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{ "quizId": "day1_leg_familiarisation", "courseId": "VLEC Managment", "title": "Day 1 - LEG Familiarisation \u0026 Tank Atmosphere Control", "subtitle": "BSM Maritime Training Centre", "passPercent": 70, "version": "1.0", "date": "2026-03-17", "questions": [ { "id": 1, "topic": "Natural Gas Liquids", "question": "Natural Gas Liquids (NGLs) are composed of which of the following?", "options": [ "Methane, Ethane, and Propane", "Ethane, LPGs, and Gas Condensates", "Butane, Pentane, and Hexane", "Methane, Nitrogen, and CO₂" ], "answer": "Ethane, LPGs, and Gas Condensates", "explanation": "NGLs are light hydrocarbons dissolved in natural gas and are made up of Ethane, LPGs (Propane \u0026 Butane), and gas condensates (Pentane and heavier fractions)." }, { "id": 4, "topic": "Ethane Properties", "question": "Which statement about Ethane is CORRECT?", "options": [ "It is a toxic gas with a strong odour", "It is colourless, odourless, and acts as a simple asphyxiant", "It is heavier than air and non-flammable", "It has a characteristic sweet smell" ], "answer": "It is colourless, odourless, and acts as a simple asphyxiant", "explanation": "Ethane is colourless, odourless, flammable, not considered toxic, but acts as a simple asphyxiant by displacing oxygen." }, { "id": 6, "topic": "Critical Properties", "question": "What does \u0027Critical Temperature\u0027 mean for a gas?", "options": [ "The temperature at which the gas ignites", "The maximum temperature at which a gas can be converted to liquid by pressure alone", "The temperature at which the gas becomes toxic", "The boiling point of the gas at atmospheric pressure" ], "answer": "The maximum temperature at which a gas can be converted to liquid by pressure alone", "explanation": "Critical temperature is the maximum temperature at which a gas can be converted to a liquid by pressure alone." }, { "id": 7, "topic": "Flammability", "question": "What is the flammable range of Ethane in air?", "options": [ "1.0 - 7.6% by volume", "2.1 - 9.5% by volume", "3 - 12.5% by volume", "5 - 15% by volume" ], "answer": "3 - 12.5% by volume", "explanation": "Ethane has a flammable range of 3-12.5% by volume in air." }, { "id": 8, "topic": "Flammability", "question": "What is the auto-ignition temperature of Ethane?", "options": [ "305°C", "510°C", "450°C", "260°C" ], "answer": "510°C", "explanation": "Ethane has an auto-ignition temperature of 510°C." }, { "id": 10, "topic": "Ethane Hazards", "question": "What extinguishing agents should be used for an Ethane fire?", "options": [ "Water jet only", "Foam and water spray", "Dry chemical or carbon dioxide", "Sand and earth only" ], "answer": "Dry chemical or carbon dioxide", "explanation": "For Ethane fires, dry chemical or carbon dioxide (CO₂) should be used." }, { "id": 12, "topic": "LEG Spill on Water", "question": "What happens when LEG is spilled on water?", "options": [ "It sinks below the water surface and dissolves", "It forms a solid ice layer on top of the water", "It boils rapidly, spreads widely, and evaporates quickly with no solid ice layer forming", "It remains as a stable pool floating on water" ], "answer": "It boils rapidly, spreads widely, and evaporates quickly with no solid ice layer forming", "explanation": "LEG boils very rapidly on water due to the large temperature difference, spreads widely, and no solid ice layer forms." }, { "id": 13, "topic": "LEG Spill on Water", "question": "What is \u0027Rapid Phase Transition\u0027 in the context of LEG spills?", "options": [ "Slow evaporation of LEG over time", "A violent physical explosion when cryogenic liquid contacts water, without combustion", "The process of LEG freezing on contact with water", "Normal boiling of LEG at atmospheric pressure" ], "answer": "A violent physical explosion when cryogenic liquid contacts water, without combustion", "explanation": "RPT is a violent physical explosion when cryogenic liquid rapidly vaporizes upon contact with water — not a chemical combustion." }, { "id": 14, "topic": "Vapour Cloud", "question": "In a vapour cloud from a liquefied gas spill, where is the flammable zone?", "options": [ "Directly at the spill point (Area A)", "Just above the spill where concentration is above UFL (Area B)", "Between the too-rich zone (B) and too-lean zone (D) — Area C", "At the outer edge where concentration is below LFL (Area D)" ], "answer": "Between the too-rich zone (B) and too-lean zone (D) — Area C", "explanation": "The flammable zone (Area C) lies between the too-rich zone (B) and the too-lean zone (D)." }, { "id": 15, "topic": "Vapour