Risk Assessment and Risk Communication in Civil Engineering

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SAFETY, RISK, RELIABILITY - TRENDS IN ENGINEERING

MALTA 2001

Risk Assessment and Risk Communication in Civil Engineering
Ton VROUWENVELDER Professor TNO/TU Delft Delft, The Netherlands Roger LOVEGROVE Mathematician BRE Watford, UK Gerard CANISIUS Civl Engineer BRE Watford, UK Milan HOLICKY Civil Engineer Klockner Institute Prague, Czech Rep.

Peter TANNER Civil Engineer CSIC Madrid, Spain

Summary
This paper summarises parts of a study carried out by Working Group WG32 of CIB into presently applied methods of risk management related to civil engineering and building structures. The complete study is reported in CIB Publication 259. The report gives an overview of advanced and simplified risk analysis techniques and criteria for risk acceptance. Then attention is given to the aspects of communication with the public and the authorities. Finally a number of practical cases are discussed. The cases are used to evaluate the theoretical issues of the first chapters. This conference paper concentrates primarily on the acceptance and communication aspects. Keywords: Risk management, risk analysis, risk acceptance, risk communication

1.

Introduction

To an engineer, the “risk” associated with a hazard is a combination of the probability that that hazard will occur and the consequences of that hazard. Consequences to be considered include injury or loss of life, reconstruction costs, loss of economic activity, environmental losses, etc. In all cases, the safety issue has to be addressed either explicitly or implicitly. When explicitly addressed, safety targets are set in terms of the maximum acceptable risks. However, it is not the engineer who makes the decision about acceptance of riskful civil engineering activities. Decisions are being made by politicians who on their turn are influenced by the press, the public opinion, pressure groups and so on. As a consequence there is a need for communication about risks between the various parties involved. The Working Group WG 32 has prepared a discussion note on this theme [1] and this paper presents a summary. 2. Risk Analysis

In risk analysis, the following steps two major can be distinguished: (1) Hazard identification and definition of relevant hazard scenarios In this step all hazards and corresponding hazard scenarios have to be identified. A hazard is defined as a set of conditions that may lead to undesirable or adverse events. Identification of hazards and hazard scenarios is a crucial task to a risk analysis. It requires a detailed examination and understanding of the system. For this reason a variety of techniques have been developed to assist the engineer in performing this part of the job (e.g. PHA, HAZOP, fault tree, event tree, decision tree, causal networks, etc) [2,3].

SAFETY, RISK, RELIABILITY - TRENDS IN ENGINEERING

MALTA 2001

(2) Estimation of probabilities and consequences Risk is commonly expressed in terms of probability and consequences of the undesired events. In a quantitative risk analysis, for every possible hazard scenario Eij following hazard H i, the possible consequences Dij and corresponding yearly probabilities P(Eij ) are estimated. The damages D ij may be: casualties, injuries, psychological damage, monetary Probability of exceedence per year 1 values or environmental values. In most large cases a selection has to be made. The probability estimations P(Eij ) are usually 0.1 at least partly based on judgement and frequent may for that reason differ quite substantially from the actual failure 0.01 frequencies. The result of the quantitative estimates of consequences and forseeable probabilities is often presented in the 0.001 form of a frequency-consequencediagram, character-ised by classes of small frequency and classes of consequences 0.00001 (Fig. 1). For communication purposes the very small classes are often described in words. In such a diagram one may also indicate the regions that are acceptable and which are not....
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