QRA for MTRCL WIL 2007

Legislation requirement and evaluation criteria

10.4 The key legislation and guidelines that are considered relevant to the development of the proposed West Island Line project are as follows:-

· Dangerous Goods Ordinance, Chapter 295;

· Environmental Impact Assessment Ordinance (EIAO), Chapter 499; and

· The EIA Study Brief, Section 3.4.6

EIAO Technical Memorandum (EIAO-TM)

10.5 The requirement for a QRA of projects that involve the storage, use and transport of dangerous goods where a risk to life is a key issue with respect to the Hong Kong Government Risk Guidelines (HKRG) is specified in Section 12 of the Environmental Impact Assessment Ordinance Technical Memorandum (EIAO-TM).

10.6 The relevant authority for a QRA study relating to an explosives magazine storage facility, the transport and subsequent use of the explosives is the Environmental Protection Department (EPD), as specified in Annex 22 of the EIAO-TM.

10.7 Annex 4 of the EIAO-TM specifies the Individual and Societal Risk Guidelines.

Hong Kong Government Risk Guidelines (HKRG), EIAO TM Annex 4

10.8 Individual risk is the predicted increase in the chance of fatality per year to an individual due to a potential hazard. The individual risk guidelines require that the maximum level of individual risk should not exceed 1 in 100,000 per year i.e. 1 x10^-5 per year.

10.9 Societal risk expresses the risks to the whole population. The HKRG is presented graphically in Figure 1. It is expressed in terms of lines plotting the frequency (F) of N or more deaths in the population from incidents at the installation. Two F-N risk lines are used in the HKRG that demark “acceptable” or “unacceptable” societal risks. The intermediate region indicates the acceptability of societal risk is borderline and should be reduced to a level which is “as low as is reasonably practicable” (ALARP). It seeks to ensure that all practicable and cost effective measures that can reduce risk will be considered.

Explosives Store (300kg Capacity)

Figure 1 Hong Kong Government Risk Guidelines

Study Objectives and Methodology

10.10 The objective of the QRA study is to assess the risk to life of the general public from the hazards that arise from the storage, use and transport of the explosives that are required to facilitate the construction of the WIL project. The results of the QRA are compared with the HKRG.

10.11 The detailed requirements of the study are (see section 3.4.6 of the EIA study brief):

· To identify all credible and applicable hazardous scenarios associated within the boundaries of the construction site during the transport, storage and use of explosives for blasting operations;

· To carry out a QRA to determine risks to the surrounding population in both individual and societal terms;

· To compare the individual and societal risks with the Criteria for Evaluating Hazard to Life stipulated in Annex 4 of the EIAO-TM;

· To identify and assess the practicable and cost effective risk reduction measures as appropriate; and

The methodology of the hazard assessment shall be agreed with the Director taking into account relevant previous studies.

10.12 The elements of the QRA are shown schematically in Figure 2. It includes the following:-

· Relevant data on the proposed storage magazine, the transport from the magazine and the use of explosives at the blast face, as well as population and vulnerable receptors, such as slopes, retaining walls etc., in the vicinity of the tunnel construction and proposed transport routes were collected and reviewed.

· A structured study, involving a “what-if” analysis, was conducted to identify all the hazards associated with the storage, transport and use of the proposed blasting explosives. A review of literature and accident databases was also undertaken. These formed the basis for identifying all the hazardous scenarios for the QRA study.

· The frequencies, or the likelihood, of the various outcomes that result from the hazards associated with the storage and transport of blasting explosives were taken from published references; such as the UK HSE, TNO, or from previous EIA QRAs that have been accepted by the relevant authority. Where necessary, these frequencies are modified to take account of project specific factors.

· The frequencies of scenarios associated with the use of explosives at the blast face were established using fault tree analysis, in conjunction with a human factor assessment to evaluate human error probabilities.

· For all identified hazards, the consequences of the event were modelled.

