Section 4 Electrical equipment for use in explosive gas atmospheres or in the presence of combustible dusts

4.1.1 The installation of electrical equipment in spaces and locations in which flammable mixtures are liable to collect, e.g. areas containing flammable gas or vapour and/or combustible dust, is to be minimised.

4.1.2 In order to eliminate potential sources of ignition from spaces and locations in which flammable mixtures are liable to collect, such hazardous areas are to be identified and electrical equipment within these areas is to be selected and installed in accordance with the requirements of this Section.

4.1.4 Equipment that is to be installed in an area where explosive gases can be present is to be selected in accordance with Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres.

4.1.5 Equipment that is to be installed in an area where combustible dusts can be present is to be selected in accordance with Vol 2, Pt 9, Ch 5, 4.4 Selection of equipment for use in the presence of combustible dusts.

4.1.6 Electrical installations in magazines, are to be in accordance with Vol 1, Pt 4, Ch 1, 6.8 Piping, cabling and electrical systems

4.1.7 For permanent secondary battery installations, see Vol 2, Pt 9, Ch 2, 7 Batteries.

4.1.8 Hazardous areas shall be fitted with a gas detection system in accordance with Vol 2, Pt 9, Ch 11 Gas detection.

4.2.1 For hazardous areas and sources of hazards for naval ships, the following principles are to apply in general.

See IEC 60092-506: Electrical Installation in ships-Part 506 – Special features – Ships carrying specific dangerous goods and materials hazardous only in bulk. An explosive atmosphere may exist due to gas and/or combustible dust.

4.3.1 When equipment is to be installed in areas where an explosive gas atmosphere may be present it is generally to be of a type providing protection against ignition of the gases encountered and compliant with the relevant Parts of IEC 60079: Explosive atmospheres, an agreed specified standard where applicable, see Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.4, Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.5 or Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.6.

4.3.2 The equipment protection type permitted depends on the hazardous area where the equipment is to be located, as defined in Vol 2, Pt 9, Ch 5, 4.5 Installation of electrical equipment. For certain locations on the ship other requirements may limit installations to specific equipment types and/or particular applications.

4.3.3 Equipment for zone 0 or zone 1, with the exception of simple apparatus as defined in Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.4 or Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.5, is to be certified or approved by a National or other appropriate Authority. Equipment without independent certification or approval may be considered for installation in zone 2.

4.3.4 In zone 0, the following may be considered:

1. intrinsically safe, category ‘a’ (Ex ‘ia’); or

2. simple electrical apparatus and components (for example, thermocouples, photocells, strain gauges, junction boxes, switching devices), included in intrinsically safe circuits of category ‘ia’, compliant with IEC 60079-14: Explosive atmospheres – Part 14: Electrical installations design, selection and erection.

4.3.5 In zone 1, the following may be considered:

1. equipment permitted within zone 0;

2. intrinsically safe, category ‘b’ (Ex ‘ib’);

3. simple apparatus as defined above, included in intrinsically safe circuits of category ‘ib’;

4. increased safety (Ex ‘e’);

5. flameproof (Ex ‘d’);

6. pressurised enclosure (Ex ‘p’);

7. powder filled (Ex ‘q’); or

8. encapsulated (Ex ‘m’); and

9. Special – Ex ‘s’, where permitted by the equipment certification.

4.3.6 In zone 2, the following may be considered:

1. equipment permitted within zone 1;

2. type of protection ‘n’ or ‘N’;

3. equipment such as control panels, protected by purging and pressurisation and capable of being verified by inspection as meeting the requirements of IEC 60079-2: Explosive atmospheres – Part 2: Equipment protection by pressurized enclosures "p"; and

4. radio aerials having robust construction, meeting the relevant requirements of IEC 60079-15: Explosive atmospheres – Part 15: Equipment protection by type of protection "n". Additionally, in the case of transmitter aerials, it is to be shown, by detailed study or measurement, or by limiting the peak radiated power and field strength to 1 W and 30 V/m, respectively, that they present negligible risk of inducing incendive sparking in adjacent structures or equipment.

