7.1              Introduction

This section presents the Hazard to Life Assessment (HA) for the proposed Project in accordance with the requirements of the EIA Study Brief section 3.4.11, and is structured as follows:

Section 7.2: Identifies the Potentially Hazardous Facilities (PHI) for this Project;

Section 7.3: Presents the project data required for the assessment;

Section 7.4: Identify potential hazards of this Project;

Section 7.5: Provides discussion on the findings of consequence assessment;

Section 7.6: Provides discussion on the findings of frequency assessment;

Section 7.7: Provides discussion on the findings of risk prediction;

Section 7.8: Presents the conclusion of the Hazard to Life Assessment and proposes potential mitigation measures to address the identified impacts.

The hazard to life assessment has been undertaken in accordance with the requirements of the Study Brief and Annexes 4 of the EIAO-TM. Potentially Hazardous Facilities (PHI) located in the vicinity of the proposed Project were identified for the assessment. The assessment concluded that the risks posed by identified PHIs on the sensitive receivers, neighbouring population and the dredging workers satisfy the Hong Kong Government Risk Guidelines.     

Appropriate mitigation measures have been recommended to further reduce the risks as low as reasonably practicable.

7.1.1         Project Background

As required under the Study Brief, a Hazard to Life Assessment (HA) has been undertaken by BMT Asia Pacific Limited (BMT), the nominated sub-consultant to conduct the Hazard to Life Assessment (HA) within the EIA.  This assessment considered the risks to the workers and users arising from the Project and has provided appropriate mitigation measures to minimise the risk to an acceptable or As Low As Reasonably Practicable (ALARP) level.

7.1.1.1         List of Abbreviations

ALARP

As Low As Reasonably Practicable

BMT

BMT Asia Pacific Ltd

CBA

Cost Benefit Analysis

CEDD

Civil Engineering and Development Department

CFA

Court of Final Appeal

CFD

Computational Fluid Dynamics

CZ

Consultation Zone

EIA

Environmental Impact Assessment

EIAO

Environmental Impact Assessment Ordinance

HA

Hazard to Life Assessment

ICAF

The Implied Cost of Averting a Fatality

MHIDAS

Major Hazard Incident Data Access Services

MS

Methodology Statement

MTIA

Marine Traffic Impact Assessment

PHI

Potential Hazardous Installations

PlanD

Planning Department

PLL

Potential Loss of Life

QRA

Quantitative Risk Assessment

TM

Technical Memorandum

UKHSE

United Kingdom, Health and Safety Executive

7.1.2         Project Overview

The purpose of the Project is to dredge the seabed of Kwai Tsing Container Basin (KTCB), as well as portions of Northern Fairway and Western Fairway to provide the necessary manoeuvring basin and approach channel to Kwai Tsing Container Port (KTCP) with adequate draft for the new generation of the ultra-large container ships (ULCS).

The location of the Project includes the whole KTCB as well as portions of Northern Fairway and Western Fairway which are shown in Figure 7.1.  Project sites are currently used by the container ships of KTCP and other vessels navigating in the vicinity.

7.1.3         Study Objectives

The objective of the HA is to assess the potential risk to construction workers and users during the construction (dredging work) of the Project due to their presence within the consultation zones of Potentially Hazardous Installations (PHIs) (LPG/oil depots), and hence the effect of this additional risk to the original risk of the PHIs. The results of the assessment are compared with the Hong Kong Government Risk Guidelines (HKRG).

The detailed requirement of the study (see Condition 3.4.11 of the EIA study brief, ESB-198/2008 [1]) is repeated as follows:

The Applicant shall follow the criteria for evaluating hazard to life as stated in Annex 4 of the TM.

The Applicant shall carry out a hazard assessment for the potential risk to construction workers and users during construction stages of the Project due to their presence within the consultation zones of PHIs (LPG/oil depots). The hazard assessment shall include the following:

i.                Identification of hazardous scenario associated with the operation of the existing PHIs present in the Study Area of the Project with a view to determining a set of relevant hazard scenarios to be included in a Quantitative Risk Assessment (QRA);

ii.              Execution of a QRA of the set of hazardous scenarios determined in (i), expressing population risks in both individual and societal terms;

iii.             Comparison of individual and societal risk with the criteria for evaluating hazard to life stipulated in Annex 4 of the TM; and

iv.             Identification and assessment of practicable and cost-effective risk mitigation measures.

The methodology to be used in the hazard assessment shall be consistent with previous studies having similar issues (e.g. EIA study for the Permanent Aviation Fuel facility for Hong Kong International Airport) or otherwise be agreed by the Director prior to carrying out of the hazard assessment.

As shown in Figure 7.2, 3 LPG/ oil depots at the southern part of Tsing Yi are located in vicinity of the proposed dredging area. They are considered as Potentially Hazardous Installations (PHI) as recorded in the PHI Register managed by the Housing, Planning and Lands Bureau.

¡      N6 : Exxon Mobil Tsing Yi East Terminal for LPG and oil at TYTL 46RP

¡                              N8 : Exxon Mobil Tsing Yi West Terminal for LPG and oil at TYTL 115

¡                              N11 : China Resources Petrochemicals Co. Ltd (now SINOPEC) LPG and oil depot at TYTL 127

The 1 km consultation zone of N6 and N11 overlaps with part of the proposed dredging area (see Figure 7.2). The potential adverse impacts to construction workers and personnel onboard of dredgers, barges and other supporting craft will be evaluated by considering the total capacity of the 2 LPG/ oil depots.

7.1.4         Risk Guidelines

The estimated risk levels of hazardous installations have been compared to the Hong Kong Government Risk Guidelines stipulated in Annex 4 of the Technical Memorandum for Environmental Impact Assessment Ordinance (EIAO-TM) to determine the acceptability.

Individual Risk Guideline: The maximum level of off-site risk should not exceed 1 in 100,000 years, i.e. 1x10-5 per year.

Societal Risk Guideline: It is presented graphically in Figure 7.3. The societal risk guideline is expressed in terms of lines plotting the frequency (F) of N or more fatalities in the off-site population from hazardous scenarios at the facility of concern. There are three areas as described below:

¡               Acceptable where the risk is so low that no action is necessary;

¡               Unacceptable where the risk is so high that they should be reduced regardless of the cost or else the hazardous activity should not proceed; and

¡               ALARP (As Low As Reasonably Practicable) where the risk associated with the hazardous activity should be reduced to a level “as low as reasonably practicable”, in which the priority of measures is established on the basis of practicality and cost to implement versus the risk reduction achieved.

7.1.5         Approach and Methodology

The proposed methodology for the HA is shown schematically in Figure 7.4:

The hazard assessment consists of the following steps and is explained in the subsequent sections:

¡      Information Collection

¡                              Hazard Identification

¡                              Frequency Assessment

¡                              Consequence Assessment

¡                              Risk Summation and Assessment

¡                              Risk Mitigation and Recommendations

An assessment of the two LPG/ oil depots has been conducted previously in the EIA study for Route 9 between Tsing Yi and Cheung Sha Wan (Route 9 EIA) (Highways Department, 1999) [2]. Information in the aforementioned report has been referenced where appropriate.

