It should further be noted that installation of two freefall lifeboats will be very expensive, probably the most expensive of all the proposals considered.
Remove all Weather Cladding on Process Modules
The removal of all weather cladding on process modules will increase natural ventilation in the process areas. The engineering evaluation of this proposal has concluded that it will have the following effects:
x Reduce ignition probability through reducing gas concentrations and extent of gas cloud within flammable region.
x Reduce explosion overpressure in case of delayed ignition, as a result of having more explosion relief areas.
x Possibly reduce smoke production slightly in the event of fire, due to improved ventilation.
x Working environment in the process area will suffer deterioration due to an increase in wind chill factors.
The increased wind chill factor in the process area is a severe negative factor, which is likely to cause strong opposition from the workforce. In this regard, the proposal is not in line with working environment standards. But improvement of ventilation rates is in line with technical safety principles designed to reduce the effects of hydrocarbon leaks. It is quite common that a compromise has to be found between these two opposing objectives.
Table B.5 presents the revised results for the option to remove all weather clad- ding. It is noted that some reductions are shown, but the reduction in impairment frequency for escape ways is not at all sufficient to reduce the value below the limit of 10-4 per year. This, together with the working environment aspect, means that this proposal will not receive much support from some of the stakeholders.
Table B.5. Risk Values for Removal of all Weather Cladding in Process Area
Alternative
Annual impairment
frequency (escape ways) FAR
PLL (/yr)
ǻPLL (/yr)
Base case 3.76ǜ 10-4 4.2 0.0147
Remove all weather
cladding 2.37ǜ 10-4 3.4 0.0118 0.0029
The point is that the above calculations express conditional probabilities and ex- pected 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 ana- lysis provides only some assignments P and E, which express the analyst’s judge- ments 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 a part of the overall description of the risk picture. Sensitivity and robustness analysis 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:
y Given possible fire scenarios; what are the smoke and radiation impacts?
What barriers can 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 only a few seconds.
The existing escape ways (external vertical towers and external gangways) do not provide any protection of personnel, so that if a fire occurs there are no barriers to protect personnel.
y 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% over a period of 40 years, the protection of escape ways will also help in less critical fires, which will be somewhat more likely to occur. In the space of 40 years, limited fires may have a probability of typically 50%.
y The company may implement uncertainty and safety management activities 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 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, however, may consider 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 on 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
actions that rely on equipment to be started or management actions to be implemented and followed up, which will often have much higher failure probability.
A sensitivity study is a natural part of a broad decision-making process. Some sen- sitivity study results are presented in Table B.6 and Table B.7.
Table B.6. Results of sensitivity study for heat shielding on existing escape way
Variation Resulting Cost/E(life)
(mill NOK)
Base case 315
10 times higher failure frequency for severe fire 32 2 times higher radiation level on escape ways 52 Increased (2 times) proportion of south-westerly wind
direction
21 Reduced (50%) proportion of south-westerly wind
direction
511 Table B.7. Results of sensitivity study for additional escape way
Variation Resulting Cost/E(life)
(mill NOK)
Base case 473
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 sensitivity study results show considerable variations; some of the results are at such levels that gross disproportion is not an obvious conclusion. This suggests that the analysis is quite sensitive to assumptions and simplifications made in the analysis of risk to personnel.
Many companies have formulated ‘zero vision’ objectives for their HES mana- gement, implying that the long-term objective is to carry out all operations without losses and damage. Sometimes it may be difficult to see the connection between such objectives and the traditional approach to decision-making, involving a nar- rowly-focused decision-making process with short-term cost minimisation as the driving force.
The decision-making process should enable a broad assessment of potential consequences and uncertainty, so that all the main aspects relating to outcomes of the decisions are available to the decision-makers. The difficult management deci- sion to be taken may be illustrated as follows:
If the decision to install extra protection is taken (with cost of about 36 million NOK), the outcome over the long residual production period (30–40 years) is either one of the following three outcomes:
(a) No fire occurs at all (about 50% probability), and the protection is wasted in terms of pay-back.
(b) A limited fire (not critical fire) occurs (about 49% probability), and the protection has some advantage, thus avoiding any injuries to personnel due to fire loads on escape ways.
(c) A critical fire occurs (about 1% probability), and the protection is very valuable in terms of allowing all personnel to escape to a safe location.
Obviously, if no extra protection is installed, the scenario alternatives are the same, but the outcomes in terms of pay-back are the opposite:
(a) No fire occurs (about 50% probability), no cost, no other effect.
(b) A limited fire (not critical fire) occurs (about 49% probability), the lack of protection means that some of the personnel will be injured during escape, but not fatally.
(c) A critical fire occurs (about 1% probability), the lack of protection implies that more than 50 persons are prevented from escaping to a safe location, many of whom may perish.
If considered in standard economic terms only, the difficult management decision is to consider the 1% probability over a 40 year field lifetime of a severe fire oc- curring, with possibly up to 30 fatalities, and whether to invest about 36 million NOK in protective systems and actions to avoid these severe consequences.
An argument against the alternative approach to avoid higher investments in risk reduction cannot be accepted if the companies are serious when they formulate
‘zero vision’ objectives. If a ‘zero vision’ objective is accepted, it must inevitably be expected that extra costs will be incurred as a consequence. Otherwise the objective should be reworded to ‘zero vision as long as it doesn’t cost anything’.