We believe that a broad decision-making process is essential in order to make decisions about such crucial aspects of major hazard prevention for an installation.
The main elements should be as outlined in Chapter 3:
•
framing of the problem•
generation and evaluation of alternatives•
managerial review and decision.4.3.1 Framing of the Problem and Alternatives
The framework for the decision-making should be a broad process involving all relevant stakeholders, the cautionary principle as well as use of the ALARP prin- ciple.
The generation of alternatives is in the present case somewhat trivial, the options being to install the reserve buoyancy in the deck or not to install it, and there are no compromises or alternative solutions.
The evaluation of alternatives should consist of quantitative and qualitative considerations and arguments.
4.3.2 Quantitative Results
We have already presented the effects in terms of average FAR values for personnel on board; see page 95. We would also expect cost-benefit and cost- effectiveness calculations to have been made. Typically, we may have the following result:
•
Expected cost (NPV) of averting a statistical lifelost through installation of reserve buoyancy: 380 million NOK We refer to the expected cost of averting loss of a statistical life as the ICAF (Implied Cost of Averting a Fatality) value. We would expect sensitivity analyses to be performed, in order to illustrate effects on quantitative results. Table 4.1 presents some illustrative results of what could come out of a sensitivity study, using ICAF to measure performance.
The sensitivity study results show considerable variation, including cases where costs of averting a statistical fatality are certainly not grossly disproportionate in relation to benefits. This applies to the two last rows of Table 4.1.
Table 4.1. Hypothetical results of sensitivity study
Variation Resulting ICAF value
(million NOK) 10 times higher failure frequency for ballast tank valves 85 10 times lower failure frequency for ballast tank valves 595 Increased influence of common mode failure for valves 117 10 times higher failure frequency for operator response in
case of emergency involving ballast tank flooding
43 10 times higher collision frequency by passing merchant
vessels
19
4.3.3 Qualitative Evaluations
The qualitative evaluations should consider aspects that are not easy to quantify, but which may be just as important as the quantitative results. Factors that should be considered include the following:
•
use of good practice•
use of codes and standards•
engineering judgement•
evaluation of robustness•
stakeholder consultation•
tiered challenge.We have already commented on some of these aspects. The provision of reserve buoyancy in the deck would be considered good practice, and is in accordance with applicable regulations from NMD.
The evaluation of robustness should be an extensive discussion. The following may serve as a brief summary of such a discussion. Reserve buoyancy in the deck is an aspect of robustness: it provides the installation with a survival capability in the case of very severe structural damage, severe damage to the ballast system or severe flooding of watertight compartments.
Experience has shown that robustness is an important aspect. The capsizing and sinking of Petrobras’ P-36 floating production installation in March 2001 showed that what were supposed to be watertight doors to compartments were open and thus susceptible to flooding. In March 2004, a supply vessel rammed at almost full speed a Norwegian semi-submersible mobile drilling unit on the Norwegian Conti- nental Shelf. The force of the collision was quite high, due to the vessels’ speed. If the installation had been 20 years old, the column in question might have been lost and the unit dependent on the reserve buoyancy. In the actual case the unit was quite new with a high structural capacity, and only minor damage resulted.
Common to both these two incidents is the fact that they occurred because of mechanisms that usually show very low contributions to personnel risk in QRA studies. This may also be stated for the mechanism of the loss of “Ocean Ranger”, as described in Section 4.1.1.
Stakeholders relevant to the decision on reserve buoyancy in the deck are the following:
•
the operator (oil company)•
partners in the field•
contractors and suppliers•
employees of oil company and contractors•
authorities.Consultation with some stakeholders is a challenge at an early stage of the concept selection stage. There are usually no employees available, few or no contractors are selected,etc. However, union representatives may act on behalf of employees.
It should be noted that the decision about reserve buoyancy in the deck must be taken at a very early stage of concept development. The possibility for the autho- rities to influence decision-making in the very early stage is often quite limited.
The authorities normally require a recommended solution to be presented for their approval or acceptance. The role of the authorities in the phase where important concept selections are made is often that of informal influence.
4.3.4 Managerial Review and Decision
A summary of the review and decision by management as a result of a broad decision-making process could be formulated as follows:
It has been noted that the assigned fatality risk on the installation will not be excessively high even if reserve buoyancy is not provided. Whether costs of provi- ding the extra barrier are in gross disproportion or not is somewhat of a borderline issue. They may be considered to be in gross disproportion if only expected values are considered. But this conclusion is quite sensitive to assumptions and premises in the cost-benefit analysis. If the collision frequency of passing merchant vessels is increased by a factor of 10, the extra cost is certainly not grossly dispropor- tionate.
It is further noted that reserve buoyancy in the deck is a robust solution to all scenarios involving severe structural damage or severe ballast system failure, including flooding of ballast compartments. It has been demonstrated by a recent near-miss, where total loss, and multi-billion NOK asset loss, was prevented by this extra barrier. At least three total losses in the past (with well over 200 fatalities) could have been prevented if such reserve buoyancy had been available.
The extra barrier is certainly in accordance with authority regulations, and is as such the preferred solution from a regulatory point of view. It is further in accor- dance with good practice, and has been adopted by owners of mobile drilling units for more than 20 years.
It is the decision of management after a balanced evaluation of quantitative as well as qualitative aspects that reserve buoyancy in the deck structure should be provided for the floating production unit in question.