7.1.6         Report Structure

This report is structured in a Hazard to Life Assessment report manner, which is presented as follows:

¡               Section 7.1 states the background of this study;

¡               Section 7.2 provides the descriptions of potentially hazardous facilities;

¡               Section 7.3 describes the project data used in this study;

¡               Section 7.4 presents hazard identification;

¡               Section 7.5 presents consequences assessment;

¡               Section 7.6 presents failure frequency assessment;

¡               Section 7.7 summarises risk assessment results and compares with the Hong Kong Government Risk Guidelines;

¡               Section 7.8 draws conclusions and gives recommendations on further risk mitigation measures;

¡               Section 7.9 lists references used in this study.

7.2              Potentially Hazardous Facilities

7.2.1         PHI Locations

The 2 LPG/ oil depots (N6 and N11) are situated on a coastal fringe of reclaimed land at elevations between 4 to 6 meters above mean sea level at the south of the Tsing Yi Island. The neighbouring area is mainly industrial. Container Terminal 9, Dow Chemical Plant and Cheung Sha Wan-Tsing Yi section of Tsing Sha Highway on Route 8 (Stonecutters Bridge) are located to the north-east; the ex-Tsing Yi Power Station site and ExxonMobil Tsing Yi West Terminal lie to the west; the proposed dredging area within the 1 km consultation zone resides to the south. Hilly areas with the slope gradually rising to 125 m ~ 334 m are situated at the north of the facilities, which forms a natural barrier to the dispersion of hydrocarbon vapours.

7.2.2         Hazardous Storage and Operations

Information on the hazardous facilities was extracted from previous EIA study for Route 9 between Tsing Yi and Cheung Sha Wan (Route 9 EIA) (Highways Department, 1999) [2]. LPG is stored at both facilities, as listed in Table 7.1. Attempts were made but failed to obtain the most up-to-date data on equipment and operations of the two PHIs, since both owners of the PHIs do not wish to disclose details of their facilities due to confidentiality issues. The reasons given were that by disclosing such information to the consultants, this will be published in the EIA report, which will be available to the general public.

Although updated information is not available, satellite maps and site surveys indicate that the equipment and operations in the two PHIs are mostly similar to those in Year 1999. Hence it was considered reasonable to adopt the equipment and operations information for the two PHIs from the previous Route 9 EIA report.

Table 7.1:      LPG Throughput and Storage

Depot

LPG Throughput (tonnes per year)

Storage Vessels

Storage Type

N6 (ExxonMobil)

Information not available

3 x 850 te

Tankers 7.5 te

Aboveground vessels(1)

N11 (SINOPEC)

35,000

3 x 700 te

Tankers 8 te

Cylinders, sand mounded bullets

Note: (1) Site survey reveals the LPG vessels are installed aboveground, although mounded type is recommended and assumed in Route 9 EIA.

Other than LPG, liquid petroleum products are stored in the SINOPEC depot N11, including leaded and unleaded gasoline, diesel, kerosene and oils. Chemical solvents, such as toluene, isopropyl alcohol, acetone and styrene monomer, are also stored in the N11 depot.

ExxonMobil depot N6 also stores and handles a range of petroleum liquids.

Other hazardous facilities in the depots include LPG cylinder filling station, fuel oil blending facility and boiler for heating heavy fuel oils.

LPG is imported from the LPG ships at the jetty to the storage vessels. The stored LPG is exported to LPG road tankers in the LPG filling stations inside the depots.

7.3              Project Data

7.3.1         Population

The Study Brief [1] requires that the risk to the construction workers and users during construction stage be assessed due to their presence within the consultation zones of PHIs (LPG/ oil depots). More specifically, the risk due to the presence of different types of population within the consultation zones (CZs) of the 2 depots needs to be assessed. The effect of population before, during and after dredging work on the risk profile of the 2 depots will be studied. Year 2009, 2012 and 2014 are used as the benchmark years for these three stages.

7.3.1.1         Construction Workers Population

The population of construction workers at the dredging site within the two CZs are 15, as estimated from normal dredging works. This group of workers includes operators, banksmen, technicians, ship captains, and other labourers on the dredging platoon, the tugboat and the barge. The population has been assumed to be constant throughout the study period.

7.3.1.2         Nearby Land Population

Area in the vicinity of the two LPG/ oil depots is of industrial use. There is no residential/ recreational development within 1 km distance. As illustrated in Figure 7.5, a few industrial sites are located near the oil depots, including Dow Chemical Plant, Tien Chu (Tsing Yi) Industrial Centre, Chemical Waste Treatment Centre, etc. Other areas in the surroundings are used for cargo handling, lorry parking, and goods storage for Container Terminal 9. Estimated population at these sites are summarised in Table 7.2.

In the Planning Department’s Projections of Population Distribution 2009-2018 [11], promulgated in December 2009, residential population at Tsing Yi South (TPU 350) has a downward trend, from 2009’s 112,200 to 2012’s 109,500 to 2014’s 107,900. Adopting this as an indicator for development in the area, it can be assumed that the industrial population in the surroundings of the PHIs will follow the same trend as the residential population. In addition, the change in nearby land population from 2009 to 2014 is not the main focus of this study; there is no population change caused by the dredging works in the KTCB. Therefore in this EIA the land population in the surroundings of the PHIs are conservatively assumed to remain the same from 2009 to 2014.

 

7.3.1.3         Nearby Road Population

Traffic population of nearby roads such as Tsing Yi Road are estimated based on the 2008 Annual Average Daily Traffic (AADT) data from Transport Department [9]. Night-time traffic density is assumed to be 10% of the day-time traffic density. The Cheung Sha Wan-Tsing Yi section of Tsing Sha Highway on Route 8 (Stonecutters Bridge) was opened in December 2009 and no traffic data is available. It is assumed half of the traffic will be diverted to this new road from the Tsing Kwai Highway (Cheung Tsing Tunnel). The future traffic data is predicted by the trend of the data from 2007 to 2008.

The average traffic population are calculated from the following formula:

 

The nearby road considered in this study is shown in Figure 7.5. Traffic population are summarised in Table 7.4.

7.3.1.4         Marine Traffic Population

The marine traffic population are adopted from the marine traffic impact assessment report of this project. Daily traffic at two locations at Year 2009 are adopted from the marine traffic survey (see Figure 7.6): South Entrance of KTCB near the Marine Department Kwai Chung Control Station (KCCS) parallel to the Stonecutters Bridge (1), and Northern Fairway near KCCS (2). Projections are made to predict the traffic at Year 2012 and Year 2014. In this study, it is conservatively assumed the overall traffic of these two fairways is the traffic of the fairway located to the south of the two PHIs (3). The average population density at the fairway (3) is estimated from the following equations:

Overall population density = S Population density of each class of vessel

Daytime population density of each class of vessel = N × P / (V × 12 hr × W)

Where N is the daytime traffic of each class of vessel, P is the typical occupancy of the vessel, V is the typical vessel speed, and W is the fairway width. The calculations are summarized in Tables 7.5, 7.6 and 7.7.

