lng terminals qra qra report – celsa lng terminal

LNG TERMINALS QRA

QRA report – Celsa LNG terminal Gasum AS

Report No.: 2020-1138, Rev. 2 Document No.: 1021772 Date: 27.05.2021

DNV GL – Report No. 2020-1138, Rev. 2 – www.dnvgl.com Page i

Project name: LNG terminals QRA DNV GL AS Oil & Gas Safety Risk Management P.O. Box 300 1322 Høvik Norway Tel: +47 67 57 99 00 NO 945 748 931 MVA

Report title: QRA report – Celsa LNG terminal Customer: Gasum AS, Kontinentalvegen 36, 4056, Tananger,

Norway Customer contact: Rune Paulsen Date of issue: 26.05.2021 Project No.: 10154156 Organization unit: Field Development & Operations Stavanger Report No.: 2020-1138, Rev. 2 Document No.: 1021772 Applicable contract(s) governing the provision of this Report: Purchase Order 51018024

Objective:

Gasum AS owns and operates the terminals for receiving, storing and distributing LNG (liquefied natural gas) to customers at the industrial facilities of Celsa, in Mo i Rana (Norway). The LNG tank are loaded via trailers and vaporized for customer use at the industrial park.

Prepared by: Verified by: Approved by:

Marta Bucelli Consultant

Jean-Baptiste Berthomieu Senior Consultant

Stephen Town Group Leader

Copyright © DNV GL 2021. All rights reserved. Unless otherwise agreed in writing: (i) This publication or parts thereof may not be copied, reproduced or transmitted in any form, or by any means, whether digitally or otherwise; (ii) The content of this publication shall be kept confidential by the customer; (iii) No third party may rely on its contents; and (iv) DNV GL undertakes no duty of care toward any third party. Reference to part of this publication which may lead to misinterpretation is prohibited. DNV GL and the Horizon Graphic are trademarks of DNV GL AS.

DNV GL Distribution: Keywords: ☐ OPEN. Unrestricted distribution, internal and external. LNG, QRA, DSB, Celsa, Gasum ☐ INTERNAL use only. Internal DNV GL document.☒ CONFIDENTIAL. Distribution within DNV GL according to

applicable contract.*

☐ SECRET. Authorized access only.*Specify distribution: DNV GL

Rev. No. Date Reason for Issue Prepared by Verified by Approved by

0 24.11.2020 Final revision after customer comments Marta Bucelli Snorre Sæternes Stephen Town

B 18.11.2020 Issued for customer comments Marta Bucelli Snorre Sæternes Stephen Town

A 10.11.2020 First issue for customer comments Marta Bucelli Snorre Sæternes Stephen Town

1 25.03.2021 Revision after DSB Comments Marta Bucelli Jean-Baptiste

Berthomieu

Stephen Town

2 27.05.2021 Revision after DSB Comments Marta Bucelli Jean-Baptiste

Berthomieu

Stephen Town

Bucelli, MartaDigitally signed by Bucelli, Marta Date: 2021.05.27 13:13:14 +02'00'

Digitally signed by Town, Stephen Andrew Date: 2021.05.27 13:19:24 +02'00'

Berthomieu, Jean-Baptiste

Digitally signed by Berthomieu, Jean-Baptiste Date: 2021.05.27 13:34:09 +02'00'

DNV GL – Report No. 2020-1138, Rev. 2 – www.dnvgl.com Page ii

Table of contents

1 EXECUTIVE SUMMARY ..................................................................................................... 1

2 INTRODUCTION .............................................................................................................. 2 2.1 Background 2 2.2 Objective and scope 2 2.3 Limitations of the scope 2 2.4 Abbreviations and acronyms 2

3 DESCRIPTION OF THE INSTALLATION ............................................................................... 3 3.1 General 3 3.2 Safety systems 4

4 RISK TERM AND CONCEPTS ............................................................................................. 5 4.1 Risk methodology 5 4.2 Risk tolerance criteria 5

5 HAZARD IDENTIFICATION ............................................................................................... 7 5.1 Hazard identification 7 5.2 Hazards related to LNG 7

6 FREQUENCY ASSESSMENT ............................................................................................. 10

7 RISK RESULTS ............................................................................................................... 1 7.1 Risk results for Case A 1 7.2 Risk results for Case B 3 7.3 Main contributors to the risk 3

