The f-N diagram is used as a agency of showing information about social hazards. In Norsok Standard Z -013, f-N curve is defined as a hazard parametric quantity that the curve represents the frequence ( f ) of accidents doing N-fatalities [ 1 ] .

Ball, 1998 cited in the Guidelines for Developing Quantitative Safety Risk Criteria [ 2 ] provinces that f-N curve and F-N diagrams may be used to picture at least three different types of information:

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The historical record of incidents

The consequences of a quantitative hazard analysis ( QRA )

Standards for judging the tolerability of hazard

To cipher values for entire hazard for the installing and the presentation in secret plan the values in an f-N diagram, a list of all of the events ( Accident Categories ) and their associated frequences and effects ( figure of human deaths, N ) will be compiled and sorted by diminishing value of N ( Number of human deaths ) . Given Table 1 with the human death hazard consequences for an illustration installing ;

Table: Fatality hazard consequences for an illustration installing

In order to understand the part of all different types of accidents to put on the line possible, Potential Loss of Life is foremost plotted. Figure 1 shows that the most open country consists of the Process leaks whereby the PLL are about 2.655 10-2. This is in verification with many instances of the seaward installing. Most frequent leaks go on in the procedure country due to the gas escape which leads by and large to ignition and farther to an detonation or a fire which by and large ends to high human death.

Figure: Hazard parts to PLL

Vinnem, 2007 defines the Potential Loss of Life ( PLL ) as the expected figure of human deaths per twelvemonth and can be formulated as follows [ 3 ] :



fnj one-year frequence of accident scenario ( event tree terminal event ) N with forces effect J

cnj expected figure of human deaths for accident scenario ( event tree terminal event ) N with forces effect J

n entire figure of accident scenarios ( event tree terminal event ) in all event trees

J entire forces effects types, normally immediate, flight, emptying and deliverance installation

In Table 2, procedure leaks are the most terrible and has a predicted effect of 2 to 5 human deaths, which occurs at a predicted frequence of 3.90 10-3. The 2nd most terrible event is the occupational accidents, which has a predicted effect of 21 to 50 human deaths, occurs at a predicted frequence of 4.20 10-3. It is followed by Riser/pipelines leaks.

Table: Table of frequence of jeopardies

Table 3 presents the F-N QRA consequences. Rearranging the information from table 2 in diminishing order of the figure of human deaths gives the information set presented in Table 3. Valuess presented in each row in the tabular array 3 calculate the cumulative frequence of happening for that event and all events predating it in the tabular array. To set this information into the signifier needed for plotting an F-N curve, the frequence must be expressed in footings of the cumulative frequence. The ensuing informations are plotted as an F-N curve in Figure 2.

Table: F-N Presentation of QRA Results

Many analysts believe that social hazard consequences are most efficaciously presented in graphical signifier. Such secret plans are usually log-log secret plans with the x-axis stand foring the effects and the y-axis stand foring the frequence of happening. Log-log graduated tables are used because the scope of values for degree Fahrenheit and N can cross multiple orders of magnitude [ 2 ] .

By definition Societal hazard ( SR ) is the relationship between the frequence and the figure of people enduring from a specified degree of injury in a given population from the realisation of specified jeopardies, Institution of Chemical Engineers 1992 [ 4 ] .

Another manner to pass on hazard standards will be to look into the significance of the incline of the F-N curve. When the F-N curve incline is equal to -1, the hazard standard is termed ‘risk impersonal. ‘ In this instance, the hazard standard would order that the frequence of an event that consequences in 100 or more human deaths must be 10 times lower than the frequence of an event that consequences in 10 or more human deaths.

Figure: F-N Curve for Hypothetical QRA Results

Guidelines suggest two ways of plotting social hazards [ 2 ] :

One manner known as Non-cumulative frequence footing. For these graphs, called f-N curves, the value plotted on the y-axis is the distinct frequence of sing precisely N human deaths.

The 2nd manner is the Accumulative frequence footing. Here graphs, called F-N curves, the value plotted on the y-axis is the cumulative frequence of sing N or more human deaths.

