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Hazardous area classification
Hazardous area classification is a system which classifies areas into zones based on the assessment of the frequency of occurrence of an explosive atmosphere and the duration of an explosive gas atmosphere. These areas are classified into Zone 0, Zone 1, and Zone 2.
Zone 0
Zone 0 is an area in which a flammable/explosive atmosphere is present continuously for long periods of time or will occur frequently.
Zone 1
Zone 1 is an area where a flammable/explosive atmosphere is likely to occur occasionally in normal operations. It may exist because of repair, maintenance operations or leakage.
Zone 2
Zone 2 is an area where a flammable/explosive atmosphere is not likely to occur but if it occurs it will exist for a short period of time due to a possible accident or deviation from normal operations. Unclassified zone:- Green Field Area (Area free from Harmful & toxic gases).
Dust Zone Classification
An area with potential of dust explosion. A dust explosion involves the rapid combustion of dust particles that releases energy and usually generates gaseous reaction products. Zones are classified into 3 categories as follows:
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 long periods or frequently.
Zone 21
A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur occasionally in normal operation.
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 a short period only.
H2S Zone Classification
There are 3 zones as per H2S zone classification as described below.
Red Zone
A Red Zone is considered to exist if there is a high risk of H2S release which could be rapidly lethal. It is considered the limit at which personnel carrying EEBA will have no time to don the mask before being overcome. Red Zone is in the principle part of the Amber Zone where the toxic risk lies in High-Risk region as per ADNOC Risk Matrix. Red Zone is the region where:
▪ The toxic risk is greater than or equal to 1E-03 per year..
▪ Locations such as confined spaces, valve pits with high H2S containing equipment, etc. where free movement is highly restricted.
Amber Zone
An Amber Zone is considered to exist outside the Red Zone where there is a tolerable risk of H2S release which could be rapidly lethal. In this zone, personnel carrying an EEBA or keeping at hand’s reach are considered to have time to don the mask before being overcome. Amber Zone is the region outside the red zone where:
▪ The toxic risk (Toxic LSIR) is greater than or equal to 1E-04 per year
▪ Toxic end point of 700 ppm from reasonably worst-case scenarios for each leak sources.
▪ Locations which contain sour gas (1000 ppm) containing equipment in very high congestion / obstruction regions (typically Volume Blockage Ratio (VBR) greater than 50% or typical highly congested offshore module) and Air Changes Rate (ACR) of 12 can’t be maintained for 95% or more and free movement of personnel and escape / evacuation is restricted. Typical examples are highly congested offshore processing platforms.
Yellow Zone
A Yellow Zone is considered to exist outside the Amber Zone if there is a possibility of H2S release which could be lethal if present for prolonged period. In this zone, personnel are considered to have time to reach the strategic locations of EEBA to don the mask before being overcome. Yellow Zone is the region outside the Amber Zone where:
▪ The toxic risk (Toxic LSIR) is greater than or equal to 1E-05 per year.
▪ Toxic end point of 100 ppm from reasonably worst-case scenarios for each leak sources at a distance more than 2m.
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