update of Øra qra · 2021. 6. 18. · 8 detection and isolation 1 review of the probability of...

DNV GL Headquarters, Veritasveien 1, P.O.Box 300, 1322 Høvik, Norway. Tel: +47 67 57 99 00. www.dnvgl.com

Memo Øra Final

Memo to: Memo No: 401814 – Rev. 0

Tommy Borgaas – Gasum LNG Production AS

Daniel Brasetvik – Gasum LNG Production AS

From: Marta Bucelli – DNV GL

Date: 2019-06-28

Copied to:

Børre Johan Paaske – DNV GL

Prep. By: Marta Bucelli – DNV GL

Olivier Baldan – DNV GL

UPDATE OF ØRA QRA

The QRA for the LNG terminal at Øraveien has been reviewed and updated. The major modifications to

the original model are represented by:

- Updated failure frequencies for the truck loading hose;

- Updated probability of failure on demand of the ESD system;

- Updated ignition modelling, considering two cases with regards to delayed ignition: one case

(Case A) where ignition is modelled using the UKOOA model and a second case (Case B) where

delayed ignition is set as 1, as for DSB guidelines; and

- Review and update of the impact models for radiation and explosion vulnerability.

The original model that has been updated corresponds to the study of 2018 (Ref. /1/) where the ship

offloading is carried out using a loading arm (Ref. to section 7.3 of Ref. /1/).

This study also includes three sensitivity cases. These cases refer to the updated model with ignition

probabilities set using the UKOOA model (Case A).

The sensitivities investigate how a different isolation philosophy for the terminal can reduce the risk,

especially in the area close to Øraveien. Dedicated modifications to the pipeline from the jetty area to

the LNG tank are considered. Especially, the sensitivity studies consider:

- Sensitivity 1: Additional ESD valve and swan-neck on the pipeline in order to isolate it and reduce

the spilled inventory in case of failure;

- Sensitivity 2: burying of the LNG pipeline in the segment close to Øraveien; and

- Sensitivity 3: Combination of the measures adopted in Sensitivity 1 and Sensitivity 2.

This memo describes the modifications and updates carried out for the cases described above. Risk

contours for every case/sensitivity are presented and discussed.

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Memo Øra Final

1 REVIEWED ASSUMPTIONS FOR ØRA QRA

The model from the 2018 study corresponding to the case with a loading arm for offloading operations

(as described in section 7.3 of Ref. /1/) has been updated. In the following Table 1-1 an overview of the

assumptions from Ref. /1/ is provided as well as the summary of the ones that have been updated.

The assumptions that have been changed are described in the following of this chapter.

Table 1-1 Overview of assumption for the reviewed model of Øra QRA

No. Description Rev. Comment

1 Safety Systems 0 No changes

2 Windrose 0 No changes

3 Meteorological parameters 0 No changes

4 Immediate and delayed ignition

probability

1 The assumption has been renamed.

Update of delayed ignition probability. Description of

ignition values adopted for Case A and Case B of the

study.

5 Surface roughness 0 No changes

6 Location of releases 0 No changes

7 Leak sizes 0 No changes

8 Detection and isolation 1 Review of the probability of failure for the ESD

system

9 Population 0 No changes

10 Impact model – Fire 1 Updated, description of the Probit model for radiation

vulnerability

11 Impact model – Explosion 1 Updated, description of the Probit model for

overpressure vulnerability

12 Traffic 0 No changes

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Memo Øra Final

1.1 Assumption 4 Immediate and delayed ignition probability

Assumption No.: 4 Revision: 1 Date: 2019-05-16

Subject: Immediate and delayed ignition

Category: Analytical assumption

Specifications:

The ignition modelling considers different types of ignition (immediate and delayed) depends on the

leak size.

Immediate ignition is here defined as ignition due to nearby sources that occurs before an

appreciable vapour cloud is produced. Therefore, in case of immediate ignition, no explosion

outcomes are considered. For delayed ignition, there is a lapse of time between the start of the leak

and its ignition.

