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Hazardous Areas - Classification  

The following pages on this website feature hazardous area information
Classification  (this page)
Protection Techniques
Equipment Selection
Australian Standards
Main Features

 

Introduction

This page refers to the requirements of Australian Standards and is intended to provide a quick reference for some common
aspects of hazardous area classification in gas zones 0, 1 & 2.

For more detailed explanations of the requirements and responsibilities regarding installations in hazardous areas, consult the
relevant standards in your country.

In Australia, the following standards refer to classification of hazardous areas:

  • Gas - AS 2430.1
  • Dust - AS/NZS 61241.3

 

Classification Example:  Class I Zone 1 Group IIA Temp Class T3

 

What is the hazard? (Class)
Class Hazard Remark
I Gases Flammable/explosive gas mixtures
II Dusts Combustible dusts
Note: Australia is aligning with IEC Standards and Classes are being replaced by Zones 0, 1 & 2 for gases and Zones 20, 21 & 22 for dusts.

 

How hazardous is it? (Zone)
Grade of Release Description Zone Remark Symbol
Continuous: Source of release is continuous or frequent during normal operation Flammable atmosphere is continuously present or present for long periods 0 Normally Hazardous Search
Primary: Source of release is periodical or occasional during normal operation Flammable atmosphere is likely to occur in normal operations 1 Normally Hazardous Search
Secondary: Source of release is not expected to occur during normal operation Flammable atmosphere is not likely to occur in normal operations and will only exist for a short period if it does occur 2 Not normally hazardous. Only hazardous under fault or abnormal conditions Search
N/A Flammable atmosphere is never present Safe Area Non-hazardous zone None
Classification of zonal ratings also needs to take into account other factors that may result in gases being present for longer periods and in greater quantities. Some examples of factors affecting zonal ratings are:
  • Specific gravity of the gas relative to air (heavier or lighter than air).
  • Pressure of gas release may affect density of gas in some areas.
  • Loss of adequate natural ventilation, caused by walls, structures, wind speed, etc may affect dispersal of gases.
  • Drains, bunds, etc may contain heavier than air gases, while roofs, covers, etc may contain lighter than air gases.
  • Inadequate maintenance, equipment failure, or damage may alter the normal grade of release.
  • Changes to process conditions may alter the normal grade of release.

 

Where is the hazard? (Group)
Group Representative
Gas		 Location Remark
I

Methane

 Coal mining, or equipment subjected to fire damp Gas, not dust
II

A

Propane

 All other industries, surface industries

B

Ethylene

C

Hydrogen

 

Auto-Ignition Temperature (Temperature Classification)
T Class Maximum Surface Temperature and
Minimum Ignition Temperature
T1 450 oC
T2 300 oC
T3 200 oC
T4 135 oC
T5 100 oC
T6 85 oC

Note: Applicable for an ambient temperature of 40 oC.

Remember: Equipment must have an equal or higher temperature class (T1-T6) than the classification of the hazardous area.

Example: A T5 certified switch can be used in areas classified as T1 to T5, but cannot be used in an area classified as T6.

 

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Disclaimer

Tecfind takes reasonable steps to ensure that this web site is kept up to date, but makes no warranties, representations or assurances, whether expressed or implied, as to the currency, reliability, accuracy or completeness of any information or data provided.
Author: Bill Wood 
Copyright © 2003 [Tecfind]. All rights reserved.