Question 27 TK01 - Tank Vessel Assistant - Dangerous Liquids

The Correct Answer is B. 1. **Why option B is correct:** An inert gas (IG) system works on the principle of fire prevention by controlling one of the three elements required for combustion: fuel (hydrocarbon vapors), heat (ignition source), and oxygen. The system generates and delivers a large volume of oxygen-depleted gas (typically flue gas from the ship’s boiler or dedicated generator) into the cargo tanks. By maintaining the oxygen concentration inside the tank atmosphere at or below $8\%$ (the internationally accepted standard, well below the approximately $11-13\%$ required for combustion of hydrocarbon vapors), the IG system ensures that even if flammable hydrocarbon vapors are present and an ignition source occurs, an explosion cannot take place due to the lack of necessary oxygen. 2. **Why the other options are incorrect:** * **A) by removing all hydrocarbon gases from the cargo tanks:** While the IG system is used during purging and gas-freeing operations (which do remove hydrocarbon gases), its primary function for explosion prevention during normal cargo operations (loading, discharging, and transit) is **not** to remove all fuel, but rather to render the mixture non-flammable by controlling oxygen. During cargo handling, hydrocarbon vapors are constantly being generated. * **C) by blanketing cargo tanks with inert foam:** Inert gas systems use gas (such as nitrogen, carbon dioxide, and sulfur dioxide from boiler exhaust), not foam, for tank blanketing. Foam is typically used for fighting fires on the deck or in the pump room, not for routine inerting of cargo tank atmospheres. * **D) by eliminating sparks and fire in the vicinity of cargo tanks:** While eliminating ignition sources (sparks, fire) is crucial for fire safety, this is achieved through strict operational procedures (e.g., non-smoking rules, intrinsically safe equipment, proper grounding). The inert gas system itself directly addresses the atmosphere within the tank, ensuring that even if an ignition source *were* somehow introduced (which is the most difficult element to control), an explosion would still be impossible.