Quantitative Methods

The ALARP (As Low as Reasonably Practicable) principle is based on the fundamental thinking of ‘acceptable’ or ‘tolerable’ risks. It allows analysts and decision makers to define boundaries to combine probability-consequence scales. These boundaries can be used to delineate acceptable and intolerable risks. This allows decision makers to evaluate whether a system or process poses certain risks which need to be treated using risk-control options. The ALARP principle can easily be combined with tools such as Risk Matrices to graphically represent the boundaries of risk tolerability.

The Bow-Tie method can be considered to be a combination of earlier developed fault tree analysis (FTA) and event tree analysis (ETA) methods. A significant milestone in the history of Bow-Tie was the catastrophic incident on the Piper Alpha platform in 1988, which shook the oil and gas industry. In the early 1990s, the Royal Dutch Shell adopted the BowTie method as part of its methodological toolbox for managing risks. Nowadays, the Bow-Tie method is also used for risk management related to different transport modes such as maritime and aviation.

The Cause-Consequence Diagram is developed from a certain initiating top event, i.e. an event that initiates a specific operational sequence or an event which activates certain safety systems. The Cause-Consequence Diagram consists of two reliability analysis methods previously elaborated, the FTA and ETA methods.

The cost-benefit analysis is about comparing the costs and benefits of a project or a major activity and using this comparison as a basis for decision-making for the implementation of the project/activity. The costs and benefits are in most cases described in monetary terms to allow comparison. However, it is sometimes difficult to express welfare gains, for example, as a monetary unit. If at the end of the analysis the benefit is higher than the total cost, a project/activity should be implemented. Experience and expected values are used to determine costs and benefits in advance.

The Delphi method was developed in order to identify possible targets in the USA during the Cold War. The Delphi method was gradually applied in civilian areas and is now frequently used for political and social questions and issues, for the development of science and technology and in the business environment (e.g. marketing, R&D). The Delphi method is a structured group communication process with the aim of answering questions or finding a consensus on facts about which uncertain and incomplete knowledge naturally exists.