Question 66 ONC01 - Master/Chief Mate Unlimited Tonnage

The Correct Answer is A. **Explanation for Option A (Correct):** When flammable liquids are handled, the primary goal of ventilation is to prevent the accumulation of flammable vapors to concentrations within the explosive or flammable range (Lower Explosive Limit - LEL and Upper Explosive Limit - UEL). Since handling activities (like pumping, transferring, or pouring) create a constant potential for vapor release, the ventilation system must be operated continuously whenever the vapors are present or likely to be present. Continuous operation ensures that fresh air is constantly introduced and vapors are extracted, maintaining the atmosphere below the LEL and ensuring the safety of personnel and the vessel. **Explanation for Other Options (Incorrect):** * **B) It should be available on standby for immediate use:** Relying on standby ventilation is insufficient. By the time vapors are detected and the ventilation is activated, dangerous concentrations (potentially above the LEL) may already exist. Prevention requires continuous operation during the activity. * **C) It should be shut down if an explosive mixture is present:** Shutting down ventilation when an explosive mixture is present is dangerous and counterproductive. If an explosive mixture exists, ventilation (often explosion-proof and high-capacity) is needed immediately to rapidly dilute the mixture until it falls safely below the LEL. Stopping ventilation allows the dangerous concentration to persist or worsen. * **D) It should be only operated intermittently to remove vapors:** Intermittent operation allows vapors to build up during the periods the ventilation is off. Effective vapor control requires constant dilution and removal to ensure that the concentration never reaches dangerous levels while the flammable liquids are being handled.