The ignition probability is based on the UKOOA model (ref. /2/). The values for immediate and

delayed ignition probabilities for every release scenario adopted in this review are the same as for

Assumption 4 (as for Ref. /1/)

This review considers two analyses with regards to delayed ignition, respectively Case A and Case B.

They are described in the following.

- Case A (ignition probability modelled according to UKOOA)

This case is useful from risk management perspective to assess which ignition sources should

be reduced and/or controlled. It also allows to demonstrate the effect of risk reduction

measures that can limit the duration of a leak.

This case considers the immediate and delayed ignition as for Assumption 4 in Rev. 0.

- Case B (unitary delayed ignition)

This case complies with the requirement set in DSB guidelines. (Ref. /3/).

While the immediate ignition is modelled as for the UKOOA model, the delayed ignition for

every release scenario is set equal to 1. This means that every release, if not immediately

ignited, will ignite when its dispersion is at its maximum with a probability of ignition of

100%. This case is required by DSB regulations [Ref. /3/].

Implication of assumption:

The results of the assessment are dependent of the ignition probabilities assumed. If the

assumptions change, the results will be impaired. The change of ignition frequencies impacts directly

the fire probabilities and can lead to alter the type of mitigation measures required.

The immediate ignition probability has a direct influence on the risks associated with jet and pool-fire

risks to personnel and assets. Delayed ignition probabilities have a key influence in determining the

likelihood of flash fire and explosion hazards and the extent of them.

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Memo Øra Final

References for this assumption:

/1/ DNV GL. QRA for Øra LNG Terminal. Report No.: 2018-0017, Rev.0. Document No.: 117U7U8E-1.

2018.

/2/ Energy Institute / UKOOA methodology, OGP Risk Assessment Data Directory, Report No.:434-6.

/3/ Loyds (2017). Retningslinjer for kvantiative risikovurderinger for anlegg som håndterer farlig

stoff. Rapportnr. 106535/R1. Tilgjenglig fra: https://www.dsb.no/rapporter-og-

evalueringer/retningslinjer-for-kvantitative-risikovurderinger-for-anlegg-som-handterer-farlig-stoff/

Prepared by: Marta Bucelli Sign: MARBUC Date: 2019-05-16

Internal Verification: Olivier Baldan Sign: OBAL Date: 2019-05-16

Comment from Gasum:

Approved by Gasum: Sign: Date:

https://www.dsb.no/rapporter-og-evalueringer/retningslinjer-for-kvantitative-risikovurderinger-for-anlegg-som-handterer-farlig-stoff/


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Memo Øra Final

1.2 Assumption 8 Detection and isolation


Subject: ESD failure probability


Specifications:

Given the safety system as described in Assumption 1 of Rev.0 (Ref. /1/), it is assumed that the

Probability of Failure on Demand (PFD) of each ESD system is 10%.

No SIL levels have been required for the plant and therefore this value of PFD is considered

reasonable according to DNV GL judgement.

The analysis assumed that successful shutdown will take place within 90 s (as for Ref. /1/).


Failure on demand of isolation will lead to longer leak/fire durations.


DNV GL expert judgement



Comment from Gasum:


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Memo Øra Final

1.3 Assumption 10 Impact criteria – Fire


Subject: Impact criteria – Fire


Specifications:

The radiation outdoor vulnerability in the proximity of the LNG unit is set using the probit model.

The probit equation for death due to heat radiation is expressed as:

𝑃𝑟 = 𝐴 + 𝐵 ln (𝑄𝑁𝑥 𝑡)

Where 𝑃𝑟 is the probit value corresponding to the probability of death due to fire exposure, 𝑄 is the

heat radiation (W/m2) and 𝑡 is the exposure time (s).

Table 1-2 shows the parameters as set for the radiation probit equation. The probit equation is used

to assess the outdoor vulnerability for fireball, jet-fire and pool-fire scenarios.

Table 1-2 Parameters used for the radiation probit model (outdoor vulnerability)

Parameter Value

A -36.38

B 2.56

N 1.3333

For flash fire scenarios, a fatality rate equal to 1 is assumed within the LFL concentration. The LFL

fraction to finish is set as 100%.


These criteria impact the on the risk results and the number of fatalities of population considered in

the vicinity.