· The consequence model employed by the QRA varied depending on the location of any explosion, i.e. above or below ground, and upon the receiver, i.e. slope, building or person.

· The consequence and frequency data were subsequently combined using ERM’s proprietary software Riskplot ^TM to produce the required risk estimates.

· Finally, the results from the risk assessment were compared to the HKRG. Recommendations have been made where required to ensure compliance with relevant best practice, and to reduce the hazard by strengthening various vulnerable receptors.

Figure 2 Schematic Diagram of QRA Process

Facility Details

Project Overview

10.13 WIL Construction is scheduled to commence in early 2009 for completion in 2014. A significant length of the WIL will be excavated in rock. The amount of rock to be extracted is approximately 480,000 m³. The rock excavation strategy as well as the interfaces between the various contractors are shown in Figure 3.

10.14 Two types of explosives will be used for the construction of WIL by Drill and Blast methods. These are:

· Cartridged Emulsion Explosives, which is classified as an explosive Class 1.1D under UN Classification and as a Category 1 (Explosive and blasting agents) Dangerous Goods under the Hong Kong Dangerous Goods Ordinance; and

· Bulk Emulsion Precursor, which is classified as an oxidising agent Class 5.1 under the UN Classification system and as Category 7 (Strong supporter of combustion) under the Hong Kong Dangerous Goods Ordinance. It is not classified as an explosive until it is sensitised immediately prior to use.

10.15 Cartridged emulsion will be delivered from the Explosive Magazine to the various construction sites by the appointed contractors using trucks licensed by Mines Division. The bulk emulsion precursor will be transported to the blast sites within the Adits/Tunnels by the appointed third party supplier. Bulk emulsion will not be stored within the magazine.

10.16 The location for the underground project magazine is an underground store near a disused Government Facility Site with an entrance near Victoria Road (see Figure 4). The proposal is to use an existing flat platform of land to access an underground store built into the mountainside beneath Mount Davis.

10.17 In much lesser explosive quantities, detonators, primers and detonating cords will be used to initiate the blast at the working face depending on the blast requirement. These are also classified as Class 1.1 explosives under the UN classification system and Category 1 (Explosives and Blasting Agents) under the Hong Kong Dangerous Goods Ordinance. Detonators approved for use in Hong Kong are of the Non-Electric Type, ie. chemically initiated.

10.18 For the purpose of this study, it is assumed that the construction project will use cartridged emulsion explosives only. This represents the worst case as the use of Bulk Emulsion Precursor will significantly reduce the amount of cartridged emulsion (Cat 1.1D explosive) required to be stored and transported.

Storage Magazine Details

10.19 The proposed magazine is to be built into the mountainside beneath Mount Davis and located near a disused Government Facility Site with an entrance near Victoria Road. The design, construction and operation of the magazine, including the transport of explosives and detonators to the point of usage, will be in accordance with the Mines Division requirements.

10.20 The magazine will comprise an access tunnel 335m long, in an extended U layout, with explosive storage chambers constructed off the side of the access tunnel. The access tunnel portals will be located adjacent to one another and overlook the Sulphur Channel. The explosive storage chambers will be located from the mid-point along the tunnel, at the area with maximum depth below the ground surface.

10.21 The overall storage capacity of the magazine is 2400kg of blasting explosives. The magazine is to comprise nine (9) chambers. Each chamber is designed to store a maximum of 300 kg of explosives. Eight chambers will store cartridged emulsion, detonating cords, boosters, and primers. The ninth chamber will be used solely for the storage of detonators.

10.22 The storage chamber for the detonators shall be sufficient to hold 9000 detonators, equivalent to two days supply. The detonators have a very low explosive mass and contain less than 1 gramme of high explosives per detonator. Therefore, the net explosive quantity from the total amount of detonators stored is less than 9 kg.

10.23 The magazine design incorporates an automatic fire detection and alarm system along the entire magazine tunnel length. Fire fighting measures such as fire hydrant system are also provided in the magazine.

