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Electrical Safety in Hazardous Areas: Enclosures, Temperature Classes and LNG Carrier Zones

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LNG Electrical Safety in hazardous areas is a critical aspect of ensuring the safe operation of liquefied natural gas carriers, where the risk of explosion or fire is high due to the presence of flammable gases and vapors. To mitigate these risks, specialized electrical equipment enclosures are designed to prevent ignition sources and ensure safe operation, even in the most hazardous zones.

LNG Electrical Safety also involves the classification of equipment into temperature classes, which determines the maximum surface temperature of the equipment and its suitability for use in specific hazardous areas. The zoning of LNG carriers into different hazardous areas, such as Zone 0, Zone 1, and Zone 2, is also crucial in determining the level of electrical safety required and the type of equipment that can be used in each area.

Enclosures and Degree of Protection

Electrical equipment is to be protected against the possibility of contacts with solids and liquids.

The degree of protection is in general rated with the code IP followed by two or three digits as follows:

IP xxy

The first digit indicates the degree of protection against contact with solids, the second digit indicates the degree of protection against contacts with liquids.

The third digit in general is omitted. If existing, it indicates the mechanical strength of the equipment enclosure.

The meaning of the three digits is given in the following Figure.

Protection Rating
Electrical Equipment Grade of Protection

Electrical Equipment Temperature Classes

Electrical equipment is also classified depending on the maximum temperature its surface is allowed to reach when the reference ambient temperature is 40 °C. Table indicates the various temperatures classes.

Temperature classes
T CLASSESMaximum Surface Temperature (Deg ˚C)
T1450
T2300
T3200
T4135
T5100
T685

Note that while the IMO Chemical Code indicates for each product the allowable temperature class, this indication is missing in the The Origins of the IGC CodeIGC Code. However, in general, according also with other Classification Societies Rules, the temperature class applicable to LNG ships would be T2. It is to be noted that ABS would be prepared to accept also T1 in particular cases. Considering in fact that the self-ignition temperature of methane vapor is 595 °C, class T1 still offers a suitable safety margin.

Hazardous Areas

Definitions

A hazardous area is an area in which an explosive gas atmosphere is present, or likely to be present, in quantities such as to require special precautions for the construction, installation and use of electrical apparatus.

In general, the hazardous areas are classified in three Zones depending on the frequency of the appearance and the duration of an explosive gas atmosphere:

1) ZONE 0

Zone 0 is an area in which an explosive gas atmosphere is continuously present or is present for long periods.

Typical Zone 0 areas are:

  • closed process vessels;
  • storage tanks;
  • closed containers;
  • areas containing open tanks of volatile, flammable liquid.

2) ZONE 1

Zone 1 is an area in which an explosive gas atmosphere is likely to occur during normal operation.

Typical Zone 1 areas are areas where:

  • flammable atmospheric concentration is likely to occur frequently because of maintenance, repairs or leakage;
  • flammable liquid or vapor piping system (containing valves, meters, or screwed or flanged fittings) is in an inadequately ventilated area;
  • flammable liquids or vapors may accumulate.

Examples are pump rooms, cofferdams surrounding Independent Cargo Tankscargo tanks where vapor may accumulate in case of leak. Restricted areas, such as double bottoms where vapors heavier than air can accumulate, etc.

3) ZONE 2

Zone 2 is an area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it does, this will be quite infrequently and for a short period of time.

Typical Zone 2 areas are:

  • locations adjacent to Zone 1 areas;
  • pressurized spaces, where flammable vapor might enter in case of failure of the pressurization system.

4) SAFE AREAS

In general safe areas are the areas which are not classified as hazardous in accordance with the above definition of zones. In particular the following are to be considered safe areas:

  • areas crossed by piping system containing hazardous fluids without valves, fittings, flanges or similar appurtenances;
  • areas where flammable liquids or vapors are transported only in suitable containers or vessels (for instance areas surrounding type “C” tanks in LPG ships);
  • areas where permanent ignition sources are present, like area where gases are burned, for example flare pits, tips, other open flames;
  • spaces separated by hazardous areas by pressurized airlocks.

