6.87. As a decisive part of establishing the context for the assessment consists of defining the assessment philosophy, assessments performed with the intention of comparing doses to regulatory limits, constraints and other criteria should be performed with a sufficient level of conservatism. Assessments performed with the intention of comparing options for the purposes of optimization, however, should be based on more realistic assumptions. Owing to the importance of applying the principle of optimization in existing situations, the distinction between these two types of assessment is particularly relevant for existing facilities.