---
title: "Class I Div 1 / Div 2 (NEC)"
description: "Class I Div 1 and Class I Div 2 are the US National Electrical Code (NEC) classifications for hazardous areas where flammable gases or vapours are or could be present. The NEC framework is the dominant US standard, paralleling but not identical to the ATEX / IECEx zone system used in the rest of the world."
canonical_url: "https://sylio.co/glossary/class-i-div-1-div-2-nec"
last_updated: "2026-06-28T02:29:38.432Z"
---

**Class I Div 1 and Class I Div 2** are the US National Electrical Code (NEC) classifications for hazardous areas where flammable gases or vapours are or could be present. The NEC framework is the dominant US standard, paralleling but not identical to the [ATEX](/glossary/atex-directive) / [IECEx](/glossary/iecex) zone system used in the rest of the world.

## NEC classes and divisions

<table>
<thead>
  <tr>
    <th>
      Classification
    </th>
    
    <th>
      Equivalent ATEX zone
    </th>
    
    <th>
      Description
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      Class I Div 1
    </td>
    
    <td>
      Zone 0 / Zone 1
    </td>
    
    <td>
      Flammable gas / vapour present in normal operation
    </td>
  </tr>
  
  <tr>
    <td>
      Class I Div 2
    </td>
    
    <td>
      Zone 2
    </td>
    
    <td>
      Flammable gas / vapour not present in normal operation
    </td>
  </tr>
  
  <tr>
    <td>
      Class II Div 1
    </td>
    
    <td>
      Zone 20 / Zone 21
    </td>
    
    <td>
      Combustible dust present in normal operation
    </td>
  </tr>
  
  <tr>
    <td>
      Class II Div 2
    </td>
    
    <td>
      Zone 22
    </td>
    
    <td>
      Combustible dust not present in normal operation
    </td>
  </tr>
  
  <tr>
    <td>
      Class III
    </td>
    
    <td>
      n/a
    </td>
    
    <td>
      Ignitable fibres (textiles, fine wood)
    </td>
  </tr>
</tbody>
</table>

NEC also adopts the IEC zone system (Zone 0/1/2 for gas, Zone 20/21/22 for dust) for newer installations alongside the legacy Class/Division system.

## Practical implications for sonic horns

US power-plant and refinery sonic-horn purchases routinely specify Class I Div 2 or Class II Div 2 certification depending on the application. European-sourced horns typically carry both ATEX and a third-party-certified NEC equivalent to satisfy US buyers.

## Related terms

- [ATEX directive](/glossary/atex-directive)
- [IECEx](/glossary/iecex)
- [IEC 60079](/glossary/iec-60079)