Residual risk

The residual risk is the danger of a system despite existing security systems. It consists of an estimable and an unknown proportion.

Ideally, falling mostly redundant safety devices only independently and randomly. The predictable from this portion of the residual risk can be minimized. The co-occurrence of disorders that occurs, for example, due to previously unknown design flaw and is therefore not random, does not allow estimation of the second fraction in general.

A nuclear power plant will not change by an earthquake be residual risk, only the known proportion of this risk is higher after the recalculation. Such a recalculation will take place in Switzerland after each flood; an event that is classified as 100 per year, might as well a 50 - or a 200 - be annual.

As time grows according to the learning curve often the experience with a system. Thus, the division between the known and the unknown proportion of the risk has changed.

For example, four of the German nuclear power plants are built to almost identical construction plans. If defects or problems on one of the four occur, the individual security calculations change for all four power plants, so even if still no problems have occurred on three.

Damage assessment

When creating a risk analysis / probabilistic safety analysis for a process plant is estimated probabilities for events that lists their possible consequences, and provides corrective action represents a very unlikely event, the consequences can be extremely large and the remedies are in principle impossible, for example, is a meltdown of a nuclear reactor with the escape of radioactive substances.

As in many areas of damage severity and probability of loss are very low, a marginal risk for most of the activities, methods, procedures, or (technical) processes set ( commercially reasonable precautions ). Since the state of the science is technically impossible to build ever, used for particularly safety-critical processes, the phrase " state of science and technology" ( technically conceivable precautions ) and less dangerous method the phrase " state of the art " ( technically feasible precautions ). The primary use of the term residual risk in nuclear technology shows that it is a young term for which can not always be made to the statistical relevance required for a determination of probabilities.

Not obvious risks of safe products

Residual risk is a risk which means an inevitable, given by the use of the product, no obvious risk in spite of inherently safer design and technical protection devices. DIN 31000, DIN 820-120, EN ISO 12100-1 and the EC Machinery Directive 2006/42/EC require manufacturers a three-stage safety strategy for the marketing of safe products in exactly the order listed:

A manual may not warn of dangers that can be constructively removed before then. These must also be removed. However, a manual must warn against remaining risks.

Manufacturers must therefore defective products in the instructions not to gloss over, as with the instructions of the manufacturer ends the responsibility and the responsibility of the user begins. These need to protect against residual risks themselves by complying with the warnings in the manual, and for example, provide recommended personal protective equipment or use.

The human factor

In the work safety refers to a hazard that can not be excluded by technical measures, as residual risk. The "human factor" involves a difficult to be calculated risk. In addition to the possible deliberate use of a technical risk by individual perpetrators (for example, in a high-security laboratory, see 2001 anthrax attacks ) and accidental human error can not be excluded. Operator error caused both

• The Chernobyl disaster (1986 ) and
• The partial meltdown at the nuclear power plant at Three Mile Iceland 1979 The meeting of two factors -. faulty connection of a pneumatic control and the "forgetting" of opening of valves after a test - enough to cause this.

Modern safety-related projects such as the European launcher Ariane know the "human factor " as a quantifiable size. One of the fundamental documents is called " Human Error " and is the basis of all risk assessments.

Calcar decision

In his calcar decision of 8 August 1978, the Federal Constitutional Court that such loss events decided that the population had to bear with the use of nuclear energy, a residual risk as " socially adequate load ", " when it practically seems excluded by the state of science and technology, will occur. "

Nuclear disaster after severe earthquake in Japan 2011

During the series of accidents at the nuclear power plant in Fukushima I, due to the Tōhoku earthquake in March 2011, the federal government called the " residual risk " as a justification for a moratorium on the lifetime extension of German nuclear power plants, whereas it is not there, according to the issued by the Nuclear Society International Journal for Nuclear Power acted to a residual risk, but a wrong, inadequate design of the plants against tsunamis.