Area classification is the engineering process of dividing a facility into zones based on how likely a flammable or explosive atmosphere is to be present. It is the map that tells you which parts of a site are dangerous, how dangerous, and therefore what equipment is allowed to be installed there. Get it right and ignition sources are kept out of hazardous atmospheres; get it wrong and a spark meets a gas cloud. This guide explains how area classification works in oil and gas.
Area Classification in one line: Area classification is the systematic assessment of a facility to identify where flammable gases, vapors, or dusts may be present and how often, then dividing those locations into hazardous areas by likelihood. Two systems are used: the IEC/international zone system (Zone 0, 1, 2 for gases) and the North American division system (Class I, Division 1 and 2). The classification, together with the gas group and temperature class, dictates which protection methods and certified equipment may be installed in each area.
Area classification starts by identifying sources of release - anywhere flammable material can escape, such as flanges, seals, vents, and open sampling points - and then judging how likely a flammable atmosphere is around each. The result is expressed as zones or divisions. In the IEC/ATEX zone system for gases: Zone 0 is where a flammable atmosphere is present continuously or for long periods, Zone 1 where it is likely in normal operation, and Zone 2 where it is unlikely and only for short periods if it occurs. Zones 20, 21, and 22 cover combustible dusts.
North American practice historically uses the division system: Class I (flammable gases and vapors), Division 1 where a hazardous atmosphere exists under normal conditions, and Division 2 where it exists only under abnormal conditions. The two systems roughly align - Zone 0 and 1 map to Division 1, Zone 2 maps to Division 2 - and modern US codes also permit the zone system. Classified areas also have an extent, the physical distance the hazard is assumed to reach around each release source.
Two further attributes complete the picture. The gas group (IIA/IIB/IIC internationally, or Groups A through D in North America) reflects how easily the specific gas ignites and how much energy a spark can carry - hydrogen and acetylene are the hardest to protect against. The temperature class (T1 to T6) caps the maximum surface temperature equipment may reach, so a hot surface cannot ignite the surrounding gas. Equipment installed in a classified area must be certified for that zone or division, gas group, and temperature class.
Almost every oil and gas facility contains classified areas. Wellheads, tank batteries, separators, compressor buildings, loading racks, and gas plants all handle flammable hydrocarbons, so the space around release sources is classified and drawn onto hazardous-area drawings. Most outdoor process areas at a well site or tank battery fall into Zone 2 or Class I Division 2, with tighter Zone 1 or Division 1 pockets right at open release points such as tank vents and hatches.
The classification drives every electrical and instrumentation decision in that space. It determines whether a device must be intrinsically safe, housed in an explosion-proof enclosure, or purged and pressurized; it dictates the certification an instrument, junction box, or control panel must carry; and it governs how conduit and cable are sealed. Installing an uncertified device in a classified area, or letting an area's classification drift as the process changes, is a direct safety and compliance failure.
Area classification is a physical-installation discipline and is invisible to the data a device produces. A pressure transmitter in a Zone 2 area reports the same signal as one in a safe area once it reaches the control system. A cloud SCADA such as Merobix reads those values over Modbus, DNP3, or OPC UA regardless of where the field device sits - but the choice of that device, its enclosure, and its wiring is governed entirely by the area classification at its location.
They are two systems for the same goal. The IEC/international system uses Zone 0, 1, and 2 for gases (and 20, 21, 22 for dusts), graded by how continuously a flammable atmosphere is present. North American practice uses Class I, Divisions 1 and 2. Roughly, Zones 0 and 1 correspond to Division 1 and Zone 2 to Division 2. Modern US codes permit either system, but a site should not mix them within one area.
The gas group (IIA/IIB/IIC or Groups A-D) reflects how easily a specific gas ignites and how much energy a spark can carry, with hydrogen and acetylene being the most demanding. The temperature class (T1-T6) sets the maximum surface temperature equipment may reach so a hot surface cannot ignite the atmosphere. Certified equipment must match the area's gas group and temperature class, not just its zone or division.
Because the whole point is to keep ignition sources out of atmospheres that might be flammable. The zone or division tells you how likely a flammable atmosphere is, which sets the protection method required - intrinsic safety, explosion-proof housing, or purge and pressurization - and the gas group and temperature class further constrain the certification. Installing equipment not rated for the area's classification defeats the protection entirely.
This page references the standards, specifications, and official documentation published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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