4.32. Disposal facilities, in particular disposal facilities for high level and intermediate level waste, are expected to perform over much longer timescales than the periods usually considered in engineering applications. Investigation of the ways in which analogous natural materials have behaved in geological formations in nature, or how ancient artefacts and structures have behaved over time, may contribute to confidence in the assessment of long term performance. Demonstration of the feasibility of fabrication of waste containers and of the construction of engineered barriers with the necessary features, for example, in underground laboratories, is important for the purpose of assessment and for contributing to confidence that an adequate level of performance can be achieved.