4.3.7 Equipment having type of protection ‘ia’, ‘ib’, or ‘d’, is to be of a Group (IIA, IIB or IIC) meeting or exceeding that required for safe operation in the presence of any gas or vapour that can be present, or is to be certified specifically for such gases or vapours.

4.3.8 All equipment is to be of a temperature classification (T1 to T6) that confirms, or is to be assessed so as to confirm, that its maximum surface temperature will not reach the ignition temperature of any gas or vapour, or mixture of gases or vapours, which can be present. The surface temperature considered may be that of an internal or external part, according to the type of protection of the equipment.

4.4.1 Where equipment is to be installed in hazardous areas, as defined by Vol 2, Pt 9, Ch 5, 4.2 Hazardous areas 4.2.3, associated with the presence of combustible dusts, it is to be of a type certified by a National or other appropriate Authority for the combustible dusts and, additionally, any explosive gases encountered.

4.4.3 Electrical equipment for use in hazardous areas is to be so designed and installed as to minimise the accumulation of combustible dust which may interfere with the safe dissipation of heat from the enclosure.

4.4.4 Where equipment is to be installed in extended hazardous areas, as defined by Vol 2, Pt 9, Ch 5, 4.2 Hazardous areas 4.2.3, associated with the presence of combustible dust, the following may be considered:

1. equipment permitted within a hazardous area as defined by Vol 2, Pt 9, Ch 5, 4.4 Selection of equipment for use in the presence of combustible dusts 4.4.1;

2. equipment having degree of protection IP5X, or better, and having a surface temperature under normal operating conditions, but in the absence of a combustible dust layer, not exceeding two-thirds of the minimum ignition temperature in degrees Celsius of the combustible dust/air mixture(s) that can be present and appropriate for any explosive gases encountered; and

3. equipment of a type which ensures absence of sparks or arcs and hot spots during normal operation.

4.4.5 Where equipment certified for combustible dusts is not available, consideration will be given to the use of equipment complying, as a minimum, with the following requirements provided no explosive gases will be present:

1. the enclosure is to be at least dust protected (IP5X) having, when tested in accordance with IEC 60529, an ingress of fine dust within the enclosure not exceeding 10 g per m³ of free air space; and

2. the surface temperature of the equipment, under normal operating conditions, but in the absence of a combustible dust layer, is not to exceed two-thirds of the minimum ignition temperature in degrees Celsius of the combustible dust/air mixture(s) that can be present; or

3. the equipment is to be certified intrinsically safe "ia" or "ib" having a temperature classification ensuring compliance with (b); or

4. pressurised and operated in accordance with procedures ensuring, prior to its re-energisation, the absence of combustible dust within the enclosure following loss of pressurisation and consequent shutdown, and having surface temperature complying with (b); and

5. simple apparatus included in intrinsically safe circuits or radio aerials, complying with Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.4, Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.5 or Vol 2, Pt 9, Ch 5, 4.3 Selection of equipment for use in explosive gas atmospheres 4.3.6 respectively.

4.5.2 The ambient temperature range for which the equipment is certified is to be taken to be –20°C to 40°C, unless otherwise stated, and account is to be taken of this when assessing the suitability of the equipment for the auto-ignition temperature of the gases and combustible dusts encountered.

4.5.3 Any special requirements laid down by the equipment certification documentation are also to be observed.

4.5.4 All switches and protective devices from which electrical equipment located in hazardous areas is supplied are to be located in non-hazardous areas. Where it is not practicable to locate the switches and protective devices in non- hazardous area then the applicable requirements of this section are to be applied to that equipment.

4.5.5 All switches and protective devices from which electrical equipment located in hazardous areas is supplied are to interrupt all poles or phases and protected against unauthorised re-connection.

4.5.6 Electrical equipment in hazardous areas, switches and protective devices are to be clearly labelled for identification purposes.

