CAPACIDAD PRODUCTIVA DE LA BODEGA 1 IDENTIFICACIÓN DE ALTERNATIVAS

The f-N curves are usually a graphic representation of the cumulative frequency distribution for the number of fatalities in the risk calculations that have been performed, see also section A1.3.

Aspect Advantages and disadvantages of f-N curves

Suitability for decision support

The f-N curves may be difficult to use in relation to risk acceptance if the limit is exceeded in one area but otherwise well below.

Adaptability to communication

• easy to understand for non experts • comparison of risk

with other activities

The cumulative expression of the f-N curve makes it somewhat difficult to comprehend.

The f-N-curves may to some extent be suitable for comparison as long as corresponding curves can be expressed for other activities. They lack however, in the same way as PLL, the ability to relate the risk to the number of exposed individuals.

Unambiguity

• precision • system limits • averaging

Unambiguous definition should be possible.

Concept independence

Acceptance criteria based on f-N curves may be formulated in a way that favours e.g. concepts with low risk potential to major accidents. However, such criteria may also be defined so as to be concept independent.

Uncertainty As for PLL.

A.2.4 Fatal Accident Rate (FAR)

The FAR value expresses the number of fatalities per 100 million exposed hours for a defined group of personnel.

The FAR is often used as a risk parameter. Several variants are used, mainly reflecting how the averaging of the risk level is done.

A.2.4.1 FAR for an entire Installation

The FAR value for an entire installation is the number of expected fatalities per 100 million exposed hours for one or several specified installations. The risk level is averaged over all positions onboard.

Aspect Advantages and disadvantages of FAR for an entire installation

Suitability for decision support

The FAR value for an entire installation is not very suitable for decision support with respect to reflection of the effect of risk reducing measures. This is due to the averaging over all exposed personnel, which means that limited effects usually will disappear almost entirely. (Area FAR is more suitable in this context).

Adaptability to communication

• easy to understand for non experts • comparison of risk

with other activities

The FARvalue is relatively easy to comprehend for non experts. The FAR value is the easiest of all parameters for comparison with risk for other activities.

Unambiguity

• precision • system limits • averaging

The FAR for an entire installation is unambiguously defined, but the averaging over the entire installation may imply a somewhat

inaccurate reflection of the risk picture.

Concept independence

FAR for an entire installation will favour a concept with high manning level in a low risk area, thereby implying that the risk level may be high in some smaller areas without necessarily showing an effect on the FAR for an entire installation.

Uncertainty The calculations required to establish the FAR for an entire

installation include calculation all through the event chain, in addition to averaging over all exposed personnel onboard. The uncertainties in the results are therefore relatively high.

A.2.4.2 FAR for a group with uniformed risk exposure

The Group-FAR is the expected number of fatalities per 100 million exposed hours for the group in question.

Aspect Advantages and disadvantages of group FAR

Suitability for decision support

More suitable than FAR for an entire installation (see section A2.4.1), because the group FAR averages over a smaller number of positions.

Adaptability to communication

• easy to understand for non experts • comparison of risk

with other activities

Similar to FAR for an entire installation, however this value and the group FAR are often mixed together unintentionally.

Unambiguity

• precision • system limits • averaging

As FAR for an entire installation but with a higher precision level than the former as to the averaging.

Concept independence

Less concept dependent compared to the FAR for an entire installation, PLL and f-N curves due to its focusing on a smaller group of personnel.

Uncertainty Uncertainty is relatively high as all FAR calculations apply far out in

the event sequence. The group FAR is better than the FAR for an entire installation due to its averaging over a smaller group.

A.2.4.3 FAR for a physically bounded area

The area-FAR is the expected number of fatalities per 100 million exposed hours in a physically bounded area.

Aspect Advantages and disadvantages of area FAR

Suitability for decision support

Better suited than PLL, f-N curves, IR, FAR for an entire installation and group FAR due to its focusing on one specific area on the

installation.

Adaptability to communication

• easy to understand for non experts • comparison of risk

with other activities

Difficult to compare with other activities because area definitions will vary. Alternatively a comparison will have to be done area by area.

Unambiguity

• precision • system limits • averaging

As FAR for an entire installation in relation to precision and system limits. Considerably better than the FAR for an entire installation as to averaging of the risk.

Concept independence

As for group FAR.