7.3.1.5         Other Factors to be Considered

Indoor / Outdoor Ratio

For this HA, the construction workers, staff in the open industrial areas such as Container Terminal 9 and dockyard, and marine traffic population will be considered as 100% outdoor. An indoor ratio of 95% and 10% are applied to the population in the industrial buildings and LPG depots respectively. Passengers in vehicles on the roads are considered as 100% outdoor. These factors have been adopted in the previous South East Kowloon Development (SEKD) CFS EIA [3] and Harbour Area Treatment Scheme (HATS) Stage 2A EIA [4].

Temporal Changes in Population

In order to account for the temporal change in population within a week, the following time periods, and corresponding proportion of population to be adopted in the modelling, are assumed with reference to the marine traffic survey of this project, SEKD CFS and HATS Stage 2A EIA studies [3] [4].

Table 7.2:      Temporal Changes in Population

Time Period

Construction Workers(1)(2)

Staff at the Industrial Sites(1)

Vehicle Passengers on the Roads(3)

Marine Traffic(4)

Weekday Day

100%

100%

100%

100%

Weekday Night

10%

10%

10%

80%

Weekend Day

50%

40%

100%

100%

Weekend Night

5%

5%

10%

80%

Note:

(1) Reference to HATS Stage 2A EIA [4].

(2) Population estimation is adjusted based on the project information.

(3) Reference to SEKD CFS EIA [3].

(4) Estimated from the marine traffic survey of this project.

 

 

 

 

Table 7.3:      Land Population Considered in this Study for Years 2009, 2012 and 2014

Site Name

Description

Total Population

Indoor Ratio

Occupancy Percentage

Population

 

 

 

 

Weekday

Weekend

Weekday

Weekend

 

 

 

 

Day

Night

Day

Night

Day

Night

Day

Night

Dow Chemical Plant(1)

Industrial site

100

0.95

1

0.1

0.4

0.05

100

10

40

5

Tien Chu (Tsing Yi) Industrial Centre(1)

Industrial site

60

0.95

1

0.1

0.4

0.05

60

6

24

3

Chemical Waste Treatment Centre(1)

Industrial site

150

0.95

1

0.1

0.4

0.05

150

15

60

8

Tai Tung (Tsing Yi)(1)

Industrial site

200

0.95

1

0.1

0.4

0.05

200

20

80

10

Taikoo Paint Factory (desolated)(1)

Industrial site

2

0.95

1

0.1

0.4

0.05

2

1

1

1

ExxonMobil Tsing Yi West Terminal (N8)(2)

LPG/ oil depot

50

0.1

1

0.1

0.4

0.05

50

5

20

3

Dockyard (next to ExxonMobil Depot)(3)

Dockyard

400

0

1

0.1

0.4

0.05

400

40

160

20

Container Terminal 9 and Related Areas(4)

Container terminal uses

3300

0

1

0.1

0.4

0.05

3300

330

1320

165

Note:

(1) Population estimated from http://www.hktdc.com and site survey.

(2) Population estimated from Route 9 EIA report [2].

(3) Assume the similar population density as the Container Terminal 9 and Related Areas.

(4) Population estimated from 2003-based TPEDM population data.

Table 7.4:      Road Traffic Population Adopted in this Study

 

 

Traffic Population

 

 

Weekday

Weekend

Year

Station

day

night

day

night

2009

Tsing Yi Road(1)

229

23

229

23

Tsing Sha Highway on Route 8 (Stonecutters Bridge) (1) (2)

501

50

501

50

Tsing Yi Hong Wan Road(1)

110

11

110

11

Tsing Ko Road(3)

6

1

6

1

Tsing Sheung Road(3)

11

1

11

1

2012

Tsing Yi Road(1)

231

23

231

23

Tsing Sha Highway on Route 8 (Stonecutters Bridge) (1) (2)

504

50

504

50

Tsing Yi Hong Wan Road(1)

144

14

144

14

Tsing Ko Road(3)

6

1

6

1

Tsing Sheung Road(3)

12

1

12

1

2014

Tsing Yi Road(1)

233

23

233

23

Tsing Sha Highway on Route 8 (Stonecutters Bridge) (1) (2)

506

51

506

51

Tsing Yi Hong Wan Road(1)

173

17

173

17

Tsing Ko Road(3)

6

1

6

1

Tsing Sheung Road(3)

12

1

12

1

 Note:

(1) Traffic estimated from 2008 AADT data.

(2) Assume 50% of the traffic from Tsing Kwai Highway (Cheung Tsing Tunnel, 2008 AADT data).

(3) Assume 20% of the traffic from Tsing Yi Road based on site survey.

 

Table 7.5:      Characteristics of Different Vessels

Vessel Class

Occupancy (persons per vessel)

Speed (m/s)

Fairway Width (m)

Cargo

O-G Cargo

20

6

800

River Trade

5

6

800

Tug & Tow

5

2.5

800

Barge (Self Propelled)

5

6

800

Passenger

O-G Passenger

500

6

800

Fast Ferry

150

15

800

Conventional Ferry

50

6

800

Fast Launch

5

15

800

Others

Tug Boats without Towage

5

6

800

Fishing Vessel

5

6

800

Local DG Vessels

5

6

800

Pleasure Vessels Powered

100

6

800

Unclassified

5

6

800

Table 7.6:      Day-time Marine Traffic Density Across the Study Area

Vessel Classes

2009

2012

2014

Cargo

O-G Cargo

3.69

3.63

3.31

River Trade

14.34

13.38

12.56

Tug & Tow

5.72

5.90

6.08

Barge (Self Propelled)

0.13

0.13

0.13

Passenger

O-G Passenger

12.06

19.29

21.70

Fast Ferry

20.99

22.15

23.02

Conventional Ferry

1.71

1.47

1.34

Fast Launch

0.92

1.00

1.03

Others

Tug Boats without Towage

3.36

3.45

3.49

Fishing Vessel

0.57

0.47

0.38

Local DG Vessels

1.42

1.42

1.41

Pleasure Vessels Powered

1.02

1.02

1.02

Unclassified

0.07

0.07

0.07

TOTAL

 

66.00

73.39

75.54

Table 7.7:      Night-time Marine Traffic Density Across the Study Area

Vessel Classes

2009

2012

2014

Cargo

O-G Cargo

2.95

2.91

2.65

River Trade

11.48

10.70

10.05

Tug & Tow

4.58

4.72

4.87

Barge (Self Propelled)

0.10

0.10

0.10

Passenger

O-G Passenger

9.65

15.43

17.36

Fast Ferry

16.80

17.72

18.42

Conventional Ferry

1.37

1.18

1.07

Fast Launch

0.73

0.80

0.83

Others

Tug Boats without Towage

2.69

2.76

2.79

Fishing Vessel

0.46

0.38

0.30

Local DG Vessels

1.14

1.14

1.13

Pleasure Vessels Powered

0.81

0.81

0.81

Unclassified

0.05

0.05

0.05

TOTAL

 

52.80

58.71

60.43

7.3.2         Meteorological Data

Meteorological conditions, principally the wind directions, stability and speeds, will affect the consequences of hazard events (e.g. flammable gas dispersion). For the area concerned, data from the Tsing Yi weather station were adopted, which is referenced to Route 9 EIA study [2]. The average ambient temperature adopted is 23°C and relative humidity is 78%. The wind direction frequencies are summarised in Tables 7.8 and 7.9.

