Question 1 QMED04 - Boiler Technician-Watertender

The Correct Answer is D **Explanation for Option D ("all of the above as necessary"):** Option D is correct because ensuring safety during hot work (like welding) on a fuel tank requires considering multiple, sometimes simultaneous, preventative measures depending on the specific circumstances (the size of the tank, the type of fuel, the location of the work, and accessibility). * **Gas Freed (A):** The tank must be cleared of flammable vapors (gas freed) below the Lower Explosive Limit (LEL) to prevent an explosion or fire when welding introduces an ignition source. This is the primary requirement for hot work. * **Filled with Water (B):** If the tank cannot be entirely gas freed, or as an added layer of safety (especially when welding near residues or scale), the tank may be filled with water (or purged with water) up to the level of the repair. Water displacement ensures that the area being welded is free of flammable gases or is too rich in water vapor to burn. * **Inerted (C):** Inerting involves replacing the oxygen in the tank atmosphere with an inert gas (like nitrogen or carbon dioxide) until the oxygen content is too low (typically less than 8%) to support combustion. This is often used for larger tanks or those that cannot be easily gas freed, as it eliminates the possibility of ignition. Since safety procedures often mandate using one or a combination of these methods (e.g., gas freeing *and* inerting, or gas freeing *and* filling with water), depending on the severity of the risk, "all of the above as necessary" is the most comprehensive and correct answer. **Explanation of why A, B, and C are incomplete (and therefore incorrect alone):** * **A) gas freed:** While essential, gas freeing alone may not be sufficient if there are persistent residues, scale, or sludge that could release vapors when heated by welding. Additional measures like inerting or flooding might be mandated. * **B) filled with water:** Filling with water is a common technique, especially for localized upper-area repairs. However, it is not always practical for very large tanks or tanks where the structure cannot safely hold the weight of the water, making it a conditional, not universal, solution. * **C) inerted:** Inerting is a highly effective method, but it requires specialized equipment and gas supply. In some smaller or specialized repair scenarios, simple gas freeing or flooding with water may be deemed a sufficient and more practical safety solution by the competent person.