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POllution Prevention and Control - Safe Transportation of Hazardous Goods by Tankers (POP&C)

Final Report Summary - POP&C (Pollution Prevention and Control - Safe Transportation of Hazardous Goods by Tankers)

The POP&C project proposed to deliver a framework and suitable tools for a methodological assessment of risk to be undertaken to provide a rational basis for making decisions pertaining to the design, operation and regulation of oil tankers. Such support can be used to make more informed decisions, which in turn will contribute to reducing the likelihood and severity of future oil spills. The POP&C project aimed to focus on prevention and mitigation in ship design and operation for both existing and new vessels. Specific objectives have been:
- to develop a risk-based methodology to measure the oil spill potential of tankers;
- to develop a risk-based methodology for passive pollution prevention (design and operational lines of defence);
- to develop a risk-based methodology for active post-accident pollution mitigation and control.

The research work was divided into seven technical work packages (WPs). These were:
- Identifying and ranking critical hazards such as collision, contact, grounding, fire, explosion and structural failure (WP2)
- Estimates of probability of capsizing / sinking from loss of stability (WP3)
- Estimates of probability of structural failure (WP4)
- Estimates of consequences within a risk-based framework, will provide pollution risk (WP5)
- Risk reduction through preventative measures (WP6)
- Risk reduction through post-accident mitigation and control measures such as decision support tools, human-machine interface, and safe refuge (WP7).

Hazard identification and raking (HAZID)
The first step of a risk assessment methodology is to carry out a HAZID study. In order to perform the HAZID study efficiently, the safety matter under consideration and scope of the study needed to be clearly defined. The scope was limited to a certain ship type, or size, specific accident scenarios, specific operational conditions, typical design and operation concepts, etc. In the context of the POP&C project, the main purpose was the identification of main hazards that lead to a vessel's loss of watertight integrity and consequently cause pollution and environmental damage. Such a hazard identification and ranking study can conveniently be carried out by analysing the incident / accident performance of a representative sector of the industry. Therefore, in order to demonstrate the methodology which is being developed, the POP&C project selected to analyse the AFRAMAX class of tankers. Reasons for this selection were the relatively large market segment of the AFRAMAX tankers, past spectacular catastrophic tanker accidents involving AFRAMAX tankers and relatively high number of single hull AFRAMAX tankers which are currently operational and expected to continue operating until they reach the recently amended (accelerated) phase-out date.

The outcomes of the risk analysis have been very positive. The most critical accident scenarios were identified and these have been later used as inputs for the other relevant work in the project. Consequent to the development of a detailed and refined historic analysis, a number of publications were produced that were co-authored by a number of partners involved in the work package, for instance the influence of regulations on the safety record of the Aframax Tankers was analysed.

Loss of damage stability
The survivability of a ship needs to be investigated probabilistically considering all possible damage sizes. This requires the probability of the damage extent for all pertinent incident categories (grounding, collision, contact, structural failure, fire and explosions) to be determined. In order to determine survivability performance of a vessel, survivability factors that are suitable to be employed for assessing tanker ships after damage were investigated. The comparison showed it clearly that MARPOL damage survival criteria set the lowest acceptable level of risk. Since the overall index-A values shows no significantly large difference, although modified factors according to MARPOL over estimated survival probability by far, it is desirable to use the framework set by the harmonised regulations so that any calibration and work can assist future harmonisation of all damage stability instruments under IMO regulations.
A probabilistic survivability / oil outflow tool to develop damage cases from collision and grounding statistics has been developed. This tool also develops the oil outflow amounts for each damage case, and statistics for all damage cases such as mean outflow, probability of zero outflow, and cumulative distributions functions for oil outflow. This tool was made available to POP&C project partners for use in this project. The development of the tool currently continues with a view that it will be available commercially after the completion of the project.

Loss of structural strength
For Aframax tanker accidents, the probability of losing the hull structural integrity in the event of losing the watertight integrity of the hull was investigated next. The structural reliability of a damaged tanker was assessed considering global and local loads acting on the hull structure considering all relevant limit states. To achieve this, the following steps were considered:
- identification of the damage scenarios for the detailed structural analysis
- non-linear dynamic collision analysis for both single and double hull tanker
- non-linear residual strength analysis on both single hull and double hull tanker for the selected limited number of scenarios
- development, validation / calibration of a simplified residual strength assessment numerical method to be able to handle large number of damage scenarios.