4.6.1 Semi-enclosed spaces are considered to be spaces limited by decks and/or bulkheads in such a manner that the natural conditions of ventilation are different from those obtained on open deck.

4.7.1 Natural or mechanical ventilation is to be provided for hazardous enclosed or semi-enclosed spaces in order to prevent accumulation of explosive gas atmosphere, leaving no areas of stagnant air. Ventilation rates are to be calculated based on IEC 60079-10-1: Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres.

4.7.2 Where the rate of ventilation air flow, in relation to the maximum rate of release of flammable substances reasonably to be expected under normal conditions, is sufficient to prevent the concentration of flammable substances approaching their lower explosive limit, consideration may be given to regarding as non hazardous, the space, ventilation and other openings into it, and the zone around the equipment contained within.

4.7.3 An alarm is to be provided on the navigating bridge and the engine control room to indicate any loss of the required ventilation capacity. Initiation of an alarm by a fan motor running or fan rotation monitoring device will not normally satisfy this requirement.

4.8.1 A space having access to a hazardous area defined as zone 1 or zone 2 may be regarded as non-hazardous if all the following requirements are met:

1. access is by means of an air-lock, having gastight steel doors, the inner of which, as a minimum, is self-closing without any hold-back arrangement;

2. a space and an air-lock are maintained at an overpressure (minimum 0,25 mbar) relative to the external hazardous area by ventilation from a non-hazardous area;

3. the relative air pressure within the space is continuously monitored and so arranged that:
   1. in the event of loss of overpressure, an alarm is given;
   2. the electrical supply to all equipment not of a type suitable for zone 1 is automatically disconnected;
   3. where the disconnection of equipment could introduce a hazard, an alarm may be given, in lieu of automatic shutdown, upon loss of overpressure; and
   4. a means of manual disconnection of electrical equipment not of a type suitable for zone 1, capable of being controlled from
   5. an attended station, is to be provided in conjunction with an agreed operational procedure; and
   6. where the means of disconnection, capable of being controlled from an attended station, is located within the space then it is to be of a type suitable for zone 1;

4. any electrical equipment required to operate upon loss of overpressure, lighting fittings (see Vol 2, Pt 9, Ch 6, 4.3 Lighting circuits 4.3.3) and equipment within the air-lock, is to be of a type suitable for zone 1; and

5. means are to be provided to prevent electrical equipment, other than of a type suitable for zone 1, being energised until the atmosphere within the space is made safe, by air changes of at least 10 times the capacity of the space.

4.8.2 A space having access to a hazardous space or zone defined as zone 2 may be regarded as non-hazardous if all following requirements are met:

1. access is by means of a self-closing gastight steel door without any hold-back arrangement;

2. it is maintained at an overpressure, (minimum 0,25 mbar) relative to the external hazardous area by ventilation from a non-hazardous area;

3. the relative air pressure within the space is continuously monitored and so arranged that:
   1. in the event of loss of overpressure, an alarm is given; and
   2. a means of manual disconnection of electrical equipment not of a type suitable for zone 2, capable of being controlled from an attended station, is to be provided; where the means of disconnection, capable of being controlled from an attended station, is located within the space then it is to be of a type suitable for zone 2;

4. any electrical equipment required to operate upon loss of overpressure (e.g. lighting fittings, see Vol 2, Pt 9, Ch 7, 4.7 Valve control and indication systems 4.7.3), is to be of a type suitable for zone 2; and

5. means are to be provided to prevent electrical equipment, other than of a type suitable for zone 2, being energised until the atmosphere within the space is made safe, by air changes of at least 10 times the capacity of the space.

4.9.1 Electric cables are not, as far as is practicable, to be installed in hazardous areas, except where serving equipment installed within the area. Through runs of cable may be accepted in locations classified as zone 1 or zone 2, where alternative routes are impracticable. Electric cables in hazardous areas are to be clearly labelled for identification purposes.

