5.14. The regulatory body should stipulate or provide guidance concerning timescales for safety assessments. Comparison of calculated doses or risks to dose limits or risk limits specified in regulatory requirements may be required for at least several thousand years and may be extended to timescales beyond this, for example, to estimate peak dose. However, it is recognized that for timescales beyond several thousand years, uncertainty concerning future conditions of the geosphere and biosphere is such that reference calculations based on appropriate simplifying assumptions may be sufficient, with account taken of scenarios for evolution of the natural characteristics of the disposal system and ‘'stylized’' approaches (i.e. under certain prescribed conditions) to human behaviour and characteristics, for example, using reference biospheres [15].