Cloud", "question": "Why does a visible white cloud form when cold LEG vapour mixes with air?", "options": [ "The gas itself is white in colour", "Condensation of moisture in the ambient air", "Chemical reaction between ethane and oxygen", "Dust particles being picked up by the vapour" ], "answer": "Condensation of moisture in the ambient air", "explanation": "Cold vapour condenses the moisture in ambient air, forming a visible white cloud." }, { "id": 16, "topic": "Cryogenic Hazards", "question": "Why can plain carbon steels NOT be used for LEG cargo systems?", "options": [ "They corrode too quickly in cold temperatures", "They become brittle and fracture at cryogenic temperatures", "They react chemically with ethane", "They are too heavy for marine applications" ], "answer": "They become brittle and fracture at cryogenic temperatures", "explanation": "Plain carbon steels undergo brittle fracture at cryogenic temperatures. 9% nickel steel is used instead." }, { "id": 18, "topic": "Ethane Reactivity", "question": "Ethane can have a dangerous reaction with which substance?", "options": [ "Water", "Nitrogen", "Chlorine", "Carbon dioxide" ], "answer": "Chlorine", "explanation": "Dangerous reaction is possible with chlorine." }, { "id": 19, "topic": "Commercial Ethane", "question": "What is a key characteristic of commercial ethane compared to pure ethane?", "options": [ "It contains no impurities", "It contains methane content; small methane in liquid leads to large methane fractions in vapour", "It is always at higher purity than lab-grade ethane", "It contains significant amounts of propane" ], "answer": "It contains methane content; small methane in liquid leads to large methane fractions in vapour", "explanation": "Commercial ethane contains methane. Even very small methane in liquid leads to large methane fractions in vapour." }, { "id": 20, "topic": "Rollover", "question": "What is a key indicator that stratification has occurred, potentially leading to rollover?", "options": [ "Sudden increase in tank pressure", "A noticeable reduction in the normal boil-off rate", "Rising liquid temperature at the surface", "Unusual vibrations in the tank structure" ], "answer": "A noticeable reduction in the normal boil-off rate", "explanation": "A key indicator of stratification is a noticeable reduction in the normal boil-off rate." }, { "id": 21, "topic": "Tank Atmosphere Control", "question": "What is the target oxygen concentration for inerting cargo tanks (industry best practice)?", "options": [ "Below 8%", "Below 5%", "2% or lower", "Below 10%" ], "answer": "2% or lower", "explanation": "Industry best practice for gas tankers is 2% or lower." }, { "id": 22, "topic": "Tank Atmosphere Control", "question": "For LEG operations, what dewpoint target should be achieved in cargo tanks?", "options": [ "-20°C or below", "-40°C or below", "-60°C or below", "0°C or below" ], "answer": "-60°C or below", "explanation": "For LEG operations, the dewpoint target is -60°C or below to prevent ice formation." }, { "id": 24, "topic": "Hold Space Inerting", "question": "What positive pressure should be maintained in hold spaces during inerting?", "options": [ "Greater than 0.050 barg", "Greater than 1.0 barg", "Greater than 0.5 barg", "Atmospheric pressure only" ], "answer": "Greater than 0.050 barg", "explanation": "Hold spaces should maintain positive pressure greater than 0.050 barg." }, { "id": 26, "topic": "Nitrogen Generation", "question": "What is the main advantage of a PSA nitrogen generator compared to a membrane type?", "options": [ "Lower cost", "Higher energy saving with high purity N₂", "Simpler maintenance", "Smaller physical footprint" ], "answer": "Higher energy saving with high purity N₂", "explanation": "PSA generators offer higher energy savings with high purity N₂ using Carbon Molecular Sieve." }, { "id": 27, "topic": "Nitrogen Generation", "question": "What principle does a membrane nitrogen generator use?", "options": [ "Cryogenic distillation", "Chemical absorption", "Selective permeation — O₂ and H₂O pass through membrane faster than N₂", "Magnetic separation" ], "answer": "Selective permeation — O₂ and H₂O pass through membrane faster than N₂", "explanation": "Membrane generators use selective permeation. Fast gases permeate through the membrane, slow N₂ passes through." }, { "id": 29, "topic": "Atmosphere Change Methods", "question": "How many tank volumes does the displacement method typically require?", "options": [ "Approximately 0.5 tank volumes", "Approximately 1.5 tank volumes", "Approximately 3 tank volumes", "Approximately 5 tank volumes" ], "answer": "Approximately 