IPL Independence

A protection layer is considered an independent protection layer (IPL) if it is effective independent of the occurrence or consequences of the initiating event, another IPL that is part of the scenario, and is unaffected by conditions that cause another IPL to fail. During hazard reviews protection layers implemented in both the BPCS (e.g., the DCS) and SIS are identified. Determining if different protection layers are truly independent so that they are credited properly in the risk analysis can be complex.