8 CONSEQUENCE ASSESSMENT .......................................................................................... 6

9 UNCERTAINTY ................................................................................................................ 9 9.1 Leak frequencies and representative hole sizes 9 9.2 Ignition probability 9 9.3 Safeti 8.23 9 9.4 Weather data 10 9.5 Exposure time to flammable events 10

10 CONCLUSION AND RECOMMENDATIONS ......................................................................... 14

11 REFERENCES ................................................................................................................ 15

Appendix A Assumptions Register Appendix B HAZID

DNV GL – Report No. 2020-1138, Rev. 2 – www.dnvgl.com Page 1

1 EXECUTIVE SUMMARY DNV GL was requested to perform a Quantitative Risk Analysis (QRA) of the LNG terminal at Celsa (Mo i Rana) and to then compare the results against the acceptance criteria from the Direktoratet for Samfunnssikkerhet og Beredskap (DSB).

The risk related to the operation and loading of the LNG unit at Celsa has been assessed using the latest issue of the DNV GL commercial software Safeti (version 8.23).

The analysis considers 2 different cases, namely case A and case B. The difference consists in the ignition modelling. Case A considers the real ignition sources surrounding the LNG tank in estimating the delayed ignition probability associated to a release scenario. For case B, the delayed ignition probability is set equal to 1 for each release scenario.

Risk acceptance is evaluated considering base case B as per DSB criteria.

The risk is assessed for the inner, middle and outer zones against DSB criteria, as follows:

- Inner zone (1E-05 /average year)

The annual risk of 1E-05 /average year covers the terminal area, stretching towards the road usedby the trucks to collect the hot billets at the storage depot.

It is assessed that only short-term passage for 3rd party is included in this risk level area.

- Middle zone (1E-06 /average year)

The annual risk of 1E-06 /average year extends to a wider area around the terminal. It covers partlythe two roads west and east of the LNG terminal.

No accommodation or permanent housing is included in the middle zone as per the currentassessment.

- Outer zone (1E-07 /average year)

The annual risk of 1E-07 /average year extends to a wider area, covering partially Stålløypa road onthe west of the LNG terminal. These contours cover the entrance of the billets storage building andthe area towards the fish farm offices. Anyway, it does not cover sensitive areas such as schools,hospitals, day care centres or large public arenas.

In order to avoid exposition to the risk of 3rd party population, it is recommended to evaluate the possibility to temporarily fence the entrance to the LNG tank area in case of an ongoing incident. As, the roads leading to the LNG tank and the the road Stålløypa can lead to exposure of 3rd party population. Such mitigating measure should be considered as part of the emergency response plan in order to avoid 3rd party population exposure to the risk.


2 INTRODUCTION

2.1 Background Gasum AS (Gasum) owns and operates the LNG terminal at the Celsa industrial facility in Mo i Rana, Norway. The LNG tank receives periodically liquid LNG from a trailer truck tank. The LNG is stored and vaporized using water/glycol heat exchangers for client use at the industrial park.

This study presents the quantitative assessment of the risk due to the LNG tank storage operations at Celsa LNG facility.

2.2 Objective and scope The objective of this analysis is to evaluate the risk according to DSB regulations and to assess it against the acceptance criteria. The necessity of whether additional safety measures are needed is also assessed.

The scopes of the quantitative risk analysis carried out for the Celsa LNG terminal are:

• Hazard identification;

• Evaluation of likelihood and consequences of hazardous events; and

• Risk evaluation and assessment. The scope is to assess whether the risk is acceptable form a safetypoint of view during the operational phase and to propose risk reducing measure when/if necessary.

2.3 Limitations of the scope The scope of this risk assessment is limited to the operational phase.

2.4 Abbreviations and acronyms DSB Direktoratet for Samfunnssikkerhet og Beredskap

HAZID Hazard Identification

LNG Liquefied Natural Gas

NG Natural Gas

PBU Pressure Build-up Unit

PFD Probability of failure on demand

QRA Quantitative Risk Assessment


3 DESCRIPTION OF THE INSTALLATION

3.1 General The Celsa facility shown in Figure 3.1 is located at Mo i Rana, in Northern Norway. Gasum owns the LNG terminal located at the industry park.

Figure 3.1 Celsa LNG terminal – Area overview

The tank is designed to receive LNG from a trailer approximately three times every two days, as described in assumption O-01 Operational Phases in Appendix A. The terminal stores LNG and vaporizes it using water/glycol heat exchanger for use at the industrial park.