10.24 The magazine portals will have re-enforced concrete barriers or portal barricades. These will be positioned in front of the entrance and exit adits of the magazine, and designed in accordance with appropriate international standards. The barricade walls are to be faced with a material designed to retain any possible debris that may be propelled from the magazine adits.

10.25 The magazine will also have necessary security arrangements. These include

· 2.5m high security fence topped with razor wire;

· Electric flood lights evenly spaced along the security fence;

· Close Circuit Television (CCTV) camera mounted at 6m above the magazine ground level;

· 24hr security patrols with at least two (2) armed guards during the day and three (3) during the night;

· Guard dog; and

· A 3 key system such that the authorised shotfirer, the contractor’s representative, and the magazine manager have separate keys, with all three (3) keys required for access to the chamber.

Transport Route Details

10.26 The overall intent is that Mines Division will deliver explosives daily to a maximum of one construction site and the project magazine, from where explosives will be transferred to the point of use by the contractors.

· Two deliveries will be made each day to most of the delivery points. The first delivery each day will be made in the early morning when roads will be relatively quieter.

· Loads will be limited to a maximum of 125kg per truck, which is the maximum load expected for the project.

10.27 The Cartridged Emulsion Explosives will be delivered to the various construction sites using the public roads as shown in Figure 5. The proposed site delivery points are the access shafts at:

1. Ex-police quarters, Kennedy Town;

2. Kennedy Town Swimming Pool (Smithfield Road);

3. Site at Kennedy Town Praya;

4. Site at end of South Lane; and

7. Site at Sai Woo Lane.

10.28 According to the current programme of work, delivery of cartridged emulsion explosives to points 1, 2, 3, 4 and 7 will be required from 2009 to 2011. Construction Phase I will require delivery of cartridged emulsion to Points 1 to 4 and 7 while Construction Phase II will only require delivery of cartridged emulsion to Points 3 and 4. There will be no overlap between the two phases.

10.29 Other access points will not be used for delivery of explosives from the magazine.

10.30 The maximum amount of anticipated daily deliveries of cartridged emulsion by the contractors to points 1, 2, 3, 4 and 7 for Construction Phase I is summarised in Table 1 below, while the maximum anticipated daily delivery to points 3, 4 for Construction Phase II is summarised in Table 2 below.

10.31 The deliveries to point 7 will either be carried out in the morning or in the afternoon. In addition to cartridged emulsion, detonating cords and cast boosters, will be stored and transported. The explosives delivery quantities are summarised in Table 1 and Table 2 for Construction Phase I and Phase II respectively. Construction Phase I has the highest transport frequency per year and hence been selected as the basis of the QRA.

Contractor	Delivery Point	Daily AM Delivery (kg/day)	No of Trips AM	Daily PM Delivery (kg/day)	No of Trips PM	Consumption (kg/day)
Contractor B	1 – Ex-police-quarters, Kennedy Town	80	1	0	0	80
Contractor B	2 – Kennedy Town Swimming Pool	80	1	0	0	80
Contractor C	3 – Site at the Kennedy Town Praya	125	2	125	2	500
Contractor C	4 – Site at the end of South Lane	80	1	80	1	160
Contractor D	7 – Site at the Sai Woo Lane	80*	1*	0*	0*	80

* Delivery may be carried out during PM instead of AM

Table 1 Explosives Delivery Quantities – WIL Construction Phase I

Contractor	Delivery Point	Daily AM Delivery (kg/day)	No of Trips AM	Daily PM Delivery (kg/day)	No of Trips PM	Consumption (kg/day)
Contractor C	3 – Site at the Kennedy Town Praya	80	1	80	1	160
Contractor C	4 – Site at the end of South Lane	80	1	80	1	160

Table 2 Explosives Delivery Quantities – WIL Construction Phase II

10.32 The licensed explosives delivery vehicles will have the following safety features:

· Diesel powered

· Battery and fuel isolation switches

· Forward mounted exhaust with spark arrestor

· Two fire extinguishers

· Lockable wood lined steel magazine mounted on the vehicle tray

· Fold down / up explosives warning signs and rotating flashing light

Use of Explosives Details

10.33 Explosives will be used for the initial construction of the storage magazine as well as for the WIL alignment. Adits / access tunnels will also be constructed by blasting.

