6.15. Waste disposal facilities are required to be designed, constructed and operated in such a way that safety is ensured by passive means [2] and, as a general rule, sudden failures are unlikely to occur; conditions that would necessitate immediate or prompt action are unlikely. However, for some types of existing disposal facility (e.g. past practices at some tailings dams), emergencies can arise rapidly. For instance, extreme weather conditions or seismic events can result in failure of a tailings dam, leading to the rapid release of large amounts of contaminants to the environment. Therefore, emergency arrangements should be established for the full range of postulated events, including events with a very low estimated probability of occurrence. Such arrangements should include arrangements for monitoring, deployment of personnel, establishment of procedures, provision of equipment and other arrangements that would allow rapid declaration of the emergency and imminent threats to human health and the environment as described in Ref. [7] and as required in Ref. [19]. The monitoring arrangements should be able to provide data in a timely way, so that appropriate responses can be undertaken in the event that default operational intervention levels2, which have been coordinated with local officials, are exceeded [7, 19]. Operational intervention levels should be such that they can be used immediately and directly (without further assessment) to determine appropriate protective actions on the basis of measurements of environmental parameters.
2) An operational intervention level is a calculated level, measured by instruments or determined by laboratory analysis, which corresponds to an interventional level or action level. It is typically expressed in terms of dose rates or activity of radioactive material released, time integrated air concentrations, ground or surface concentrations, or activity concentrations of radionuclides in environmental, food or water samples [20].