Primary barrier material must have the ability to maintain its integrity at the low temperaNces 36 Nickel steel(invar)stainless steel and aluminum are satistactor mperature s may be fitted depending ents but it is not normally required as the ships hull may be used as the secondary barrier if the temperature of the barrier is higher than-50 C and construction is of arctic D steel or equivalent. An independent secondary barrier of nickel steel,aluminium or plywood may be used provided it will perform a secondary function correctly. Insulation materials may be Balsa,mineral wool,glass wool,polyurethane or es possible to construct a primary barrer of polyurethane's as this will contain and cargo Gas detection equipment needs to be fitted in the inner barrier and void spaces in cargo pump rooms and in control rooms. The type of equipment depends upon the cargo being carried and the type of space nflammable gas vapours and toxic vapours as well as oxygen Visual and av ilable ached R器ervmi Membranes are very thin (less than 2mm)and are therefore susceptible to damage,tanks are never partially loaded. Boil off With LNG reliquifaction is not economically viable.It is a requirement by class that a suitable method be installed for the handling of this gas e common be Alternately,the gas may be vented although port restrictions mean it may not always be possible. For LPG boil off can be reliquified or a suitable venting system clear of the ship may safe gasss on the engine.Combustion problems and on the Safety Primary barrier material must have the ability to maintain its integrity at the low temperatures. 36% Nickel steel(invar), stainless steel and aluminium are satisfactory at normal LNG temperatures. Secondary barriers may be fitted depending upon the arrangements but it is not normally required as the ships hull may be used as the secondary barrier if the temperature of the barrier is higher than - 50 oC and construction is of arctic D steel or equivalent. An independent secondary barrier of nickel steel, aluminium or plywood may be used provided it will perform a secondary function correctly. Insulation materials may be Balsa, mineral wool, glass wool, polyurethane or pearlite. It is possible to construct a primary barrier of polyurethane's as this will contain and insulate the cargo. Usually, secondary barriers are of low temperature steel or aluminium, neither of which becomes brittle at low temperatures. Gas detection equipment needs to be fitted in the inner barrier and void spaces in cargo pump rooms and in control rooms. The type of equipment depends upon the cargo being carried and the type of space involved measurement of inflammable gas vapours and toxic vapours as well as oxygen content should be monitored. Visual and available warnings must be given when high levels are approached. Toxic gasses must be measured every four hours except when personnel are in the spaces when the interval is 30 mins. Membranes are very thin (less than 2mm) and are therefore susceptible to damage, tanks are never partially loaded. Boil off With LNG reliquifaction is not economically viable. It is a requirement by class that a suitable method be installed for the handling of this gas One common method is to utilise the gas as fuel for the propulsion plant. A suitable method of disposing with excess energy should be fitted. Typically for a steam powered vessel this would take the form of a steam dumping arrangement. Alternately , the gas may be vented although port restrictions mean it may not always be possible. For LPG boil off can be reliquified or a suitable venting system clear of the ship may be used. Burning in the main engine can be very problematic, not least with the ensuring safe gas tightness on the engine. Combustion problems and the probable production of noxious gasses are also areas of concern. Safety During transit gas will boil off and venting may be employed to release pressure but methane is a green house gas and pollution regulations may restrict such venting. Any venting of gas 5