10.34 The initial excavation of the magazine access tunnel will be by mechanical methods. This will extend for 40 m until the tunnel has passed beneath Victoria Road. Drill and blast excavation will then be adopted for a further 10 m for trial blasting, followed by full face excavation if ground conditions are suitable.

10.35 The WIL alignment will be constructed in a similar manner as the magazine adit/tunnel. The adit blasting will generally commence at the bottom of the shafts, which are at typical depth of 20-40m but can be as deep as 80-90m near UNV Station. Blasting cover protection will be provided to all shafts prior to blasting being carried out in the adits.

10.36 The following safeguards will be implemented during blasting.

10.37 Vibration Monitoring. It is a requirement to monitor every blast in Hong Kong to record blast induced ground vibrations. A dedicated Geotechnical Engineer is responsible for ensuring that the controlling and other nominated sensitive receivers for each blast are monitored to record the vibration levels in terms of Peak Particle Velocity (mm/sec).

10.38 Trial Blasts. Trial blasts will be carried out for the first series of blasts for the tunnels and adits and different areas or sectors of the project if required. The trial blasts will be used to demonstrate that the different types of blasting are safe, and the blasting monitoring and control procedures are effective. The trial blasts are conducted with cartridged emulsion explosives.

10.39 Advance Notice of Blasts. As part of the process of issuing a License to Possess and a Permit to Use dangerous goods, Mines Division will require that highly visible warning notices/signs be posted at several locations to warn the public that blasting will take place. These warning signs will be posted near the intended blasting location, even though all blasts will be conducted underground. The Contractor is required to write the blasting date and time on the notice.

10.40 Contractors are required by Law to have a comprehensive Safety Management System and this is implemented and supervised by on-site safety teams. Independent third party auditors make annual checks of documentation and safety records.

Population Data

10.41 Population data used for the storage and transport risk assessment have been collected by a combination of survey, the Code of Practice for Fire Safety (which defines the maximum occupancy requirement for the design of commercial buildings), Planning Department Zoning Plans and the census. Three types of population have been considered:

· Pedestrian population on footpaths and pavements next to delivery routes;

· Road population; and

· Building population.

10.42 For the use of explosive, all the features along the WIL alignment have been considered in a three dimensional analysis. The features subject to the study include man made slopes and retaining walls, existing man made features, natural terrain hillside and boulders, existing buildings and structures, and utilities. The population data was determined for the features that may be impacted by the hazards.

10.43 Details of population adopted in this Hazard to Life assessment are provided in Appendix 10.

Hazard Identification

10.44 Hazard identification consisted of review of explosive properties, review of scenarios in previous relevant studies, review of historical accidents and discussions with blasting specialists. In addition, an expert panel review was commissioned by ERM/MTRC to review the key assumptions and methodology for the risk assessment for the storage, transport and use of explosives in the context of the WIL Quantitative Risk Assessment. The review was held at ERM office in Hong Kong on 21-23 July 2008.

Type of Explosives

10.45 The blasting explosives configuration to be used for WIL will be either:-

· A Detonator, containing less than a gram of high explosive such as PETN, which is sufficient to detonate a Primer. The primer can be a single stick of cartridged emulsion, or 12 grams of PETN or Pentolite (PETN/TNT mixture). This in turn provides sufficient energy to set off the sensitised bulk emulsion that is loaded into the blast hole.

· Alternatively, a number of cartridged emulsion sticks can be loaded into the blast hole and ignited by a single detonator.

