This section of the Report
presents the findings of the hazard assessment for the Tung Chung to Ngong Ping
Cable Car System as stipulated in the Environmental Impact Assessment (EIA)
Study Brief No. ESB-068/2001 Section 2.1
‘Objective of the EIA Study’ part (viii) – to identify the risk to
the passengers and workers of the cable car should there be an incident at Hong Kong International Airport (HKIA)
fuel storage tank farm and Section 3.3.10 of the Study Brief.
The objective of the risk assessment is to quantify the potential risk to site workers and passengers on the cable car, during and following construction, should there be incidents in the aviation fuel storage area at HKIA (hereafter referred to as the tank farm). The risks are evaluated against the established criteria in Annex 4 of the Technical Memorandum on Environmental Impact Assessment Process (TM).
As defined in the Study Brief the scope of this assessment is to:
· identify all potentially hazardous scenarios associated with the aviation fuel storage at HKIA that will impose risk to cable car passengers and workers during construction and operational phases;
· conduct Quantitative Risk Assessment to assess the associated risk and express the risks in both individual and societal terms;
· identify practicable and cost effective risk mitigation measures if required.
This study brief deals with Dangerous Goods Storage in accordance with EIAO Technical Memorandum, Section 12, Annex 4 and Annex 22.
The following sections
present the background information used in the assessment, define potential
hazard scenarios, develop the consequence analyses and quantify risks and
provide recommendations and mitigations
measures where appropriate.
The relative location of the cable car with respect to the Aviation Fuel Tank Farm on the airport island is illustrated on Figure 10.1, from which it can be seen that the closest distance between the facilities is about 270m. Potential concerns associated with these two facilities being located in the same general vicinity relate to the risks to passengers or workers in the event of a fire, or a spillage of fuel which could ignite. The events triggering fires at the tank farm are described in detail in the subsequent sections.
For the construction phase the concerns relate to the number of cable car workers (up to 100 number) involved in construction of the Angle Station and towers. For the operational phase both the cable car workers (3-6 number) at the Angle Station and the passengers (refer to Section 10.2.4) need to be considered.
The scenario of
spillage of fuel being released to the drainage system and thereafter
discharging to the Sea Channel has been discounted as the drainage system at
the airport was specifically designed to avoid drainage from around the tank
farm discharging into the Sea Channel.
From the tank farm area the stormwater drains discharge to Tung Chung
Bay (to the east of the Airport) as shown in Figure 10.2. There are a series of measures in place at
the Airport to minimize the risks of discharge of fuel to sea such as flap
valves and shut down mechanisms for the drainage outlets as reported in the New
Airport Master Plan EIA Update (1998).
The stormwater system drains via a “Spill Trap Containment System” to
the Outfall No. 10 which is located, approximately 700m from the tank farm to
the east of the Airport Island as indicated in Figure 10.2.
As described in
Section 10.32,, the tank farm is enclosed within inner and outer
bunds. This is to ensure that there is
no direct discharge of any spilled fuel or stormwater run-off from the area
which could be contaminated by fuel without the run-off first passing through
an oil-water separator. Valves are provided on the stormwater discharge pipes
from the tank farm and will be normally kept closed. These are only opened for discharge of stormwater to the
airport drainage system under close supervision of the tank farm operations
staff. The provision of oil separators,
free swinging gates and outfall penstocks in the “Spill Trap Containment
System” further reduces the potential of a fuel oil draining to the sea from the
tank farm area.
As a fire in the tank farm would generate smoke plumes containing toxic gas such as CO and CO2 and heat which may pose certain risks to the cable car passengers, this study has assessed the risk to the users of the cable car system in the context of fire (heat and smoke) scenarios.
Figure 10.1 Location of Tank Farm
Figure 10.2 Drainage Basins and Outfalls
Aviation fuel, Jet A-1, is
stored in tanks above the ground at in the south side
support area of HKIA at with
a distance of 1.32 km from the southern runway of the HKIA
(refer to Figure 10.3). The tank farm
maintains an uninterrupted aviation fuel supply even during typhoons.
The tank farm comprises nine tanks: six large tanks, each with 20,000 nominal cubic metres of storage capacity (39m in diameter and 20m in height) and three small tanks with 10,000 nominal cubic metres of storage capacity (27.5m in diameter and 20m in height).
