# AEx tD — Certification marks and hazardous-area classifications: cross-market equivalences

For AEx tD, market / system is US; stated equivalent is Zone 21; governing standard / law is ISA 60079-31, verified against its source on 2026-08-11.

- **Designation:** AEx tD _(verified: appears in the quote below)_
- **Market / system:** US _(verified: appears in the quote below)_
- **Stated equivalent:** Zone 21 _(verified: appears in the quote below)_
- **Governing standard / law:** ISA 60079-31 _(verified: appears in the quote below)_

## What the source says

> AEx tD US Zone 21 ISA 60079-31

## Source

- https://www.euroswitch.com/wp-content/uploads/euroswitch-hazardous-area-guide_V6.pdf

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/).