Design Option Safety Assessment (DOSA) provides a method for ’front-end’ comparative selection of the safest option from any group of possible development schemes. It can also be used to rate the elements of a single scheme in terms of their relative risks, thereby indicating where efforts could best be made for the reduction/mitigation of hazards.

The method is qualitative, requiring experienced personnel for implementation, but derives a quantitative relative score for each scheme (or element) reviewed. Higher scoring schemes are likely to be more hazardous than those with lower scores.

There are three basic routines (made up of six steps of analysis) steps in the procedure:

  1. Scoring of Relative Importance of Elements

    The elements of a scheme are compared with each other to obtain their relative importance in terms of potential hazard effect. This is done on a matrix and score as follows:

    2 = element has more potential than comparison element.

    1 = element has some potential as comparison element.

    0 = element has less potential than comparison element.

  2. Scoring of Accidental Events

    A set of accidental events are applied to each element of each scheme, using a matrix and a scoring method similar to that in 1. above.

  3. Summation

    Elements and accidental event scores for each scheme are multiplied, and then multiplied by a risk factor (0 = no risk, 10 = very high risk) to obtain a final score for each design option.

The method has been adapted for use on a standard personal computer spreadsheet software and used for selection of a subsea development scheme. The study was presented together with outlines of the work subsequently undertaken to indicate how risk reductions were obtained in the finally accepted scheme.

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