Zone 0, 1, and 2 Locations (Gas)

Zone 0 is where the gas is present continuously or for long periods, Zone 1 where it is likely in normal operation, and Zone 2 where it is only present under fault. It maps roughly onto Divisions but with finer gradation, and it comes with its own protection techniques and equipment markings drawn from IEC standards.

The rule that saves you grief is do not mix the two systems in one area. Pick Division or Zone for a given classified space and stay in that language, because the protection methods and markings are not interchangeable across the two schemes.

When it applies

Article 505 offers the Zone system for gases and vapors as an alternative to the Division method, matching the international IEC scheme. Zone 0 is where an explosive atmosphere is present continuously, Zone 1 where it is likely in normal operation, and Zone 2 where it is only expected under abnormal conditions. It is common on projects built to global standards.

Common mistakes

• Mixing Zone and Division equipment and documentation on the same area without a clear conversion.
• Assuming Zone 2 always maps cleanly to Division 2; the boundaries and marking differ.
• Overlooking that equipment must be marked and listed for the Zone scheme.

In the field

On an international refinery job the design came in Zones, so I keep all my equipment marking and documentation in that same system. Trying to translate on the fly between Zone and Division is where errors creep in.