Question 21 QMED05 - Machinist-Pump Technician

The Correct Answer is D **Explanation for Option D ("all of the above as necessary")** Emergency welding repairs on the upper area of a fuel tank carry a significant risk of fire or explosion, as flammable vapors (hydrocarbon gases) are highly concentrated in the ullage space (the upper area) of the tank. Safety regulations (such as those established by the IMO, SOLAS, or local regulatory bodies) mandate that a "hot work" permit must be obtained, requiring thorough preparation of the area to eliminate fire hazards. The preparation methods needed often include a combination of techniques, making "all of the above as necessary" the most comprehensive and correct answer: 1. **Gas Freed (B):** The initial step is always to clean the tank, wash it thoroughly, and ventilate it until the atmosphere is tested and confirmed to be below the required safe limit for hot work (typically less than 1% LEL – Lower Explosive Limit). This process is known as "gas freeing." 2. **Inerted (C):** If the tank cannot be completely gas freed due to logistical constraints or if the atmosphere cannot consistently remain below the LEL threshold, it must be "inerted." Inerting involves filling the tank with an inert gas (usually nitrogen or flue gas) to displace oxygen to a level too low to support combustion (typically below 8%). This is a common safety requirement for welding on adjacent compartments. 3. **Filled with Water (A):** If welding is performed directly on the bottom or side plating, filling the tank with water (hydrocarbon-free water) up to a level well above the repair area (or until the tank is completely full) is a standard safety precaution, especially when gas freeing is difficult or insufficient. For welding on the *upper area* (as specified in the question), the tank must be filled with water up to the deckhead to displace all vapors from the workspace, essentially eliminating the fire hazard from below the deck plate being repaired. Since any of these methods (or a combination thereof, especially gas freeing plus inerting the adjacent areas) might be required depending on the specific risk assessment, tank condition, and location of the repair, D is the definitive correct answer. **Explanation of Why Other Options Are Incorrect (Standing Alone)** * **A) filled with water:** While sometimes necessary (especially for bottom/side repairs or upper repairs where the tank cannot be gas freed), simply filling the tank with water may not be sufficient if vapors exist in adjacent compartments or if the water level is not high enough to displace vapors from the actual repair area. * **B) gas freed:** Gas freeing is the *ideal* state for hot work, but it is often difficult or impossible to achieve a consistent "gas-free" state (below the LEL threshold) in large shipboard fuel tanks or their adjacent piping systems. If gas freeing fails, alternative measures (C or A) must be used. * **C) inerted:** Inerting is an excellent safety measure for preventing combustion but does not remove the vapors. If welding is performed, the integrity of the inert gas layer must be constantly monitored, and it is generally considered the secondary option if gas freeing is impossible. It is not always required if gas freeing is successful. Therefore, because the safety procedure depends entirely on the specific conditions and risk assessment, all three preparatory actions may be necessary to ensure a safe environment for welding.