No Interdependence of Barriers
No interdependence between the barriers means that these barriers shall not be impaired or cease to function simultaneously, as a consequence of a single failure or a single incident.
Example of ‘no interdependence’ of barriers
– Two barriers during drilling -well fluid and BOP. In case of failure of first barrier (well fluid) due to increased formation pressure, BOP is not impaired. Hence no interdependence.
– However Upper Pipe ram and Lower Pipe Ram BOPs are dependent barriers because if the BOP control system fails during kick, both BOPs will not function. Hence there is interdependence between the two.
– Two barriers on pressure vessel – pressure switch high (PSH) and pressure safety valve (PSV). In case of failure of PSH due to control logic malfunction, functioning of PSV is not impaired. Hence no interdependence.
Source: Guidance Notes on Petroleum and Natural Gas (Safety in Offshore Operations) Rules, 2008, Oil Industry Safety Directorate (India), 2012. Regulatory Guidance