The main equipment included in the analysis is:

• LNG tank (capacity 300 m3);

• Water/glycol LNG vaporizers (2, E-01A/B); and

• Gas line (above ground) to the industry park.


Detailed information about process conditions are provided in Appendix A (see Assumption T-01 ESD segments at the LNG terminal).

Figure 3.2 shows the flow diagram for the LNG terminal at Celsa.

Figure 3.2 Flow diagram of the LNG terminal at Celsa

3.2 Safety systems 3.2.1 ESD system The ESD system can be triggered automatically by the gas and fire detection system (see chapter 3.2.2) or by the operator using local push buttons.

A push button is available at the loading area, near the inlet piping where the driver of the trailer connects the hose for the tank filling. It is assumed that in case of release from the loading hose, the driver will be the first one to detect it and initiate ESD.

3 additional push buttons are available for the driver on both side of the trailer near the hose and at the trailer door (when open) at the driver cabinet on the trailer. During loading, in case of necessity, the driver needs to push manually one of the ESD buttons (if the ESD system has not already automatically been initiated by the detectors) and stop the pump on the truck. The ESD at the trailer is connected with an ESD-link to the LNG terminal ESD.

All the automatic valves at the terminal will close upon activation of the ESD. These are shown in the yellow boxes in Assumption T-01.

3.2.2 Detection system The LNG terminal is provided with 4 gas detectors at the inlet piping to the tank and at the evaporators. The gas detectors shut down the terminal upon confirmed gas detection. LNG leak detectors at low point are placed at the LNG tank. They operate with 1 out of 1 logic and the ESD is activated upon confirmed gas detection by one of the detectors at the installation.


4 RISK TERM AND CONCEPTS

4.1 Risk methodology The assessment has been carried out following the QRA guidelines recently published by DSB [Ref./3/]. The approach goes through 4 phases:

• Hazard identification,

• Frequency assessment,

• Consequences assessment;

• and risk assessment and evaluation of mitigating measures.

4.2 Risk tolerance criteria The DSB safety criteria [Ref. /2/ and /3/ are applied to assess whether or not the risk levels arising from the operation of the LNG terminal are acceptable, and whether or not any additional safeguards are required to reduce the risk levels to as low as reasonably practicable.

DSB’s criteria are summarized in Table 4-1 and Figure 4.1.

Table 4-1 Summary of DSB risk tolerance criteria

Hazardous zones Individual Risk Description

Inner zone 1E-05 per year This is basically the business's own area. In addition, for example,

LNF area (Landbruks-, natur- og friluftsområder) can be included

in the inner zone. Only short-term passage for third parties.

Middle zone 1E-06 per year Public road, rail, dock and similar. Permanent industry and office

can also be found here. In this zone, there should not be

accommodation or housing. Scattered housing can be accepted in

some cases.

Outer zone 1E-07 per year Areas regulated for residential purposes and other uses of the

general population can be included in the outer zone, including

shops and smaller accommodations.

Outside Outer Zone Not defined Schools, kindergarten, nursing homes, hospitals and similar

institutions, shopping centres, hotels or large public arenas must

normally be placed outside the outer zone.


Figure 4.1 DSB criteria for hazardous zones.


5 HAZARD IDENTIFICATION

5.1 Hazard identification The hazard identification has been carried out during the HAZID workshop, held online through TEAMS videoconference on October 1st, 2020.

The following scenarios have been identified during the workshop:

• Loss of containment from the equipment (valves and piping) at the tank area;

• Loss of containment from the hose at the tank area; and

• Loss of containment from the LNG trailer.

The segments at the LNG unit are pressurized and filled with LNG or Natural Gas (NG) all the time (except the loading hose (segment 2)).

Therefore, the loss of containment from any equipment connected to the tank or other equipment is assessed as a credible scenario.

5.2 Hazards related to LNG Due to its properties, LNG may result in different type of consequence, how it is spilled and whether it exposes personnel or materials. This paragraph describes what can happen if LNG is released in the atmosphere and the possible resulting effects.

If a small quantity of LNG is released in the atmosphere, it will evaporate. With a large quantity of LNG, insufficient heat can be transferred so that a pool may form, which will then evaporate. Depending on the size of the outflow and the local conditions (e.g. presence of ignition sources), the following effects may occur:

• Fire and explosion;

• Rapid Phase Transition;

• Cryogenic exposure;

• Suffocation; and

• Greenhouse gas effects.

