Question 16

The Correct Answer is C ### 2. Explanation for Option C (125% of cargo pump capacity) Option C is correct because the primary function of an inert gas system (IGS) during cargo operations is to replace the volume of cargo being removed from the tanks. 1. **Demand Driver:** The maximum rate at which cargo can be discharged (unloaded) dictates the maximum volume of inert gas required per unit of time. This discharge rate is defined by the maximum combined throughput capacity of the ship's cargo pumps. 2. **Regulatory Requirement:** According to international safety regulations (e.g., SOLAS Chapter II-2), the inert gas system must be capable of delivering inert gas at a flow rate of at least 125% of the maximum rate of discharge capacity of the ship's cargo pumps. 3. **Safety Margin:** The 125% margin ensures that there is sufficient capacity to maintain a positive pressure in the tanks, compensate for leaks, and allow for adequate purging and cooling of the gas, even during peak discharge operations. ### 3. Explanation of Why Other Options Are Incorrect **A) 125% of fan capacity** This is incorrect because it is a circular definition. The required gas supply capacity (the goal) determines the size and capacity of the fans (blowers) installed, not the other way around. The capacity requirement must be linked to operational demand (cargo discharge rate). **B) 125% of forced draft rate** This is incorrect. Forced draft refers to the rate at which combustion air is supplied to the ship's boilers. While inert gas systems often use cleaned flue gas from the boilers, the forced draft rate relates to boiler power production, not the specific volumetric requirements needed to compensate for cargo removal from the tanks. **D) 125% of shore side loading rate** This is incorrect. When loading cargo, the tanks are filled with liquid, and the existing inert gas is simply displaced and vented (or returned to shore). The critical demand for gas supply occurs during *discharge* (unloading), when the IG system must actively pump gas into the tanks to prevent a vacuum and maintain safety pressure. Therefore, the required capacity is based on the ship's maximum discharge potential (pumps), not the shore's loading potential.