The following example is provided for illustration purposes only.
For this example the delivery operator has determined that the tank has a maximum capacity of 10,000 gallons. Therefore, the maximum amount of product that can be stored in the tank should not exceed 9,000 gallons (10,000 x 0.9 = 9,000), which equals 90% of the tank’s maximum capacity.
The delivery operator obtains a reading (this may be accomplished by sticking the tank or reading a product inventory printout from an automatic tank gauge) of the amount of fuel currently in the tank. The reading indicates there is 4,700 gallons.
This means that the maximum amount of product that can be safely delivered to the tank without exceeding 90% is 4,300 gallons (9,000 - 4,700 = 4,300). 90% is the overfill threshold for triggering an audible / visual alarm or restricting the flow of product into the tank.