Table 7.8:      Wind Direction Frequencies for Day

Wind Direction (Degree)

B 2.8

D 1.4

D 3.8

D 7.7

E 2.9

F 1.1

0

0.005

0.0031

0.0042

0

0.0018

0.011

30

0.0016

0.001

0

0

0.0003

0.0037

60

0.0021

0.0008

0.0005

0

0.0003

0.0052

90

0.0164

0.0052

0.0091

0.0005

0.0013

0.0144

120

0.1206

0.0157

0.0598

0.0104

0.0091

0.0204

150

0.1639

0.0167

0.0196

0.0021

0.0031

0.0151

180

0.0994

0.0133

0.0047

0.001

0.0005

0.0063

210

0.0264

0.0037

0.0013

0.001

0

0.0029

240

0.0232

0.0044

0

0

0

0.0021

270

0.0381

0.006

0.0008

0

0.0005

0.0029

300

0.0378

0.0107

0.0044

0

0.0008

0.007

330

0.0759

0.017

0.0237

0.0042

0.0076

0.0284

Table 7.9:      Wind Direction Frequencies for Night

Wind Direction (Degree)

B 1.0

D 1.0

D 4.0

D 7.8

E 3.0

F 1.1

0

0

0

0.0074

0.0003

0.0059

0.0626

30

0

0

0.0012

0

0.0009

0.0344

60

0

0

0.0009

0

0.0009

0.057

90

0

0

0.0222

0.0018

0.0113

0.1044

120

0

0

0.1015

0.0092

0.0495

0.1646

150

0

0

0.0285

0.0033

0.0163

0.0825

180

0

0

0.0033

0.0033

0.0018

0.0181

210

0

0

0.0015

0.0009

0

0.0086

240

0

0

0.0018

0

0

0.0068

270

0

0

0.0003

0.0003

0.0003

0.0104

300

0

0

0.0053

0

0.0042

0.0222

330

0

0

0.0267

0.0027

0.022

0.0931

7.4              Hazard Identification

The information on the hazardous operations is adopted from the Route 9 EIA study report [2]. A number of hazardous events may arise from the storage and operations associated with LPG and other petroleum products. The proposed dredging area is about 300 m and 800 m away from the waterfront of the depots N11 and N6, respectively. Only hazards which can extend and pose risk to the dredging area are considered in this assessment.

7.4.1         Hazards Related to LPG Facilities

Liquid petroleum gas (LPG) is a mixture of liquefied propane and butane (3:7) under pressure. Upon release to the ambient environment it vaporises and mixes with air, forming a dense flammable gas cloud which tends to flow and disperse close to the ground along the natural terrain. A significant amount of LPG is stored and processed at both PHI sites. Uncontrolled release of LPG may disperse over a long distance and result in a fire upon ignition or an explosion in a congested area.

LPG related facilities at the two PHIs are identified as follows (with reference to the Route 9 EIA study [2]):

¡      Ship unloading facilities at jetties – equipped with loading arms and hoses

¡      Jetty pipework – equipped with emergency shutdown valves at the ship interface and shore line, for rapid isolation during unloading if a leak or rupture occurs

¡      Distribution pipework within the terminal to the storage vessels

¡      Storage vessels – equipped with isolating and relief valves and fire protection systems (leak detection systems are provided to warn if leaks occur), protected by sand mounding

¡      Export pipework to the tanker loading bays and LPG cylinder filling facilities

¡      Export facilities to LPG barges

Accidental LPG release could result from leaks or catastrophic rupture of the following pressurised LPG equipment:

¡      Ship LPG tanks and associated pipes

¡      Mounded/ Above ground storage vessels and associated pipes

¡      LPG road tankers and associated pipes

¡      Unloading arms/ pipes

¡      Export arms/ pipes

Subsequently the potential hazardous events could be:

¡      Jet fire

¡      Flash fire

¡      Vapour Cloud Explosion (VCE)

¡      Fireball

¡      Boiling Liquid Expanding Vapour Explosion (BLEVE)

Jet fire caused by an immediate ignition of LPG release from a hole may impinge on a nearby LPG container, and lead to catastrophic failure of the container over a period of time into BLEVE. This is possible for ship LPG tanks and LPG road tankers. However, escalation of fire to BLEVE is considered unlikely for mounded LPG storage vessels in the SINOPEC depot.

Representative LPG accidental release scenarios considered in the assessment are summarised below in Table 7.10.

 

 

Table 7.10:    LPG Accidental Release Scenarios Considered

Facility Type

Equipment Involved

Failure Event

Release Type

Potential Hazardous Outcomes

LPG import

Ship LPG tanks

Tank rupture

Instantaneous

Flash fire, fireball, BLEVE

 

 

Tank leak

Continuous

Flash fire, jet fire

 

Unloading arm/ pipe

Arm/ Pipe rupture

Continuous

Flash fire, jet fire

 

 

Arm/ Pipe leak

Continuous

Flash fire, jet fire

LPG storage

Mounded LPG vessels

Vessel rupture

Instantaneous

Flash fire, VCE, fireball

 

 

Vessel leak

Continuous

Flash fire, VCE, jet fire

LPG storage

Above ground LPG vessels

Vessel rupture

Instantaneous

Flash fire, VCE, fireball, BLEVE

 

 

Vessel leak

Continuous

Flash fire, VCE, jet fire

LPG export

Export bays

Arm/ Pipe leak

Continuous

Flash fire, VCE, jet fire

LPG road tanker

LPG tanker

Tanker rupture

Instantaneous

Flash fire, VCE, fireball, BLEVE

 

 

Tanker leak

Continuous

Flash fire, VCE, jet fire

7.4.2         Hazards Related to Other Petroleum Products and Chemical Solvents

Other petroleum products and chemical solvents, as described in Section 7.2.2, are also stored in the PHIs. Compared with LPG, these products are much less volatile and flammable due to their higher boiling points and flash points. They are in liquid form under normal condition, and thus stored in vessels under ambient temperatures and pressures. Accidental spillage of these petroleum products will result in pool fire, either confined in the bund area or spread on the sea surface. In the Permanent Aviation Fuel Facility (PAFF) EIA study [8], a number of release scenarios have been identified in association with the oil storage depot of Jet A1 aviation fuel. These scenarios are used as a reference for the possible scenarios in this Study. They are summarised in Table 7.11.

