Risk assessments of harbour operations involving lng carriers

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This presentation describes the historic development of a risk based approach to LNG carrier collisions.

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Risk assessments of harbour operations involving lng carriers

  1. 1. Risk Assessments of Harbour Operationsinvolving LNG CarriersThe historic development towards todays practiceFebruary 2013
  2. 2. Introduction The LNG industry has been spared ship collisions and other tragic safety incidents. This is no a coincidence, rather it is the result of a strict safety regime for LNG shipping. However, the fleet of LNG carriers operating globally is now approaching 400, and it is set to keep increasing even more quickly in the future. Smaller ships dedicated to coastal trades will also become popular. In other words, the probabilities for collisions and navigational events are increasing. The industry has been through several decades of learning about LNG safety characteristics and how to design for it in efficient manners. The approach to safety has also evolved during these years, starting from very prescriptive requirements for how things shall be done, and moving towards today’s situation where a risk based approach is commonly accepted. This presentation describes the historic development of a risk based approach to LNG carrier collisions.Risk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 2
  3. 3. Gathering of collision statistics EU HARDER project Distribution of Striking Ship Speeds The HARDER (Harmonization of Rules and Design Rationale) HARDER Data, 344 Colision Cases project was a research project launched in 2000. Its aim was 120 to make a thorough study of the "probabilistic" approach to assessing a vessel’s damage stability. This was a preparation 100 stage for the introduction of such an approach to almost all types of ships covered by the SOLAS Convention (Safety of No. of Collision Cases 80 Life at Sea). Amongst other things, the project gathered statistical data for 60 ship collisions, for example the number of accidents at different ship speeds as is presented in the graph to the right. 40 20 0 0-4 4-6 6-8 8-10 10-12 12-14 14-16 16-18 Ship Speed Intervals (knots) * DNV was coordinator of the HARDER projectRisk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 3
  4. 4. Development of probabilistic models for hole sizes in LNG tanks Joint Sponsor Project In 2004-2005, another project with several members was undertaken. The aim of this project was to take the results of the HARDER project further, and determine what they mean specifically for LNG carriers. In 2006, it was agreed to adopt a risk based approach to hole sizes in LNG cargo tanks due to collisions. The project developed probabilistic models for determining hole sizes in collision events. This probabilistic approach is described in the next two slides. * DNV was project manager of this JSPRisk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 4
  5. 5. Damage modelling of collision events FEM modelling 90m Vessel / Bulb / 90º A FEM (finite element method) model was built to determine the internal damages caused by collision events. This was done for a selection of different ship sizes, different speeds, different angles of hit, and different bow shapes. By using the FEM model, the energy absorption in the collision events was calculated “backwards” from the actual damage. 130m Vessel / Bulb / 90ºRisk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 5
  6. 6. Determine hull indentation due to collision Statistics Based on results from thousands of crash simulations, a statistical relationship between collision energy and hull indentation is produced. From this data, it can be easily determined if a collision involves enough energy to break through enough hull structure to reach the LNG cargo tanks. HARDER data for probability of collisions at various speeds and angles can then be introduced, and based on this, probabilities for indentation depths can be calculated. Knowing the distance from the LNG carrier’s hull side to the containment barriers of the cargo tanks, indentation depth can be translated directly to potential penetration of the barriers.Risk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 6
  7. 7. Risk reduction through mitigation measures Assess risk level The initial risk assessment indicate certain probabilities for events with hull indentations deeper than the distance to LNG cargo containment barrier. This means that in such events the cargo tanks would be breached, which are unacceptable situations that must be avoided. Mitigate risks The risk level must be reduced so that any indentations deeper than hull to tank distance will not occur. This can be done by introducing mitigation measures. Examples include:  Reduce speed of passing vessels (meaning less chance of high energy collisions with deep indentations  Build break-waters (meaning less chance of high speed impacts from other ships while at jetty)  Introduce escort tugs (meaning less chance of bad manoeuvring)Risk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 7
  8. 8. Conclusion Risk analysis offers flexible solutions By proper application of risk analysis methodologies, cost- efficient solutions can be found without jeopardizing safety.Risk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 8
  9. 9. Safeguarding life, property and the environment www.dnv.comRisk Assessments of Harbour Operations involving LNG CarriersFebruary 2013© Det Norske Veritas AS. All rights reserved. 9

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