The maximum amount of liquid that can be safely contained in a UST. Most safe fill amounts are set at 90% some areas will allow 95%. Safe Fills are set to allow for expansion of product during temperature changes. As products warm up they will expand in volume. A typical safe fill for 10,000 gallon (nominal size) would be 10030 (actual capacity) x .90 (90%) = 9027 (safe fill).