10.46 Both of the cartridged and bulk emulsions contain mainly ammonium nitrate (single salt), water, hydrocarbon such as fuel oil, and aluminium (only for the cartridged emulsion). Bulk emulsion is less sensitive than the cartridged emulsion, as indicated by the requirement of an explosive booster to initiate its detonation.

10.47 Cartridged Emulsion and Bulk Emulsion Precursor will not explode due to friction and impact found in normal handling. However, they can be detonated under heat and confinement or severe shock, such as that provided by an explosive. In a fire, pools of molten ammonium nitrate may be formed and if the molten mass becomes confined it may explode. In a fire ammonium nitrate may melt and decompose with the release of toxic fumes (mainly oxides of nitrogen).

Hazards of Explosives

10.48 Explosives present a hazard to both property and people. This hazard manifests itself in the following five ways:

· Blast and pressure wave;

· flying fragments or missiles;

· thermal radiation;

· cratering; and

· ground shock.

10.49 Blast and pressure waves can cause injury due to sensitive human organs such as the ears and lungs. However, considerable overpressures are required for fatalities to occur, and consequently people need to be fairly close to the scene of the direct explosion effects to be significant.

10.50 Other effects due blast or over-pressure are associated with collapse of buildings and other structures/ objects or the impact of debris and fragments from damaged building structure, and the vehicle or container in which the explosives are held. Alternatively, injury may occur when people are ‘swept’ away, or due to the violent movement of internal organs within the body.

10.51 An explosion will involve the formation of a short duration fireball, which is formed as the fuel content of the emulsion is oxidised. However, although a fireball may be produced it will be of very short duration. Generally it is considered that the thermal hazards from an explosives detonation event are of less concern than the blast and fragment hazards.

10.52 An explosion in an underground storage chamber may produce external airblast from two sources; the exit of blast from existing openings such as the magazine adits, and the rupture or breach of the chamber cover by detonation. However, airblast hazards from a blast that ruptures the earth cover are negligible relative to the ground shock and debris hazards.

10.53 The detonation of explosives liberates energy by a rapid chemical reaction process, which produces and sustains a shock wave in the surrounding rock. The degree of vibration of the rock particles decreases with increasing distance from the blast. However, the vibration of the rock particles can cause damage and structural failure to buildings and other structures/ objects if it is sufficiently strong.

Review of Incidents

10.54 A review of reported safety incidents involving the use of explosives (industrial applications) was carried out. Records were retrieved mainly from the UK Health and Safety Executive (UK HSE)’s Explosives Incidents Database Advisory Service (EIDAS), US Mine Safety and Health Administration (MHSA) and Western Australia’s Department of Consumer and Employment Protection (DOCEP). The records provided are also supplemented with information obtained from various sources. Analysis of accident data are provided in the Appendix 10.

Scenarios for QRA Study

10.55 Scenarios for the QRA study were identified based on the review of incident records and previous similar QRA studies of explosives.

10.56 Scenarios considered for the transport of explosives are:

· Accident involving explosives delivered and transferred from magazine to delivery point 1

· Accident involving explosives delivered and transferred from magazine to delivery point 2

· Accident involving explosives delivered and transferred from magazine to delivery point 3 – Construction Phase 1

· Accident involving explosives delivered and transferred from magazine to delivery point 3 – Construction Phase 2

· Accident involving explosives delivered and transferred from magazine to delivery point 4

· Accident involving explosives delivered and transferred from magazine to delivery point 7

10.57 Scenarios considered for the storage of explosives are:

· A fire leading to the detonation of a full load of explosives within the magazine access tunnel whilst transferring explosives to or from the appropriate storage chamber; and

· A fire within any explosive storage, or detonator, niche causing the detonation of the full quantity stored within that particular niche.

10.58 Scenarios considered for the use of explosives are:

· Higher vibration generated by the blast face due to human errors and other reasons such as manufacturing defects causing deviation from the confirmed design;

· Higher vibration and air overpressure due to the detonation of a full load, 125kg, of explosives within the tunnel whilst transferring explosives to the appropriate blast site.