Mathematically, the equation for an F-N standard curve may be presented as: [ Ball 1998 ]

Eq 2


F = the cumulative frequence of N or more human deaths

N = the figure of human deaths

a = antipathy factor ( frequently between 1 and 2 )

K = invariable

In Norse Regulatory Requirement, it has been a tendency of an increasing focal point on the ALARP rule compared to Risk Acceptance standards broad used before 2004 [ 3 ] . The ALARP rule implies that all hazard decrease proposals that are good founded should be implemented unless it may be shown that costs and/or other negative effects are in gross disproportion to the benefits [ 3 ] .

Using guidelines given by [ 4 ] , we obtain the Hypothetical QRA Results with EU Societal Risk Criterion. It demonstrated that the incidence of high human deaths in the studied system is negligible while few accidents can go on frequently but with low human deaths.

Figure: Conjectural QRA Results with EU Societal Risk Criterion

Based on the Advisory Committee on Major Hazards, 1976 a serious accident in a peculiar works was improbable to happen more frequently than one time in 10,000 old ages, which could be regarded on the boundary line of acceptableness, ACMH 1976. This has frequently been taken as an ground tackle point for the F-N curve where the opportunity of an accident affecting 10 or more human deaths should non transcend 1 in 10,000 per twelvemonth [ 4 ] . In the 2nd Canvey study, HSE 1981, it was suggested that an event with 1,500 human deaths and the frequence of 2 ten 10-4 per twelvemonth ( 2 in 10,000 ) could be judged as unbearable [ 4 ] .

Discussion of sustainability/justifiability of present employee hazard degrees in Norse sector ( Part C )


In the subdivision, it is discussed whether the hazard degrees for employees in the Norse crude oil sector are at degrees that are sustainable/justifiable in a social context, and it is besides identified countries in a demand for farther betterments in the offshore operations.

The footing of our treatment is the paper: “ On the hazard to forces in the offshore industry ” by J.E Vinnem, 2008. Vinnem uses assorted beginnings including information from the Risk Level Project [ 5 ] to categorise constituents of the human death hazard image in occupational accidents, major accidents on the installing, and transit accidents during transportation between shore and seaward installings. From here he gives anticipations of what the current hazard degrees are [ 6 ] .

From quantitatively every bit good as qualitatively perspectives, Vinnem makes the most relevant anticipations about happening of human deaths in the Norse national sector for the period 2008-2012. In his survey, J.E. Vinnem, 2008 uses Bayesian attack which implies that the hazard values show our belief ( uncertainness ) about what will happen in the hereafter in footings of accidents and effects. Thus sensitiveness surveies have been used extensively in order to research the sensitiveness of the hazard theoretical account to fluctuations in informations and premises.

Through performed appraisal and based on predicted figure of human deaths in the Norse Continental Shelf, and based on analysis the causes of human deaths every bit good as the fluctuation of human deaths between 1985 and 2005, J. E. Vinnem came to a decision that there are indicants that tendencies of fatal accident happening become few and rare. The comparative distribution of the hazard degree from major jeopardies has about reduced up to 50 % by 2008.

This subdivision is divided into three parts: 1 ) the cardinal findings of the paper “ On the hazard to forces in the offshore industry ” , 2 ) lessons learned and tendencies in human deaths rates and 3 ) the betterment needed for sustainable employee hazard degree in Norse sector.

Key findings

Fatal accident rates in worldwide offshore operations

Based on the OGP Annual statistical sum-ups, Vinnem demonstrates a general lessening of fatal accidents rate worldwide for the period 1997 and 2006 with the highest figure of human deaths of 32 loss of life in 2004. The lowest registered is 10 lives, in 2005 [ 6 ] . The high value of human deaths found in 2004 is due to two chopper accidents that occurred in 2004 [ 6 ] .

[ 6 ] found that non all the relevant accidents are included in the OGP study. As an illustration he pointed out that the Risk Level Project study paperss 10 human deaths in offshore accidents in the UK in the period 2001-06, when the OGP study considers for the same period, seven human deaths offshore [ 6 ] . Others accidents non included in the OGP are the capsize of P-36 offshore Brazil in 2001 followed by an detonation and fire which resulted in 11 human deaths ; a combustion runaway occurred offshore Egypt, without human deaths in 2004.

