This article is about Aramco Standard Hazardous Area Classification, Type of Protection, Gas Group, Intrinsic Safe Meters, Comparing NEC 500 to ATEX and focusing to the engineers, technicians and supervisors. You will find lot of documents related to this article. Just navigate our website www.paktechpoint.com and find more articles. Please! Do not forget to subscribe our You tube channel also. Thanks in Advance.
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Hazardous Area Classification:
ATEX: (Atmospheres Explosibles) – It came from Europe’s intrinsic safety regulation, European Union’s commonly called ATEX. NEC-505 is similar to ATEX.
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NEC 500 Divisions
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ATEX Zones
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Definitions
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Division 1
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Zone ‘0’
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In which an explosive gas / air mixture is continuously present for long period.
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Zone ‘1’
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In which as explosive gas air mixture is likely to occur under normal operation.
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Division 2
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Zone ‘2’
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In which an explosive gas-air mixture is not likely to occur in normal operation
and if it occurs it exist only for short time. |
Example 1:
Area classification Class I (Zone 0 / Division1)
Symbol for equipment built to American Standards A
Type(s) of protection designation Exia
Gas classification group (not required for protection Techniques indicated in NEC 505.6, FPN No. 2) IIC
Temperature classificationT6
Example 2:
Type of Protection:
Zone ‘0’
– Ex ‘ia’ and Ex ‘s’ (Specifically certified for use in Zone ‘0’).
– Ex ‘ia’ and Ex ‘s’ (Specifically certified for use in Zone ‘0’).
Zone ‘1’
– Any type of protection suitable for Zone-0 and Ex‘d’, Ex ‘b’, Ex ‘p’, Ex ‘e’.
– Any type of protection suitable for Zone-0 and Ex‘d’, Ex ‘b’, Ex ‘p’, Ex ‘e’.
Zone ‘2’
– Any type of protection suitable for Zone–0 or Zone-1 and Ex ‘N’ or ‘n’, Ex ‘o’, Ex ‘q’.
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Designation
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Technique
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Zone
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Ex ‘d’
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Flame proof or Explosion proof
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1
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Ex ‘e’
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Increased Safety
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1
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Ex ‘N’ or ‘n’
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None Sparking
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2
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Ex ‘ia’
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Intrinsic Safety
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0
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Ex ‘ib’
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Intrinsic Safety
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1
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Ex ‘p’
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Pressurization
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1
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Ex ‘o’
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Oil Immersion
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1
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Ex ‘q’
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Sand or Powder filled
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1
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Ex ‘s’
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Special Protection
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0
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Gas Group:
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Representative Gas
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IEC
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USA
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Methane
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I
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D
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Propane
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IIA
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D
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Ethylene
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IIB
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C
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Hydrogen
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IIC
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B
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Carbon Disulphide
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IIC
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–
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Intrinsic Safe Meters:
In hazardous area only I.S. meters such Meggers, Vibration meters and Temperature meters shall not be used unless the hot permits obtained.
Safety Barriers: (Zenner Barriers) Diode shunt barriers are used in intrinsically safe zone to limit the current and voltage.
Grounding System:
Safety Ground Definition:
All exposed and non-exposed non-current carrying by the metallic parts that could be energized its hazards. That’s why all safety ground must connect to the plant ground system.
Circuit / IS Ground Definition:
Reduce the electrical Interruption being the signal transmission.
Reduce the electrical Interruption being the signal transmission.
Signal / Circuit / IS Ground:
G + Y (Green + Yellow)
G + Y (Green + Yellow)
Safety Ground:
G (Green)
G (Green)
Comparing NEC 500 to ATEX
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ATEX: EX II 2 G EEX ia IIC T4
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II 2G
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“II” designates the tool is approved for all non-mining areas. “2” represents a
rating for Zone 1 and above. “G” designates atmosphere, in this case gas vapors and mist. |
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EEx
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Explosion protection based on European ex-regulation.
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ia
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The type of protection, the energy in a device is reduced to a safe value.
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IIC
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Gas Group “IIC” indicates compatibility with the most dangerous gas group.
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T4
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Maximum temperature of a surface that may be in contact with the ex-atmosphere under fault conditions. T4 rating is 35 C.
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FM Classification: N.I. Class 1. Div 2, Groups A-D
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N. I.
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Non-incendive aparatus, internal energy is limited so a specified atmosphere cannot be ignited by its use.
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Class I
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For use of gases, vapors and liquids (not dust , fibers of filings)
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Div 2
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Certified for use division 2, explosive atmospheres not normally present, may rarely exist for short duration.
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Groups A-D
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Rated for use with explosive gasses as defined y group A-D, including acetylene, hydrogen and propane
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Note: European ATEX and North America NEC-505 classification are nearly identical excepting the AEx v/s EEx marking.
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Hazardous Location Classifications:
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NEC
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IEC
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Environment
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Class I
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–
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Explosive gases or vapors are present.
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Class II
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–
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Combustible dusts are present.
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Class III
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–
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Ignitable fibers or flying are present.
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Division 1
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Zone 0
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A location where a hazardous concentration of gases or vapors exists approximately 10 ~ 100 % of the time (subject to interpretation as above).
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Division 1
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Zone 1
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A location where a hazardous concentration of gases or vapors exists approximately 1 ~10 % of the time (subject to interpretation as above).
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Division 2
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Zone 2
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A location where a hazardous concentration of gases or vapors exists approximately 0.1 ~ 1 % of the time (subject to interpretation as above).
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Group A
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Group IIC
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A hazardous atmosphere containing acetylene or other similar gases or vapors.
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Group B
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Group IIC
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A hazardous atmosphere containing hydrogen or other similar gases or vapors.
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Group C
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Group IIB
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A hazardous atmosphere containing ethylene or other similar gases or vapors.
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Group D
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Group IIA
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A hazardous atmosphere containing pentane or other similar gases or vapor.
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Group E
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–
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A hazardous atmosphere containing metal dust, such as aluminum.
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Group F
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–
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A hazardous atmosphere containing carbon black, coal, or coke dust.
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