Difficulties in formulating risk criteria.

Any framework of risk criteria must use measures of risk which provide sufficient information to ensure that consistent decisions can be taken. Where multiple fatality accidents are possible the risk cannot be adequately described by a single parameter let alone a single number. There are advantages end difficulties associated with the various approaches that are advocated for interpreting risk estimates. Although it is useful for criteria to be developed they can only be indicative and so major decisions must be made and defended on a case-by-case basis.