Meanwhile Vinnem noticed that the estimated FAR values will non be significantly affected if it is considered an addition of volume of exposure hours of 694 million manhours from 39 companies in 75 states by 2006 [ 6 ] .

The instance of Norse offshore operations

In Norse sector, major accidents occurred rather often during the first 20 old ages of operations in the Norse sector, but from 1985 to 2006 their incidence got declined. The last enkindled hydrocarbon leak on an installing in the Norse sector was in November 1992 [ cited in [ 6 ] ] . Due to the absence of major accidents between 1985-2006, [ 6 ] argues that the likeliness of major accidents in the Norse sector is reduced extensively.

An mean FAR calculated in [ 6 ] and normalized against exposure hours in the period 1974-2006 and 1967-2006 shows 0.66 human deaths per 100 million exposure hours ( 1974-2006 ) for production installings and 45.4 human deaths per 100 million exposure hours ( 1967-2006 ) for nomadic installings. [ 6 ] points out that the high value of human deaths for nomadic installings is linked to the capsize of nomadic adjustment unit Alexander Kielland, 1980, with 123 human deaths [ 5 ] . A best manner to cipher an norm Army for the liberation of rwanda without the influence of the really high figure of human deaths like the one in the Alexander Kielland accident, [ 6 ] suggests to cipher an happening frequence for major accidents, based on history. In this instance the expected figure of human deaths per major accident in the hereafter are derived in [ 6 ] as 0.25 major accidents per 100 million exposure hours ( 1974-2006 ) for the production installings, while for the nomadic installings, the value becomes 1.10 major accidents per 100 million exposure hours ( 1967-2006 ) .

Since major accidents have non occurred for many old ages, [ 6 ] performs the computation of the frequence of major accidents foremost for a considered period 1980-2006 and so for the period 1990-2006. The consequences obtained are compared with other alternate attack such QRA that consider the predicted frequence and human deaths for single installings in the hereafter.

The tabular array below shows a sum-up of human deaths per 100 million exposure hours for the different periods as computed by J.E Vinnem [ 6 ] .

Table: Computed human deaths per 100 million exposure hours based on J.E. Vinnem, 2008, beginning [ 6 ]


Fatalities per 100 million exposure hours

( 1980-2006 )

( 1990-2006 )

Assumed expected 8 human deaths per major accident in the hereafter

QRA surveies, and assumed expected 5 human deaths for single installings in the hereafter by J.E. Vinnem

Expert ratings & A ; judgement

( refined over old ages ) with input from the Risk Level Project [ 3 ]

Average assumed for the period 1990-2006 and the

footing for the values in the Risk Level Project [ 3 ]















The Numberss of human deaths obtained were based on premise of expected possible loss of life in the hereafter per major accident for production installings every bit good as for nomadic installings.

From the tabular array above, [ 6 ] found that the assorted anticipations of the human death Numberss for production installings were moderately consistent ; connoting that the uncertainness associated with this anticipation should be limited. However the anticipations for nomadic installings were non rather as consistent [ 6 ] .

For the class of chopper conveyance in Norse sector, the conducted analysis by [ 6 ] shows that average fatal Accident Rate for the period 1997-2006 was estimation at 1.89 10-6 human deaths per individual flight hours while for the period 1987-2006 the mean fatal Accident Rate has turned out to be 1.15 10-6 human deaths per individual flight hours.

The anticipation of future hazard degree.

To foretell the hereafter hazard degree [ 6 ] utilizations Bayesian attack for five twelvemonth period from 2008 to 2012. The premise taken was that the mean fatal accident during the last 10 old ages is the most applicable for the future five old ages.

Another of import rule adopted in the Vinnem ‘s paper is the triangulation, the same attack was used in the Norse Risk Level Project, 1998 cited in [ 5 ] to foretell the tendencies of hazard degree for the period 1998-2008. This was implemented through input from assorted beginnings and positions, quantitatively every bit good as qualitatively, including information from the Risk Level Project.

For different classs, separate premises were made to suitably account the complexness of each system to be analyzed. In the tabular array 5 is given the estimated human deaths for each class.