Frequency analysis

10.59 The details of the frequency assessment are provided in Appendix 10. The results are summarised below.

Frequency analysis for Transport of Explosives

10.60 The basic event frequencies assumed for road accidents were based on that ‘The Risk Assessment of the Transport of Explosives in Hong Kong QRA Report’ (ref. 4) due to its relevancy to WIL project, ie. transport of explosives in Hong Kong.

Event	Event type	Value
Vehicle crash	Frequency	1.8 x 10^-7 /km
Crash fire	Frequency	7.7 x 10^-11 /km
Non-crash fire	Frequency	1.4 x 10^-9 /km
Explosives initiation in fire	Probability	0.1
Explosives initiation in impact	Probability	0.001
Explosives initiation due to unsafe Explosives	Frequency	3.28 x 10^-12 /km

Table 3 Explosives Initiation Fault Tree Inputs

10.61 The frequency of explosives initiation during road transport is thus estimated as 3.31 x 10^-10/km, using a fault tree approach.

Frequency analysis for Storage of Explosives

10.62 The overall initiating event frequency within the storage magazine is based upon the UK HSE recommended value of 1 x 10^-4 per storehouse year (see Section 6.1.1 of Appendix 10).

Frequency analysis for Use of Explosives

10.63 A failure mode analysis was carried out to determine the potential failure modes associated with the use of explosives, leading to higher vibration. The scenario of 2 or more maximum instant charges (MIC) detonated at the same time was identified for the risk assessment. Fault tree analysis was conducted, in conjunction with human factor assessment to determine the occurrence frequency of 2 or more MIC detonated at the same time.

10.64 Table 4 summarises the overall frequency for failure scenarios leading to higher vibration for the whole WIL project. The blast linear length refers to the total pull length by the drill and blast operation. For the WIL alignment, the blast linear length includes the two running tunnels, two station blocks and associated adits and is estimated as about 9.3 km. For the Magazine Store, the blast linear length covers the access tunnel and the 9 niches, and is estimated about 0.4 km.

Sections	Blast Linear Length	Occurrence Frequency for multiple MIC detonated at the same time per Section (Occurrence for the whole project)
Sections	Blast Linear Length	2MIC	3MIC	4MIC	5MIC	6MIC
WIL Alignment	9.3 km	4.09E-01	1.16E-03	6.86E-06	6.86E-06	6.86E-06
WIL Magazine Store	0.4 km	1.05E-02	2.73E-05	1.89E-07	1.89E-07	1.89E-07
Overall for WIL project	9.7 km	4.19E-01	1.19E-03	7.05E-06	7.05E-06	7.05E-06

Table 4 Overall Frequency for Failure Scenarios leading to Higher Vibration for the Whole Project Phase

Consequence analysis

10.65 This section gives a brief summary of the approach adopted to model the consequences of an explosion within the magazine. Details are given in Appendix 10.

10.66 The probability of fatality due to blast over-pressure, have been estimated using the method detailed by the UK HSE Explosives Storage and Transport Committee (ESTC) (ref. 5). The probability of fatality due to the possible damage / failure of a building, or slope, due to ground shock has also been modelled using methods detailed with the Hong Kong CEDD Geo Reports (ref. 7-8). The fatality contours are calculated at 1%, 50% and 90% fatality.

10.67 Ground shock or vibration levels at a given receptor will depend on the distance between the receptor and the blasting point. The estimation of ground vibration levels has used the method published in the Hong Kong CEDD Geo Guide 4 Cavern Engineering (ref. 6).

Consequence Distances

10.68 The consequence distances for explosion events using the ESTC model are summarized in Table 5. In this table, the ‘indoor’ refers to the population located inside buildings, and the ‘outdoor’ refers to the population located outside buildings ie in open area. A sample calculation of ground vibration level is shown in Table 6.

