🔍 Key Concepts

• Inert gas systems on tank vessels and their purpose (preventing explosions in cargo tanks) • The relationship between oxygen percentage and the flammable range of hydrocarbon vapors • Regulatory limits for maximum oxygen content in inert gas supplied to cargo tanks (46 CFR and SOLAS)

💭 Think About

• Think about what oxygen level is generally considered low enough that hydrocarbon vapors in a tank cannot burn, even if there is an ignition source. • Compare each choice with what you know about normal air composition and the approximate oxygen level at which combustion becomes impossible. • Ask yourself: would a higher oxygen percentage still safely keep the tank atmosphere outside the flammable range under all normal conditions?

✅ Before You Answer

• Recall that normal air has about 21% oxygen by volume; use this as a reference point when judging what is truly 'inert.' • Verify in 46 CFR or SOLAS II-2 what maximum oxygen content is allowed in inert gas supplied to cargo tanks. • Check which option represents a level that is safely below the minimum oxygen concentration needed for combustion, with a good safety margin.