/3/ DSB (2013). Sikkerheten rundt anlegg som håndterer brannfarlige, reaksjonsfarlige, trykksatte og eksplosjonsfarlige stoffer Kriterier for akseptabel risiko. Tilgjengelig fra:

https://www.dsb.no/rapporter-og-evalueringer/sikkerheten-rundt-anlegg-som-handterer-brannfarlige-reaksjonsfarlige-trykksatte-og-eksplosjonsfarlige-stoffer/

/4/ Lloyd’s Register, Retningslinjer for kvantitative risikovurderinger for anlegg som håndterer farlig stoff. Report no.: 106535/R1. 18 October 2017.

/5/ TNO. Guidelines for quantitative risk assessment (Purple Book). 2005.



Comment from Gasum:




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Memo Øra Final

1.4 Assumption 11 Impact criteria – Explosion


Subject: Impact criteria - Explosion


Specifications:

The overpressure and radiation outdoor vulnerability in the proximity of the LNG unit are set using

the probit model.

The probit equation for death due to explosion is expressed as:

𝑃𝑟 = 𝐴 + 𝐵 ln 𝑃𝑁

Where 𝑃𝑟 is the probit value corresponding to the probability of death due to overpressure exposure

and 𝑃 is the peak overpressure (Pa).

Table 1-3 shows the parameters adopted for the probit equation used to assess the outdoor

vulnerability due to explosion.

Table 1-3 Parameters used for the explosion probit equation (outdoor vulnerability)

Parameter Value

A -16.7319

B 2.44

N 1


These criteria impact the on the risk results and the number of fatalities of population considered in

the vicinity.


/3/ DSB (2013). Sikkerheten rundt anlegg som håndterer brannfarlige, reaksjonsfarlige, trykksatte og eksplosjonsfarlige stoffer Kriterier for akseptabel risiko. Tilgjengelig fra: https://www.dsb.no/rapporter-og-evalueringer/sikkerheten-rundt-anlegg-som-handterer-brannfarlige-reaksjonsfarlige-trykksatte-og-eksplosjonsfarlige-stoffer/

/4/ Lloyd’s Register, Retningslinjer for kvantitative risikovurderinger for anlegg som håndterer farlig stoff. Report no.: 106535/R1. 18 October 2017.

/5/ TNO. Guidelines for quantitative risk assessment (Purple Book). 2005.



Comment from Gasum:




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Memo Øra Final

2 REVIEWED RELEASE FREQUENCIES

Table 2-1 summarizes the yearly frequencies for the release scenarios (01-31) considered in the study.

The failure frequency for the loading hose from the truck (cases 18-21) is evaluated using the PHMSA

data (Ref. /7/).

For all the other cases, the failure frequencies are calculated using the RIVM guidelines (Ref. /6/).

Table 2-1 Summary of release frequencies adopted for the scenarios

Case Description Frequency (/year)

1 LNG Hose leak to skimmer basin, ESD success 1.00E-04

2 LNG Hose leak to skimmer basin, ESD failure 1.11E-05

3 LNG Hose Rupture onto dock area, ESD success 1.00E-05

4 LNG Hose Rupture onto dock area, ESD failure 1.11E-06

5 Leak from pipeline between offloading and storage tanks,

during offloading, ESD success 1.19E-04


during offloading, ESD failure 1.68E-06

7 Rupture of pipeline between offloading and storage tanks,

during offloading, ESD success 3.02E-06


during offloading, ESD failure 3.35E-07


outside offloading 2.64E-04


outside offloading 5.28E-05

11 Rupture of pipeline between offloading and storage tanks at

vulnerable corner, outside offloading 1.33E-04

12 Rupture of pipeline between offloading and storage tanks at

vulnerable corner, outside offloading 2.67E-04

13 Small LNG leak from storage tank or piping, ESD success 2.25E-04

14 Large LNG leak from storage tank or piping, ESD success 4.50E-05

15 Small LNG leak from storage tank or piping, ESD failure 1.15E-04

16 Large LNG leak from storage tank or piping, ESD failure 9.50E-06

17 Tank rupture 4.50E-06

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Memo Øra Final

Case Description Frequency (/year)

