Zone classification is a system for rating hazardous locations by how often an explosive gas or dust atmosphere is likely to be present.
A method of categorizing hazardous areas based on how frequently and for how long an explosive atmosphere is likely to be present. Under the zone system, gas and vapor areas are classified as Zone 0, 1, or 2, and combustible dust areas as Zone 20, 21, or 22, with lower numbers indicating more frequent presence. Classification determines what electrical equipment can be safely used in each area.
At a fuel terminal, the interior vapor space of a storage tank is designated Zone 0, the area around the tank vents Zone 1, and the surrounding yard Zone 2, with explosion-protected lighting and instruments selected to match each zone.
The Class/Division system has traditionally been used in North America, while the zone system originates from international IEC standards; the U.S. National Electrical Code recognizes both, and OSHA permits either approach when properly applied.
Zone 0 is where an explosive gas atmosphere is present continuously or for long periods, Zone 1 is where it is likely to occur during normal operation, and Zone 2 is where it is unlikely and would exist only briefly.
Classification is typically performed by qualified engineers using the properties of the materials present, process conditions, ventilation, and potential release sources, and it should be documented and reviewed whenever processes change.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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