12C                                  Quantitative Risk Assessment for Existing Gas Receiving Station

12C.1                            Introduction

The study presented in Annex 12B covers the details of the Quantitative Risk Assessment (QRA) for the two Gas Receiving Stations (GRSs) to be built at the Black Point Power Station (BPPS) which will receive natural gas through two subsea pipelines from the Mainland.  This section extends the analysis to consider also the existing GRS (Figure 12C.1), although this is not included in the EIA Study Brief.

The proposed pipelines from the Mainland China will terminate at two gas receiving stations (GRSs) at BPPS.  One will be located adjacent to the existing GRS (co-located GRS), the second will be located on reclaimed land to the north of the BPPS site (GRS on reclamation).  The two GRSs are not expected to be constructed concurrently.  The co-located GRS will be constructed in 2011 (i.e. First Phase construction) while the construction of the GRS on reclamation is expected to commence within 24 months of commissioning of the first pipeline, in around 2014. 

As the two GRSs are not expected to be constructed concurrently, the following cases can be considered in the analysis:

1)        Existing GRS operating and co-located GRS under construction (2011);

2)        Existing and co-located GRS operating (2011);

3)        Existing and co-located GRS operating and GRS on reclamation under construction (2014);

4)        3 GRSs operating (2021).

In Annex 12B, the following cases have already been assessed:

a)        Only co-located GRS in operation;

b)        Co-located GRS in operation and construction of the GRS on reclamation;

c)        Both co-located and GRS on reclamation operating.

Since the separation distances between the existing and co-located GRS is similar to that between the co-located GRS and the GRS on reclamation, the results of case b) and c) can be applied respectively to case 1 and case 2.

Therefore, this Annex focuses on results for the following two cases:

·           Case 3: Existing and co-located GRS operating and GRS on reclamation under construction (2014); and

·           Case 4: All 3 GRSs operating (2021)

Detailed information of the study methodology is presented in Annex 12B.  The same methodology is applied for the existing GRS, except that coordinates are updated to reflect the actual location of equipment and leak frequencies are modified to take into account the different lengths of piping and number of equipment items such as heaters. 

Figure 12C.1  GRS Locations

Black Point Power Station
 

Existing GRS
 

GRS on Reclamation (GRS ‘B’)
 

Co-located GRS (GRS ‘A’)
 


 

12C.2                            Results

Individual Risk Results

The individual risk (IR) contours associated with the case 3 in 2014 are shown in Figure 12C.2.  The maximum risk is less than 1´10-5 per year at all locations and hence meets the HKRG requirements.

Figure 12C.2  Individual Risk Contours (2014) – Case 3

 

The results for case 4 in 2021 are presented in Figure 12C.3.  With three GRSs operational, the IR has increased and exceeds in some locations 10-5 per year. However, the 10-5 per year contour does not extend offsite and hence meets the HKRG requirements.

 

Figure 12C.3  Individual Risk Contours (2021) – Case 4

Societal Risk Results

Figure 12C.4 shows the FN Curves for the GRS at the BPPS for construction year 2014 with 2 GRS in operation and the GRS on reclamation being constructed.  Compared to the results presented in Figure 12.9, Section 12, the risks have only increased slightly due to the predicted slight increase in surrounding marine population.  The results are within the acceptable region. 

Figure 12C.4  FN Curves for GRS – case 3 in year 2014

For the year 2021, when all 3 GRSs will be operational, the risks are low (Figure 12C.6) due to the remote location of the site and low population in the vicinity.

Figure 12C.5  FN Curves for GRS – case 4 in year 2021

12C.3                            Conclusions

Individual risks associated with the facilities meet the HKRG.

Societal risks associated with the operational phases of the project are low and lie in the acceptable region of the FN curves.

No significant increase in societal risks was found for the construction phases of the project. The slight increases found are due to increase in marine population predicted.  Recommendations are nevertheless made in accordance with best practice to mitigate these construction phase risks: 

·           The most hazardous maintenance operations on the existing GRS will be avoided during the construction of the GRS on reclamation.

·           Procedures for evacuation of construction workers will be in place in case of particularly hazardous operations on existing GRS and co-located GRS.

·           Specific emergency procedures will be put into place for the evacuation of construction workers.

·           Additional gas detectors along the boundary or gas and fire alarms for the detection from the GRSs in operation for escape and evacuation of construction workers will be considered.

·           The construction of a temporary steel wall or other appropriate barrier between the existing GRS and the GRS on reclamation will be considered to prevent gas spreading towards the construction site in case of a gas leak in the existing GRS.  This will also prevent the gas coming in contact with the ignition sources at the construction site, limit exposure of personnel to any direct flame from the existing GRS and provide time for construction personnel to evacuate the site.