Section 2 Classification of hazardous areas
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 7 Safety Systems, Hazardous Areas and Fire - Chapter 2 Hazardous Areas and Ventilation - Section 2 Classification of hazardous areas

Section 2 Classification of hazardous areas

Parent topic: Chapter 2 Hazardous Areas and Ventilation

2.1 General

2.1.1 The hazardous areas as specified may be extended or restricted depending on conditions such as fluid system pressure and composition, or by the use of structural arrangements such as fire walls, windshields, special ventilation arrangements, etc. For special requirements relating to units intended for the storage of oil in bulk, see Pt 7, Ch 2, 9 Additional requirements for electrical equipment on oil storage units for the storage of oil in bulk having a flash point not exceeding 60°C (closed-cup test). For special requirements relating to units intended for the storage of liquefied gases in bulk or other hazardous liquids, see Pt 7, Ch 2, 10 Additional requirements for electrical equipment on units for the storage of liquefied gases in bulkand Pt 7, Ch 2, 11 Additional requirements for electrical equipment on units intended for the storage in bulk of other flammable liquid cargoes and Pt 11, Ch 10 Electrical Installations.

2.1.2 Relatively small non-hazardous areas surrounded by or confined by hazardous areas, or Zone 2 areas within Zone 1 areas, are to be classified as the adjacent surrounding hazardous area.

2.1.3 For gas disposal systems, other than permanently ignited flares, and for vents for large quantities of hydrocarbon gas from production facilities, the classification and extent of the surrounding hazardous areas should be based on dispersion calculations.

2.1.4 For permanently ignited flares, consideration is to be given to possible ‘flame out’ conditions or intentional periods of cold venting and the hazardous areas created by such are to be determined.

2.1.5 Within these Rules, all reference to the extent of the hazardous zones given as a radius, refers to the horizontal extent of the zone, except where specifically stated as being a spherical zone; for vertical extent of zones, see Pt 7, Ch 2, 2.5 Vertical extent of hazardous zones.

2.2 Zone 0

2.2.1 Areas to be classified as Zone 0 include:
  1. The internal spaces of closed tanks and piping for containing active non-degassed drilling mud, oil that has a closed-cup flashpoint below 60°C or flammable gas and vapour, pipes of the mud-circulating system between the well and the final degassing discharge as well as oil and gas products containment system, e.g. escape gas outlet pipes, or spaces in which an oil-gas-air mixture is continuously present or present for long periods;
  2. Unventilated spaces containing a source of release (i.e. flange, valve, etc.) separated by a single gastight bulkhead or deck from a tank containing flammable liquid or gas; and
  3. A region around the outlet from non-pressurised tank vents or other sources, or from cold vents where discharge, which releases flammable gases or vapours frequently, continuously or for long periods. The size of this hazardous region should be based on guidance from a recognised Standard (i.e. EI (formerly IP) Part 15, API RP 505, IEC 60092-502, IEC 61892-7, EN60079-10-1, 2009 MODU Code) or established through distribution modelling.

2.3 Zone 1

2.3.1 Areas to be classified as Zone 1 include:

  1. Adequately ventilated closed or semi-enclosed spaces containing primary grades of release, see Pt 7, Ch 2, 1.2 Definitions and categories 1.2.8.(b);
  2. Mechanically ventilated closed spaces containing a source of release (i.e. flange, valve, etc.) separated by a single gastight bulkhead or deck from a tank containing flammable liquid or gas. Or an unventilated closed space not containing any sources of release separated by a single gastight bulkhead or deck from a tank containing flammable liquid or gas;
  3. In open spaces, the area surrounding a primary grade of release. The extent of the Zone 1 hazardous area will be based upon the primary grade source of release. The size of this hazardous region should be based on guidance from a recognised Standard (i.e. EI (formerly IP) Part 15, API RP 505, IEC 60092-502, IEC 61892-7, EN60079-10-1, 2009 MODU Code) or established through distribution modelling.
  4. In open spaces, the area within 3 m from pig launcher and receiver doors. This may be reduced to 1,5 m if the equipment is washed through with nitrogen or water washed before opening;
  5. In open spaces, the area local to any opening associated with an enclosed Zone 1 area, any ventilation outlet from a Zone 1 space, or any access, such as a doorway or non-bolted hatch to an enclosed Zone 1 hazardous area, is to be classified as a Zone 1 space. The extent of the external Zone 1 hazardous area will be based upon the largest source of release with the enclosed Zone 1 area based on guidance from a recognised Standard (i.e. EI (formerly IP) Part 15, API RP 505, IEC 60092-502, IEC 61892-7, EN60079-10-1, 2009 MODU Code) or established through distribution modelling;
  6. Semi-enclosed spaces, such as inadequately ventilated pits, ducts or similar structures situated in locations which would otherwise be a Zone 2, but where their arrangement is such that gas dispersion cannot easily occur.
  7. For units containing drilling facilities, specific reference is to be made to the requirements given in the Chapter 6 - Machinery and Electrical Installations in Hazardous Areas for All Types of Unitsregarding the extent of Zone 1 hazardous areas on MODUs as well as the following Pt 7, Ch 2, 3 Hazardous areas – Drilling, workover and wirelining operations and the guidance given in EI (formerly IP) Part 15 for drilling facilities.
  8. For tanker storage facilities containing flammable liquids or flammable liquefied gases, reference is to be made to requirements given in IEC 60092-502 regarding the extent of Zone 1 hazardous areas. Additionally, for tanker storage facilities containing flammable liquefied gases specific reference is to be made to Pt 11, Ch 10 Electrical Installations regarding the extent of the Zone 1 hazardous area.

