Question 19 QMED04 - Boiler Technician-Watertender

The Correct Answer is B **Explanation for Option B (The tank cooling system has malfunctioned):** Low-pressure CO2 systems are fixed fire extinguishing installations where carbon dioxide is stored as a liquid in large, insulated tanks. To maintain the CO2 in its liquid state and keep the system pressure stable (typically around 300 psi or 20-21 bar), the storage tank must be continuously refrigerated (cooled) to maintain a temperature of approximately 0°F (-18°C). If the cooling system malfunctions or fails, the temperature inside the tank will rise rapidly. According to the principles of saturated vapor pressure, even a small increase in temperature will cause excessive vaporization of the liquid CO2, leading to a significant and direct rise in internal pressure, immediately activating the high-pressure alarm. *** **Why the other options are incorrect:** * **A) The pilot cylinder discharge valve is leaking:** Pilot cylinders are used to actuate the main discharge valve during system activation. A leak in the pilot line or valve would affect the ability of the system to operate correctly (or deplete the pilot charge) but has no direct connection to the pressure or temperature control within the large, separate main CO2 storage tank. * **C) An excessive amount of insulation has been installed on the tank and piping:** Insulation is designed to minimize the heat input into the refrigerated tank. Excessive insulation would actually improve the efficiency of the cooling system and help maintain the low temperature, thus helping to keep the pressure *low* and stable, not causing it to rise. * **D) An air leak has developed in the tank:** A leak in the tank or piping would cause the CO2 contents to escape to the atmosphere (which is at a much lower pressure), resulting in a gradual **pressure drop**, not a high-pressure condition. Low-pressure alarms are designed to detect leaks, not high-pressure alarms.