A ball float type overfill prevention device alerts when the tank is how full?

The correct answer indicates that a ball float type overfill prevention device is designed to alert when the tank reaches 95% full. This device typically utilizes a buoyant ball that rises with the liquid level in the tank. When the tank fills to 95% of its capacity, the ball floats high enough to trigger a signal or alarm, indicating that the tank is approaching its maximum capacity and that immediate action may be needed to prevent potential overfilling.

This threshold of 95% is crucial for ensuring that there is sufficient space in the tank to accommodate fluctuations and expansions that may occur due to temperature changes or other factors. Additionally, it serves as a safety measure to prevent spills or leaks, which can be harmful to the environment and result in regulatory violations.

Understanding that overfill prevention devices aim to maintain safe operational levels is key. Other options such as 90%, 92%, and 98% represent levels that would not trigger the alert at the designed safety threshold, allowing less margin for error and increasing the risk of overfilling before action is taken. Therefore, the 95% mark is strategically chosen to balance safety and operational efficiency.