A possible universal approach for risk assessments

23 March 2016  •  Author(s): François Bianco, Isabella Mariani and Hanspeter Schlatter from the Swiss Federal Railways (SBB) Signalling Department

For European Railway Review François Bianco, Isabella Mariani and Hanspeter Schlatter from the Swiss Federal Railways (SBB) Signalling Department present their risk assessment method and suggest that a possible universal approach could be used.

A possible universal approach for risk assessments

Common solutions versus different approaches in Europe

In any technical system there is no safety measure that entirely eliminates risk, as the concept of absolute safety is utopian – particularly in railway. As a consequence socially- and economically-acceptable safety values have to be established. In Europe the definition of a common risk assessment method is challenging, especially due to the cultural differences that influence every country’s decisions. An ongoing debate has been conducted for many years that aims to synthesise a harmonious solution. This led in 2009 to the definition of a European Common Safety Method (CSM) which1 states that; in case of significant changes in a railway system, the member countries have to assess the risk by applying codes of practices, given as a set of written rules, or by comparing the new system to an equivalent reference system using the GAMAB (‘globalement au moins aussi bon’) principle2 . In case none of these two methods can be used, the risk acceptability is performed using an explicit risk estimation.

For evaluation of the risk acceptance different approaches can be applied i.e. using quantitative analyses. For example: for hazards that arise from pure technical failures and which can have critical or catastrophic consequences, the so-called ‘harmonised design targets’ are, according to the CSM, defined as upper limits for technical failure rates that must not be exceeded3,4. Another approach represents the risk assessment according to the ALARP method (‘as low as reasonably practicable’), which focuses on a cost-benefit analysis and is socioeconomically oriented2 . Alternatively, the MEM (‘minimum endogenous mortality’) approach considers risk acceptability estimation on risk limits for the individual, i.e. the risk to which an individual using this system is exposed2 . This approach is also applied in the explicit risk analyses methodology recommended by the Swiss Federal Office of Transport (FOT) for railway projects that are not able to comply with all the statutory regulations. The aim is to prove that, despite the lack of compliance with the law, no unacceptable individual risks to passengers and railway employees can arise5 . There are many examples across Europe, beside transport, where the concept of individual risk is applied, for instance in civil engineering, natural hazards, or energy production.

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