The tanks are enclosed by two bunds as illustrated on Figure 10.1 and the outer containment bund has a capacity of 75,000m3, which is equivalent to half of the total nominal storage capacity of the tank farm. Details of the site, inner bund and outer bund are shown in Annexes G-1 and G-2.
The drainage system at the airport was specifically designed to avoid drainage from around the tank farm discharging into the Sea Channel. From the tank farm area the stormwater drains discharge to Tung Chung Bay (to the east of the Airport) as shown in Figure 10.2. There are a series of measures in place at the Airport to minimize the risks of discharge of fuel to sea such as flap valves and shut down mechanisms for the drainage outlets as reported in the New Airport Master Plan EIA Update (1998). The stormwater system drains via a “Spill Trap Containment System” to the Outfall No. 10 which is located, approximately 700m from the tank farm to the east of the Airport Island as indicated in Figure 10.2.
There is no direct discharge of any spilled fuel or stormwater run-off from the area which could be contaminated by fuel without the run-off first passing through an oil-water separator. Valves are provided on the stormwater discharge pipes from the tank farm and will be normally kept closed. These are only opened for discharge of stormwater to the airport drainage system under close supervision of the tank farm operations staff. The provision of oil separators, free swinging gates and outfall penstocks in the “Spill Trap Containment System” further reduces the potential of a fuel oil draining to the sea from the tank farm area.
Air eliminators in the pipeline/tank farm fuel flow system remove entrained air and thereby minimize risk of explosion within the filters.
The area within 15m of the
storage tanks is classified as an area in which ignition sources must be controlled and where safety
procedures are being implemented by HKIA for operators working in the
area. All areas beyond 15
metres from the storage tanks are safe in
normal operations.
For security and safety reasons, stringent controls on personnel access has been implemented at the tank farm area and CCTVs and microwave security system have been installed.
Of particular significance to this assessment are the automatically controlled Emergency Shut Down Valves which are provided at the inlets/outlets of the pipework of the storage tanks and pumps control system for use in case of emergency. Fire fighting systems have been installed including a fresh water fire hydrant system, storage tanks spray water-cooling system and base foam injection system.
Figure 10.3 Layout of HKIA Island
The 5.7km long Bi-cable Cable Car System will convey up to 16 passengers in each of the gondolas/cabins between the two terminals, at Tung Chung and Ngong Ping, with a journey time of 17 minutes (in one direction). Initial capacity of the cable car system per direction per hour is 1500 passengers and can be increased to 3500. A total of 25 cabins will be operating in the initial stages of the Project. The height of the cable car at the Airport Island Angle Station is 50mPD (i.e. 43m from the ground). The Cable Car System should comply with the Aerial Ropeway (Safety) Ordinance (Cap. 211) and the Code of Practice of the Design, Manufacture and Installation of Aerial Ropeways (2002 edition) issued by the Electrical and Mechanical Services Department and any other amendments and existing ordinances in force.
Since details of the staffing of the cable car operation are not yet available, an estimation of the workforce employed during construction and operational phases is based on experience of similar systems as summarized in Table 10.1.
Table 10.1 Workforce estimation in Construction and Operation Stage
|
Construction Phase |
Operation Phase |
|
Cable Car site on airport island |
Angle Station |
||
Day |
Night |
||
Quantity |
100# |
3* |
6* |
* Information of workforce from Future Cable Car Operator.
# Estimated Figure.
The estimated number of passengers exposed to hazards associated with the operation of the tank farm is outlined in this section. Table 10.2 shows the estimated daily patronage of the cable car system extracted from the Tourism Commission, Economic Services Bureau.