4.9.2 In addition to the requirements of Vol 2, Pt 9, Ch 3, 8 Electric cables, optical fibre cables and busbar trunking systems (busways), cables for circuits that are not intrinsically safe, which are located in hazardous areas, or which may be exposed to cargo oil, oil vapour or gas, are to be either:

1. armoured or braided for earth detection; or

2. otherwise adequately protected against mechanical or chemical damage, within zone 2 or non-hazardous areas only; or

3. as otherwise specifically permitted elsewhere within this Section; or

4. mineral insulated with copper sheath.

4.9.3 Armouring, braiding and other metal coverings of cables installed in hazardous areas are to be effectively earthed at least at both ends, see Vol 2, Pt 9, Ch 1, 2.4 Earthing and bonding 2.4.4.

4.9.4 Where there is risk of intermittent contact between armour and exposed metalwork, non-metallic impervious sheath is to be applied over metallic armour of cables.

4.9.5 Cables associated with intrinsically safe circuits are to be used only for such circuits. They are to be physically separated from cables associated with non-intrinsically safe circuits, e.g. neither installed in the same protective casing nor secured by the same fixing clip. Consideration may be given to other arrangements complying with IEC 60079- 14: Explosive atmospheres – Part 14 : Electrical installations design, selection and erection.

4.9.6 In zone 0, cable joints may only be used in intrinsically safe circuits.

4.9.7 Cable runs in zone 1 or zone 2 are, where practicable, to be uninterrupted. Where discontinuities cannot be avoided, cable joints are to:

• be made in an enclosure with a type of protection appropriate to the location; or
• provided the joint is not subject to mechanical stress, be epoxy filled, compound filled or sleeved with heatshrunk tubing, in accordance with the manufacturer’s instructions.

4.10.1 See IEC 60092: Electrical installations in ships – Part 502: Tankers – Special features.

4.11.1 Ships with closed spaces carrying vehicles, helicopter and aircraft with fuel having a flashpoint not exceeding 60ºC:

1. except where exempted by (b) electrical equipment fitted within the space and within the exhaust ventilation trunking for the space is to be of a type acceptable for zone 1;

2. where the ventilation system required by the Naval Administration is arranged to operate continuously and is sufficient to provide at least ten air changes per hour, whenever vehicles are on board, above a height of 45 cm from the vehicle deck, or any platform on which vehicles are carried, electrical equipment having an enclosure of ingress protection rating of at least IP 55 may be accepted as an alternative to that of a safe type.

4.12.1 Electrical equipment essential for the safety and operation of the ship is to be of a type providing protection against ignition of the gases and/or combustible dusts that can be present, selected in accordance with IEC 60092-506: Electrical installations in ships – Part 506: Special features – Ships carrying specific dangerous goods and materials hazardous only in bulk.

4.12.2 In addition to the requirements of IEC 60092-506: Electrical installations in ships – Part 506: Special features – Ships carrying specific dangerous goods and materials hazardous only in bulk, pipes such as ventilation and bilge pipes having ends opening into a hazardous area are to be considered a hazardous area. Enclosed spaces such as pipe tunnels and bilge pump-rooms containing such pipes and with equipment and components such as pumps, valves and flanges are to be considered as extended hazardous areas unless protected by overpressure.

4.12.3 Electrical equipment not essential for the safety or operation of the ship and which is not of a type providing protection against ignition of the gases and/or combustible dusts that can be present is to be completely disconnected and protected against unauthorised re-connection. Disconnection is to be made outside the hazardous areas and be effected with isolating links or lockable switches.

4.12.4 Electrical equipment and all cables, including through runs and terminating cables, are to be protected against mechanical damage. Cables are to be either enclosed in screwed heavy gauge steel drawn or seam-welded and galvanised conduit, or protected by electrically continuous metal sheathing or metallic wire armour braid or tape.

4.12.5 Cable penetrations of decks and bulkheads are to be sealed against the passage of gas or vapour.

4.13.3 The relevant group and temperature class for electrical equipment in hazardous zones are, respectively, IIB and T3.