18 LNG leak during loading of tank vehicle, ESD success 4.97E-04

19 LNG leak during loading of tank vehicle, ESD failure 5.52E-05

20 LNG rupture during loading of tank vehicle, ESD success 1.24E-04

21 LNG rupture during loading of tank vehicle, ESD failure 1.38E-05

22 Instantaneous tank leak while filling 1.74E-06

23 Leakage from parked tank trailer 5.00E-07

24 LNG leakage from inlet piping evaporation system, successful

shutdown 4.90E-03

25 LNG leakage from inlet piping evaporation system, shutdown

failure 5.44E-04

26 LNG rupture from inlet piping evaporation system, successful

shutdown 3.42E-04

27 LNG rupture from inlet piping evaporation system, shutdown

failure 3.80E-05

28 Gas leakage from outlet piping evaporation system, successful

shutdown 4.90E-03

29 Gas leakage from outlet piping evaporation system, shutdown

failure (overfilling of skimmer 5.44E-04

30 Gas rupture from outlet piping evaporation system, successful

shutdown 3.42E-04

31 Gas rupture from outlet piping evaporation system, shutdown

failure (overfilling of skimmer 3.80E-05

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Memo Øra Final

3 REVIEWED RISK CONTOURS

The model has been reviewed and updated according to the assumptions presented in Section 2 of this

memo. Particularly:

- The probability of failure of the ESD system has been set as 10%, according to assumption 8.

- Radiation and overpressure vulnerabilities are assessed using the Probit model, as described in

Assumption 10 and 11.

- Two different cases are considered with regards to delayed ignition probability, as described in

assumption 4 and in the following.

In the following of this chapter, the risk contours for Case A and Case B are presented.

3.1 Case A. Ignition probability modelled according to UKOOA

For Case A, the probability of immediate and delayed ignition for every release scenario is assessed

using the UKOOA model (Ref. /2/).

The risk contours for Case A are presented in Figure 3-1.

Figure 3-1 Risk contours for Øra LNG terminal for Case A - Ignition sources modelled.

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Memo Øra Final

3.2 Case B. Unitary delayed ignition

For Case B, the probability of immediate ignition for every release scenario is assessed using the UKOOA

model while the delayed ignition probability is set as 1, as for DSB guidelines (Ref. /3/).

The risk contours for Case B are presented in Figure 3-2.

Figure 3-2 Risk contours for Øra LNG terminal for Case B - Unitary delayed ignition

3.3 Conclusion and recommendations

DNV GL has updated the QRA for the LNG terminal at Øraveien in accordance with the DSB requirements.

The risk is calculated using the Safeti 8.11 DNV GL’s commercial software. The risk levels are compared

with the DSB acceptance risk criteria.

From the analysis, it has been concluded that:

- The annual risk of 1E-05 covers part of Øraveien and Løytnant Don’s vei, as well as part of the

jetty area. E-05 risk level contour is not confined to the plant boundaries, but it exceeds them;

- The annual risk of 1E-06 does not cover permanent housing, but includes parts of some

neighbour industrial facilities; and

- The annual risk of 1E-07 does not include any vulnerable sensible target, as schools, hospitals or

day care center.

DNV GL recommends looking into possible mitigating measures, in particular to limit the risk contours

towards the roads and the jetty areas.

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Memo Øra Final

The main contributors to the risk towards that area are the crash of cars/truck with the pipeline carrying

liquid/gas LGN from the jetty area to the tank. This risk can be eliminated by burying the pipeline (as

described in Sensitivity 2).

Limiting the amount of LNG released from the pipeline is assessed as another way to reduce the risk

contours. This case is shown in Sensitivity 1.

A total of three sensitivities cases are investigated in the following in order to lower the risk of the

Gasum Øra LNG terminal to acceptable levels.

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Memo Øra Final

4 SENSITIVITY CASES

Three sensitivity cases have been run for the Øra LNG Terminal, as follows:

- Sensitivity 1: Additional ESD valve and Swan-neck on the gas pipeline from the ferry at the jetty

area to the LNG tank;

- Sensitivity 2: burying the segment of the pipeline close to Øraveien; and

- Sensitivity 3: Combination of the measures described in Sensitivity 1 and Sensitivity 2.