Table 10.2 Estimated Daily Patronage
Year |
High Scenario |
Medium Scenario |
Low Scenario |
|||
Average Day |
Peak Day |
Average Day |
Peak Day |
Average Day |
Peak Day |
|
2006 |
7000 |
25300 |
5300 |
19100 |
3800 |
13600 |
2011 |
8100 |
29200 |
5900 |
21100 |
4200 |
15100 |
2016 |
9600 |
34800 |
6400 |
23000 |
4600 |
16500 |
Based on the assumption that the cable car operates 16 hours per day, the incoming patronage per hour is shown in Table 10.3 below:
Table 10.3 Calculated Hourly Patronage
Year |
High Scenario |
Medium Scenario |
Low Scenario |
|||
Average (/hr) |
Peak (/hr) |
Average (/hr) |
Peak (/hr) |
Average (/hr) |
Peak (/hr) |
|
2006 |
438 |
1581 |
331 |
1194 |
238 |
850 |
2011 |
506 |
1825 |
369 |
1319 |
263 |
944 |
2016 |
600 |
2175 |
400 |
1438 |
288 |
1031 |
When the Cable Car operator receives notification of a fire or suspected incident at the tank farm, he will immediately cease boarding passengers. Any passengers on the system at such times will continue their journey until all passengers are cleared from the system. It must be stressed that it takes 17 minutes to clear all passengers from the system. Thus the number of passengers on the system in each direction can be estimated [i.e. (Hourly Patronage / 60) x 17 minutes] and the results are given in Table 10.4 below:
Table 10.4 No. of Patronage in System per Direction
Year |
No. of passengers in system in a Tank Fire Hazardous Event |
|||||
High Scenario |
Medium Scenario |
Low Scenario |
||||
Average |
Peak |
Average |
Peak |
Average |
Peak |
|
2006 |
124 |
448 |
94 |
338 |
67 |
241 |
2011 |
143 |
517 |
104 |
374 |
74 |
267 |
2016 |
170 |
616 |
113 |
407 |
81 |
292 |
Aviation fuel is a mixture of aliphatic hydrocarbons with 10-16 carbon atoms and some aromatic hydrocarbons and naphthalene derivatives. It is a colourless/pale yellow oily liquid with a “fuel” odour. It is flammable and toxic if inhaled at high concentrations or ingested. According to Dangerous Goods Regulations, aviation fuel is classified as Category 5, Class 2 Dangerous Goods. The Institute of Petroleum has produced a code for area classification (IP, 1990a) which includes a system for classifying petroleum liquids including crude oil and its products into Classes 0, 1, II(1), II(2), III(1), III(2) and Unclassified based on their flash points. Under this system, the aviation fuel is classed as II(1) as its flash point is a minimum of 38°C .
The physical and chemical properties of aviation fuel are summarised in Table 10.5 below:
Table 10.5 Physical and Chemical Properties of Aviation Fuel (Jet A-1)
Property |
Value |
Molecular Weight |
156 g/mole |
Liquid density |
800 kg/m3 |
Boiling Point |
200-260oC |
Specific Gravity at 15oC |
0.8 (liquid) |
Flash Point |
38oC or above |
Flammable Limits |
0.7-5% vol. |
Burning Rate |
0.04 mm/sec |
An inspection of the EIA
Report (Ref.
1) for Permanent Aviation Fuel Facility (PAFF) for Hong Kong
International Airport was undertaken to draw out information by
which to determine whether the construction or operation of the cable car
system could be affected by the tank farm.
All the data and assumptions used were compared and contrasted to
identify differences. Table 10.6
summarizes the hazard scenarios considered
in both the PAFF and this study and highlights the differences. Further details
of each of the scenarios are given in the subsequent sections.
Table 10.6 Comparison of Hazard Scenarios
Scenario |
Considered in PAFF |
Considered in Tung Chung Cable Car Hazard Assessment |
Tank fire |
Yes |
Yes |
Tank to tank escalation |
Yes
|
Yes |
Bund fire |
Yes |
Yes |
Bund fire escalation |
Yes
|
Yes |
Catastrophic failure leading to failure of the top plate of tank |
Yes |
Yes |
Aircraft incident |
No (as the tank farm is not under the flight path) |
Yes (although as for the PAFF it was considered that the system is not under the flight path, this scenario is addressed later in this section) |
Hazards from Submarine Pipeline |
Yes |
Pipeline leakage is outside the scope of the EIA study brief. However this scenario has |
Hazards due to Marine Transport |
Yes |
No (Not applicable ) |
Hazards at the Jetty |
Yes |
No (Not applicable) |
Tank fire caused by Cable
Car Operations |
No (Not applicable) |
Yes |
Tank fire caused by activities during construction of cable car |
No (Not applicable) |
Yes |
A comparison of the fuel tanks assumed in the PAFF and those at the tank farm at HKIA is summarized in Table 10.7.