Table 7.11:    LPG Release Events at SINOPEC Depot

Jetty Transfer

Fire due to rupture/ leak of oil products from loaded vessel

Fire due to rupture/ leak of loading arm during unloading

Fire due to rupture/ leak of jetty equipment

Fire due to rupture/ leak of jetty riser

Fire due to rupture/ leak of submarine pipeline from jetty to tank farm ESD valve

Tank Farm Storage

Fire due to discharge from tank vent

Tank head fire or explosion in tank head space

Multiple tank head fires

Tank failure due to overpressure

Explosion in empty tank (under maintenance)

Bund fire

Fire outside bund due to rupture/ leak of pumps, pipework and fittings

Fire on sea due to release through drainage

Fire due to instantaneous tank wall failure, bottom seam failure

Fire due to instantaneous tank wall failure, unzipping

Aircraft impact

Fire due to multiple tank failure

Tank boilover

Fire due to release from top of tank due to overfilling

Vapour cloud explosion or flash fire

Fire due to 10% instantaneous release from the top of a tank

 

 

7.5              Consequence Assessment

The consequence assessment is conducted in two steps: (1) Source term modelling to determine the release rate, duration and quantity; (2) Effect modelling to determine the gas dispersion, fire and explosion effects based on the output of source term modelling.

In this study, the simulation software SAFETI 6.51 by Det Norske Veritas (DNV) is used to calculate the hazardous releases and the effect zones.

7.5.1         Source Term Modelling

LPG is modelled as a mixture of 70% butane and 30% propane. For instantaneous failure of an LPG storage vessel, 2 release cases of 100% and 50% inventory are considered except for above ground LPG vessels, where an additional case of 20% inventory is considered. For transient or continuous release, the release rate is determined by hole size, storage and ambient conditions, and modelled by discharge models in SAFETI. Duration of discharge is calculated from inventory and release rate. LPG release scenarios modelled for the study are listed in Tables 7.12 and 7.13 below. The release conditions assumed for these scenarios are tabulated in Table 7.14 and 7.16.

Table 7.12:    LPG Release Events at SINOPEC Depot

Case

Facility

Failure Description

A1.1

LPG import

Tank rupture (full inventory)

A2.1

LPG import

Tank rupture (half inventory)

A3.1

LPG import

Catastrophic tank leak due to collision

A4.1

LPG import

100 mm tank leak due to collision

B1.1

LPG import

Full bore rupture of marine loading arms

B2.1

LPG import

50 mm leak of marine loading arms

B3.1

LPG import

150 mm leak of jetty pipeline

C1.1

LPG storage

Catastrophic tank leak

C2.1

LPG storage

100 mm tank leak

C3.1

LPG storage

25 mm tank leak

C4.1

LPG storage

5 mm tank leak

D1.1

LPG export

150 mm leak of filling pipeline

D2.1

LPG export

Leak of LPG cylinders

D3.1

LPG road tanker

100 mm leak during road tanker filling

D4.1

LPG road tanker

Rupture of road tanker on road

D5.1

LPG road tanker

100 mm leak of road tanker on road

D6.1

LPG road tanker

5 mm leak of road tanker on road

D7.1

LPG road tanker

BLEVE during road tanker on road

D8.1

LPG road tanker

BLEVE during road tanker loading

Table 7.13:    LPG Release Events at ExxonMobil Depot

Case

Facility

Failure Description

A1.1

LPG import

Tank rupture (full inventory)

A2.1

LPG import

Tank rupture (half inventory)

A3.1

LPG import

Catastrophic tank leak due to collision

A4.1

LPG import

100 mm tank leak due to collision

B1.1

LPG import

Full bore rupture of marine loading arms

B2.1

LPG import

50 mm leak of marine loading arms

B3.1

LPG import

150 mm leak of jetty pipeline

C1.1

C1.2

C1.3

C1.4

LPG storage

Catastrophic tank leak

100% inventory

50% inventory

20% inventory

C2.1

C2.2

C2.3

C2.4

LPG storage

100 mm tank leak

100% inventory

50% inventory

20% inventory

C3.1

LPG storage

25 mm tank leak

C4.1

LPG storage

5 mm tank leak

D1.1

LPG export

150 mm leak of filling pipeline

D2.1

LPG export

Leak of LPG cylinders

D3.1

LPG road tanker

100 mm leak during road tanker filling

D4.1

LPG road tanker

Rupture of road tanker on road

D5.1

LPG road tanker

100 mm leak of road tanker on road

D6.1

LPG road tanker

5 mm leak of road tanker on road

D7.1

LPG road tanker

BLEVE during road tanker on road

D8.1

LPG road tanker

BLEVE during road tanker loading

7.5.2         Effect Modelling

Gas Dispersion

The UDM model is used for the dispersion of LPG for non-immediate ignition scenarios. The model takes into account various transition phases, from dense cloud dispersion to buoyant passive gas dispersion, in both instantaneous and continuous releases.

Upon release of flammable gas, a number of possible outcomes may occur depending on whether the gas is ignited immediately or ignited after a period of time. The dispersion characteristics are influenced by meteorological conditions and material properties, such as density of the released gas.

Fire scenarios of different kinds may be developed in the presence of ignition source in the proximity of gas release. Vapour cloud explosion may occur in a confined space or a congested area. If no ignition source exists, the gas cloud may disperse downwind and be diluted to the concentration below its Lower Flammable Limit (LFL). In this case, the gas would become too lean to ignite and have no harmful effect.

Jet Fire

For material stored under pressure (pressurised storage or from liquid height above release point), a release will become a jet fire when ignited. The combustion of the jet is influenced by the momentum of the release.

Fireball and BLEVE

Immediate ignition of an instantaneous release of the contents inside a pressurised vessel will result in a fireball. Fireball is characterised by its high thermal radiation intensity and short duration time. The principal hazard of fireball arises from thermal radiation, which is not significantly influenced by weather, wind direction or source of ignition. A BLEVE is similar to a fireball except that it is caused by integrity failure from fire impingement and therefore occurs as escalation events. The physical effects are calculated in the same way as fireballs.

Thermal Radiation of Fires

The following Probit equation [10] has been used to determine lethal doses for various fire scenarios.

Pr = - 36.38 + 2.56 ln Q4/3 t

where Q is the thermal radiation intensity in W/m2 and t is the exposure time in seconds.

Buildings are assumed to offer protection to occupants again hazards from fires. The protection factor is assumed to be 90% for indoor population.

