Absolute Limits versus Ideal Standards

Similarly, absolute limits are popular with lawyers guilt or innocence is (assuming no sampling or analysis issues) more clear-cut and simple to explain. 

However, it is also common to use standards to set up the infrastructure, policies, controls, or rules that mean that incidents and risks occur with acceptably rare probabilities. These standards might be described as strategic standards. For example, controls on ammonia in sewage treatment works (which are back-calculated from environmental standards) are designed to promote good fisheries in the receiving river. The intention is to reduce serious incidents to an acceptable frequency in each river because the infrastructure of sewage treatment appears to function at this level of acceptable risk. This may result in a compromise, which is essentially that standards are set up as particular types of summary statistics and not as absolute limits. 

Those recommending standards should also state whether their number is self-contained. Is failure of their standard all that is needed to justify decisions Otherwise, they should describe how the number is to be used with other information 

The difference between decision making on the basis of a standard alone and on the basis of a standard plus other information can be described as one aspect of the direct versus the indirect model. In the direct model, action is defined exactly as that needed to secure compliance with the standard, for example, as permit conditions for discharges to water that are calculated to meet an environmental standard in a river. The classic cases here are substances like ammonia or cadmium in rivers and other mandatory standards in various European directives. 

those recommending standards need to explain how failure should be defined and determined and so help estimate the potential extent of failure in the environment That is, what percentage of water bodies fail a particular standard This is required, in principle, even if there is little hope that money will be found to make estimates of actual compliance. It is a first step toward knowing who is causing failure and so to an estimate of the costs and benefits to society of using the standard. 

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