Each tank ship having an inert gas system must have portable instruments to measure concentrations of hydrocarbon vapor in inert atmospheres. The ship must also carry instruments that can measure concentrations of _________.
• Inert gas systems on tank ships – why they are used and what they are designed to control • The role of flammability limits and what gas must be monitored to avoid entering a combustible range • Difference between gases used to create an inert atmosphere and the gas that supports combustion
• Think about which gas, if present in too high a concentration, could allow hydrocarbon vapors to ignite even in an inerted tank. • Ask yourself: when checking if a tank atmosphere is safely inert, which specific gas level tells you whether the atmosphere can support combustion or not? • Consider what you actually need to measure in addition to hydrocarbon vapor to confirm the space is too ‘lean’ to burn.
• Verify which gas is essential for combustion to occur and is therefore key to judging whether a tank is truly inerted. • Confirm from regulations or study materials what additional gas concentration must be checked along with hydrocarbon vapor in an inerted cargo tank. • Eliminate choices that are mainly used as inerting agents rather than as indicators of whether the atmosphere can support burning.
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