Scenario	Description	TNT eqv. (kg)	Indoor		Outdoor
Scenario	Description	TNT eqv. (kg)	Harm Prob.	Impact distance (m)	Harm Prob.	Impact distance (m)
R01	Initiation of explosives during transport of explosives from magazine to delivery point 01 via route 01	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
R02	Initiation of explosives during transport of explosives from magazine to delivery point 02 via route 02	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
R03	Initiation of explosives during transport of explosives from magazine to delivery point 03 via route 03	120	90%	15	90%	12
			50%	18	50%	13
			1%	42	1%	16
R04	Initiation of explosives during transport of explosives from magazine to delivery point 04 via route 04	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
R07	Initiation of explosives during transport of explosives from magazine to delivery point 07 via route 07	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
S01	Initiation of explosives at delivery point 01	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
S02	Initiation of explosives at delivery point 02	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
S03	Initiation of explosives at delivery point 03	120	90%	15	90%	12
			50%	18	50%	13
			1%	42	1%	16
S04	Initiation of explosives at delivery point 04	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
S07	Initiation of explosives at delivery point 07	77	90%	13	90%	11
			50%	15	50%	11
			1%	36	1%	14
M1	Explosion within magazine chamber 1 – 8 (Cartridge Explosives)	300	90%	17	90%	21
			50%	17	50%	24
			1%	22	1%	63
M2	Explosion within magazine chamber 9 (Detonators)	9	90%	5	90%	7
			50%	5	50%	8
			1%	7	1%	20

Table 5 Consequence Distances for Explosive Initiation using ESTC Model

Feature	Min Distance from closest chainage (m)	Closest Blast Chainage	Explosive charge used (kg)	PPV expected (mm/s) - 2 charges per delay	PPV expected (mm/s) - 3 charges per delay	PPV expected (mm/s) - 4 charges per delay	PPV expected (mm/s) - 5 charges per delay	PPV expected (mm/s) - 6 charges per delay
Bld1	33	SYPSHW_EB_100010	4.1	61	78	93	106	119
Bld2	29	SYPSHW_WB_100013	3.6	66	85	101	116	129

Table 6 Sample Calculation of PPV Level for each Feature at 2 or more MIC detonated at the same time

Risk Summation

Individual Risk Results

10.69 The individual risk (IR) contour associated with WIL project are shown in Figure 6, Figure 7, Figure 8 and Figure 9. In these figures, the ‘indoor’ refers to the population located inside buildings, and the ‘outdoor’ refers to the population located outside buildings ie in open area.

10.70 The IR contours for ‘indoor’ and ‘outdoor’ have been presented separately as the fatality probability is different for indoor and outdoor population. The current version of the Riskplot model enables to present indoor and outdoor fatality separately. This approach is more rigorous than the equivalent fatality model since the effect distances for indoor and outdoor fatality could be quite different.

For the delivery routes, it is observed that no section of routes has an IR exceeding 5 x 10^-8 per year. The highest risk contour at 1 x 10^-7 (in red colour of Figure 6 and Figure 7) represents the scenario of detonation of a full load of explosives within the tunnel whilst transferring explosives to the blast site, as part of use. For rock excavation using explosives, features at risk were identified and the maximum risk of fatality to any individual is estimated as 4.4 x 10^-10 per year. This is much lower than the Individual Risk Criteria of 1 x 10^-5 per year.

10.71 The IR contour for magazine is a 2 dimensional representation and hence does not account for the relative elevation of the magazine portal with respect to the receptor at risk. Also considering the most exposed individual in the vicinity of the magazine, the individual risk is below 1 x 10^-5 per year and hence is acceptable.

Societal Risk Results

10.72 The societal risk results for the transport, storage and use of explosives have been combined to produce the overall societal risk results (Figure 10).

10.73 During phase 1 of the construction, there is an option to deliver explosives to point 7 at AM or PM time, whereas deliveries to other points will be as per the timing indicated (see Table 1). The FN curve for transport has been presented for delivery to point 7 pm case which is the worst amongst the am and pm case for pt 7 and it includes delivery to other points as well. The FN curve for use of explosives covers construction of the WIL alignment and the magazine store.