Table: Assumed human deaths per 100 million exposure hours based on J.E. Vinnem, 2008, beginning [ 6 ]


Fatalities per 100 million exposure hours

Occupational Accidents

Major Accidents on Installations







The premise for the occupational accidents is based on a long period registered without occupational human deaths. The last occupational human death on nomadic units in the Norse sector was on 13.12.1993 [ 5 ] . While the last human deaths on production and nomadic installings were in 2002, in November and April, 2002 [ 6 ] .

Sing the Major Accidents on Installations, Vinnem supplements the no happenings of fatal accident in the period 1990-2006, with informations from QRA surveies and the Risk Level Project. It followed that assorted anticipations of the human death Numberss observed for production installings were moderately consistent which was a verification that the uncertainness associated with this anticipation would be limited [ 6 ] .

For Helicopter Transportation Accidents, [ 6 ] takes into history the consequence of recent betterments and the new introduced Sikorsky and Super Puma theoretical accounts for personal offshore transit. The paper besides considers the end of the White Paper guidelines with a mark to cut down by 50 % of the human death frequence. All those steps combined to stipulated actions by the chopper safety, ( that include Flight informations monitoring, New engineering, TCAS 1 hit turning away system, EGPWS, Enhanced Ground Proximity Warning System, De frost ( rotor ) , Survivability in Sea province 6 ) , Vinnem demonstrates the taken actions for fleet modernisation will decidedly take down the hazard for major chopper accidents in the hereafter.

On this footing, the paper “ On the hazard to forces in the offshore industry ” by J.E Vinnem, 2008 has subjectively considered that a representative norm value for the period 2008-2012 may be 90 human deaths per 100 million individual flight hours for Helicopter conveyance. The suggested value corresponds to 70 % as an mean accomplishment of the 50 % decrease which was established as the end for the period 2002-2012 [ 6 ] .

In table 6 is summarized the predicted hazard degree for the period 2008-2012 based on Vinnem, 2008 [ 6 ] :

Table: Predicted Future Fatalities – Norse Sector 2008-2012 based on J.E. Vinnem, 2008 [ 6 ]


Fatalities per 100 million exposure hours

Occupational Accidents

Major Accidents on Installations

Helicopter Transportation Accidents









The values obtained from predating tabular array were used by [ 6 ] to eventually foretell the expected figure of fatal accidents in the period 2008-2012 for the full Norse Continental Shelf. 2.4 fatal accidents were predicted for the occupational accidents ; 0.26 for the chopper accidents ; while 0.35 fatal accidents were predicted for the major accidents on installings.

In order to exemplify the uncertainness of the anticipations [ 6 ] has applied the undermentioned anticipation intervals for the figure of fatal accidents in the five twelvemonth period 2008-2012:

Occupational accidents: 0-3 fatal accidents

Helicopter accidents: 0-2 fatal accidents

Major accidents: 0-2 fatal accidents

Lessons learned and Trends in Fatality Ratess

The paper “ On the hazard to forces in the offshore industry ” by J.E Vinnem, 2008 and the survey of the “ Risk Level in Norwegian Petroleum Activities: Drumhead study ” by PSA, 2012 shows that there has been a important decrease of the figure of fatal accidents since the origin of the “ Trends in hazard degree – Norse Continental Shelf ” undertaking in 1999/2000 [ 6, 7 ] .

Within PSA ‘s country of duty offshore and on land, there were no fatal accidents occurred during 2011. Five people have died in occupational accidents over the past 10 old ages [ 7 ] . For production installings there is a downward tendency over the full period, the degree was stable until 2000 and the frequence has been falling since twelvemonth 2000.

The hazard degree undertaking has set 21 defined jeopardy and accident state of affairss ( DFUs ) to depict the development in hazard degrees. Based on DFU, there have been no major accidents, harmonizing to definition, on installations on the Norse Continental Shelf after 1990. None of the DFUs that indicate major accident hazard on installations have resulted in human deaths during the period. The last clip there were human deaths in connexion with one of these major accident ‘s DFUs was in 1985, with the shoal gas runaway on the nomadic installation “ West Vanguard [ 7, 8 ]

However a fatal accident occurred at a land-based works in 2005 [ 9 ] ; in 2009 there was one fatal accident within the PSA ‘ s country of authorization on the Norse Continental Shelf, on Oseberg B, 7th May 2009, during dismantlement of scaffolding [ 10 ] .