Flash Fire

An LPG release, if not ignited immediately, will vaporise and form a gas cloud around the release source. This cloud can move in the downwind direction, entraining air as it disperses and get diluted. If it gets ignited before it is diluted to below its LFL, a flash fire will result. Major hazards from flash fire are thermal radiation and direct flame contact. Since the flash combustion of a gas cloud normally lasts for a short duration, the thermal radiation effect on people near a flash fire is limited. Humans who are encompassed outdoors by the flash fire will be fatally injured.  A fatality rate of unity is assumed for outdoor population and 90% protection factor is assumed for indoor occupants.

Vapour Cloud Explosion

If the vapour cloud passes through an area of congestion (e.g. pipe racks, confined space) and gets ignited, the confinement will limit the degree of expansion of the burning cloud, causing an explosion and damage to the surroundings by the overpressure it causes. In the SAFETI package such event is modelled by the Baker-Strehlow model, and the hazardous effects are modelled by two concentric circular areas corresponding to heavy and light building damage, respectively.

Pool Fire

The major consequence of a liquid fuel release incidence is liquid pool fire, either it is confined in the bund or spilled onto the sea. The effect radius of an unconfined pool fire is reasonably approximated as the pool radius, while a confined pool fire (e.g. bund fire) is approximated by the pool size plus the flame drag caused by the wind, which is consistent with the PAFF EIA report. [8]

7.5.3         Consequence Results

The consequence results of jet fire, fireball/ BLEVE, flash fire and VCE from a release source are determined from SAFETI and tabulated in Tables 7.14 and 7.16. Fires due to large LPG releases (instantaneous, 150 mm leak and 100 mm leak) could extend outside the depots and imposes risks to the offsite populations, including the construction workers at the dredging site. Impacts of small fires are contained inside the boundary. For late ignition of a gas cloud formed by instantaneous release, it should be noted that ignition could occur before the cloud reaches its maximum cloud size or maximum travel distance from the release point. Therefore, the distances and cloud sizes in Tables 7.14 and 7.16should be regarded as the upper limit of the hazardous zone for the accidental release.

 

7.5.3.1         SINOPEC LPG/ Oil Depot

LPG Release

Table 7.14:    List of Consequences of Hazardous Events for the SINOPEC Depot (N11)

Facility

ID

Sub ID

Containment

P (barg)

T (oC)

Amount (kg)

Release Size

Jet Fire

Fireball

Flash Fire

VCE

 

 

 

 

 

 

 

 

Max Jet length (m)

Radius (m)

Duration (s)

Max Downwind Distance (m)

Heavy Building Damage (m)

Light Building Damage (m)

LPG import

A

1.1

ship tank

3.75

23

700000

rupture

 

236

26

830

 

 

LPG import

A

2.1

ship tank

3.75

23

350000

rupture

 

188

22

640

 

 

LPG import

A

3.1

ship tank

3.75

23

700000

rupture

 

236

26

830

 

 

LPG import

A

4.1

ship tank

3.75

23

700000

100mm

108

 

 

270

 

 

LPG import

B

1.1

marine loading arm

5.55

23

700000

100mm

108

 

 

270

 

 

LPG import

B

2.1

marine loading arm

5.55

23

700000

50mm

62

 

 

140

 

 

LPG import

B

3.1

pipeline

5.55

23

700000

150mm

149

 

 

380

 

 

LPG storage

C

1.1

tank

3.75

23

700000

rupture

 

236

26

830

405

810

LPG storage

C

2.1

tank

3.75

23

700000

100mm

108

 

 

270

405

810

LPG storage

C

3.1

tank

3.75

23

700000

25mm

33

 

 

62

405

810

LPG storage

C

4.1

tank

3.75

23

700000

5mm

10

 

 

8

 

 

LPG export

D

1.1

pipeline

5.55

23

700000

150mm

149

 

 

380

405

810

LPG export

D

2.1

cylinder

5.55

23

50

1mm

 

 

 

2

 

 

LPG road tanker

D

3.1

road tanker

5.55

23

8000

100mm

108

 

 

270

91

182

LPG road tanker

D

4.1

road tanker

5.55

23

8000

rupture

 

55

8

165

91

182

LPG road tanker

D

5.1

road tanker

5.55

23

8000

100mm

108

 

 

270

91

182

LPG road tanker

D

6.1

road tanker

5.55

23

8000

5mm

10

 

 

8

 

 

LPG road tanker

D

7.1

road tanker

5.55

23

8000

rupture

 

55

8

165

91

182

LPG road tanker

D

8.1

road tanker

5.55

23

8000

rupture

 

55

8

165

91

182

 

Petroleum Product Release

Due to the lack of available information on the petroleum product storage facilities at the two depots, it is not possible to directly model consequence distances from petroleum product release scenarios from the SINOPEC Depot.  A comparison between release consequence distances from an oil storage facility of a larger scale, and the distances from the dredging workers to the depot facilities was used to demonstrate the risk impact posed by the depot on the dredging workers. This is because the change in risk levels of the depots due to the dredging works, i.e. the presence of dredging workers within the Consultation Zone of the PHIs, is the main concern of this study.

Release consequence distances from the Permanent Aviation Fuel Facility (PAFF) EIA study [8], are used for comparison in this regard. That project related to a gross aviation fuel capacity of 264,000 m3.  Table 7.15 shows the release consequence distances from PAFF EIA study.

Table 7.15:    Maximum Representative Consequence Distances in the PAFF EIA [8]

Petroleum Product Release Scenario

Hazard Distance (m)

Jetty Transfer

 

Fire due to rupture/ leak of oil products from loaded vessel

236

Fire due to rupture/ leak of loading arm during unloading

69

Fire due to rupture/ leak of jetty equipment

236

Fire due to rupture/ leak of jetty riser

69

Fire due to rupture/ leak of submarine pipeline from jetty to tank farm ESD valve

148

Tank Farm Storage

 

Fire due to discharge from tank vent

Not significant

Tank head fire or explosion in tank head space

Not significant

Multiple tank head fires

Not significant

Tank failure due to overpressure

Not significant

Explosion in empty tank (under maintenance)

Not significant

Bund fire

18

Fire outside bund due to rupture/ leak of pumps, pipework and fittings

4

Fire on sea due to release through drainage

219

Fire due to instantaneous tank wall failure, bottom seam failure

< 399

Fire due to instantaneous tank wall failure, unzipping

< 399

Aircraft impact

< 399

Fire due to multiple tank failure

399

Tank boilover

Not significant

Fire due to release from top of tank due to overfilling

Not significant

Vapour cloud explosion or flash fire

Not significant

Fire due to 10% instantaneous release from the top of a tank

39

 

 

The nearest distances from the dredging works area to the SINOPEC Depot jetty and storage area are 257 and 494 metres respectively. It can be seen that the consequence distances under Jetty Transfer scenarios in PAFF EIA are less than 257 m and those under Tank Farm Storage scenarios are less than 494 m. This indicates that even when the SINOPEC Depot has similar storage and transfer capacities as PAFF, the dredging workers will not be affected by the hazard consequences from leakage of petroleum products.

