【正文】 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。C (T4).Since surface temperature exceeding 135176。CExplosion group IICTemperature class T5These extracting requirements imply 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。Cor explosionprotected equipment in Degree of protection IP 55 Maximum surface temperature T3 Flammable liquids with a flash point below 23176。 temperature class T5.Carbon disulfide, which would be required to e under temperature class T6, is not permitted to be carried below deck, and need, therefore, not be considered.Also, details relating to explosion group and temperature class are not always available or in some cases are unkwown. Examples for the groups of solid bulk are shown in attached.In the following the correct choice of explosionprotected equipment is dealt with. As in the case of the areas subject to explosion hazard of 2. to above , a subdivision is used. Explosive substances in packaged form conforming to class 1, except for goods in division , patibility group SExplosive, dusty atmosphere: Degree of protection IP 65 Maximum surface temperature 100176。C in packaged form, flammable gases or highly dangerous bulk cargoes, which under certain conditions develop a potentially explosive gas atmosphere. Extended hazardous areas include: Areas with a gastight, closable door to areas subject to explosion hazard and not provided with overpressure ventilation or separation by a gas lock. If ventilation by overpressure with at least 6 air changes per hour or separated by a gas lock, these areas are considered to be safe. In case of the failure of ventilation system a visual and audible alarm is to be given and the equipment, which is not of certified safe type (. IP 55) must be automatically or manually switched off. Bilge pump spaces and pipe tunnels with ponents, such as flanges, valves, pumps, etc., which serve the area subject to explosion hazard. If ventilated (exhaust air) with at least 6 air changes per hour, these areas are considered to be safe. In case of the failure of ventilation system a visual and audible alarm is to be given and the equipment, which is not of certified safe type (. IP 55) must be automatically or manually switched off. Areas on the open deck within a spherical of 3 m around the exhaust openings of ventilation ducts from hazardous areas.4. Choice of equipment for use in areas subject ot explosion hazardIn practice, the choice of explosionprotected equipment, taking into account explosion group and temperature class, has to be problematical.The following facts may be recalled: The ignition penetration charcteristics of gases through gaps are reflected in the explosion group, while the maximum admissible temperature of electrical equipment is reflected in this temperature class. The maximum temperature of electrical equipment must always be below te ignition temperature of the explosive gas atmosphere.Explosion group and temperature class are based on the physical properties of the substances, which may form an explosive gas atmosphere.Aa abbreviations for the explosion group A/B/C are used and for the temperature class T1 – T6, with the most stringent requirements being represented by explosion group C and temperature class T6. The problem is that the IMO danger classes mentioned previously cannot be directly correlated to the explosion groups and temperature classes. In particular, products of classes 1, 2, 3, 6 and 8 contain a wide range of pletely different substances, which owing to their physical properties make high demands on explsion protection, .C in packaged form, flammable gases or highly dangerous bulk cargoes, which under certain conditions develop a potentially explosive gas atmosphere.It is assumed that in the event of failure, . damage to the packaging and discharge of a liquid with a flash point below 23176。C or T3, IP 55 (sulphur T4, IP55).6. For class 1 in bulk only for some goods the electrical equipment must b