A positive shutoff overfill prevention device must stop fuel flow when the tank is more than what percentage full?

• A. 85%
• B. 90%
• C. 95%
• D. 97%

Answer: (C)

A positive shutoff overfill prevention device is designed to prevent the overflow of product from storage tanks and is crucial for safety and environmental compliance. The requirement for this device to stop fuel flow when the tank is more than 95% full is based on industry standards and regulations aimed at minimizing the risk of overfilling.

When a tank reaches 95% capacity, there is insufficient room to accommodate additional fuel without the risk of spillage, which can lead to hazardous situations such as leaks, environmental contamination, and fire hazards. This 95% threshold is strategically set to allow for some expansion of the product due to temperature changes and to avoid the displacement of liquid that can occur during filling.

In contrast, the other percentages listed would not provide adequate safety margins. For example, stopping at 90% might still allow for enough fuel to overflow in certain situations, particularly under adverse conditions like temperature fluctuations or during the last stages of filling. Hence, the 95% mark is crucial to maintaining safe operational practices and ensuring that overfilling does not occur.