LIGHTING SYSTEMS FOR ILLUMINATION

Normal lighting should provide approximately 75% of the total illumination an area of a plant that is densely filled with processing equipment and buildings. Sparsely filled areas such as road ways and perimeter fences can be fully illuminated with normal lighting, unless emergency escape routes exist in these areas.

Emergency lighting should therefore provide between 25% and 30% of the illumination in processing areas. These criteria generally apply to both outdoor and indoor locations, and to onshore and offshore installations. Emergency lighting should be supplied by power from emergency diesel generators, except for lighting that illuminates escape routes. Escape route lighting requires a source of battery power that should last for at least one hour from a loss of all other power sources. The battery may be integral with the lighting fitting or a common battery and local distribution panel for a room or group of rooms, access ways, corridors and the like. The lighting level for escape lighting does not need to be high, a typical value is 20 lUX for indoor areas is adequate. Individual oil companies have their own recommendations on these subjects.

Offshore and marine installations are by nature very compact and therefore some additional requirements are generally required, especially with regard to escape routes. Escape lighting should be provided for exit doorways, sleeping cabins in the living quarters, stairways, walkways, corridors, lounges, recreation rooms, dining rooms and gallies. It is essential to illuminate embarkation stairways, helideck, helideck offices, survival craft stations, waiting room, and areas that are associated with personnel having to leave the facility in an organized manner. If in doubt provide more than is a minimum requirement.

Emergency lighting has some separate requirements to escape lighting. For example the personnel operating the plant need to be able to see and operate control panels, visual display units, start-up emergency generators and systems, carry out switching operations, test for hazardous gas, test certain equipment and generally manage an emergency situation. They require a minimum amount of emergency lighting. Consequently the following areas and functions need to be properly illuminated.

• Plant main control room and radio room.
• Emergency generator room or module.
• Main switch room.
• Main generator room or module.
• All areas in the living quarters.
• All workshops, stores, cranes and utility areas.
• Offshore installation manager (OIM) offices.
• Obstructed areas within the plant.
• Vent stacks and flare booms.
• Perimeter areas.

During an emergency the personnel should be able to access portable lamps and torches. These should be located adjacent to exit doors, in operational rooms, plant rooms, emergency accommodation areas, OIM’s offices, central control room and muster areas. They should be provided with charger units and be suitable for zone 1 hazardous areas, and be capable of operating for at least five hours.

Where possible the control of lighting fittings should be from a non-hazardous area, i.e. one adjacent to the hazardous area, using double pole switches. The supply neutral should be switchable.

In rare situations this may not be practical in which case a switchboard or distribution board suitable for the hazardous area and the environmental conditions will need to be installed e.g. Zone 1, IP55 or 56, with a suitable gas group and temperature class.

It is often a good practical consideration to use only lighting fittings in a plant that are suitable for Zone 1 areas that are also exposed to wet weather conditions e.g. IP66 enclosures of at least Ex (e) hazardous area types, unless of course they are installed indoors in areas where water sprays are not needed. Indoor process areas such as gas compressor modules require water-based fire-fighting deluge systems. Such locations require waterproof electrical fittings of all types, e.g. lighting, junction boxes, local control stations, local control panel. Locations such as control rooms, computer rooms, electronic equipment rooms, accommodation areas and offices do not require such hazardous area fittings, and good quality domestic or light industrial fittings are usually suitable and aesthetically acceptable.

Some areas are suitable for floodlighting and high-pressure sodium fittings can be used.

The incoming three-phase supply to the lighting distribution panels should be provided with four pole switches or circuit breakers, to ensure that the neutral is opened when the panel is de-energized for maintaining sub-circuits in hazardous areas. The sub-circuit loading should be arranged to give a balanced load on the incoming supply. Each sub-circuit will be a single-phase consumer, for which the single-phase two-wire supply can be taken between one phase and neutral of a four wire system, or a single-phase two-winding step down transformer can be used. The use of a small transformer will ensure that the voltage required for the light fittings is well matched. Occasionally a 440 V three-phase supply is used throughout a plant, for which the line-to-neutral voltage is 254 V.

A single- phase nominal voltage of 254 V is out of range for the products of some manufacturers of lighting fittings. A choice of 415 V/240 V, 400 V/230 V or 380 V/220 V would enable a wider choice of standard equipment to be used.

Fluorescent lamps should be chosen and located carefully where they illuminate rotating shafts, so as to avoid a stroboscopic effect that shows the shaft to appear stationary even though it is in fact rotating at a high speed.

Lighting schemes within modules and compact plant areas should be divided into at least two groups so that a supply failure does not put the whole area into darkness. This consideration applies to both normal and emergency schemes.

When designing a lighting circuit it is customary practice to size the cables so that the farthest lamp from the supply receives no less than 95% of its nominal voltage. In addition it is assumed that all the lighting fittings are energized when this design calculation is made.