Hazardous Area Zone Classifications

Hazardous area is defined as an area in which an explosive gas atmosphere is present, or may be expected to be present, in sufficient quantities to require special precautions for the construction, installation and use of potential ignition sources.

Zone Classification

  • Zone 0
    Area in which an explosive atmosphere consisting of a mixture of air with flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently.
  • Zone 1
    Area in which an explosive atmosphere consisting of a mixture of air with flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally.
  • Zone 2
    Place in which an explosive atmosphere consisting of a mixture of air with flammable 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 a short period only.

For the purpose of area classification, a source of release is defined as a point from which a flammable gas, vapour or liquid may be released into the atmosphere.

Grade of Release

  • Continuous Grade Release
    A release which is continuous or is expected to occur frequently or for long periods.
  • Primary Grade Release
    A release which can be expected to occur periodically or occasionally during normal operation.
  • Secondary Grade Release
    A release which is not expected to occur in normal operation and, if it does occur, is likely to do so only infrequently and for short periods.

Notes:

  1. Normal operation is defined as when the plant equipment is operating within its design parameters. Normal operation includes start-up and shutdown conditions but does not include planned maintenance activities.
  2. Minor releases of flammable material may be part of normal operation, i.e. vented instrument gas from control valves is considered to be minor releases.
  3. Failures, such as the breakdown of seals, flange gaskets or spillage caused by accidents, which involve repair or shut down are not considered to be part of normal operation.

About the Author

Ver Pangonilo
A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia and Professional Electrical Engineer (PEE) - Philippines with extensive experience in concept select, front-end engineering, HV & LV detail design, construction and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and waste water pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).
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