Therefore, hazard scenarios from the petroleum product storage facilities at the SINOPEC Depot will give no (zero) risk impacts to the dredging workers of the Project.  Therefore, risks are quantified as zero.

 

7.5.3.2         ExxonMobil LPG/ Oil Depot

LPG Release

Table 7‑16: List of Consequences of Hazardous Events for the ExxonMobil Depot (N6)

Facility

ID

Sub ID

Containment

P (barg)

T (oC)

Amount (kg)

Release Scenario

Jet Fire

Fireball

Flash Fire

VCE

 

 

 

 

 

 

 

 

Max Jet length (m)

Radius (m)

Duration (s)

Max Downwind Distance (m)

Heavy Building Damage (m)

Light Building Damage (m)

LPG import

A

1.1

ship tank

3.75

23

850000

rupture

 

249

28

920

 

 

LPG import

A

2.1

ship tank

3.75

23

425000

rupture

 

201

23

710

 

 

LPG import

A

3.1

ship tank

3.75

23

850000

rupture

 

249

28

920

 

 

LPG import

A

4.1

ship tank

3.75

23

850000

100mm

108

 

 

270

 

 

LPG import

B

1.1

marine loading arm

5.55

23

850000

100mm

108

 

 

270

 

 

LPG import

B

2.1

marine loading arm

5.55

23

850000

50mm

62

 

 

140

 

 

LPG import

B

3.1

pipeline

5.55

23

850000

150mm

149

 

 

380

 

 

LPG storage

C

1.1

tank

3.75

23

850000

rupture

 

249

28

920

432

864

LPG storage

C

1.2

tank

3.75

23

425000

rupture

 

201

23

710

432

864

LPG storage

C

1.3

tank

3.75

23

170000

rupture

 

149

18

500

244

488

LPG storage

C

2.1

tank

4.04

23

850000

100mm

108

 

 

270

432

864

LPG storage

C

2.2

tank

4.04

23

425000

100mm

108

 

 

270

432

864

LPG storage

C

2.3

tank

4.04

23

170000

100mm

108

 

 

270

244

488

LPG storage

C

3.1

tank

4.04

23

850000

25mm

33

 

 

62

432

864

LPG storage

C

4.1

tank

4.04

23

850000

5mm

10

 

 

8

 

 

LPG export

D

1.1

pipeline

5.55

23

850000

150mm

149

 

 

380

432

864

LPG export

D

2.1

cylinder

5.55

23

50

1mm

 

 

 

2

 

 

LPG road tanker

D

3.1

road tanker

5.55

23

8000

100mm

108

 

 

270

91

182

LPG road tanker

D

4.1

road tanker

5.55

23

8000

rupture

 

55

8

165

91

182

LPG road tanker

D

5.1

road tanker

5.55

23

8000

100mm

108

 

 

270

91

182

LPG road tanker

D

6.1

road tanker

5.55

23

8000

5mm

10

 

 

8

 

 

LPG road tanker

D

7.1

road tanker

5.55

23

8000

rupture

 

55

8

165

91

182

LPG road tanker

D

8.1

road tanker

5.55

23

8000

rupture

 

55

8

165

91

182

Petroleum Product Release

The nearest distances from the dredging works area to the ExxonMobil Depot jetty and storage area are 699 and 968 metres respectively. Based on similar arguments as the petroleum product storage facilities at the SINOPEC Depot, hazard scenarios from the petroleum product storage facilities at the ExxonMobil Depot will give no (zero) risk impacts to the dredging workers of the Project.  Therefore, the risks are quantified as zero.

7.6              Frequency Assessment

7.6.1         Frequencies of Accidental Release Scenarios

After the consequence assessment of the 2 PHIs, a failure frequency assessment is conducted for the LPG release scenarios from the 2 depots, as specified in Tables 7.12 and 7.13. A base frequency is assigned to each failure cases, and multiplied by a factor based on the number of equipment units involved and the operation frequencies. The release frequencies are further distributed among a range of release sizes and the tank inventory to derive the frequencies of each specific event. These failure frequencies of the LPG release scenarios are summarised in Table 7.17 and 7.18.

Table 7.17:    Frequencies of Failure Events at SINOPEC Depot

Case

Facility

Failure Description

Event Frequency, per year

A1.1

LPG import

Tank rupture (full inventory)

6.9E-8

A2.1

LPG import

Tank rupture (half inventory)

2.8E-7

A3.1

LPG import

Catastrophic tank leak due to collision

6.8E-6

A4.1

LPG import

100 mm tank leak due to collision

6.1E-5

B1.1

LPG import

Full bore rupture of marine loading arms

6.8E-4

B2.1

LPG import

50 mm leak of marine loading arms

6.2E-3

B3.1

LPG import

150 mm leak of jetty pipeline

7.7E-5

C1.1

LPG storage

Catastrophic tank leak

2.0E-5

C2.1

LPG storage

100 mm tank leak

2.9E-5

C3.1

LPG storage

25 mm tank leak

1.6E-4

C4.1

LPG storage

5 mm tank leak

2.4E-4

D1.1

LPG export

150 mm leak of filling pipeline

7.7E-5

D2.1

LPG export

Leak of LPG cylinders

2.8E-1

D3.1

LPG road tanker

100 mm leak during road tanker filling

2.7E-5

D4.1

LPG road tanker

Rupture of road tanker on road

3.3E-6

D5.1

LPG road tanker

100 mm leak of road tanker on road

7.9E-6

D6.1

LPG road tanker

5 mm leak of road tanker on road

1.6E-5

D7.1

LPG road tanker

BLEVE during road tanker on road

5.8E-8

D8.1

LPG road tanker

BLEVE during road tanker loading

1.5E-5

 

 

Table 7.18:    Frequencies of Failure Events at ExxonMobil Depot

Case

Facility

Failure Description

Event Frequency, per year

A1.1

LPG import

Tank rupture (full inventory)

3.0E-8

A2.1

LPG import

Tank rupture (half inventory)

1.2E-7

A3.1

LPG import

Catastrophic tank leak due to collision

3.3E-7

A4.1

LPG import

100 mm tank leak due to collision

3.0E-6

B1.1

LPG import

Full bore rupture of marine loading arms

3.8E-4

B2.1

LPG import

50 mm leak of marine loading arms

3.4E-3

B3.1

LPG import

150 mm leak of jetty pipeline

4.3E-5

C1.1

C1.2

C1.3

C1.4

LPG storage

Catastrophic tank leak

100% inventory

50% inventory

20% inventory

 