1.5 tank volumes", "explanation": "Displacement requires approximately 1.5 tank volumes. Dilution requires approximately 3." }, { "id": 30, "topic": "Atmosphere Change Methods", "question": "When using displacement with nitrogen to inert air-filled tanks, how should nitrogen be introduced?", "options": [ "From the bottom, since N₂ is heavier than air", "From the top, since N₂ is lighter than air at the same temperature", "From the sides only", "It doesn\u0027t matter where it\u0027s introduced" ], "answer": "From the top, since N₂ is lighter than air at the same temperature", "explanation": "Light gas (nitrogen) is introduced over heavy gas (air) — top in, bottom out — piston effect." }, { "id": 31, "topic": "Gas Densities", "question": "At 20°C, which gas is LIGHTEST?", "options": [ "Nitrogen (0.97 SG)", "Air (1.00 SG)", "Ethane (1.049 SG)", "Methane (0.668 SG)" ], "answer": "Methane (0.668 SG)", "explanation": "Methane is lightest at 0.668 kg/m³. Order: Methane \u003c Nitrogen \u003c Air \u003c Ethane \u003c IG \u003c CO₂ \u003c Propane." }, { "id": 33, "topic": "Purging Operations", "question": "What is the optimal back pressure to maintain during displacement purging?", "options": [ "0.5 barg", "0.02 barg", "1.0 barg", "No back pressure needed" ], "answer": "0.02 barg", "explanation": "0.02 barg back pressure prevents funnel effect and short-circuiting." }, { "id": 34, "topic": "Inert Gas vs Nitrogen", "question": "Why is nitrogen preferred over inert gas (IGG) for LEG cargo tank inerting?", "options": [ "Nitrogen is cheaper to produce", "IG contains ~14% CO₂ which becomes dry ice at -78.5°C — problematic for LEG", "Nitrogen has higher oxygen content", "IG is too hot for cargo tanks" ], "answer": "IG contains ~14% CO₂ which becomes dry ice at -78.5°C — problematic for LEG", "explanation": "IG contains ~14% CO₂ which becomes dry ice at -78.5°C, causing blockages in LEG systems." }, { "id": 35, "topic": "Regulatory Requirements", "question": "According to IGC Code 9.1.2, what must be used as an intermediate step when changing atmosphere with flammable cargoes?", "options": [ "Dry air", "An inerting medium", "Cargo vapour", "Steam" ], "answer": "An inerting medium", "explanation": "IGC Code 9.1.2 requires an inerting medium as an intermediate step for flammable cargoes." }, { "id": 36, "topic": "Inerting Standards", "question": "According to ICS Tanker Safety Guide, what safety factor is applied for inerting?", "options": [ "Safety factor of 1.5", "Safety factor of 2", "Safety factor of 3", "Safety factor of 4" ], "answer": "Safety factor of 2", "explanation": "A safety factor of 2 is used to account for mixing imperfections and equipment inaccuracies." }, { "id": 37, "topic": "Ethane Physical Properties", "question": "As ethane temperature rises from -90°C to -5°C, what happens to vapour pressure and liquid density?", "options": [ "Both increase", "Vapour pressure increases, liquid density decreases", "Both decrease", "Vapour pressure decreases, liquid density increases" ], "answer": "Vapour pressure increases, liquid density decreases", "explanation": "Vapour pressure increases (~0.5 to ~21 bara) while liquid density decreases (~545 to ~410 kg/m³)." }, { "id": 38, "topic": "Purging Methods", "question": "What is the main advantage of series purging over parallel purging?", "options": [ "Faster completion time", "Lower nitrogen consumption", "Higher final purity", "Simpler valve lineup" ], "answer": "Lower nitrogen consumption", "explanation": "Series purging has lower nitrogen consumption — sequential tank-to-tank flow is more efficient." }, { "id": 39, "topic": "Safety", "question": "Flammable vapour/air mixtures should NEVER be passed through what?", "options": [ "Cargo pumps", "Cargo compressors", "Heat exchangers", "Level gauges" ], "answer": "Cargo compressors", "explanation": "Flammable vapour/air mixtures must never pass through cargo compressors — risk of ignition." }, { "id": 40, "topic": "Ethane Safety Data", "question": "What is the first aid action if liquid ethane contacts the skin?", "options": [ "Apply warm oil to the affected area", "Immerse frostbitten areas in warm water, remove contaminated clothing, wash for 15 minutes", "Apply ice to the affected area", "Rub the affected area vigorously to restore circulation" ], "answer": "Immerse frostbitten areas in warm water, remove contaminated clothing, wash for 15 minutes", "explanation": "Immerse in warm water until thawed, remove contaminated clothing, wash 15 minutes. Do NOT rub." } ], "courseFolder": "VLEC Managment", "quizFolder": "Day 1 Revision" }
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