5.4.1 Generation of Alternatives
A task force group has been appointed by management in order to find possible solutions to the problem associated with the protection of escape ways. The following alternatives have been proposed:
1. Minor improvement in order to compensate for increased risk due to new equipment, but no further reduction.
2. Installation of protective shielding on existing escape ways together with overpressure protection in order to avoid smoke ingress in to the enclosed escape ways.
3. Installation of additional escape routes with sufficient protection in order to provide redundant escape routes.
An additional option is obviously to do nothing at all: accept the situation as it is.
5.4.2 Assessment of Alternatives
The task force group has analysed these options, and provided the following information:
x Risk reduction in terms of ǻPLL (PLL – Potential Loss of Life), in relation to the base case, after implementation of the new equipment, see Table 5.2.
The term ǻPLL gives the change in expected number of fatalities resulting from installation of risk reducing measures. PLL expresses the expected number of fatalities for the period considered.
x Risk reduction in terms of reduction in escape ways impairment frequency, in relation to the base case, after implementation, see Table 5.2.
x Risk increase during installation phase, in terms of ǻPLL, see Table 5.4.
There is an increase during execution of modifications, and a reduction when the modifications have been completed. The ǻPLL in Table 5.4 is the “net” reduction in expected fatalities, i.e., the reduction in PLL from operations, with a possible increase in PLL during installation subtracted.
x Expected cost of each alternative, see Table 5.3.
It is observed that only Option 3 has an annual impairment frequency for escape ways which is below the limit stipulated in the regulations, 1 x 10-4 per year. Option 2 is close however, 1.25 x 10-4 per year, which is in the order of 1 x 10-4 per year.
Table 5.4 shows that Options 2 and 3 have considerable cost levels per averted statistical life lost (ICAF). If these values are considered in isolation in a quantita- tive context, they would usually be considered grossly disproportionate in relation to the benefits, the reduction of PLL over 40 years.
Table 5.2. Overview of key risk parameters for the decision alternatives
Options Alternative
Annual impairment
frequency
(escape ways) FAR
PLL (/yr)
ǻPLL (/yr)
0 Base case 3.76x 10-4 4.2 0.0147
1 Limited risk reduction 3.75x 10-4 4.4 0.0154 í0.0007 2 Protective shielding 1.25x 10-4 3.4 0.0118 0.0029 3 Additional escape way 9.40x 10-5 2.5 0.0088 0.0059
4 Do nothing 3.9x 10-4 4.8 0.0168 í0.0021
Table 5.3. Overview of expected cost parameters for the decision alternatives
Options
Investment cost (mill NOK)
Annual operating cost (mill NOK)
0 Base case 0 0
1 Limited risk reduction 2 0.05
2 Protective shielding 30 0.4
3 Additional escape way 110 0.1
4 Do nothing 0 0
Table 5.4. Overview of key risk and cost parameters for the decision alternatives
Options NPV (40 yrs)
(mill NOK)
ǻPLL (40 yrs)
ICAF E(Cost)/E(saved lives) (mill NOK) 0 Base case
1
Limited risk
reduction 2.7 0.0 (Extreme)
2 Protective shielding 35.7 0.1 315
3
Additional escape
way 111.4 0.2 467
4 Do nothing
With respect to decisions about protection of escape ways, the options considered for decision-making were as noted above:
x install limited scope improvements x install extensive heat shielding x install additional escape ways x do nothing.
From a very narrow risk management point of view, the alternative “do nothing”
may sometimes seem attractive, because there are no costs involved, and the calculations show that there is a 99% probability that no protection will be needed during 40 years. If insurance can cover the 1% case and no legal actions can be taken against the company, this may be seen as the best alternative. The second best options is the “limited scope improvements”, because the cost is limited. This is more or less what the company in question decided in reality.
In this way of thinking, the option “extra escape ways” is the worst, because the cost is high, and the option “extensive heat shielding” is the second worst.
Now, what decision to make is a management task, and would depend on the priorities of the decision-maker. The above analysis is only the quantitative part, which does not provide sufficiently broad support for making the decision. Of equal importance are the qualitative considerations of the risk aspects and the risk reduction proposals. This corresponds to adding the following dimensions (see Section 3.3.3);
A. aspects related to the consequences B. aspects related to the uncertainties C. aspects related to manageability.
The point is that the above calculations express conditional probabilities and expected values P(A|K) and E[X|K), for some events A and unknown quantities X (A may express the occurrence of an accidental event and X may express the number of fatalities next year), given the background information and knowledge K. What we are concerned about are A and X, the actual observable quantities, but our analysis provides just some assignments P and E, which express the analysts’
judgements based on K, and could deviate strongly from the observables. Key factors that could lead to such deviations need to be addressed and communicated to management, as part of the overall risk picture. Sensitivity and robustness analy- sis are tools that can be used to illustrate the dependence of these factors and the background information K. Some examples of such sensitivity and robustness analyses are presented and discussed below. The main aspects related to the categories A–C are:
x Given possible fire scenarios, what are the smoke and radiation impacts?
Which barriers will reduce the possible consequences and avoid fatalities?
How reliable and robust are these barriers? Vulnerabilities?
With the oil export pumps being the main threat, the smoke production from fires will be very dense and poisonous. The heat loads may be limited due to the smoke, but still at such levels that personnel will be fatally injured after few seconds.
The existing escape ways (external vertical towers and external gangways) do not provide any protection of personnel, to the extent that if a fire occurs, there are no barriers in order to protect personnel.
x The analysis assigns a probability of a fire of 1% during a 40 year period.
However, a fire may occur and the additional fire protection will have a considerable positive effect in protecting personnel.
Even though the frequency of critical fires is as low as 1% during 40 years, the protection of escape ways will also help in less critical fires, which will be somewhat more likely to occur. In a period of 40 years, limited fires may have a probability of typically 50%.
x The company may implement uncertainty and safety management activi- ties that contribute to avoiding the occurrence of hazardous situations and thus accident events. Although there is a risk (expressed by the P and E, diligent efforts are made to avoid events A and obtain desirable outcomes X). These activities are mainly related to human and organisational factors, as well as the prevailing HES culture.
One could argue that most hydrocarbon leaks are due to manual inter- vention on process equipment. In theory, all non-essential personnel could be removed from all areas where effects could be experienced during the use of escape ways in a fire scenario. Management may consider, however, that this places too much restriction on the operation of the installations, so that this is not feasible in practice.
On the issue of robustness, it should be noted that heat and smoke protection of escape ways is a passive way of protecting personnel, which does not require any mobilisation or action in an emergency. Therefore, it is usually considered to be a robust way of reducing risk, as opposed to decisions that rely on equipment to be started or management actions to be implemented and followed up, which will often have a much higher failure probability.
A sensitivity study would be a natural part of a broad decision-making process.
Some hypothetical results of a sensitivity study are presented in Table 5.5.
Table 5.5. Hypothetical results of sensitivity study for additional escape way
Variation Resulting ICAF
(mill NOK)
Base case 467
10 times higher failure frequency for severe fire 47 2 times higher radiation level on escape ways 62 Increased (2 times) proportion of south-westerly wind direction 31 Reduced (50%) proportion of south-westerly wind direction 719
The illustrative sensitivity study results show considerable variations, which sug- gest that the analysis is quite sensitive to assumptions and simplifications made in the analysis of risk to personnel.