10.74 The risks for all cases are within the Acceptable Region as per EIAO.

10.75 The potential Loss of Life (PLL), or equivalent fatalities per year, is given in Table 7. The total PLL for the whole WIL project is 3.44 x 10^-5 per year, or equivalent to, one fatality every 30,000 years.

Figure 10 FN Curves

Case	PLL (per year)	Percentage Contribution (%)
*Transport of Explosives*
Delivery of explosives from magazine to delivery point 1	1.26E-06	3.66%
Delivery of explosives from magazine to delivery point 2	1.68E-06	4.89%
Delivery of explosives from magazine to delivery point 3	9.39E-06	27.29%
Delivery of explosives from magazine to delivery point 4	6.04E-06	17.57%
Delivery of explosives from magazine to delivery point 7	8.80E-06	25.57%
*Use of Explosives*
Construction of magazine	1.13E-08	0.03%
Construction of WIL alignment	1.26E-06	3.67%
Detonation of explosives within the tunnel whilst transferring explosives to the blast site at delivery point 1	8.99E-08	0.26%
Detonation of explosives within the tunnel whilst transferring explosives to the blast site at delivery point 2	1.74E-07	0.51%
Detonation of explosives within the tunnel whilst transferring explosives to the blast site at delivery point 3	1.82E-06	5.29%
Detonation of explosives within the tunnel whilst transferring explosives to the blast site at delivery point 4	3.35E-06	9.73%
Detonation of explosives within the tunnel whilst transferring explosives to the blast site at delivery point 7	4.28E-07	1.25%
*Storage of Explosives*
Proposed magazine, including transport within the adits	9.04E-08	0.26%
Total	3.44E-05	100.00%

Table 7 Potential Loss of Life

References

1. MTR, West Island Line, Consultancy Agreement C703, SYP and UNV Stations, and SHW to KET Tunnel, Blast Assessment Report, Volume 1-8, June 2008

2. MTR, West Island Line, Consultancy Agreement C704, KET Station and Overrun Tunnel, Modifications to SHW Station, Blast Assessment Report, Volume 1-3, July 2008

3. MTR, West Island Line, Consultancy Agreement C703, SYP and UNV Stations, and SHW to KET Tunnel, Explosives Magazine at Victoria Road Controlling Blast Report, June 2008

4. DNV The Risk Assessment of the Transport of Explosives in Hong Kong, EPD 1997.

5. HSC, Selection and Use of Explosion Effects and Consequence Models for Explosives, Advisory Committee on Dangerous Substances, 2000

6. CEDD, Geoguide 4 - Guide to Cavern Engineering, Chapter 5, pp77-78

7. CEDD, GEO Report 15, Assessment of Stability of Slopes Subjected to Blasting Vibration, by H.N. Wong & P.L.R. Pang, 1992

8. CEDD, GEO Report 81 Slope Failures along BRIL Roads : Quantitative Risk Assessment and Ranking, by ERM-Hong Kong, Ltd, 1999

9. Lees, Frank P, Loss Prevention in the Process Industries, second edition, 1996.

10. Lees, Frank P, The Assessment of Major Hazards: A model for fatal injury from burns, trans IChemE Vol 72, Part B, 1994.

11. Merrifield, R. and Moreton, P A. An Examination of the Major Accident Record for Explosives Manufacturing and Storage in the UK. Journal of Hazardous Materials A:63 (1998) 107-118. 1998.

12. Guidelines for Quantitative Risk Assessment. CPR18E. “Purple Book”. Committee for Prevention of Disasters (The Netherlands). 1999.

13. Advisory Committee on Dangerous Substances (ACDS), Major Hazard Aspects of the Transport of Dangerous substances, HSC 1991.

10. Hazard to life

Introduction

Background