Method Development for Environmental Risk Assessment of Shipwrecks

Licentiate thesis, 2013

Potentially polluting shipwrecks containing oil or other hazardous substances may pose a threat to the marine environment. This is a global problem and many shipwrecks stem from the Second World War and have been deteriorating on the sea floor since then. Only in Swedish waters there are more than 2,700 wrecks that warrant further investigation and 31 of these are given a very high priority due to the environmental threat they pose. These wrecks are together estimated to contain between 1,000 and 15,000 tonnes of bunker oil. Every shipwreck poses a unique threat depending on, for example, the type of vessel, cause of sinking and environmental preconditions. Currently, there is no comprehensive method for assessing the environmental risk posed by shipwrecks and providing necessary support to decision-makers. It is not feasible to remediate all shipwrecks due to costs but a proactive approach would make it possible to avoid the need and high cost of reactive response in case of an oil leakage. In order to effectively use resources, proper decision support is needed. Risk assessments and the overall process of risk management are important means to provide such decision support. The purpose of this thesis has therefore been to develop a framework for risk management of potentially polluting shipwrecks and a tool for quantification of the probability of release of hazardous substances from such shipwrecks. This was achieved through a comparison of current methods for risk assessment of shipwrecks in order to identify development needs. Based on the comparison, a generic framework for risk management of shipwrecks was suggested. Furthermore, the tool for estimating release probabilities was developed based on a probabilistic fault tree approach with the aim to support the risk assessment part of risk management. The tool makes it possible to consider possible events that may damage the wreck as well as physical and environmental conditions affecting the wreck. The results from the comparison of current methods for risk assessment of shipwrecks showed that none presented a holistic risk assessment guide and that there is a lack of quantitative risk assessment tools for shipwrecks. Few methods considered uncertainties and the need of sensitivity analysis. The generic framework for risk management of shipwrecks clearly shows the important steps that need to be performed and how they are linked. It also emphasizes the need of proper assessments to facilitate an efficient resource allocation for these types of environmental threats. The tool for probabilistic risk assessment of shipwrecks enables uncertainty analysis and is a first step towards a holistic risk assessment