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Although the previous step tries to clarify the risk environment, threats, and vulnerabilities, this step tries to find strategies and activities that should be used to act against this situation and abate the risk. Already-known and different strategies that can be taken should be recognized, and the efficient ones should be elected through a cost—benefit analysis process. Having the information of the previous steps is crucial: If we do not know the risk environment, then there is no guarantee an activity can reduce the risk. Employing the AHP tool, decision trees, the use of a plus/minus/interesting (PMI) tool which weighs pros and cons of each option is also helpful. A review of decision-making techniques is given in Huitt 140]. The journal Risk Analysis [41] presents a 0—1 knapsack formulation that tries to perform a valid cost—benefit analysis when a number of mitigation options and a limited amount are available. Although monetary value is incurred by owners and operators of the gas network, there are benefits that the aforementioned article tried to maximize subjected to total some of cost which can be paid for. Knowing this, the following formula is used:
| (20.4) |
| max |
E?= i h'x<
subject to
| where bj is the benefit derived from implementation of countermeasure i Wj is the cost of countcrmeasure i W is the available budget N is the total number of available countermeasures |
(20.5)
Xi e 0,1 V/
|
(20.6)
In this formula, the total benefit (Eqn (20.4)) derived from implementing cost- effective countermeasures is trying to be maximized, while in Eqn (20.5) the total cost spent is trying to not be more than W. The problem is solved using a dynamic programming method. It may be good to say that in the same paper a concise risk- management procedure is presented that is partly similar to what we have presented here.
A range of different options may be used. In fact, a combination of these options should be chosen based on a cost—benefit analysis. For example, to have a robust system in a gas supply network, we can either purchase high-quality pipes with no control system or low-quality pipes with high-tech control systems, or even a combination of both.
