Electrical safety on LNG carriers is paramount, requiring specialized equipment like explosion-proof fittings and intrinsically safe systems to prevent ignition in potentially explosive atmospheres.
Regular maintenance, crew training, and advanced monitoring systems further enhance the safety and efficiency of LNG transport operations.
Installation of Electrical Equipment in Hazardous Areas
General Consideration
Use of light alloy (Mg, Al, Ti, ) material is to be specially considered in hazardous areas.
Where reasonably practical, electrical apparatus in general and switch and control apparatus in particular, should be installed outside the hazardous areas. These electrical apparatus may be installed in open air in a non-hazardous area.
Portable hand-lamps, communication equipment and other test equipment should be Ex i type. All equipment is to be installed so as to avoid mechanical damage. All flanges of pipes crossing hazardous areas are to be electrical bonded so as to avoid electro-static discharges.
Internal earthing is to be provided for all Ex d equipment in addition to external earthing. All circuits and apparatus in hazardous areas should be provided with means to ensure quick disconnection in the event of any fault.
Protection and control apparatus should be as far as practicable located in non-hazardous areas. All electrical apparatus (for every apparatus or sub-groups) should be provided with an effective means of isolation, including neutral.
Cables should run in metal conduits or should be armored type. Correct terminations using proper sized cable glands should be provided. Unused cable openings of all electrical apparatus are to be closed with plugs suitable for the type of protection of that apparatus.
In general, copper or aluminum conductors above 16 mm2 should be used. Plugs and sockets should be preferably of PUSH-IN, TWIST-ON type to avoid ignition while insertion or removal. The adequate IP protection is to be provided. The most common test equipment should be:
- Insulation Resistance Megger of Ex i type.
- Earth Megger of Ex i type.
- Hotspot Detection equipment (infrared).
Maintenance and Inspections
For maintenance and inspection, the following is are to be closely examined:
- All bolts are in place.
- Any openings are sealed.
- No modifications/alterations have been done.
- Internal and external earthing properly in place.
- Cable glands are double-compression, ELP type.
- No physical damage visible.
- No damage to flame path visible.
- All threaded connections-have minimum 5/6 threads engagement.
- Flange faces are smooth and original (while opening stuck covers particular attention is to be paid).
- Light alloy paint (even for the purpose of maintenance) has not been applied on any external surface of the equipment. This is to prevent frictional sparking.
- Equipment has not been tampered with open covers, etc.
- No components have been added, removed or replaced, unless this carried out by specialized personnel in accordance with approved plans.
Prior to any maintenance/repair:
- equipment should be always de-energized before attempting any repair;
- any equipment, which was originally explosion proof, may loose its integrity if not maintained properly.
Summary of Equipment/Circuit Characteristics in Hazardous Areas
General Requirements
1) ZONE 0
No electrical equipment is permitted in Zone 0. If this is not practicable only Ex ia equipment is allowed. This means that transformers, motors, lights, switch gear or control gear are not allowed in Zone 0.
2) ZONE 1
Table 1 indicates the types of electrical equipment generally admitted in Zone 1 and the relative type of required certification.
| Table 1. Electrical equipment in Zone 1 | |
|---|---|
| EQUIPMENT | ALLOWED PROTECTION TYPE |
| Motors | Ex d, Ex p |
| Transformers and capacitors | Ex d |
| Control and instrument transformers | Ex i |
| Lighting fixtures | Ex d |
| Switch gears and control gears | Ex d |
| Communication/Telephone equipment | Ex i |
| Portable hand lamps | Ex i |
3) ZONE 2
Table 2 indicates the types of electrical equipment generally admitted in Zone 2 and the relative type of required certification.
