Learning Lab Denmark - INCUBEus

Quantitative Risk Assessment

The most simple approach to practical risk assessment is to identify and quantify relationships between potential risks from using a specific technology (such as dioxin or radiation leaks) and physical harm observed in humans or other living organisms. In this way one can estimate how harmful a failure of a given technology might be.

The problem with this approach is that it is very difficult to obtain statistical data on the frequency of failures or of human errors. In these cases 'event tree methods' or 'probabilistic risk assessment methods' (PRA) are used. Probabilistic Risk Assessment assigns probabilities to each of the systems' constituent components, and then the overall reliability of the system is determined by aggregating the separate failure probabilities of each of the components possible errors.

This simple approach to risk assessment has drawn much criticism. Ironically, it has mainly been used in assessing risks of some of the most dangerous human endeavours: nuclear power plants and aerospace technology.

The main arguments against this method are as follows: Firstly, what people perceive as an undesirable effect depends on their values and preferences. Secondly, the interactions of humans and/or technological subsystems are much more complex than an a priori risk assignment can capture. Thirdly, organisational failures are not taken into account. Fourthly, having a low probability of a major disaster is not considered equal to having a high probability of a small accident (which quantitative risk assessment presumes by attributing equal weight for magnitude and probabilities). Fifth, quantitative risk assessment does not accept participation by interest groups, the public, or laypersons, which is not in tune with modern democratic principles.

Further reading
Event tree methods, see IAEA (1995). Guidelines of Integrated Risk Assessment and Management in Large Industrial Areas, International Atomic Energy Agency, Vienna.

PRA methods, see U.S. Atomic Energy Commission. 1975 "Reactor Safety Study - An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants.", Washington DC, U.S. Nuclear Regulatory Commission (WASH-1400).

Margolis, H. (1996). Dealing with Risk. Why the Public and the Experts Disagree on Environmental Issues. University of Chicago Press, Chicago.

Beck, U. (1986). Risk Society: Towards a New Modernity, Sage Publications, London and Newbury Park, CA.

Comment this page

Nine Technologies

A. Air Transport
B. Buildings
C. Land Transport
D. Marine Transport
E. Bridges and Dams
F. Oil Tankers
G. Chemical Industry
H. Medical Industry
I. Nuclear Industry

Nine Theories

Quantitative Risk Assessment
Decision Analysis
Cost-benefit Analysis
Normal Accident Theory
High Reliability Organisations
Risk communication
Arena Theory
Cultural Theory

Five Categories

Hazard (0-1000)
Range (km2)
Fear Factor (0-10)
Media Effect (0-100)