Outside the NCS, there have been several serious chopper accidents associated with crude oil activities in 2009. On 12th March there were 17 human deaths when a Sikorsky S-92 ditched into the sea off Newfoundland and on 1st April 16 individuals lost their lives when a Super Puma L2 chopper ditched off the Scottish seashore On 18th February the pilots of a Super Puma EC-225 performed a controlled landing in the sea on the ETA P Field off Scotland. All 18 people on board were rescued [ 10 ] .

In Norway, a controlled exigency landing was performed with a Sikorsky S-92 on Tor on 8th April [ 10 ] .

Traditionally, the industry has selected indexs to exemplify safety tendencies in crude oil activities based on the frequence of occupational accidents ensuing in lost on the job clip. In recent old ages it has been acknowledged that the tendencies in hazard degrees in the crude oil industry are non merely a affair of concern to everyone involved in the industry but are besides of involvement to the populace at big [ 11 ] . Today, the penchant has been for a scope of indexs to be used to mensurate tendencies in certain cardinal HES factors [ 11 ] to give a broad scope image of the safety state of affairs.

In this survey we found that the results of the Vinnem ‘s paper: “ On the hazard to forces in the offshore industry ” in term of human deaths anticipation are an understanding with the statistics records of PSA studies trough the RNNS undertaking for the period 2008-2012. This is a verification that the applied Bayesian attack combined with qualitative and quantitative methods to foretell tendency hazard degree have yielded satisfactory consequences.

The ascertained lessening of fatal accident and human deaths rate in the NCS, is besides experienced for the instance of personal hurts recorded in the offshore operation. Serious personal hurts have shown a favourable tendency in recent old ages, making 0.6 per million hours worked for the whole NCS in 2011 – significantly below the norm for the predating 10 old ages [ 7 ] . Even with more hours worked overall, serious hurts fell from 23 in 2010 to 17 in 2011.

The figure 4 shows the tendencies of serious personal hurts on Mobile and production installations in relation to working hours. On nomadic units, the personal hurt frequence invariably decreased from 2.9 to 1.58 serious personal hurts per million working hours for the period 2001-2004. For the production the same state of affairs is observed with a lessening from 1.89 to 0.79 for the same period.

From 2005 to 2008, the state of affairs remained more stable whereby the figure of serious forces hurts varied around 1.77 and 1.25 for Mobile installations and 1.1 and 0.65 for production installations. From 2009 to 2011, the figure of serious forces hurts on Mobile has known a important lessening with 36 % of lessening of serious forces hurts in 2009 compared to old twelvemonth. For production there was non important alteration but from 2010 it was however below the norm for the predating decennary. Nine such hurts were recorded in 2011, compared with five the twelvemonth before [ 7 ] .

Figure: Serious personal hurts on Mobile and production installations related to working hours

The frequence of terrible forces hurt on production and nomadic installings, as reported in the figure 4, shows choice in early twelvemonth of 2001 while for the undermentioned old ages au to 2011, there has been a considerable diminution of hurt frequence on Mobile every bit good as on productions installations. On nomadic installations in 2011 shows an addition in the frequence for serious personal hurts from 0.4 in 2010 to 0.7 in 2011. The hurt frequence is merely below the norm for the 10 old old ages [ 7 ]

It should be noted that the figure of manhours on production installings is typically 3-4 times that on nomadic installings. It should besides be noted that two human deaths have occurred on a crane vas during periods when it was runing in the Norse sector, in 2003 and 2007 [ 6 ] .

To what extent farther betterments are needed?

Though major accidents have non occurred in the Norse sector after 1985, there were instances of close girls. Two near-misses have occurred in the Norse sector during the last few old ages, the unignited subsea runaway on Snorre Alpha in November 2004, and the monolithic unignited gas leak on the Visund FPU in January 2006 [ 9 ] .

