The main purpose of this thesis has been to identify the general usage of the applications textit{inhibit} and textit{override} for a collection of installations operated by Statoil ASA. The applications are provided by a Safety and Automation System (SAS) that performs monitoring, control and safeguarding of the plant and its process. Logs that keep track of the SAS operator's actions and other facility-related events have been received from each installation, and regarded with respect to:* the general evolvement and trend of the application usage* instances of inhibits/overrides of long-term character* redundant signals that are inhibited/overridden simultaneously* critical time periods that exhibit high activity* tags that are frequently involved in the application usageThe results that were obtained for each above-mentioned point made it possible to give a stetement of how the installations are controlled through utilization of the safety-impairing, but useful applications.