5.2.1 Fire and explosion 5.2.1.1 Flash fire A flash fire is a non-explosive combustion of a flammable vapour cloud. In general, a flash fire occurs when a vapour cloud encounters a source of ignition (such as a naked flame, combustion engine, sparks etc.). This is in the case of delayed ignition. The vapour cloud is often ignited on the edge (where the concentration is lower), after which the fire spreads to all the flammable mass and then continues burning up to the UFL until all the mass is gone. Different flame fronts can exist, which might propagate back to the LNG pool (if any), resulting in a pool fire.


This hazard is included in the analysis.

5.2.1.2 Jet fire A jet fire usually occurs in the event when LNG is immediately ignited when it is released in a continuous stream (i.e. immediate ignition, no puddle or vapour cloud is initially formed). However, residual jet fires are also possible in case of delayed ignition of a flammable cloud where the flame front travels all the way back to the source of the release.


5.2.1.3 Pool fire A pool fire occurs when a pool of LNG (which occurs with large releases) is ignited or when the flammable vapour cloud is ignited above the pool. In the latter case, the flash fire will ignite the pool. LNG pool fires cause a significant amount of thermal radiation (due to the luminous flame), which decreases as function of distance from the pool fire.


5.2.1.4 Semi-confined and confined vapour cloud explosions A vapour cloud explosion can occur when a large quantity of gas is ignited (delayed) in a confined or semi-confined space (e.g. congested area).


5.2.2 Rapid Phase Transition (RPT) This is an extremely rapid physical phase transition resulting from the temperature difference from liquid LNG to methane vapour, especially as a consequence of immersion in water. There is no combustion with RPT. The pressure wave that is created by small quantities of LNG vaporising instantaneously when overheating occurs due to mixing with water, will propagate with the speed of sound and deteriorate like any other pressure pulse. Usually no specific modelling is carried out for RPT, because it is improbable that the effects of RPT make a significant contribution to the total danger area of a large leak that has already taken place.

RPT is usually relevant for leaks over water and therefore is not considered in the analysis.

5.2.3 Cryogenic exposure If LNG is stored under atmospheric conditions, the temperature will be -162 °C. Due to the cryogenic conditions, there is a danger of frostbite symptoms on exposure to persons, structural materials (steel), components, instrumentation and cabling because of the low temperature.

Exposure of persons causes frost burn. Exposure of carbon steel causes brittleness which can result in structural failure.

The analysis does not cover cryogenic risk as it is considered to have negligible contribution to 3rd party risk.

5.2.4 Suffocation LNG is not carcinogenic or toxic. LNG and the resulting vapour clouds have a suffocating effect because air is rarefied or expelled which in the case of long-term exposure can result in death by suffocation. Considering


that the pure gas is colourless and odourless, this must be taken account of primarily in confined spaces. For large releases, persons in the immediate vicinity may suffer from low oxygen concentrations (<6 vol%). Concentrations of 50% by volume (methane in air) will cause obvious suffocation symptoms like difficulties in breathing and rapid breathing at the same time as the ability to respond deteriorates and muscle coordination weakens.

Suffocation is not assessed in the analysis as the area is open.

5.2.5 Greenhouse effects Unburned natural gas is a greenhouse gas and if LNG is released, it contributes to global warming and climate change.

The analysis does not cover greenhouse effect as it is an environmental hazard.


6 FREQUENCY ASSESSMENT An overview of the estimated leak frequencies per ESD-segment, leak category and release phase is provided in Table 6-1 and Figure 6.1. Figure 6.2 represents the contribution to the total release frequency per leak size.

The total leak frequency of the LNG terminal is calculated as 1.38E-02 /year.

The main contributors to the leak frequency are, in contributing order:

• Segment 04 - LNG Tank, 40% of total release frequency. Liquid releases contribute for circa 25% to the total release frequency from the tank;

• Segment 06 - Evaporator, 40% of total release frequency. Gas releases contribute for 31% to the total release frequency from the evaporators;

• Segment 03 - Inlet piping, circa 9.5%; and

• Segment 05 - Piping to evaporators, circa 9%.

The frequency presented in Table 6-1 for the loading hose (Segment 02) includes also releases from the trailer. Anyway, this contributes for about 1% to the total release frequency at the LNG terminal.

Small releases are the main contributors to the release frequency at the LNG terminal. They contribute to 83% of the total. Medium releases contribute for 9% while the large ones for 8%.