2.7E-6

1.4E-6

2.7E-6

C2.1

C2.2

C2.3

C2.4

LPG storage

100 mm tank leak

100% inventory

50% inventory

20% inventory

 

4.1E-6

1.5E-6

4.1E-6

C3.1

LPG storage

25 mm tank leak

1.6E-4

C4.1

LPG storage

5 mm tank leak

2.4E-4

D1.1

LPG export

150 mm leak of filling pipeline

4.3E-5

D2.1

LPG export

Leak of LPG cylinders

2.8E-1

D3.1

LPG road tanker

100 mm leak during road tanker filling

2.7E-5

D4.1

LPG road tanker

Rupture of road tanker on road

4.6E-6

D5.1

LPG road tanker

100 mm leak of road tanker on road

1.1E-5

D6.1

LPG road tanker

5 mm leak of road tanker on road

2.3E-5

D7.1

LPG road tanker

BLEVE during road tanker on road

8.2E-8

D8.1

LPG road tanker

BLEVE during road tanker loading

2.1E-5

7.6.2         Event Tree Analysis

Event tree analysis (ETA) is used to develop the evolution of a failure event from its initial release to the final outcome scenarios, namely, jet fire, flash fire, fireball, etc. It depends on various factors such as release type (instantaneous or continuous), ignition sources and probabilities, and degree of congestion to cause a vapour cloud explosion.

The event tree for the LPG release scenarios in this assessment is shown in Figure 7.7. It has been adopted from the Route 9 EIA study [2]. The probabilities used are also shown in the event tree.

The event trees for the 3 above ground LPG storage vessels in ExxonMobil Depot N6 are further refined to include the possibility of BLEVE events upon flame jet impingement and unsuccessful fire protection considering they are installed aboveground. The outcome event tree is shown in Figure 7.8.

7.7              Risk Results

7.7.1         Risk Summation

Risk summation combines the estimation of the likelihood and consequences of hazardous events, as well as the meteorological data and population in the hazard effect zones, to give a numerical measure of the fatalities. The risk analysis is conducted by the SAFETI package and the outcome results are presented in terms of individual risk (as individual risk contours), and societal risk (as F-N curves or potential loss of life). The risk outcome will be compared with the Hong Kong Government Risk Guidelines set out in Annex 4 of the EIAO-TM, as specified in Section 7.1.4.

7.7.2         Individual Risk

The individual risk contours of the SINOPEC and ExxonMobil Depots are presented in Figures 7.9 and 7.10 respectively. The 1×10-5 per year risk contours extend slightly outside the PHI boundaries, but are mostly close to the site boundary and does not go into the proposed dredging works area. Further away from the depot and jetty, the risk gradually diminishes to lower risk levels. The individual risk levels of the two PHIs therefore marginally satisfy the Hong Kong Government Risk Guidelines for individual risk.

It should also be noted that individual risk is solely determined by the LPG/ oil depots (N6, N11) and is not related to the actual population. Therefore, individual risk is not affected by the presence of the dredging workers of the Project.

7.7.3         Societal Risk

F-N curves for the SINOPEC and ExxonMobil Depots before, during and after the dredging works project (at Years 2009, 2012 and 2014 respectively) are presented in Figures 7.11 and 7.12.

The societal risk levels for “all neighbouring population” (including dredging workers) for both depots have only insignificant changes from Year 2009 to 2012 to 2014. The reason for the change is due to changes in land, road and marine population nearby the PHIs. The F-N curves of the two PHIs all lie in the ALARP region, which is consistent with the previous Route 9 EIA study [2].

It should be noted that the proposed dredging project does not cause the societal risk levels of the two PHIs to go into the ALARP region. Comparing to the overall societal risk from the two depots, the presence of dredging workers of the proposed project is marginal. Therefore it can be concluded that with the dredging works project taking place, the societal risk levels of the LPG/ oil depots still satisfy the Hong Kong Government Risk Guidelines for societal risk.

7.8              Conclusion and Recommendations

7.8.1         Conclusions

This QRA study examined the effect from the proposed dredging work near Tsing Yi Island on risk levels posed by the SINOPEC N11 and ExxonMobil N6 LPG/ oil depots. Major hazardous incidents which could potentially impact on the dredging area were evaluated in terms of their hazard consequences and occurring frequencies. The overall risk levels show that the two depots marginally meet the Hong Kong Government Risk Guidelines, which is consistent with previous studies. The increase in societal risk caused by the presence of dredging workers is minimal comparing to the overall risk level, and is not permanent. Therefore it can be concluded that the risks posed by two PHIs on the neighbouring population and the dredging workers satisfy the Hong Kong Government Risk Guidelines.

The risks associated with operational phase activities relate to the infrequent need for maintenance dredging.  Maintenance dredging activities will be less frequent and involve smaller volumes of material compared to the capital works dredging and thus, it may be surmised that risks associated with maintenance dredging will similarly satisfy Hong Kong Government Risk Guidelines.

7.8.2         Further Mitigation Measures

In spite of the negligible additional risk, mitigation measures are recommended to further reduce the risks as low as reasonably practicable.

Sound communication channel should be established with the oil companies, Marine Department, and Fire Services Department for effective notification and emergency evacuation in case of accidents.

Proper safety and emergency training should be given to the relevant operation staff at the dredging site. Emergency plans and procedures should be prepared and drills should be performed periodically.

7.9              References

 

1.         EIA Study Brief No. ESB-198/2008 – Providing Sufficient Water Depth for Kwai Tsing Container Basin and Its Approach Channel.

2.         Route 9 between Tsing Yi and Cheung Sha Wan Detailed Feasibility Study EIA (Atkins China Ltd.), Highways Department, August 1999.

3.         Comprehensive Feasibility Study for the Revised Scheme of South East Kowloon Development EIA (Ove Arup & Partners HK Ltd.), Territory Development Department, July 2001.

4.         Harbour Area Treatment Scheme Stage 2A EIA (ENSR Asia (HK) Ltd.), Drainage Services Department, August 2008.

5.         Ministerie van VROM (TNO), Guidelines for Quantitative Risk Assessment, PGS3 “Purple Book”, 2005.

6.         Reeves, A.B., Minah, F.C. and Chow, V.H.K., ‘Quantitative Risk Assessment Methodology for LPG Installations’, Conference on Risk & Safety Management in the Gas Industry, EMSD & HKIE, Hong Kong, 1997.

7.         Code of Practice for Oil Storage Installations 1992, Building Authority, Hong Kong.

8.         Permanent Aviation Fuel Facility for Hong Kong International Airport EIA (ESR Technology Ltd.), Airport Authority Hong Kong, Feb 2007.

9.         Annual Traffic Census 2008, Transport Department, HKSAR Government.

10.        Committee for the Prevention of Disasters, Guidelines for Quantitative Risk Assessment “Purple Book”, CPR 18E, 2005.

11.        Projections of Population Distribution 2009-2018, Planning Department, HKSAR Government.