Statistical Inventory Reconciliation (SIR) is a method in which an approved third party vendor performs a computerized evaluation of reconciliation records as a method of leak detection.
Fuel is a volatile product and it is difficult to evaluate product shortages as being due to a leak in the system or due to shrinkage, evaporation, etc. SIR vendors use a computer program to analyze dip levels, meter readings, and deliveries to identify trends which point to problems in inventory management or a leak.
The services provided by SIR vendors vary, but some require thirty days of completed inventory sheets, and others allow you to input all data directly to the computer. Since this method of leak detection must try and account for many variables, including poor stick readings, tilted tanks, wrong dip charts, etc., it is not as reliable as a precision test. However, it does provide a great deal of day-to-day diligence for fuel management problems.
SIR is not carried out by the owner or operator of a tank system. Records are analyzed by a company whose method of analysis has met the leak detection protocols of being able to detect a leak as small as 0.38 litres per hour, 95 times out of 100 with a false positive rate of less than 5%.
For SIR analysis to be meaningful the operator must practice strict discipline in gathering inventory contorl dip and meter readings.