Every sensitivity considers as starting model Case A, as described in section 4.1 and in assumption 4.

Sensitivity 3 case is also run with delayed ignition equal to 1.

The three sensitivity studies are described in the following Chapter 5.1.

4.1 Description

4.1.1 Sensitivity 1

Sensitivity 1 considers the introduction of an ESD valve and a swan-neck on the pipeline from the jetty

to the LNG tank. Their effect is to isolate the pipeline in case of release, reducing the amount of spilled

LNG.

The ESD valve is assumed as buried. The failure frequency of the pipeline is therefore not increased from

case A (and B). Figure 4-1 shows the location of the ESD valve and the swan-neck adopted in the study.

The ESD valve and swan-neck divide the pipeline in 3 sections. The study assumes that the ESD valve is

located approximately halfway from the jetty to the tank (pipeline length from the jetty to the ESD valve

420 m). The swan-neck divides the other half of the pipeline in two more segments, approximately 100

m (between the ESD valve and the swan-neck) and 140 m (from the swan-neck to the LNG tank).

Figure 4-1 Overview of Sensitivity 1: location of ESD valve and swan-neck

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Memo Øra Final

Gasum is considering locating the ESD valve further away from the road and closer to the terminal

(effectively extending slightly the length of the first segment of the pipeline from the loading arm and

reducing slightly the length of the second segment between the ESD valve and swan neck) compared to

what is assumed in this study (ESD valve half-way). This is assessed to not have a significant impact on

the risk contours; however, in practice it is beneficial to keep a distance between the ESD valve location

and the road to avoid possible external impacts.

The pipeline from the jetty to the tank is filled with liquid LNG during the offloading operation (once a

week, for 7-hour duration).

The effect of the ESD valve and the swan-neck is to divide the pipeline in 3 isolatable segments when

filled with liquid. In this way, in case of a leak with successful ESD activation, the inventory released will

be lower and the consequence will be reduced.

When the terminal is not offloading, the pipeline is filled with gas (not purged). The study assumes that

the ESD valve can isolate the pipeline when filled with gas in 2 isolatable segments, while the swan-neck

has no effect. T

The overall effect of the modification described in Sensitivity 1 is to reduce the consequences in case of a

release. In the following, the release case 5 (leak from pipeline between offloading and storage tank,

during offloading, ESD success) is used for demonstrative purpose of the effect of the ESD valve and

swan-neck on the released inventories.

Table 4-1 presents the release frequency and the released inventory for case 5 when the pipeline is a

unique isolatable segment from the jetty area to the storage tank.

Table 4-1 Overview of release scenario 5 without ESD valve and Swan-neck at the pipeline

from the jetty area to the tank.

Case Description Frequency (year) Released inventory

5 Leak from pipeline between offloading and

storage tank, during offloading, ESD success 1.19E-04 17390 kg

Table 4-2 shows the release frequencies and the release inventories for each of the three isolatable

segments when the pipeline from the jetty to the tank is split using the ESD valve and the swan-neck.

Table 4-2 Overview of release scenario 5 in sensitivity 1, with ESD valve and swan-neck

Case Description Frequency (year) Released inventory

5-1

Leak from pipeline between offloading and

storage tank, during offloading, ESD success –

before ESD valve

5.94E-05 9015 kg

5-2



after ESD valve, before swan-neck

1.98E-05 3430 kg

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Memo Øra Final

5-3



after swan-neck

3.96E-05 6225 kg

The total failure frequency of the pipeline for the sensitivity case is the same as in Case A (and B).

Anyway, in case a release happens in one of the three isolatable segments, the spilled inventory is much

lower (for case 5-1, for instance is reduced of almost 50%) with consequent impact on the consequences.

4.1.2 Sensitivity 2

In sensitivity 2, the segment of the pipeline from the jetty area to the LNG tank close to Øraveien

(shown in the red rectangle in Figure 4-2) is buried.