| Table 2. Electrical equipment in Zone 2 | |
|---|---|
| EQUIPMENT | ALLOWED PROTECTION TYPE |
| Motors | Ex d, Ex p, Ex n, Ex e |
| Transformers and capacitors | Ex d, Ex p |
| Control and instrument transformers | Ex i |
| Lighting fixtures | Ex d, Ex n, Ex e |
| Switch gears and control gears | Ex d, Ex o, Ex e |
| Communication/Telephone equipment | Ex i |
| Portable hand lamps | Ex i |
Summary of Spaces in Which Certified-Safe Electrical Equipment is Located on Board an LNGC
Table 3 delineates the allowable electric equipment, which can be installed on board an Rules and Regulations for LNGCLNGC, based on the definition of a “Gas Dangerous Space“, as defined in the IGC Code and in the Rules.
| Table 3. LNGC Equipment in Hazardous Areas | ||||
|---|---|---|---|---|
| SPACE | ELECTRICAL EQUIPMENT | TYPE | ||
| Area | Zone | |||
| 1 | Cargo containment system and cargo piping | 0(1) | Termocouples, straingauges, photocells, switching devices, and other similar equipment and relevant circuits | Ex ia |
| Submerged electric motors(1) | See note | |||
| Electric cables for submerged electric motors(1) | See note | |||
| 2 | Hold space, when cargo is contained in a cargo containment system not requiring a secondary barrier | 1 | Thermocouples, strain gauges, photocells, switching devices, and other similar equipment and relevant circuits | Ex ib |
| Electric cables for submerged electric motors | See note | |||
| Lighting fixtures | Ex p, Ex d | |||
| Transducers , anodes, and similar equipment | See note | |||
| Electric motors for valve operation of ballast system | Ex d | |||
| General alarm audible indicators | Ex d | |||
| 3 | Cargo Compressor room | 1 | Termocouples, strain gauges, photocells, switching devices, and other similar equipment and relevant circuits | Ex ib |
| Lighting fixtures | Ex d(2) | |||
| Electric motors (if any – not for driving compressors) | Ex d, Ex p | |||
| General alarm, visible and audible indicators | Any certified safe equipment | |||
| Gas detection system sensors | Any certified safe equipment | |||
| 4 | Zones on open deck within 3 m of any cargo outlets and any opening of cargo compressor room | 1 | Termocouples, strain gauges, photocells, switching devices, and relevant circuits | Ex ib |
| All other electrical apparatus | Any certified safe equipment | |||
| 5 | Zones on open deck upto an height 2,4 m above the deck extended 3 m forward and aft cargo area | 1 | See item 4 | |
| 6 | Areas of open deck and semienclosed spaces within 3 m of any tank relief valve outlet | 1 | See item 4 | |
| 7 | Cargo hose store compartment (if any) | 1 | Thermocouples, strain gauges, photocells, switching devices, and other similar equipment and relevant circuits | Ex ib |
| Lighting fixtures | Ex p, Ex d | |||
| 8 | Enclosed or semienclosed spaces containing not fully welded cargo piping | 1 | See item 4 | |
| 9 | Areas 1,5 m surrounding the Zone 1 space at item 4(3) | 2 | All electrical equipment | Ex n, Ex m |
| 10 | Areas 22 m or (B-3 m), whichever is the less beyond the Zone 1 space at item 6(3) | 2 | See item 4 | |
| 1) According with the generaldefinition, this should be considered as Zone 0. However, the tank of LNG carrier is a safe space because , when there is cargo , vapor, this is completed saturated and no oxygen is present, and, in all other conditions, the spaces is always inerted or completely vapor free. Based on this, IGC Code and Rules accept the cargo pumps electric motors in the space 2) All switches and protective devices are to be in safe-areas 3) These areas are not actually applicable, being presently discussed at IACS | ||||
The content of Table 3 has been prepared to verify how the Rules can match (or not) the normal applicable requirements for Hazardous Areas. For instance, it does not completely match the content of Table 2. These differences depend by the fact that the IGC Code was written before the classification in zone of the hazardous areas became generally accepted and by the specific peculiarities of the LNG ships.
The only special precaution required by the IGC Code and the Rules for Use of Cargo Pumps on Liquefied Gas Carriersthe cargo pump motors, is that they should be capable of being completely isolated from their electrical supply, and tagged/locked out “de-energized” during gas-freeing operations.
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