EX hazardous area zones

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Ex Standards
 
Hazardous area zones and equipment categories.

Gases, vapours, mists and dusts can all form explosive atmospheres with air. Hazardous area classification is used to identify places where, because of the potential for an explosive atmosphere, special precautions over sources of ignition are needed to prevent fires and explosions. Hazardous places are classified in terms of zones on the basis of the frequency and duration of the occurrence of an explosive atmosphere.
For gases, vapours and mists the zone classifications are:
  • Zone 0 A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal for more than 1000hrs per year.
  • Zone 1 A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation between 10-1000hrs per year.
  • Zone 2 A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for less than 10hrs per year.
For dusts the zone classifications are:
  • Zone 20 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for for more than 1000hrs per year.
  • Zone 21 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation between 10-1000hrs per year.
  • Zone 22 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for less than 10hrs per year.
 
Hazardous Area Electrical Equipment

When designing systems where equipment is required for use in a hazardous area environment the equipment must meet the requirements of the classified zone.

Hazardous Area Zone 0


 
  • Ex ia - Intrinsically Safe
  • Ex s - Special protection, must be certified for use in Zone 0

Hazardous Area Zone 1

 
  • Any equipment suitable for Zone 0
  • EX d - Fame Proof
  • Ex p - Pressurised or Purging
  • Ex q - Powder filled
  • Ex o - Oil Filled/immersion
  • Ex e - Increased Safety
  • Ex ib - Intrinsically Safe
  • Ex m - Encapsulation

Hazardous Area Zone 2
 
  • Any equipment suitable for Zone 0 or Zone 1
  • Ex n - Certified that the equipment is not capable under normal operation of igniting a surrounding explosive atmosphere.
 
Temperature Classification

Temperature classification is an important part of hazardous area equipment designation and gives the maximum surface temperature that any part of the equipment can reach under operational or fault conditions, assuming an ambient temperature of 40oC.


 
  • T1 - Surface temperature must not exceed 450oC
  • T2 - Surface temperature must not exceed 300oC
  • T3 - Surface temperature must not exceed 200oC
  • T4 - Surface temperature must not exceed 135oC
  • T5 - Surface temperature must not exceed 100oC
  • T6 - Surface temperature must not exceed 85oC