Table 10.7 Comparison of Tank Design of PAFF and HKIA
Feature |
PAFF Tank Farm |
HKIA Tank Farm |
Diameter |
40m |
39 m and 27.5m |
Height |
Between 23m to 32m |
20m |
Volume of the largest tank |
39,000 cubic meters |
20,000 cubic meters |
Height of Inner Bund |
4.6m |
~1.5m |
Height of Outer Bund |
2m |
~1.2m |
Distance between tank and inner bund wall |
10m |
Min. 10m
|
Distance between inner and outer bund walls |
8m |
12 – 75m |
ESD valves |
On the inlet and outlet pipeline of the tank farm |
Both on inlet and outlet with Nitrogen backup in case of electrical failure. |
ESD initiating |
Manual push-buttons |
Manual push-buttons |
Leak detection system |
Provided for the delivery pipeline |
Provided for the delivery pipeline (for testing purpose). The leakage test for each section of pipe to be performed fortnightly. |
Fire Fighting Facility |
Sea water pumps to provide fire water for tank cooling |
Fresh Water fire fighting system |
Tank Spray Cooling |
Yes |
Yes |
Base foam injection facilities |
Yes |
Yes |
Bund |
110% of the contents of the largest tank in the bund and secondary bund wall |
110% of the contents of the largest tank in the bund together with a outer bund that can hold 50% of the total volume |
Drainage discharge Manual Shut Off Valve |
Yes |
Yes |
Interceptor. |
Yes |
Yes |
Tank fire
Fixed cone roof tanks are generally used for flammable liquids and combustible liquids as is the case for aviation fuel, which is flammable with a flashpoint of 38°C or above. Tank fires are essentially treated as pool fires, in which the liquid surface and hence the base of the flame is elevated and is surrounded by a metal wall.
Tank-to-Tank Escalation
The Tank-to-Tank Escalation
can result in an adjacent tank fire.
However all
storage tanks at HKIA are installed with a water spray cooling system and the
adjacent tanks (in the sector opposite the tank on fire) will be cooled in the
event of a tank fire.
As mentioned in the PAFF
report
(Ref. 1),, Purdy’s studies on tank fire
escalation modelling have provided some general observations regarding the
escalation potential for non-volatile fuels (such as aviation fuel). A relatively long response time was found
for tank escalation to occur. The
radiation level on the adjacent tanks was approximately 13-15kW/m2
given the distance between tanks was 15m.
At this level the heat is not sufficient to threaten the structural
integrity of the adjacent tanks particularly when cooled by water spray. The studies also suggested that escalation
potential was greater for smaller diameter tanks (around 10m) and less for
larger diameter tanks, as in the case of this study (the diameters of the tanks
at HKIA are 27.5m and 39m).
In summary, the time
required to develop an escalation condition depends upon a number of factors
such as tank separation, water cooling, tank fire extinguishing system, wind
speed/direction as well as the emergency response time of Fire Services. In a tank farm fire drill it was demonstrated
that Fire Services could arrive the tank farm within three minutes from the
nearest Fire Station at HKIA. .Therefore the The time required scale for
a tank-to-tank escalation, with cooling, will be much greater
than the time sufficient for cable car passengers to
be evacuated (noting that the entire evacuation procedure for cable car
passengers requires 17 minutes). With reference to the above studies, detailed
analysis of tank-to-tank escalation fire hazard is deemed unnecessary in this
assessment because of the length of time taken for the escalation to
develop. However,
emergency plan for cable car passenger evacuation in the event of tank fire
needs to be developed (see Section 10.7).
Bund fire
A bund fire can result from release of liquid fuel from a tank caused by catastrophic failure, overfilling or pipe failures together with a subsequent ignition of the released fuel. There are a number of potential ignition sources such as hot works, vehicles, lightning, etc. Although there is a very stringent procedure to control the ignition source within the tank farm and the chance of ignition is small, the bund fire scenarios are addressed below.
Bund Fire Escalation
In the case where a bund
fire occurs at the tank farm following release of fuel into a bund, the water
spray cooling system would be activated. The water spray cooling system would
effectively reduce the amount of heat generated by the fire that may result in
an increase in the liquid temperature of the tank contents of the adjacent
storage tanks and correspondingly increase in the evaporation rate and
eventually lead to a tank fire. The operator of the tank farm would also report
the fire to the Fire Services Department. Under normal circumstances, the Fire
Services would arrive at the tank farm within 35 minutes to
reach the site and handle the fire. In
addition, API 650BS 2654 tanks are designed to withstand fire
engulfment for a considerable period before failure occurs by means of relief
of vapours in the event of fire by failing along the roof to shell
connection. Therefore failure due to
flame engulfment is expected to take a significant time, and by the time it
occurred, all passengers would have been evacuated (i.e. 17 minutes to clear
the system). As such, further analysis
is not necessary provided an emergency plan is developed for cable car
passengers (see Section 10.7).