Table 6-1 Leak frequency per ESD-segment, leak category and release phase for Celsa LNG terminal

ID Name Phase Small Medium Large Total Contribution (%)

2 Loading hose (*) Liquid 1.44E-04 N/A 3.60E-05 1.80E-04 1.3%

3 Inlet pipe to the tank Liquid 1.11E-03 1.09E-04 7.02E-05 1.28E-03 9.3%

4 LNG Tank Liquid 2.93E-03 2.90E-04 1.98E-04 3.41E-03 24.8% Gas 1.80E-03 2.00E-04 1.35E-04 2.13E-03 15.5%

5 Piping to evaporators Liquid 1.08E-03 9.19E-05 7.80E-05 1.25E-03 9.1%

6 Evaporators Liquid 8.87E-04 1.25E-04 1.84E-04 1.20E-03 8.7% Gas 3.54E-03 3.76E-04 3.81E-04 4.30E-03 31.3%

Total 1.15E-02 1.19E-03 1.08E-03 1.38E-02 100% * Note. The failure frequency presented in table for the loading hose (Segment 2) is calculated using the PHMSA database.

This includes releases from the trailer as well.


Figure 6.1 Leak frequency contribution per ESD-segment and release size for Celsa LNG terminal


Figure 6.2 Contribution per leak size


7 RISK RESULTS Two cases (Case A and Case B) have been considered for the risk assessment at Celsa LNG terminal, differing for the ignition modelling.

• Case A considers the ignition sources in the area around the LNG tank allowing the calculations of the delayed ignition probability associated to the release scenarios.

• Case B assigns to each release scenario a delayed ignition probability of 1.

The specifications for Case A and B with regards to ignition modelling and ignition sources considered in the area are described in Appendix A, particularly in:

• A-09 Immediate and delayed ignition;

• A-13 Ignition sources: traffic;

• A-14 Ignition sources: other;

• O-02 Manning at the LNG terminal; and

• O-03 3rd party population.

After inquiry from DSB (ref. /4/), the effect of the exposure time to flammable events on the calculated risk has been investigated. DNV acknowledges the fact that DSB guidelines recommend to considering the whole duration of the different events (until heat load below 1.5 kW/m2) when applying the probit function to assess the possible fatalities. The DSB recommendations have been applied within the Safeti software to calculate the iso-risk contours for longer fire duration than 20 s. The software has its own limitations that do not allow the user to extend the exposure time above a duration of 100 seconds, to avoid effect from very low radiation levels.

In the following of chapter 7.1 and 7.2 the risk results for Case A and B are presented for an exposure time to flammable events of 100 seconds, respectively. Impact of this parameter is further discussed in section 9.5.

7.1 Risk results for Case A Figure 7.1 shows the location specific individual risk in the form of iso-risk contours corresponding to the frequency (/average year) at which a fatality can be expected should somebody be present continuously at a particular location.

The risk level of 1E-05 /average year covers the area of the LNG terminal (purple contour), and partially the nearby road where the trailers transporting the billets drive.

1E-06 /average year (red contour) covers the area around the terminal, similarly to the previous risk level.

The risk level of 1E-07 /average year (yellow contour) includes a larger area around the LNG terminal at Celsa, and partially covers partially Stålløypa road west to the terminal.


Figure 7.1 Iso-risk contour for the LNG terminal at Celsa for Case A. 100 s exposure time to flammable events.


7.2 Risk results for Case B Figure 7.2 shows the location specific individual risk in the form of iso-risk contours corresponding to the frequency ( /average year) at which a fatality can be expected should somebody be present continuously at a particular location.

In Case B, every release, if not ignited immediately, has time to spread in the area to its maximum before results in a fire or/and an explosion.

As a result, the risk level 1E-05 /average year (purple contour) extends to a bigger area at the industrial park. It covers partially the nearby roads where the trailers transporting the billets drive.

1E-06 /average year (red contour) covers a wider area as well, which is similar as the risk level of 1E-05 /average year.

1E-07 /average tear (yellow contour) extends to a wider area, covering partially Stålløypa road on the west of the LNG terminal. These contours cover the entrance of the billets storage building and the area towards the fish farm. No particularly sensitive population groups (such as hospital or kindergarten) are included in the 1E-07 /average year risk contour.

The iso-risk contours shown in Figure 7.2 represent the case for 100 s exposure time to flammable events.

Figure 7.2 Iso-risk contour for the LNG terminal at Celsa for Case B. Maximum exposure duration 100 s.

