Nov 12 - Health & Safety Laboratory's Current Report For Gibraltar LNG Storage Facility

The Health and Safety Laboratory (HSL) has applied the GB Health and Safety Executive (HSE) methodology that is used to provide statutory advice on whether to grant hazardous substances consent to a proposal from Shell to build a liquefied natural gas (LNG) storage facility for the new power station in Gibraltar.

The methodology produces ‘Three-zone maps’ (3ZMs) that are the basis for advice, i.e. either “advise against” or “do not advise against”. The methodology was applied to two options for the design of the bund surrounding the storage tanks: option 1 had a single bund around all five storage tanks and option 2 a subdivided bund.

The result for both options is “do not advise against”. For Shell’s option 1, a planning condition would be required that Shell designs the proposed barrier wall to protect the road and cruise terminal from fire scenarios.

Shell will need to apply for hazardous substances consent and 3ZM should then be further assessed and confirmed by HSL, taking account of any further design features.

Any increase in LNG storage capacity or LNG delivery frequency to support bunkering would need reconsideration.

The LNG storage facility for the new power station will qualify as an upper tier site under the European Seveso III directive and will require safety reports to be submitted and assessed at pre-construction and pre-operation stages.

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1 INTRODUCTION 1.1 BACKGROUND

The Government of Gibraltar was considering proposals prior to awarding a contract to build a storage facility for liquefied natural gas (LNG) to fuel the new power station. The Gibraltar Environmental Agency employed the Health and Safety Laboratory (HSL) to provide advice on safety relating to major accident hazards. HSL is part of the Health and Safety Executive (HSE) and within Great Britain (GB), HSE provides such advice to Local Planning Authorities as well as being part of the GB Competent Authority (CA) under the European Seveso III Directive on the control of major accident hazards (together with the local environmental agency). In GB, the Seveso III Directive is implemented via the combination of:

•   The Control of Major Accident Hazards Regulations (COMAH 2015); and

•   Planning (Hazardous Substances) Regulations, 2015 (PHSR).

  Under PHSR, the new LNG storage facility would be a “hazardous installation”. Within GB, HSE provides statutory advice to Hazardous Substances Authorities (HSAs), usually part of Local Planning Authorities, on whether to grant hazardous substances consent to proposed hazardous installations. Hazardous substances consent is an important mechanism in the overall control of major hazards as it enables the HSA to consider whether the presence of a significant quantity of a hazardous substance is acceptable in a particular location. HSE also provides statutory advice to Local Planning Authorities on whether to allow further developments in the vicinity of a hazardous installation. In any of these cases, HSE either advises against or does not advise against the proposal.

  Under COMAH 2015, the new LNG storage facility would qualify as an upper tier COMAH site. Briefly, the requirements include having a major accident prevention policy (MAPP), a safety management system to implement it, an internal (on-site) emergency plan, and preparation of a safety report that demonstrates that “all measures necessary” are in place to prevent and control major accident hazards. Requirements on the CA include assessing the safety report and regularly inspecting the installation. The local Emergency Planning Authority is required to produce an external (off-site) emergency plan.

  Requirements before the new LNG storage facility can be brought into operation include:

1.2

Granting of hazardous substances consent;
Assessment of a pre-construction COMAH safety report; and Assessment of a pre-operation COMAH safety report.

OBJECTIVE

The Gibraltar Environmental Agency asked HSL for advice on whether proposals for the new LNG storage facility would meet the requirements for a “do not advise against” outcome, using HSE’s methodology. This was at a pre-consents stage because hazardous substances consent would only be applied for by the successful bidder once the contract had been awarded.

This report outlines the methodology used and its application to the winning bid from Shell.

2 METHODOLOGY

The HSE assessment involves conducting a risk assessment using a defined methodology and criteria. The methodology uses a “cautious best estimate” approach.. HSE conducts all of the required risk assessments in order that they are both independent and consistent, for example when applied to competing proposals. The outcome of the methodology is a “three zone map” (3ZM) whose three contours are calculated by combining the hazards and risks of a range of different very unlikely but high consequence failures specific to each development.

