7.4.5 Quantitative Risk Assessment For the Design Safety Case, the broad approach to QRA is as for the guidance for the Production Safety Case, except that the level of detail maybe less. Design philosophies may also specify return frequencies to be used for accidental loads, such that, although the accident loads are not defined, the frequency of them being exceeded is known. Combined with basic facts about location, ventilation and the expected process details, the risk maybe estimated to a degree that is sufficient to show that risks are not intolerable. Example In a Design Safety Case, the quantitative risk assessment for an offshore process area might use leak frequencies for process units based on comparison with similar existing designs. Consequence assessment using exact process parameters may only be needed in certain circumstances. For example, setting the distance between an onshore boundary fence and the process equipment, or determining the length of abridge between two offshore platforms.
