Risk Assessment. Marvin Rausand
In 2012, the directive was updated once more and is now called the Seveso III Directive (2012/18/EU of the European Parliament and of the Council of 4 July 2012 on the control of major‐accident hazards involving dangerous substances).The application of the Seveso III directive depends on the quantities of dangerous substances present (or likely to be present) at an establishment. Two levels (“tiers”) of duty are specified in the directive, corresponding to two different quantities (or thresholds) of dangerous substances. Sites exceeding the higher, “upper tier” threshold are subject to more onerous requirements than those that qualify as “lower tier.”Similar legislation is implemented in several other countries, such as 29 CFR 1910.119, “Process safety management of highly hazardous chemicals,” in the United States. This law requires that process hazard analyses be carried out.
The EU machinery directive. This directive (89/392/EEC) covers safety aspects of a wide range of machines that was introduced in 1989 and revised in 2006 (2006/42/EC). This directive requires that risk analyses are carried out for some dangerous machines, and a specific risk analysis standard, ISO 12100 (2010), has been developed for this purpose. Similar legislation has been implemented in several countries.
The Health and Safety at Work, etc., Act of 1974. HSWA is the principal health and safety law in the UK. It places general duties on employers to ensure the health, safety, and welfare of their employees at work, and also to conduct their undertaking in such a manner that persons outside their employment are not exposed to risk. Employers must carry out various risk assessments to ensure that these duties are met “so far as is reasonably practicable” (SFAIRP).
The Offshore Installations (Safety Case) Regulations 1992. These regulations were issued by the UK Health and Safety Executive (HSE) and require that specific risk assessments be carried out and that a safety case be developed and kept “alive” (i.e. updated). The regulations were revised in 2005 and later again in 2015.
The US Maritime Transportation Security Act 2002. This act is designed to protect US ports and waterways from a terrorist attack. It requires vessels and port facilities to conduct risk and vulnerability assessments.
Norwegian offshore safety regulations. In Norway, regulations concerning the implementation and use of risk analyses in petroleum activities have been issued by the Petroleum Safety Authority Norway and the Norwegian Ministry of the Environment. A special standard, NORSOK Z‐013 (2010), has been developed to support the required risk assessments.
More on safety legislation within different applications can be found in Chapter 20.
3.5 Validity and Quality Aspects of a Risk Assessment
All risk analyses require a wide range of data and assumptions that may be more or less uncertain. Whenever possible, the data and the assumptions should reflect reality as closely as possible. This is not always feasible, and some decision‐makers question the validity of the results from risk analysis. A pertinent answer to this type of question is given by Garrick (2008):
[…] there is seldom enough data about future events to be absolutely certain about when and where they will occur and what the consequences might be. But “certainty” is seldom necessary to greatly improve the chances of making good decisions.
Whenever possible, assumptions should be made to err on the side of conservatism. Such assumptions, known as “conservative best estimates,” are to ensure that the assumptions do not result in underestimation of risk and, ultimately, unsafe decisions (NSW 2003). Uncertainty in risk assessment is discussed in Chapter 18.
The quality of the risk analysis should rather be measured in terms of how well it supports the decisions that we want to make based on the analysis. Some general criteria could then be that
The risk assessment provides support to the decision problem.
The documentation is such that decision‐makers can understand and use the results in their decision‐making.
The risk assessment should provide a sound basis for risk management.
Every reasonable effort has been made to secure the completeness, consistency, and correctness of the analysis.
The best available and relevant information has been used.
A risk analysis represents a model of a certain phenomenon that we are interested in, namely risk. The objective is to give a description and/or a quantification of what the risk is. Similarly to all models, a risk analysis is based on numerous simplifications. Modeling is always a balance between representing the phenomenon that we are concerned with and the efforts required to develop the model. For that reason, we try to leave out aspects that have limited influence on the results the model produce.
The effect of this simplification is that we always need to be careful if we attempt to apply an existing risk analysis to provide decision support for other decisions than the ones that the analysis originally was developed for. Even if it is the same phenomenon that we describe, there may be other aspects that are relevant to include in the model when the decision is changed. This has among others been observed when risk analyses that originally were developed to support design development of a system later has been used to support operations of the same system. This issue is discussed further in Chapter 16.
3.6 Problems
1 3.1 What is the difference between risk analysis and risk assessment?
2 3.2 What are the main steps in the risk assessment process and what are the main objectives/activities in each step?
3 3.3 Consider a railway line running between two cities, with crossings, stations, signals, and so on. Assume that you are going to do a risk assessment with the objective to determine the risk to people. How would you define and delimit the study object?
4 3.4 For the railway line in the previous problem, give some examples of generic events, specific events, and representative events.
5 3.5 For the same railway line, identify possible causes of the generic event “derailing” and see if these causes are applicable to all events if you define a set of representative events for “derailing.”
6 3.6 Assume that you have performed a risk assessment for a shipping company operating several large passenger ferries. You are going to present the results to three groups: The shipping company management, the safety department of the shipping company and to passengers. What would be different in the way that you present the results for the three groups?
7 3.7 A requirement for scientific work is that what we have done can be reproducible, which means that when using the same input and the same models, we should arrive at the same results. Will a risk assessment meet this requirement?
References
1 EU (1996). Council Directive 96/82/EC of 4 July 2012 on the control of major‐accident hazards involving dangerous substances. Official Journal of the European Union L 10/14.1‐1997.
2 EU (2012). Directive 2012/18/EU of the European Parliament and the Council of 4 July 2012 on the Control of Major‐Accident Hazards Involving Dangerous substances (Seveso III Directive). Official Journal of the European Union, L 197/1 24.7.2012.
3 Garrick, B.J. (2008). Quantifying and Controlling Catastrophic Risks. San Diego, CA: Academic Press.
4 IAEA (1994). Safety Assessment of Research Reactors and Preparation of the Safety Analysis Report. Safety Series 35‐G1. Vienna, Austria: International Atomic Energy Agency.
5 IAEA (2002). Procedures for Conducting Probabilistic Safety Assessment for Non‐Reactor Nuclear Facilities. Technical report IAEA‐TECDOC‐1267. Vienna, Austria: International Atomic Energy Agency.
6 ISO