Burying that part of the pipeline will prevent the risk of crash from cars/trucks (hazard identified in the

HAZID, Ref. /1/). Therefore, the accident scenario number 11 and 12 (as described in Table 2-1) are not

accounted for this sensitivity case.

Figure 4-2 Overview of Sensitivity 2: buried pipeline

4.1.3 Sensitivity 3

Sensitivity 3 represents a combination of 1 and 2. The ESD valve and swan-neck are introduced on the

pipe in order to isolate it (as in Sensitivity 1) and its closer segment to Øraveien is buried (as in

Sensitivity 2).

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Memo Øra Final

4.2 Risk Contours

4.2.1 Sensitivity 1

Figure 4-3 presents the risk contours for the Sensitivity 1 case.

Figure 4-3 Risk contours for Sensitivity 1

4.2.2 Sensitivity 2

Figure 4-4 presents the risk contours for the Sensitivity 2 case.

Figure 4-4 Risk contours for sensitivity 2.

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Memo Øra Final

4.2.3 Sensitivity 3

Figure 4-5 presents the risk contours for the Sensitivity 3 case. Figure 4-6 shows the risk contours for

the Sensitivity 3 case when delayed ignition is set as 1 for every release scenario.

Figure 4-5 Risk contours for Sensitivity 3

Figure 4-6 Risk contours for Sensitivity 3 with delayed ignition equal to 1 for every release scenario.

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Memo Øra Final

4.3 Conclusion and recommendations

DNV GL has run three sensitivity studies for the Øra LNG terminal. The three cases consider:

- Sensitivity 1: Additional ESD valve and Swan-neck on the gas pipeline from the ferry at the jetty

area to the LNG tank;

- Sensitivity 2: burying the segment of the pipeline close to Øraveien; and

- Sensitivity 3: Combination of the measures described in Sensitivity 1 and Sensitivity 2.

In the following the results are discussed.

The risk contours from the sensitivity 1 case are very similar to the Case A results. The combined effect

of the ESD valve and swan-neck in reducing the amount of LNG spilled from the pipeline in case of

failure is not enough to limit the risk level E-05 to the plant boundaries.

This solution is therefore not considered to be of significance in reducing the risk for the LNG terminal at

Øraveien.

The risk contours for sensitivity 2 (burying pipeline) are reduced. E-05 risk level is limited to the tank

area at the plant. E-06 and E-07 cover part of Øraveien and the jetty area, but no vulnerable areas are

involved. The risk reduction is even more significant for sensitivity 3, where the combination of ESD and

buried pipeline lowers the E-06 risk at Øraveien.

For this last case, a further study is developed, where delayed ignition is set as 1 for every release

scenario. In this case, the E-05 is not limited to the plant area but covers the jetty area and part of

Øraveien. Compared to the Case B (described in sections 4.2), the risk contours are significantly smaller.

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Memo Øra Final

5 REFERENCES

/1/ DNV GL. QRA for Øra LNG Terminal. Report No.: 2018-0017, Rev.0. Document No.: 117U7U8E-

1. 2018.

/2/ Energy Institute / UKOOA methodology, OGP Risk Assessment Data Directory, Report No.:434-

6.

/3/ Loyds (2017). Retningslinjer for kvantiative risikovurderinger for anlegg som håndterer farlig

stoff. Rapportnr. 106535/R1. Tilgjenglig fra: https://www.dsb.no/rapporter-og-

evalueringer/retningslinjer-for-kvantitative-risikovurderinger-for-anlegg-som-handterer-farlig-

stoff/

/4/ Lloyd’s Register, Retningslinjer for kvantitative risikovurderinger for anlegg som håndterer farlig

stoff. Report no.: 106535/R1. 18 October 2017.

/5/ TNO. Guidelines for quantitative risk assessment (Purple Book). 2005

/6/ RIVM. Reference Manual Bevi Risk Assessments, version 3.2. National Institute of Public Health

and Environment (RIVM) in Netherland. 2009.

/7/ DNV GL. Failure frequencies for fuel loading transfer systems. Phase 1: Review of data sources

for transfer leaks. Report No.: 10040979, Rev.1. 2018.




update of Øra qra · 2021. 6. 18. · 8 detection and isolation 1 review of the probability of...

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