The three hazardous area zones, may have different denomination depending on the countries. However, the principle of the zone classification remains quite similar:

  • NORTH AMERICA (NFPA / API / NFPA 70E or NEC)
    Division II-Z2
    Division I-Z0 + Z1.
  • JAPAN
    Classes 1, 2 & 3.

Hazardous Areas of LNG Carriers

In general, the classification of the hazardous areas is necessary to establish which kind of electrical apparatus/equipment may or may not be installed in each of the hazardous area zones.

While the classification of the hazardous areas in zones has been adopted by several Rules applicable to the marine field, for instance the Rules relative to the offshore drilling units, both the IGC Code and the Rules do not adopt such classification for the gas carriers and consider only safe or dangerous areas, without defining whether a certain area of the ship should be considered Zone 1 rather than Zone 2, etc.

However, as the classification of the hazardous areas in zones is today normally applied, it is possible that the next editions of the IGC Code and IACS will adopt it also for LNG carriers.

The lack of definition of hazardous zones on LNG carriers might appear as a serious source of ambiguity and uncertainty on the allowable types of electrical apparatus in the various zones of the ship, however, this is not a true problem. The Rules clearly indicate which kind of equipment is to be used in the various areas of the ship making the definition of the hazardous zones in this particular case unnecessary.

Author
Author photo - Olga Nesvetailova
Freelancer
Literature
  1. The Society of International Gas Tanker and Terminal Operators (SIGTTO). Liquefied Gas Handling Principles on Ships and in Terminals (LGHP4) / 4th Edition: 2021.
  2. The international group of liquefied natural gas importers (GIIGNL). LNG custody transfer handbook / 6th Edition: 2020-2021.
  3. American Gas Association, Gas Supply Review, 5 (February 1977).
  4. ©Witherby Publishing Group Ltd. LNG Shipping Knowledge / 3rd Edition: 2008-2020.
  5. CBS Publishers & Distributors Pvt Ltd. Design of LPG and LNG Jetties with Navigation and Risk Analysis / 4th Edition.
  6. NATURAL GAS PROCESSING & ITS ENERGY TRANSITION ROLE: LNG, CNG, LPG & NGL Paperback – Large Print, November 14, 2023.
  7. American Gas Association, Gas Supply Review, 5 (February 1977).
  8. The Society of International Gas Tanker and Terminal Operators (SIGTTO). Ship/Shore Interface / 1st Edition, 2018.
  9. Department of Transportation, US Coast Guard, Liquefied Natural Gas, Views and Practices Policy and Safety, p. IV-3.
  10. Department of Transportation, US Coast Guard, Liquefied Natural Gas, Views and Practices Policy and Safety, p. IV-4.
  11. Federal Power commission, Trunkline LNG Company et al., Opinion No. 796-A, Docket No s. CP74-138-140 (Washington, D. C.: Federal Power Commission, June 30, 1977).
  12. Federal Power Commission, Final Environmental Impact Statement Calcasieu LNG Project Trunkline LNG Company Docket No. CP74-138 et al., (Washington, D. C.: Federal Power Commission, September 1976).
  13. Federal Power Commission, «FPC Judge Approves Importation of Indonesia LNG».
  14. OCIMF, ICS, SIGTTO & CDI. Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gases / 1st Edition, 2013.
  15. Federal Power Commission, «Table of LNG imports and exports for 1976», News Release, June 3, 1977, and Federal Energy Administration, Monthly Energy Review, March 1977.
  16. Office of Technology Assessment LNG panel meeting, Washington, D. C., June 23, 1977.
  17. Socio-Economic Systems, Inc., Environmental Impact Report for the Proposed Oxnard LNG Facilities, Safety, Appendix B (Los Angeles, Ca.: Socio-Economic Systems, 1976).
  18. «LNG Scorecard», Pipeline and Gas Journal 203 (June 1976): 20.
  19. Dean Hale, «Cold Winter Spurs LNG Activity»: 30.
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