Overall risk assessment framework
An environmental consequence analysis model, referred as 'the United States (US) Marine Board study' where a non-linear consequence function was generated for varying amounts of oil spills based on a reference oil spill by considering only physical parameters of the oil spill, was utilised to assess the environmental pollution risk. The use of this consequence model was decided based on a POP&C study where the validity of consequence function introduced by US Marine Board for EU waters was confirmed. The nonlinear consequence function used in the methodology is based upon four metrics:
- area of slick;
- length of oiled shoreline;
- area of oiled shoreline;
- toxicity in the water column.

A series of case studies evaluating the application of risk control options (RCOs) and pollution control options (PCOs) utilising information from other work packages were conducted. These include alternative tank arrangements, alternative partial loading approaches, increased scantlings and the effects of updated damage extents based upon analytical work. In addition, case studies such as inserting ballast tanks and application of dynamic under-pressure to cargo tanks have been investigated where both qualitative and quantitative assessment were made. The use of the quantitative environmental risk assessment methodology in risk based design and optimisation process was also demonstrated with examples.

A final case study evaluated a conceptual Aframax tanker that applies some of the lessons learned in the course of the POP&C project. Whereas this design is at an early concept level all arrangements and systems have already been applied in the industry. Risk reductions on the order of 35 % are achievable. Optimisation of this design is certainly possible. Assessment of the cost effectiveness of the design requires evaluation of the impact on construction, operational and fuel costs however there is a clear indication that significantly more environmentally friendly tankers are feasible.

Risk reduction through prevention
The objective of this study within POP&C project was to determine a risk reduction index representing the effects of application of operational measures on the risk of oil spills from tanker vessels. Thus, the first step of the study was to identify and assess risk control options that could be chosen in order to avoid accidents leading to oil spills. Numerous methodologies have been envisaged in order to determine the critical basic events where could be applied risk control options. Finally, a methodology based on the use of Monte Carlo simulations has been undertaken in order to select the most influential basic events.

Alongside to bridge simulations where a limited number of simulations can be made, fast tract simulations were carried out running the same DST tool on a personal computer. The effectiveness of a number of simulation-based risk control options in terms of reduction in frequency of occurrences was determined.

Risk reduction through mitigation and control
The pollution mitigation and control objective was to formulate a pollution mitigating and control framework capable to cover adequately oil spill incidents / accidents generated from vessels (tankers). This work started with the formulation of a list of pollution control options focused on onboard procedures and activities (operational issues and salvage activities along with close proximity to the ship actions). Oil confronting operations (recovery, skimmer effectiveness, etc.) was left outside the scope of the study. Therefore, a detailed and complete analysis of the ETs (Event trees) created previously within the project and the corresponding scoring procedure held in the brainstorming session.

The identified generic decision support tools, employed either independently or in tandem with several others were assessed to be useful in reducing the consequences of major accidents, thus reducing the environmental risk associated with Aframax tankers.

One basic conclusion is that nearly all PCO's may succeed in reducing the severity of the initial incident when used by one scale (from a catastrophic accident to a severe one). It is noted that this reduction is of great importance since in a catastrophic scenario the ship does not survive and the situation is described as unmanageable whereas in a severity 3 scenario the pollution is significant and urgent action should be taken however the ship survives and the situation could be controlled, if the appropriate external aid is available. It is noted that PCO's were found to be more effective in SH scenarios than in DH regarding the specific reduction (from severity 4 to severity 3). The upper bound of effectiveness of some of the PCO's used in SH scenarios was closed to 90 %. That means that they have succeeded 9 times out of 10 in avoiding a total loss and occurrence of big unmanageable sea pollution.

For the DH scenarios the most effective PCO's have an upper bound of effectiveness that does not exceed the 60 %. The methodology has examined 19 out of 21 PCOs in all 215 scenarios.

Impact of the project on its industry and research sector

The POP&C project contributed to the European Union's scientific and technological objective of 'Increasing road, rail and waterborne safety and avoiding traffic congestion' through the risk-based pollution prevention and control options that:
- provided a framework to assess the oil spill potential of both existing tankers and new designs in a rational way;
- integrated existing and developing technologies to provide operational assistance so as to improve the safety of tankers;
- assessed the effectiveness of computer-based decision support tools and information services on the condition of vessel operational responsiveness, to yield risk reduction through prevention and mitigation;
- encouraged best practice in the tanker shipping community.

Foremost among these contributions, POP&C could assist in reducing the number and severity of oil pollution incidents by providing a more rational basis for designing, operating, and regulating oil tankers. Reducing oil pollution at sea is an important step towards achieving environmental and economic sustainability for the future transportation systems.

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