crosses a Zone 21 area, and on minerals, fertiliser, grain, polymer and coal handling sites it almost always does, the device needs a dust marking as well as a gas marking. A gas-only certificate is not a partial answer to a dust zone; it is silent on it.
A practical checklist before you specify anything
- Obtain the current hazardous area classification drawings and the accompanying schedule, not a verbal summary.
- Trace the actual routes your users walk and note the most onerous gas zone and the most onerous dust zone on each.
- Record the gas group and dust group for the substances involved, and the temperature class driven by their ignition temperatures.
- Record the ambient temperature extremes at the site, including solar gain on open plant and cold starts in winter operations.
- Confirm whether the site is classified by zone or by division, and if the site is under NEC, which article applies.
- Write all of that into the specification before you look at a single product page.
Where the IS-04Z1 is aimed
The SAMS IS-04Z1 is designed for Zone 1 and Zone 21, covering gas and dust on one device, with an ATEX target marking of II 2 G Ex ib IIC T4 and a NEC 500 Class I Division 1 target. Certification is in progress ahead of a Q4 2026 launch, so the current conversation with a buyer is about matching a classification to a specification rather than issuing a certificate. Regional context by country is on the market pages, including the United States, Germany, Australia and India, and the rest of the compliance series is in our insights library.
Frequently asked questions
How many hours a year is a Zone 1 area?
Some guidance attaches an indicative figure of between ten and a thousand hours a year to Zone 1, against more than a thousand for Zone 0 and under ten for Zone 2. These are planning aids used by some codes of practice. The standard defines zones by likelihood and duration in normal operation, not hours, so a classification should be argued on the process.
Can one location be classified for both gas and dust?
Yes. Dust and gas are classified independently, so one physical location can be Zone 2 for gas and Zone 21 for dust, and equipment there has to satisfy both. Dust zones are driven by layers and housekeeping as much as by clouds, so a fertiliser bagging hall or mineral handling plant can carry a more onerous dust classification than visible dust suggests.
What are the North American equivalents of IEC gas groups IIA, IIB and IIC?
NEC Class I is divided into Groups A, B, C and D, characterised by acetylene, hydrogen, ethylene and propane respectively, against the IEC gas groups IIC, IIB and IIA. Class II dusts are divided into Groups E, F and G, covering metal dusts, carbonaceous dusts and dusts such as grain, flour and plastics, against IEC dust groups IIIC, IIIB and IIIA.
Can a site in the United States use zones instead of divisions?
Yes. NEC Article 505 offers the zone system as an alternative for Class I locations, and Article 506 does the same for combustible dusts and fibres using Zones 20, 21 and 22. Classification then follows the IEC approach and marking uses the AEx form, but equipment must still be listed for the location by a nationally recognised testing laboratory.