When filling a tank, the positive shut off device must close before the fittings at the top of the tank are exposed to fuel, or when the tank is a maximum of what percentage full?

The correct answer is 95%. This regulation is in place to prevent overfilling of storage tanks, which can lead to spillage and potential environmental hazards. The positive shut-off device serves as a critical safety mechanism during the fueling process by automatically stopping the flow of fuel when the tank reaches a predetermined capacity, in this case, 95%.

At this percentage, the risk of overflow is minimized, ensuring that the tank is not filled to its maximum capacity, which could cause fuel to become pressurized or create an unsafe situation. By stopping the fill process before reaching this point, the design helps to maintain safety standards and protects against leaks that might occur if the tank were to overflow.

The other choices, while relevant, either exceed the safer threshold or fall below the necessary capacity needed for effective monitoring and management of the tank fill process. Thus, 95% is established as a standard that balances filling efficiency with safety considerations.