Work out tank ullage instantly with clear inputs, formula shown and shareable results.
Ullage is the empty space above the product. The figure that matters operationally is safe ullage — the space up to the safe fill limit, not to the top of the tank. Dividing safe ullage by the incoming rate gives the time available before the receipt must be stopped or diverted.
Ullage
Safe ullage = capacity x safe fill % - current volume; time available = safe ullage / incoming rate
Tank filling must be controlled by independent high-level alarm and automatic overfill protection, not by ullage arithmetic. Overfill of flammable liquids can cause vapour cloud explosions.
It provides the time and volume margin for high-level alarms, operator response and valve closure. Buncefield-type overfill incidents happen when that margin is consumed.
Measured, by independent level instrumentation, and cross-checked against calculated ullage from flow totalisers. Discrepancy between the two is an early indication of a leak or a metering fault.