Question 21 TK01 - Tank Vessel Assistant - Dangerous Liquids

The Correct Answer is A **Explanation of Option A (Correct):** The primary function of an inert gas system (IGS) on a tanker is to prevent explosions by rendering the atmosphere within the cargo tanks non-combustible. It achieves this by introducing a large volume of inert gas (usually flue gas or nitrogen) into the tank spaces. This inert gas displaces the oxygen and simultaneously dilutes the concentration of any flammable hydrocarbon vapors present. By reducing the oxygen level (typically to below 8% by volume) and keeping the flammable vapor concentration low, the IGS ensures that the tank atmosphere remains outside the "flammable range" (the range between the Lower Explosive Limit, or LEL, and the Upper Explosive Limit, or UEL). If the concentration of fuel or oxygen is below the LEL, combustion cannot occur. **Explanation of Incorrect Options:** * **B) De-energizes the "charged mist" effect:** While inert gas systems can help mitigate static electricity buildup (which is sometimes referred to in terms of charged mist or spray loading), this is a secondary benefit. The core function is atmospheric control through oxygen displacement and dilution, not the de-energization of static charges. * **C) Maintains a positive pressure on the vent header to cool the flammable vapors:** An IGS does maintain a slight positive pressure to prevent air ingress (which would raise the oxygen level), but the goal of this pressure is not to "cool the vapors." Furthermore, cooling the vapors is not the primary mechanism by which the IGS prevents explosions; it is atmospheric dilution. * **D) Inert gas filters out the flammable vapors from the cargo tank spaces:** Inert gas is pumped *into* the tanks, not used as a filter to remove vapors. While the vapors are sometimes displaced and vented to the atmosphere during loading/unloading operations, the gas itself is an additive (a diluent), not a filtering mechanism.