6.51. The considerations in paras 6.43-6.50 show that the establishment of appropriate time frames and time windows for safety assessment necessitates judgement and the balancing of competing factors. The rationale for the time frame and time windows adopted for safety assessment should be described clearly. In particular, if one of the factors set out in para.6.44 limits the assessment to a period shorter than the period over which the disposal facility could, in principle, give rise to non-negligible hazards, a clear justification should be provided for not extending the assessment time frame. For example, an assessment of radiation exposures from waste from uranium mill tailings disposed of at the surface would not be meaningful if it were to be extended beyond time periods over which glaciation is to be expected (see para. 6.46), although the hazard potential of the waste extends substantially beyond this timescale.