Decisions based on a single ISM

This limitation applies specifically to an approach where only one ISM sample is taken per DU. Because a 95% UCL cannot be calculated from a single ISM result, this approach is precluded when a 95% UCL is required by regulation. It may also not be accepted because of the inherent uncertainty associated with using a single, unreplicated estimate of the mean and the potential to underestimate the actual mean.