‘Three-zone maps’ (3ZMs) are a key input to the process whereby HSE provides hazardous substances consent and land-use planning advice to local authorities in GB. The relevance of the 3ZM is described in HSE’s land-use planning methodology (PADHI) [1]. For new proposed developments within the zones of a 3ZM for an existing hazardous installation, PADHI indicates whether HSE would advise against or not advise against the development. For example:

•   Developments within the inner (red) zone are largely limited to other industrial developments;

•   Within the middle (blue) zone, residential developments are limited in terms of both number of housing units and housing density;

•   Within the outer (green) zone, large institutional developments such as hospitals and schools are excluded;;

•   Outside the outer zone, no type or size of development would be advised against.
  Table 1 provides a further summary of advice for new developments in the vicinity of a

  hazardous installation, based on PADHI [1].

  For a proposed new hazardous installation, HSE’s advice is based on a consideration of whether developments that HSE would ‘advise against’, as defined by PADHI, already exist within the relevant zones of the 3ZM. The possible outcomes of the UK HSE methodology are either to ‘advise against’ or ‘do not advise against’ the granting of hazardous substances consent.

Table 1: Summary of advice on new developments in the vicinity of a hazardous installation

3 3ZM FOR SHELL PROPOSAL 3.1 INTRODUCTION

The Shell proposal consists of 5 × 1000 m3 storage tanks [2, 3]. Each tank comprises an inner and outer stainless steel skin with the annulus under vacuum and filled with insulation. Both the inner and outer skins are stainless steel vessels and the inner is rated as a pressure vessel. The outer tank contains ‘vacuum plate’ vents that would release LNG into the surrounding bund if there was any failure of the inner tank. Beyond the bund there are further walls to prevent LNG entering the sea even if failure of the bund occurred. The bund slopes to an impounding basin and the LNG transfer piping approaches the tanks only from the end closest to the impounding basin. The bund and impounding basin designs minimise the size of any LNG pool and hence the consequences of any possible release.

Shell proposed two options for the bund design:

1. a single bund surrounding all five storage tanks and draining into the impounding basin;

2. a sub-divided bund, so that there is a separate bund around each storage tank, each draining into the impounding basin [4].

HSL carried out an initial review [5] of the Shell concept design proposal including a teleconference to clarify points of information and subsequently calculated the 3ZMs.

3.2 INPUT ASSUMPTIONS

Most of the input assumptions comprised factual information based on the information already supplied by Shell. Some key issues that affected input assumptions for the risk assessment are discussed below, and were the subject of a meeting with Shell and further information was provided by Shell.

3.2.1 Boiling liquid expanding vapour explosion (BLEVE) fireball

Although the proposed storage tanks are pressure vessels, a boiling liquid expanding vapour explosion (BLEVE) scenario has not needed to be included. The further information provided by Shell [6, 7] demonstrates that the outer skin of the tanks and perlite insulation will be capable of protecting against a pool fire or jet fire causing a BLEVE. In addition, Shell has undertaken to minimise the potential for jet fires that could impinge on the storage tanks through the location and orientation of equipment during detailed design.

3.2.2 Catastrophic failure of the tanks

The storage tanks have been modelled as standard single-walled pressure vessels, although their construction has double stainless steel walls. This is expected to overestimate the risk.

3.2.3 Loading ESD system

Shell [7] has confirmed the independence of the two emergency shut-down (ESD) systems and manual shutdown. This confirms the UK HSE standard assumptions that have been used to produce the 3ZM.

3.2.4 Bund design

Further information was provided about the dimensions of the bund [8,9,10] and a meeting took place at HSL for further clarification. The two options were considered:

1. Single bund around all five tanks, draining to impounding basin;

2. Subdivided bund, draining to impounding basin.

It was clarified that all LNG piping connections to the storage tanks, and the vacuum plates, are at the end of the tanks closest to the impounding basin and furthest from the access road to the Cruise Ship Terminal. Calculations are expected to be conservative because they assume that the LNG from any release will flow uphill to fill the bund or appropriate section of subdivided bund, as well as flowing downhill into the impounding basin. Because the outer stainless steel tank is designed so that it will not fail if the inner tank fails, then any release will be via the vacuum plates at the impounding basin end of the storage tanks.

