# Zone 0 — Certification marks and hazardous-area classifications: cross-market equivalences

For Zone 0, market / system is NEC 500; meaning is The most hazardous environments (continuous explosive atmosphere) have no direct NEC 500 equivalent, verified against its source on 2026-08-11.

- **Designation:** Zone 0 _(verified: appears in the quote below)_
- **Market / system:** NEC 500 _(verified: appears in the quote below)_
- **Meaning:** The most hazardous environments (continuous explosive atmosphere) have no direct NEC 500 equivalent _(verified: appears in the quote below)_

## What the source says

> Zone 0 gap: The most hazardous environments (continuous explosive atmosphere) have no direct NEC 500 equivalent. NEC 505 and IEC both define Zone 0, requiring EPL "a" equipment.

## Source

- https://exknowledge.com/pages/nec-500-vs-atex-iec.html

Last verified: 2026-08-11. Review by: 2027-08-11.
Part of [Certification marks and hazardous-area classifications: cross-market equivalences](https://referencesource.org/certification-standards-equivalence/).