CHAPTER – 1
CHAPTER – 1
AREA CLASSIFICATIONS
AREA CLASSIFICATIONS
IMPORTANT IMPORTANTMandatory rules (or "must") are characterised by the word "SHALL" throughout the Mandatory rules (or "must") are characterised by the word "SHALL" throughout the text. Advisory rules or recommendations are indicated by the word "SHOULD." The text. Advisory rules or recommendations are indicated by the word "SHOULD." The words shall and should have been used
words shall and should have been used to remain in line with to remain in line with the terminology used bythe terminology used by American National Standard Institute.
American National Standard Institute.
REFERENCES REFERENCES
API-RP 500A, NFPA-497, NEC Article-500, IP standards, KNPC standards API-RP 500A, NFPA-497, NEC Article-500, IP standards, KNPC standards
CHAPTER
CHAPTER – – 1 1 REVISION REVISION – – 1 1 MAY MAY 19981998 PAGE
AREA CLASSIFICATIONS
TABLE OF CONTENTS
PAGE 1.1 INTRODUCTION 3 1.1.1 CONTROLLED AREA 3 1.1.2 RESTRICTED AREA 3 1.1.3 HAZARDOUS AREA 3 1.1.4 NON-HAZARDOUS AREA 31.2 HAZARDOUS AREA CLASSIFICATION 4 1.2.1 CLASS 4 1.2.2 GROUPING OF FLAMMABLE OR COMBUSTIBLE
MATERIALS 4
CLASS I MATERIALS GASES AND VAPORS 4 CLASS II MATERIALS - DUST 5 CLASS III COMBUSTIBLE FIBRES 5
1.2.3 DIVISION 5 1.2.4 RELATIONSHIP BETWEEN DIVISION AND ZONE 6
1.3 AREA CLASSIFICATION FOR WORK PERMITS 6 1.3.1 WORK PERMIT AREA 6 1.3.2 WORK PERMIT FREE AREA 6
AREA CLASSIFICATIONS
1.1 INTRODUCTION
Substances handled by petroleum installation include flammable and combustible liquids / vapours and gases. To have a safe work environment, hazards need to be identified in work places and effective controls needs to be developed. In view of the above our premises have been broadly defined as: (a) Controlled area
(b) Restricted area (c) Hazardous area
1.1.1 CONTROLLED AREA
“Controlled Area” is the entire KNPC premises fenced or otherwise, to which access is controlled or restricted.
1.1.2 RESTRICTED AREA
“Restricted area” is within the “Controlled area” in which entry is permitted only to authorized persons and a valid gate pass is necessary to enter these premises.
1.1.3 HAZARDOUS AREA
“Hazardous area” is the area within the “Restricted area” where flammable atmosphere is more likely to be present.
A flammable atmosphere is defined as having sufficient concentration of flammable gas, vapor, mist or combustible dust, capable of being ignited.
1.1.4 NON-HAZARDOUS AREA
A Non-Hazardous Area is the area within the controlled area or restricted area, which is not classified as a hazardous area.
1.2 HAZARDOUS AREA CLASSIFICATION
Use of hazardous area classification system helps in identifying the extent of areas in which explosive mixtures with air may occur under normal and expected abnormal conditions. In this system, areas are classified and grouped according to the flammable/combustible materials, which may be present.
Class-I - Group A,B,C,D include all flammable gases and liquids. Class-II - Group E,F,G include all combustible dusts.
Class-III - All combustible fibers.
The classified areas are further subdivided into Division-1 and Division-2 areas.
Industry standards and work practices, which deal with area classification, are API-RP-500A, NFPA-497, NEC Article-500 and IP model code of Safety. KNPC standards are in line with these standards.
Hazardous Area classification is used for proper selection and safe installation of electrical/instrument equipment. However, these should also be considered while locating or installing other equipment, which may present an ignition source, e.g. fired heater, boiler, IC engines, welding machines etc.
1.2.1 CLASS
Class-I locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.
Class-II locations are those that are hazardous because of the presence of combustible dust. (Ex: coke)
1.2.2 GROUPING OF FLAMMABLE OR COMBUSTIBLE MATERIALS
Depending on the type of flammable material, classified areas are categorised in accordance with material groups descibed as A,B,C, etc.
CLASS I MATERIALS - GASES AND VAPORS
These are divided into groups A, B, C & D. Following are groups of common materials in
KNPC:-Group - A Acetylene
Group - B Hydrogen, Ethylene.
Group - C Hydrogen Sulphide or gases or vapours of equivalent hazard.
Group - D Most Hydrocarbons e.g. Benzene, Butane, Propane, gasoline, Naphtha etc.
CLASS II MATERIALS - DUST Group - E Metal dust
Group - F Carbonaceous dust (Coke dust, charcoal, coal, and carbon black).
Group - G Other dust, flour, starch, grain dust.
CLASS III MATERIALS - COMBUSTIBLE FIBRES (not applicable in KNPC)
1.2.3 DIVISION
Having decided that a location should be classified, and having designated the gas or vapor as group A, B, C or D, the next step is to designate the location as either Division-1 or Division-2.
Division 1 – Locations where explosive mixtures are likely to exist under normal operating condition, e.g. area immediately surrounding open vents or open transfer of flammable or combustible materials.
1.2.5 RELATIONSHIP BETWEEN DIVISION AND ZONE
In KNPC engineering drawings hazardous areas are classified as per US standards. There is no technical equivalent relationship between this system and the “Zone" categorisation followed in Europe. The final selection shall be the responsibility of the respective authority. However for guidance purpose, the following table provides a rough comparison.
Division (US) Zone (EU)
Class-I Flammable Gas Area Class-I Div1 Zone 0 or 1
Class-I Div2 Zone 2
Class-II Combustible dust area Class-II Div1 Zone ‘Z’
Class-II Div2 Zone ‘Y’
1.3 AREA CLASSIFICATION FOR WORK PERMITS 1.3.1 WORK PERMIT AREA
In general, “controlled area” shall be considered as “work permit area” with following exceptions:
a) Areas classified as ‘ Work Permit Free Area’
b) Routine activities in ‘Non-Hazardous Area’ such as office work, driving vehicles along unrestricted roads etc.
1.3.2 WORK PERMIT FREE AREA
Certain areas within the restricted area may be designated as a ‘Work Permit Free Area’ for a defined task as approved by KNPC Safety, e.g., approved smoking areas, areas designated for pre-fabrication work, Workshops, etc. Such areas are to be clearly indicated.
