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Quantified Risk Assessment (QRA) work on the Heather platform showed the condensate flash drum to be the largest single contributor to impairment of the Temporary Refuge (the safe location where personnel muster while waiting to be evacuated in an emergency). The key problem was the large inventory of high volatility fluids which would contribute significantly to the hydrocarbon gas released in the event of a leak. The two options available to reduce the risk to the target figure were i) reduce the inventory or ii) increase the blowdown rate to flare so that there was less gas available to leak. Several studies concluded that increasing blowdown rates was not possible as the blowdown piping was already at it’s limit and the only solution was to replace the vessel with a smaller one to reduce the inventory.
PDE were asked to provide an independent review of the proposals prior to DNO committing to this extremely costly recommendation.
Unlike previous studies, PDE did not focus on reducing the risk with one single modification, but instead identified ten options that would each partially reduce the risk. The options were ranked using a high level cost-benefit analysis and when tabulated it could be seen how many of the options had to be implemented to achieve the target risk. It was also identified that part of the basis for the QRA work was out of date and current data would result in a lower risk. The findings were presented to DNO who approved the recommendations. PDE managed the Contractor's Process team to design the modifications and were the authorising signatory for all Process deliverables. Using a combination of several small upgrades, DNO achieved 90% of their target risk reduction for significantly less cost than a new vessel and demonstrated an ALARP (As Low As Reasonably Practical) approach to risk had been taken.
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