7.3 Main contributors to the risk Risk ranking points (RRPs) are introduced in the model as shown by the blue dots in Figure 7.3. RRPs represent locations where the risk is measured in detail. They are used to assess the scenarios that have the major contribution to the risk and to assess the type of outcome (fire, explosion) that can develop in a specific location.


Figure 7.3 Risk Ranking Points for Celsa LNG terminal QRA study for Case B with 100 s exposure time.

RRP A is covered in 1E-05/ average year and 1E-06 /average year contour contours (see Figure 7.2 ). The calculated risk at RRP A is 2.29E-04 /average year. Table 7-1 lists the release scenarios from segments that give the main contribution to the risk at RRP A for Case B. The releases scenarios not listed in the table give a contribution to the risk of 2% or lower.

Large liquid release scenarios from the tank and evaporators are the main contributors to 1E-05 /average year risk level. They contribute in total for circa 70% of the total risk. These scenarios have the more serious consequences and the highest release frequency (as shown in Table 6-1).

Table 7-1 Main contributors to 1E-05 /average year risk (RRP A) for case B

ID Segment no - Name Release phase

Release size

ESD % Risk Total risk

(/avge year)

1-A 04 – LNG tank Liquid Medium Yes 53.8 1.23E-04

2-A 04 - LNG tank Liquid Large Yes 36.8 8.44E-05

3-A 05 – Piping to evaporators Liquid Large Yes 4.9 1.13E-05

4-A 06- Evaporator Liquid Large Yes 2.4 5.41E-06

5-A 05 – Piping to evaporators Liquid Large Yes 2.6 5.64E-07

RRP B is covered in the 1E-05/ average year and 1E-06 /average year contour (see Figure 7.2). The calculated risk at RRP B is 4.93E-06 /average year. Table 7-2 lists the release scenarios from segments that


give the main contribution to the risk at RRP B for Case B. The releases scenarios from segments not listed in the table give a contribution to the risk of 2% or lower.

Table 7-2 Main contributors to 1E-06 /average year risk (RRP B) for case B


Release size


(/avge year)

1-B 04 – LNG tank Liquid Medium Yes 56.7 3.28E-05

2-B 04 - LNG tank Liquid Large Yes 39.7 2.30E-05

3-B 06- Evaporator Liquid Large Yes 1.8 1.02E-06

RRP C is covered in the 1E-07 /average year contour (see ). The calculated risk at RRP C is 2.11E-07 /average year. Table 7-3 lists the release scenarios that give the main contribution to the risk at RRP C for Case B. The releases scenarios not listed in the table give a contribution to the risk of 2% or lower.

Table 7-3 Main contributors to 1E-07 /average year risk (RRP C) for case B


Release size


(/avge year)

1-C 04 - LNG tank Liquid Large Yes 99.0 2.10E-07

2-C 04 - LNG tank Liquid Large No 1.0 2.11E-09

The contribution of each consequence scenario from the main segments listed above are presented in detail in Appendix C.


8 CONSEQUENCE ASSESSMENT In the case B (delayed ignition set as 1) the main contributors to the risk are flash fires, pool fires and jet fires with resulting pool fires.

A total of 5 scenarios have been identified to be the main contributors to the risk, as described in chapter 7.3. These are summarized as:

• Liquid Large releases from the LNG tank;

• Liquid Medium releases from the LNG tank;

• Liquid large releases from the evaporators;

• Liquid large releases from the piping connection the LNG tank to the evaporators;

• Hose rupture.

The main consequence of a rupture from the LNG tank, the hose and the piping to the evaporators is a continuous release with rainout and delayed flash fire with explosion with additional effects from pool fire. Immediate horizontal jet fire with additional pool fire effects is another consequence of these continuous releases with rainout, but it contributes significantly less to the risk.

From the evaporators instead, the continuous releases do not result in rainout (and therefore in pool fire) but the main consequence is flash fire with explosion effects.

Figure 8.1 shows the dispersion characteristics for large liquid releases from the tank (segment 04). Figure 8.2 shows the flash fire, jet fire and pool fire characteristics for the same release scenario.

100% LFL from releases from the tank includes an area within circa 45 m distance. Releases from the evaporators have similar dispersion characteristics, with the difference that the highest concentrations of gas are generally closer to the release point than for the tank case. In fact, the inventory in the evaporator is limited if compared with the tank and the release is not able to sustain itself for long time in case of successful ESD.


Figure 8.1 Dispersion characteristics for large release from the tank. Panel A: Max footprint. Panel B: Side view of the cloud (at its maximum spread). Reference to 100% LFL.