3.3 DISCUSSION OF 3ZM RESULTS

3ZMs were calculated for the two options and are shown in the Annex below. Figures 1 and 2 apply to options 1 and 2, respectively.

The calculations do not include any future bunkering operations, either in terms of the increased deliveries into the storage tank nor any flows out of the storage tank to supply bunkering. Reassessment would be needed with suitable assumptions before any advice could be given about bunkering.

The 3ZMs need to be considered in terms of compatibility with existing developments, as further discussed below.

3.3.1 Housing to East of proposed site at the North Mole

In both cases the 3ZMs indicate that the middle (blue) zone does not reach the housing to the East of the proposed LNG storage facility. That is compatible with the HSE PADHI guidance [1].

3.3.2 Access road and cruise ship terminal

For option 1, where the bund around the storage tanks is not subdivided, the inner zone (red) and middle zone (blue) in Figure 1 are shown covering the access road and cruise ship terminal. However this does not take into account that the LNG carrier will not be berthed and LNG offloading operations will not take place when a cruise ship is present. In addition, Shell [2] has undertaken to provide a barrier wall, at least 2 metres high, on the south side of the terminal to limit the hazard zone by providing a solid obstacle to vapour flow. The size of the inner zone is determined by pool fire and flash fire scenarios and such a barrier could also provide shelter from thermal radiation.

HSE sometimes makes a “Do not advise against” decision subject to a recommendation for a planning condition to include specific design features. Hazardous Substances Consent is often granted prior to the detailed design phase of a project and the planning condition allows the design feature to be fully specified during detailed design.

For the Shell proposal, “Do not advise against” would be appropriate for option 1, provided that there was also a planning condition that Shell designs their proposed physical barrier wall to protect the road and cruise terminal from fire scenarios, i.e. protection from thermal radiation from fire scenarios and to provide a vapour barrier to protect against flash fire. It is expected that such a barrier should be achievable. Shell should provide modelling results to HSL to demonstrate the suitability of the barrier as part of detailed design.

For option 2, in which the bund around the tanks is subdivided, the middle zone (blue) in Figure 2 is shown covering the access road. However this does not take into account that the LNG carrier will not be berthed and LNG offloading operations will not take place when a cruise ship is present. In this case, the result would be “Do not advise against”.

4.1

4 CONCLUSIONS AND RECOMMENDATIONS CONCLUSIONS

The Shell concept design (with two options) was assessed at a pre-consents stage to allow the Government of Gibraltar to make a decision about the preferred bidder.

For option 1, the result would be “do not advise against”, subject to a planning condition to provide a suitable barrier wall to protect the access road and the cruise ship terminal.

For option 2, in which the bund surrounding the LNG tanks would be sub-divided, the result would be “do not advise against”.

4.2 RECOMMENDATIONS

Shell will still need to apply for hazardous substances consent at a suitable stage in the project. At that stage, the 3ZM should be further assessed and confirmed by HSL, taking account any further design features.

HSL’s analysis was based on the quantity of LNG storage required for the new power station. Although LNG bunkering may be a future requirement, any future storage requirements are presently unknown. Any increase in LNG storage capacity or LNG delivery frequency to support bunkering would need a modification to the hazardous substances consent.

Hazardous substances consent fulfils one of the requirements the European Seveso III Directive. The LNG storage facility for the new power station will also qualify as an upper tier site under Seveso III, that part of Seveso III being implemented in GB as the Control of Major Accident Hazards (COMAH) 2015 Regulations. Upper tier sites need to produce a safety report to demonstrate that ‘all measures necessary’ are provided to prevent and control major accident hazards. A pre-construction safety report will be required to be submitted in time for assessment to take place before construction. The pre-construction safety report will then need to be updated into a pre-operational safety report, to be assessed before the storage facility commences operation.

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