During the period 2003 – 2010, a sum of 146 good control events were reported on the Norse Continental Shelf, of which merely about 10 events have been investigated [ 7 ] . Since the major accident potency inherent in good control events is incontestable, it is of extreme importance that more probes of such event are made. This will supply the necessary penetration in causal mechanisms, complex connexions and model conditions that contribute to such events, which in bend is a stipulation for efficient steps and experience transportation in the industry. Increased attempts directed toward barrier direction, more probes of good command events and operational hazard appraisals, will be instruments to guarantee apprehension of major accident hazard in connexion with good command events [ 8 ] .

On the other manus we could reason that every bit long as major accidents have non occurred for many old ages, it is a good mark of improved mechanisms put in topographic point by the Norse policy and the industry for hazard direction every bit good as robust barrier to forestall incidences go oning or developping. Meanwhile in the norm over the full production period for the Norse sector, it is unknown the existent extent of these betterments.

The PSA has adopted a set of chief precedences with focal point on direction, proficient and operational barriers, forestalling environmental injury and groups peculiarly exposed to put on the line [ 12 ]

Based on information obtained for J.E Vinnem paper and the usage of PSA ‘s published studies, below is suggested countries needed for betterment. The list may be long but here we use few that were judged the most of import.


This emphasizes the importance of doing criterions such as NORSOK D-001 and D-010 more aggressive as respects qualifying demands that contribute to uninterrupted betterment. Following the runaway and a ruinous detonation on the Deepwater Horizon offshore oil boring platform April 20th, 2010 it has been an increased focal point on better proficient solutions associated with systems for observing good boots, presentation of safety-critical information for the driller and boring fluid lumberman, design of the boring cabin and systems/technology for pore force per unit area anticipations [ 8 ] .

Harmonizing to Magne Ognedal, director-general in the Petroleum Safety Authority Norway ; in order to work purposefully on uninterrupted safety betterments, “ the information will organize a cardinal portion of the footing for be aftering our activities on possible alterations to Norway ‘s ordinances and with supervising ” .


The barrier index related to major accidents shows that a comparatively big figure of installings had reasonably significant non-conformities from the expected industry degree. This means that the sector has a clear betterment potency with respect to guaranting that these barriers are sufficiently robust [ 13 ] .


The PSA has duty to supervise the manner company managements work to cut down major accident hazard over a figure of old ages. PSA audit consequences, experience from major accidents nationally and internationally and recognized accident theory indicate that direction plays a cardinal function for major accident hazard.

Enterprises and determinations taken by direction define and influence conditions which are of significance for such menaces.

The PSA will concentrate peculiar attending in 2012 on internal followup by the companies and the overview they have of their ain operations. Follow-up, including of contractors, is a cardinal tool for exerting direction duty in this country.

Much attending will besides be devoted by the PSA to the duty of boring contractors, how they understand and exercise this duty, and how direction in the companies works to cut down major accident hazard.

Groups exposed to put on the line

In the subdivision 4.3. , it has been reported a high degree of serious personal hurts. This constitutes a menace for a certain group of employee exposed to hazard. Specific steps should be adopted by companies to cut down the menace of hurt and unwellness for groups peculiarly exposed to such hazards.

Harmonizing to PSA, the hazard of occupational hurt and illness autumn unevenly on different classs of workers in the crude oil industry. Groups of contractor employees have more hazard factors in their working environment, and their exposure is higher than for operator forces [ 12 ] . Among the precedences should be the cutting noise degrees to forestall hearing harm, steps to cut down the high cost of occupational unwellness and hurt


The paper “ On the hazard to forces in the offshore industry ” by J.E Vinnem, 2008 has shown that that accident statistics from the yesteryear may be used in order to foretell the figure of accidents and human deaths in the hereafter.

Due to the absence of major accidents after 1985, it might be argued that the likeliness of major accidents in the Norse sector is reduced extensively. But there have been recent near girls in the Norse sector as celebrated above, and at that place have been major accidents in the UK sector every bit good as in more distant countries. A balanced rating is hence needed.

The hazard degrees decrease registered with operation of production installing, nomadic units and the chopper transit in the Norse sector implies that considerable betterment has been made in all three chief classs.

To make ‘zero vision ‘ which is adopted across the industry every bit good as for sustainable employee hazard degree in Norse sector a uninterrupted betterment towards will be needed in all three countries.