【正文】 mply considerable costs, are in some cases difficult to put into practice technically and need frequently due to restrictions on the kind of cargo carried not be applied. However, if a ship is intended to carry all admissible substances without restrictions as to the danger calsses, their observance is to ensured.In practice, in many cases relaxations are possible, as transports of substances can be excluded. Some important special arrangements, for instance, are as follows: If no hydrogen, no hydrogen mixtures and no cargo in bulk which may develop hydrogen under certain conditions are carried on board ships, explosion group IIC as stipulated for explosion protection in above may be reduced to IIB. Where in the cargo holds of container ships tranports of class 1 goods (explosion substances) and of hydrogen mixtures can be excluded, the electrical equipment has to meet the following requirements only:Degree of protection IP 55Explosion group IIBTemperature class T45. Choice of equipment for use in extended hazardous areasElectrical equipment chosen for use in these areas has to meet the following minimum requirements:In general, equipment in used which does not produce sparks in normal operation and the surfaces of which do not attain inadmissible temperatures, or equipment wih simplified pressurised enclosure or vapourproof enclosure。 degree of IP 55.The surface temperature must not exceed a value below the ignition temperature of the products intended to be carried, . in general a value below 135176。C (T4).Since surface temperature exceeding 135176。C occue rarely only and the equipment, such as lighting, switches, ventilator motors and distributors, in these areas meets the prescribed degree of protection requirements anyhow, special measures are in most cases not required.Use of explosionprotected equipment of of equipment with Ex(n) type protection is, of cource, also possible.6. Installation and operation of electrical equipmentA special provision should be mentioned here, which in practice is of partucular significance. So far, the condition of the electrical equipment has been described, which will make it suitable for operation also in the event of dangerous cargo being carried. However, dangerous cargo is by no means carried all the time. Therefore, systems are frequently installed such that part of the electrical equipment does not ply with the requirements for transports of dangerous cargo, with this equipment being operated also during normal service, . when no dangerous cargo is carried, and disconnected only in the event of dangerous cargo in fact being carried.In this connection the following is to be observed:If electrical equipment is installed which is not suitable for use during tranportation of dangerous cargo, it must be disconnected and capable of being safeguarded against unautyhorized reconnection. The disconnection device is to be located outside the hazardous area and should, for instance, include lockable switches in its design. Where electrical equipment is important for ensuring the safety of the crew, the cargo or the ships, it should not be disconnected and must ply with the requirements for use in hazardous areas.7. Special provisionsA special arrangement in the Baltic Sea area is of particular significance for a number of roro vessels (cargo and passenger vessels).The carriage of dangerous goods on board roro vessels operating in the Baltic Sea and of late also in the national North Sea area is subject to the “Memorandum of Understanding“ as amended in Copenhagen on 8/10 January 1992 and signed by Denmark, Finland, Sweden, Poland and the Federal Republic of Germany. The funtions arising from this memorandum in the area of the FRG have been entrusted to Germanischer Lloyd by the Federal Ministry of Transport.The reason for this special arrangement are that arrangements existed in the Baltic Sea prior to entry into force (1984) of SOLAS, Regulation 54 already and that some of the distance covered by the vessels are very short, so that rail/road traffic (RID and ADR) had to be taken into account to a large extent. Apart from detailed special provisions for passenger and cargo vessels (prohibition of certain substances) and regulations for stowage on and below deck, in closed and open holds, requirements have been laid down for explosion protection of electrical equipment, providing for at least 20 changes of air per hour during loading and unloading operations and during voyage.Simplified explosion protection of electrical equipment, as against the measures required to be taken subject to SOLAS reg. 54, owing to the frequent changes of air is conditionally possible. This measure is also referred to as primary explosion protection.In specific cases, which can not be dealt with, explosion protection of electrical equipment is required throughout the full height of the hold。 in other cases it is sufficient to provide explosion protection up to a height of 45 cm, while above that height provisions are made for limited explosion protection (measures for extended hazardous areas).Explosion GroupsCountryGermanyInternationalUSASpecificationVDE 0171/IECCONELEC(VDE 0171/)NECTerminologyExplosion ClassExplosion GroupGroupAcetone, ammonia, ethyl alcohol, petro, benzene, methane, propane1IIADAcetaldehyde, ethylene, town gas (coal gas)2IIBCHydrogenCarbon disulphideAcetylene3a3b3cIICBAAll gases in Class 33nTemperature ClassesIgnitin temperature of bustible substances 176。CIgnition GroupVDE 0171/Temperature ClassDVE 0171/, ICE 797 and 8 450 300 200 135 100 85G1G2G3G4G5T1T2T3T4T5T6Characteristics of Electrical Equipment for Use in Areas Subject to Explosion Hazard (Comparable Zone 1) in the Carriage of Solid Bulk Cargoes (Example)Dangerous GoodsIMOClassHazardProtection against