Figure 8.2 Flash fire, jet fire and pool fire characteristics for large liquid release from the tank. Panel A: Flash fire envelope. Panel B: Intensity radius for jet fire. Panel C: Intensity radius for

Pool fire. Reference to 100% LFL.


9 UNCERTAINTY

9.1 Leak frequencies and representative hole sizes The leak frequency and the hole size category distribution represent the foundation of risk analysis, and the risk is directly proportional to leak frequency.

Uncertainties are related to both the total leak frequency and the categorization between small, medium and large leaks. The effect on risk level from total leak frequency is however considered to be subordinate to the effect of distribution between leak sizes. Furthermore, the leak frequency model used for equipment and piping is based on an offshore method and therefore it might not describe satisfactorily the equipment onshore. In any case, the use of offshore data is assessed to be conservative.

The parts count that is applied for the frequency estimation is based on provided P&IDs and therefore it is considered a robust estimate of the number of equipment at the plant. The uncertainties lie in the use of generic leak data and in neglecting the technical condition of the equipment on the plant during the estimation of the frequency.

9.2 Ignition probability The results from the risk analysis are highly dependent on the ignition probabilities. The ignition probability affects the fire frequency and, hence the risk. Recognized ignition probability models are used as basis for the risk modelling. These models are uncertain due to the limited statistical data connected to ignited HC releases and the unknowns related to the actual mechanism causing them. Therefore, although the choice of recognized models, the analysis suffers some degree of uncertainty connected to the ignition probabilities.

However, this uncertainty is addressed by presenting the results of Case B which uses the conservative approach recommended by DSB Guideline (Ref. /1/) with a delayed ignition probability of 1.

9.3 Safeti 8.23 The risk is calculated in Safeti 8.23 using the impact models incorporated in PHAST 8.23. Each consequence model has its limitations and strives to describe the reality as best as possible with regards to some conservatism to handle the uncertainties in modelling.

The main limitation of the impact models (such as dispersion, jet fires, pool fire, explosion) in PHAST is that it does not accurately take into account physical obstacles or barriers that can 'block' fire effects or prevent the spread of a flammable cloud.

A physical obstacle such as a wall, influences also the incoming wind, generating increased turbulence. This effect cannot accurately be modelled in Safeti and is only considered in a limited manner by modifying the roughness of the surface.

Possible vortexes or recycling of gas dispersion in the area are also not considered. It is expected that this will result in more dilution if considered, resulting in smaller gas clouds with lower distances to LFL.


9.4 Weather data The windrose and weather conditions used in this assessment are based on data from the Meteorological Institute and is considered to be robust. The weather station used in the analysis is the one from Mo i Rana airport, which is relatively close to Mo i Rana industrial park.

9.5 Exposure time to flammable events It has been agreed with DSB that the only applicable risk results are for 100 seconds exposure time to flammable events.

Therefore, any decisions regarding implementation of mitigating measures and the operation of the installation must be based on the risk results with a maximum exposure time of 100 seconds as considered.

However this parameter has been assessed to have an impact on the risk results. Indeed, if the default exposure time of 20 seconds is applied in the calculations, the risk contours become as presented in the figures below.

It is observed that the 1E-05 and 1E-06 / yr risk contours are almost merged and cover bigger areas than when the maximum time allowed for exposition to flammable events is only 20 seconds (cf. section 9.5). However, the 1E-07/yr risk contour do not seem to be affected by the change of this specific parameter. This is explained by the facts that the extent of the 1E-05 and 1E-06/yr are mostly driven by short to medium duration events that are longer than 20 seconds. Their radiation levels do not lead to fatalities at 20 seconds exposure times but they do when the exposure time is increased to 100 seconds. It should be noted that the 1E-05 /yr risk contour for 100 s exposure time is limited to the Celsa area and does not cover public roads but partly the Celsa building nearby (that could be considered as 2nd party). As an example, 100s of exposure to app. 5-6 kW corresponds to a 50% probability of fatality, ref. /3/.

While the 1E-07/yr risk contour is mostly due to large/long duration events such as large release from tank with failure of ESD system, where in theory the duration could last longer than 3600 seconds. These events have the particularity to end in flammable events that lead to immediate fatalities such as flash fire, have flammable outcomes that will lead to fatalities within 20 seconds duration such as jet fires. Thus, changing the exposure time will not change the number of fatalities when applying the probit function.


Figure 9.1 Iso-risk contour for the LNG terminal at Celsa for Case A. 20 s exposure.


