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In-depth | Safety regulationS

A s the hunger for remote offshore exploration has intensified, administrations at IMO have

recognized that Search and Rescue alone will be unlikely to meet all possible accident scenarios.

For this reason, 1 July 2010 saw entry into force of new regulations, amending Safety of Life at Sea (SOLAS) and demanding more emphasis on casualty prevention. They also demand that future ships should be designed for improved survivability so that, in the event of a casualty, persons can stay safely onboard for ultimate rescue.

The rules incorporate criteria for a casualty threshold, defined as the amount of damage a ship can sustain according to its design and still be safe for those on board. Catching the eye are new overall assessments for essential systems’ availability.

Alternative design and arrangement have long been incorporated in SOLAS, but the latest developments augment

this thinking to include the provision of safe areas onboard and operability standards for the essential systems to be maintained, so that a ship can sustain essential functions and support people until assistance is available, or until the damage can be recovered after a casualty. This will require redundancy of propulsion and other essential systems; on-board safety centres, from where safety systems can be controlled, operated and monitored; and the new requirements offering a means of verification. The ship’s crew may not be able to move a ship to a port or place of refuge for reasons of stability, for example, and so the new requirements define systems operability to maintain the safety of people or systems onboard.

Initially driving the IMO’s Maritime Safety Committee was concern over larger passenger ships, working on the principle that ‘a ship is its own best lifeboat’. This approach envisages that

passengers and crew should normally be able to evacuate to a safe area onboard and stay there. In addition, essential systems such as propulsion and steering must be sustainable.

offshore equivalenceHowever, as the number of large accommodation vessels set to work in increasingly remote locations for offshore construction has increased, so too has impetus grown for the rule changes to be transposed for use within the IMO’s guideline Code of Safety for Special Purpose Ships. The Code, which was revised in 2008 and entered force in May 2010, applies to vessels of more than 500gt and carrying more than 12 special personnel. Under SOLAS provisions, any vessel carrying more than 12 personnel (not crew or special personnel) automatically becomes a passenger ship.

The general aspirations of IMO were translated into specific ship

New software, developed by Safety at Sea to address the International Maritime Organization’s (IMO) regulations on a ship’s safe return to port (SRTP), offers potential for aspects of offshore vessel design.

Safety at Sea takes systematic approach

Offshore Marine Technology 1st Quarter 2011

Casualty scenarios handled by i-SyS include flooding to single WT compartments, fire casualty threshold and the loss of single main vertical fire zones due to fire.

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17Offshore Marine Technology 1st Quarter 2011

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design guidelines as part of detailed contributory work undertaken in the EU-funded SAFEDOR project, which included a new methodology that is leading on to the development of sof tware codes to provide the engineering verification results. Par t ic ipants included sof tware developer Safety at Sea (SaS) and the University of Strathclyde’s Ship Stability Research Centre. Subsequently, SaS has continued the development of the codes, with the new software being marketed as I-SYS.

Systems assessmentThe I-SYS software, in line with the overall assessment framework, allows the designer to assess if a given essential system is critical or not and, if so, that it is operable when the ship is subject to number of damage scenarios. Critical systems are identified in the overall assessment of essential systems to have a possibility to fail to operate adequately as a consequence of one or more fire casualty case, each not exceeding the fire casualty threshold, or as a consequence of one or more flooding case, each not exceeding a single watertight (WT) compartment.

The resulting package has already been used in a number of projects in the passenger ship sector, forming the basis for systems capabilities post damages on behalf of Daewoo Shipbuilding and Marine Engineering (April – July 2009) and Samsung Heavy Industries (two projects, one running January – May 2010, and the other from June – August 2010).

Also proceeding has been initial work in the offshore sector. SaS has used a comparable methodology to work on requirements as they relate to fire protection, vessel subdivisions and systems redundancy.

Luis Guarin, director, safety engineering, SaS, said that the new software codes offered key opportunities in relation to offshore construction, field development support vessels and other offshore craft, if they have large accommodation blocks. A further potential application includes I-SYS being used as a support tool for the assessment

of dynamic positioning systems.“We have carried out two initial

jobs for Samsung Heavy Industries,” Guarin said. “One of these focused on risk assessment of fire protection arrangements in some areas below the main deck for a field development support vessel under construction for Saipem. This included advanced fire engineering calculations and escape route analysis, by simulations. Alternative design evaluations were also made of fire protection arrangements in machinery spaces, as per the stipulations of IMO MSC/Circ.1002.

“In the second project, which focused on an offshore construction vessel, we carried out evacuation and escape route analyses on behalf of ULSTEIN Sea of Solutions, as part of analyses required by Norwegian Maritime Directorate [NMD] regulations.”

Edwin van Leuwen, ULSTEIN Sea of Solutions project manager, said: “Due to the type of operations performed by these types of heavy-lift / pipelaying ships they always have a large number of people on board and are therefore classed special purpose ships and follow cruise ship rules for SOLAS to a large extent.

“On previous projects we did escape analyses ourselves, based on rule calculation methods. The potential of the SaS escape route analysis program looked far more efficient than our own calculation method. We challenged SaS with a very tight schedule as it was, yet they delivered on time while providing us with some suggestions to improve the arrangements, in order to avoid congestion of people. After the first draft report based on SOLAS requirements, additional requirements from NMD were analysed. The analysis showed compliance of the arrangement with both SOLAS and NMD requirements.”

SaS’s Guerin added: “Results of the overall assessment are given in a form of listings of systems affected by analysed damage scenarios. Additionally, for each damage scenario, or set of scenarios, a list of unique ‘restoring solutions’ can be generated. These solutions provide guidance for eliminating

system vulnerabilities.”In detail, I-SYS uses a set of Boolean

logical expressions to define physical systems’ dependencies, including equipment, piping, pumps, switchboards, cabling and tanks, and a set of binary decision diagrams to solve input equations. A fire or flooding casualty occurring within a space or group of spaces affects directly or indirectly the systems and functions embedded within the ship environment.

Casualty scenarios include flooding to single WT compartments, fire casualty threshold and the loss of single main vertical fire zones due to fire.

future capabilityGuarin said that work was rapidly developing to extend the use of the I-SYS package. “So far, in general, the assessment has been focused on evaluating systems’ design. WT subdivision is optimised separately. It is our intention in the short term future to modify and use the software to evaluate the impact of subdivision on the SRTP capabilities. This requires an interface linking automatically the systems’ components and the watertight subdivision.”

Already, the use of I-SYS had proved far reaching for ship designers in general, he continued: “Changes have been made to electric distribution / piping systems topology. So far, we have been able to identify mainly gaps in the electric distribution system and piping systems – for instance, lack of redundancy in piping or cabling, and, in various systems, lack of bypass and / or isolation valves for technical water.

“In future, a major part of development work will be to enhance the user interface. Modelling of systems and post-processing of results is currently rather time consuming but, based on the experience so far, we are writing the specification requirements for a graphical user interface that will allow importing WT subdivision and A-class bulkheads’ geometric information into the systems’ definition environment. This interface will also allow more efficient post-processing of results.” OMT

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