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Overview of Hazardous Areas

Petrochemical facility requiring specialist assessment for hazardous areas

What is a Hazardous Area?

A hazardous area is a location where the potential for fire or explosion exists caused by the presence of ignitable gases or dusts in the atmosphere. Examples of these locations include oil & gas facilities, chemical processing plants and pharmaceutical manufacturers.
Hazardous areas are defined as:
 
• “Zones” under worldwide IEC standards (and their local versions, such as ATEX in Europe)
• “Divisions” under North American NEC standards.
 
  • Under the “Zone” system, hazards are defined for gas as Zone 0, 1 or 2, with 0 as the highest hazard, and for dust as Zone 20, 21 or 22, with 20 as the highest hazard.
  • Under the “Division” system, hazards are defined for gas as Class I Division 1 or 2, with 1 as the highest hazard, and for dust as Class II Division 1 or 2, with 1 as the highest hazard. 
 
 
The classification of Zones and Divisions is related to the frequency and duration that ignitable gases or dusts may be present in the atmosphere.
 
  • Zone 0/20: > 1000 hours /year
  • Zone 1/21: 10 to 1000 hours/year
  • Zone 2/22: < 10 hours/year
 
  • Class I & II Div 1: > 10 hours /year
  • Class I & II Div 2: < 10 hours/year
 

Codes and Standards

Depending on where you are in the world, different codes and standards may apply. Typically, whatever the scheme, they all cover hazardous classification and the protection methods that may be used to prevent explosions in these areas.
 
  • Worldwide: IEC defines the most-widely adopted hazardous area standards.
  • In Europe, the ATEX scheme closely follows IEC standards
  • In North America: the NFPA (National Fire Protection Association) is the primary agency for the protection of installations from fire and explosion.

 

Recognised Methods for Explosion Protection

For an explosion to occur, 3 conditions must exist:
 
  • Explosive material is present in a suitable concentration                               
  • The presence of air or oxygen
  • A source of ignition

 
Thus, most forms of explosion prevention and protection rely on the elimination of one or more of these factors. eg preventing leaks or spillages of flammable material, or removing sources of ignition.
Under the various codes and standards, there are a number of recognised methods for explosion protection.
 
This table shows methods under the IEC/ATEX schemes.
 
 
This table shows methods under North American schemes.
 
 

Classification of flammable materials

Depending on their properties, gases and dusts are classified by group. These properties include factors such as ignition energy, auto-ignition temperature, upper and lower explosive limits, flash point, etc.
Group definitions may vary between certification schemes.
 
 

 

Temperature Classification

Temperature classification (also known as temperature class, or T class) defines the maximum surface temperature that a product destined for use in a potentially hazardous atmosphere is allowed to operate at, relative to an ambient temperature of -20°C to +40°C.

All flammable gases have an auto-ignition temperature. If a flammable mixture of the gas is exposed to a component above the auto-ignition temperature, then the mixture will ignite. Therefore, when selecting equipment, the Temperature class must be below the auto-ignition temperature of the potentially explosive atmosphere where it will be installed.

 

For full hazardous area information, download our Hazardous Location Chart from the Resources section

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