Figure 9.2 Iso-risk contour for the LNG terminal at Celsa for Case B. Maximum exposure duration 20 s.

Figure 9.3 represents the probability of death for the Purple Book probit function as a function of exposure time (for 20, 15, 10 and 5 seconds exposure times) and a protection factor of 1.


Figure 9.3 Probability of death for the Purple Book probit function as a function of exposure time (for 20, 15, 10 and 5 seconds exposure times) and a protection factor of 1.

Increasing the exposure time leads to higher probability of death when exposed to the same radiation levels. So, in theory, increasing the “allowed” exposure time of individual in the QRA could lead to higher number of fatality for low/medium radiation level (15-25 kW/m2) as individuals will be exposed longer. As the risk contours extent reflect the individual risk to become a fatality, it would be expected that the reach of the different risk contours will then increase.


10 CONCLUSION AND RECOMMENDATIONS DNV GL was requested to perform a Quantitative Risk Analysis (QRA) of the LNG terminal at Celsa (Mo i Rana) and to then compare the results against the acceptance criteria from the Direktoratet for Samfunnssikkerhet og Beredskap (DSB).

The risk related to the operation and loading of the LNG unit at Celsa has been assessed using the latest issue of the DNV GL commercial software Safeti (version 8.23).

The analysis considers 2 different cases, namely case A and case B. The difference consists in the ignition modelling. Case A considers the real ignition sources surrounding the LNG tank in estimating the delayed ignition probability associated to a release scenario. For case B, the delayed ignition probability is set equal to 1 for each release scenario.

Risk acceptance is evaluated considering base case B as per DSB criteria.

The risk is assessed for the inner, middle and outer zones against DSB criteria, as follows:

- Inner zone (1E-05 /average year)

The annual risk of 1E-05 /average year covers the terminal area, stretching towards the road used by the trucks to collect the hot billets at the storage depot. It is assessed that only short-term passage for 3rd party is included in this risk level area.

- Middle zone (1E-06 /average year)

The annual risk of 1E-06 /average year extends to a wider area around the terminal. It covers partly the two roads west and east of the LNG terminal.

No accommodation or permanent housing is included in the middle zone as per the current assessment.

- Outer zone (1E-07 /average year)

The annual risk of 1E-07 /average year extends to a wider area, covering partially Stålløypa road on the west of the LNG terminal. These contours cover the entrance of the billets storage building and the area towards the fish farm offices. Anyway, it does not cover sensitive areas such as schools, hospitals, day care centres or large public arenas.

In the event of an incident, measures for closing the entrance to the industrial area, and specifically the passage on Stålløypa and the road around the terminal, should be considered as part of the emergency response plan in order to avoid 3rd party population exposure to the inner zone risk level (1E-05 /average year). People accessing the area nearby the LNG terminal shall receive special training and use personal protection equipment, including gas metering equipment to detect small gas release and initiate emergency procedures.


11 REFERENCES /1/ DSB (2011). Temaveiledning om omtapping av farlig stoff. Tilgjengelig fra:

https://www.dsb.no/lover/farlige-stoffer/veiledning-til-forskrift/temaveiledning-om-omtapping-av-farlig-stoff/#forebyggende-sikkerhetstiltak--15---krav-til-installasjoner2

/2/ 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/

/3/ DSB (2017) Retningslinjer for kvantitative risikovurderinger for anlegg som håndterer farlig stoff. Rapportnr. : 106535/R1 Rev.: Sluttrapport A, 18 oktober 2017

/4/ Email from Celin Tonheim (DSB) on 11.05.2021 inquiring the exposure time used to calculate fatalities at Celsa terminal.

DNV GL – Report No. 2020-1138, Rev. 2 – www.dnvgl.com A-1

APPENDIX A Assumptions Register

DNV GL – Report No. 2020-1138, Rev. 2 – www.dnvgl.com B-1

APPENDIX B HAZID Log

APPENDIX C Details main contributors to the risk at the RRP A,B and C

About DNV GL DNV GL is a global quality assurance and risk management company. Driven by our purpose of safeguarding life, property and the environment, we enable our customers to advance the safety and sustainability of their business. We provide classification, technical assurance, software and independent expert advisory services to the maritime, oil & gas, power and renewables industries. We also provide certification, supply chain and data management services to customers across a wide range of industries. Operating in more than 100 countries, our experts are dedicated to helping customers make the world safer, smarter and greener.

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