Thursday, August 31, 2017

HAZARDOUS AREA CLASSIFICATIONS Part 2 - AREA CLASSIFICATION


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  1. AREA CLASSIFICATION
Hazardous areas are classified with respect to the potential danger of an explosion and areas are divided into Zones:

ZONE 0 – (Continuous Hazard) An area in which an explosive atmosphere is continually present or present for long periods, over 100 hrs. per year.( Zone 0 for gases; Zone 20 for dusts) Type of Protection used: “I” i.e. ‘ia’.

ZONE 1 – (Intermittent Hazard) An area in which an explosive atmosphere is likely to occur in normal operation, between 10 ~ 100 hrs. per year. (Zone 1 for gases; Zone 21 for dusts) Type of protection used: For I.S. “Ib”; “d” for FLP; “p”; “q”; “o”.

ZONE 2 – (Hazard under Abnormal Conditions) An area in which an explosive atmosphere is not likely to occur in normal operations and , if occur , will exist for only a short time; between 0.1 ~ 10 hrs. per year. (Zone 2 for gases; Zone 22 for dusts) Type of protection used : “I”; “d”; “e”; “n”; “p”; “q”; “o”.

Zone nomenclature used in IEC/CENELEC/EUROPE. While Division 1 & 2 (gases & dusts) used in North America.

• Class 1 for gases,2 for dusts,3 for fibers is used in North America.



          North American Hazard Categories :


CLASSES
GROUPS
Class I
(Gases & Vapors)
Group A (Acetylene)
Group B (Hydrogen)
Group C (Ethylene)
Group D (Methane)
CLASS II (Dusts)
Group E (Metal Dusts)
Group F (Coal Dust)
Group G (Grain Dust)
CLASS III (Fibers)
No sub-groups
 
GAS GROUPS OR APPARATUS GROUPINGS

• Group I (Mining Only)

• Group II (Surface Industries)- IIA, IIB , IIC.

• Gases are grouped together based on the amount of energy reqd. to ignite the most explosive mixture of gases with air.

• These categories used in European & IEC standards.

• In North American standards Gas Groups A/B/C/D for gases & vapors while E/F/G for Dusts are used. No subgroup for Class 3(fibers & flyings).

Group I – Methane - Ignition energy of 320 Micro Joules

• Concerned only with underground mining where Methane & coal dust are present.

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