When must the overfill alarm be triggered to alert the delivery operator?

The overfill alarm is designed to activate at a specific point to prevent spills during the delivery of fuel. The correct answer indicates that the alarm must be triggered when the tank is 90% full. This is a critical safety measure, as it provides a warning to the delivery operator that the tank is close to being full, allowing them to halt the incoming fuel flow before the tank reaches its maximum capacity.

Setting the alarm at 90% full gives an essential buffer zone to accommodate any fluctuations or varying conditions during fuel delivery, protecting against accidental overfilling, which can lead to spills or environmental contamination. Therefore, positioning the alarm at this level is a key safety protocol, reinforcing the importance of adhering to established guidelines for the safe operation of underground storage tanks (USTs).