Question 37 TK02 - Tank Vessel Assistant - Liquefied Gas

The Correct Answer is C ### Why Option C is Correct: An inert gas system (IGS) is designed specifically to prevent the formation of a flammable atmosphere within the cargo tanks. Flammability requires three components (the "fire triangle"): fuel (hydrocarbon vapors), heat (ignition source), and oxygen. The IGS works by introducing an inert gas (usually scrubbed, cooled exhaust gas from the ship's boiler or an independent generator) into the cargo tanks, effectively **displacing the air and thus reducing the oxygen concentration**. By maintaining the oxygen level significantly below the necessary threshold (typically mandated to be below 8% by volume, and often operated below 5%), the environment is rendered non-combustible, regardless of the presence of hydrocarbon vapors or a potential ignition source. ### Why Other Options are Incorrect: **A) by removing all hydrocarbon gases from the cargo tanks:** This is incorrect. While the goal is to prevent flammability, an inert gas system operates on the principle that hydrocarbon vapors *will* be present (especially during loading, discharging, and transit). The IGS is not designed primarily to remove the fuel; it is designed to remove the oxygen necessary for the fuel to burn. Procedures like gas-freeing are used to remove hydrocarbons, but the IGS's primary protective function relies on oxygen reduction. **B) by eliminating sparks and fire in the vicinity of cargo tanks:** This is incorrect. While ship safety protocols strive to eliminate ignition sources (sparks, static electricity, hot work), the inert gas system is a physical defense barrier that assumes an ignition source *might* be present. If the atmosphere is truly inert (low oxygen), a tank explosion cannot occur even if an ignition source is introduced. The IGS protects against the consequence of an ignition source; it is not the primary mechanism for eliminating the source itself. **D) by blanketing cargo tanks with inert foam:** This is incorrect. Inert gas systems use gas (such as cleaned boiler flue gas or nitrogen) to fill the tank volume and displace air. Foam systems (like high-expansion foam) are typically used for surface fire suppression in engine rooms or on deck, not for the continuous inerting of enclosed cargo tanks to prevent explosions.