2.4 Zone 2

2.4.1 Areas to be classified as Zone 2 include:
  1. Adequately ventilated closed or semi-enclosed spaces containing secondary grades of release, see Pt 7, Ch 2, 1.2 Definitions and categories 1.2.8.(c)
  2. In open spaces, the area beyond the Zone 1 specified in Pt 7, Ch 2, 2.3 Zone 1 2.3.1.(c) and Pt 7, Ch 2, 2.3 Zone 1 2.3.1.(d), and beyond the semi-enclosed space specified in Pt 7, Ch 2, 2.3 Zone 1 2.3.1.(f). The extent of the Zone 2 hazardous area will be based upon the primary grade source of release. The extent of the external Zone 2 hazardous area will be based upon the largest source of release with the enclosed Zone 1 area based on guidance from a recognised Standard (i.e. EI (formerly IP) Part 15, API RP 505, IEC 60092-502, IEC 61892-7, EN60079-10-1, 2009 MODU Code) or established through distribution modelling;
  3. In open spaces, the area surrounding a secondary grade of release, any ventilation outlet from a Zone 2 space or any access to a Zone 2 space. The extent of the Zone 2 hazardous area will be based upon the source of release based on guidance from a recognised Standard (i.e. EI (formerly IP) Part 15, API RP 505, IEC 60092-502, IEC 61892-7, EN60079-10-1, 2009 MODU Code) or established through distribution modelling;
  4. Mechanically ventilated closed spaces not containing a source of release separated by a single gastight bulkhead or deck from a tank containing flammable liquid or gas;
  5. For units containing drilling facilities, specific reference is to be made to the requirements given in the Chapter 6 - Machinery and Electrical Installations in Hazardous Areas for All Types of Units regarding the extent of Zone 2 hazardous areas on MODUs as well as the following Pt 7, Ch 2, 3 Hazardous areas – Drilling, workover and wirelining operations and the guidance given in EI (formerly IP) Part 15 for drilling facilities;
  6. For tanker storage facilities containing flammable liquids or flammable liquefied gases, reference is to be made to requirements given in IEC 60092-502 regarding the extent of Zone 2 hazardous areas. Additionally, for tanker storage facilities containing flammable liquefied gases specific reference is to be made to Pt 11, Ch 10 Electrical Installations regarding the extent of the Zone 2 hazardous area and;
  7. Air locks between a Zone 1 and a non-hazardous area, see Pt 7, Ch 2, 4.1 General 4.1.3.(c); and
  8. For drilling units, specific reference is to be made to the requirements given in the Chapter 6 - Machinery and Electrical Installations in Hazardous Areas for All Types of Units regarding the extent of Zone 2 hazardous areas on MODUs, as well as the following Pt 7, Ch 2, 3 Hazardous areas – Drilling, workover and wirelining operations.

2.5 Vertical extent of hazardous zones

2.5.1 The relationship between the hazard radius and the full 3-dimensional envelope of the hazardous area is dependent upon the height and orientation of the release and the hazard radius. If the release height and the generated hazardous radius zone are greater than 1 m above the deck, then the developed hazardous area is independent of potential hazardous accumulations of flammable releases at deck level. If the release height and the generated hazard radius are less than 1 m above the deck, then the developed hazardous area is dependent on potential hazardous accumulations of flammable releases at deck level and the subsequent hazardous area needs to take into account the generated hazardous area at deck level. The vertical extent of a hazardous area should be based on guidance from a recognised Standard (i.e. EI (formerly IP) Part 15, API RP 505, IEC 60092-502, IEC 61892-7, EN60079-10-1, 2009 MODU Code) or established through distribution modelling.

2.5.2 For tanker storage facilities containing flammable liquids or flammable liquefied gases, reference is to be made to requirements given in IEC 60092-502 regarding the vertical extent of a hazardous area. Additionally, for tanker storage facilities containing flammable liquefied gases specific reference is to be made to Pt 11, Ch 10 Electrical Installationsregarding the vertical extent of a hazardous area.

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