.
Fire Following Overtopping of Bund
In the PAFF EIA Report the conservative scenario in which the top plate of the tank ruptures, is considered, releasing a quantity of fuel from the top of the tank instantaneously. This case is also relevant to the HKIA tank farm. Part of the released fuel could potentially overtop the bund wall due to momentum and initial surge or splashing of the liquid, even though a bund wall as well as a secondary containment earth bund is provided. It can be seen in Figure 10.4 (which indicates that the minimum distance between Tank T-11-006 and the outer bund wall is 32m and that for Tank T-11-008 is 22m) that spillage from tanks T-11-006 and T-11-008 are considered to be the worst case for overtopping the secondary containment bund with respect to the cable car.
The PAFF report assumed that the top most plate of the tank wall may fail resulting in spillage onto the bund. Each plate is about 3m high which represents about 10% of the tank height. Therefore it is assumed in the PAFF report that 10% of the total contents of a storage tank would spill out and fall vertically onto the bund like a waterfall and 10% of this spillage could further splash over the bund and fall onto the secondary bund. It was also assumed that 10% of the fuel falling onto the secondary bund would further overtop the secondary bund. The height of the tank ranged from 23 to 32m.
The height of the bund wall
in the PAFF is 4.6m and the distance between the tank and the bund wall is 10m.
The distance between the bund wall and the security wall (secondary bund) is
7.5m. Beyond the security wall, there is boundary fence which is 4m from the
security wall and a drainage ditch to be provided to trap any liquid splashed
over the security wall.. (i.e. the
splashing is completed and all liquid would be contained within 22m from the
tank)
By comparison, tanks at HKIA are 20m high with a top plate of 2.81m high. The maximum fuel level is at 19m. Therefore in the event of roof failure, about 1.8m of fuel could be released which is equivalent to about 10% of total contents of the tank.
It can be seen in Figure
10.4 that the minimum distance between a tank and the inner bund is 10m and the
minimum distance between the inner and outer bund is 12m. The inner bund is 1.2m high which is lower
than that in the PAFF. In view of the fact that there are uncertainties
associated with estimating the volume of fuel splashed and the HKIA tanks are
less high and have a wider distance between bund walls, it is appropriate to
adopt the same assumptions used in the PAFF report, i.e. 10% of the fuel may
splash over the inner bund and 10% of this may splash over the outer bund. As a result, about 100-200m3
(depending on the size of the tank) fuel will spread over the emergency access
road up to the gulley (the distance from this gulley to the Angle Station is about 200m but
still within the tank farm). This
assumption has been supported by a demonstration, andpictures
presented in Annex G3 show that liquid will collect near and drain into the
gulley provided along the emergency access road within the tank farm. Thus, none of the fuel will reach the public
road and most of the fuel will enter the stormwater drain provided in the tank farm. As described in Section 10.2.11.3 these drains connect to outfall
number 10 on the east of the Airport Island.
In the extremely unlikely case that if the fuel drain to sea via outfall
no. 10, the fuel would move to the surface and then if ignited a pool fire
could occur at sea. The pool fire would
be 700m away from the Angle Station and will not, therefore, affect the cable
car.
The fuel remaining on the emergency access road (within the tank farm) could be ignited to form a pool fire if an ignition source were present, although the probability of ignition is small within the site boundary. The minimum distance from such a fire to the Angle Station is around 200m.
About 10-20m3 of
liquid may overtop the outer bund and splashes onto the lawn area which is a
28m wide open dished grassed
area. A cross section showing the
details of bund walls and the lawn is given in Figure 10.5. A trial has been
carried out to assess how the far the fuel can reach when the liquid splashes on the
lawn area. The result shows that the fuel would reach approximately half width
of the grassed
area (demonstration pictures are
attached in Annex G3). The fuel will then drain into an open drainage channel,
which parallels the tank farm boundary fence within and along the grassed strip
(about 1.2m depth and 35cm width and 150m long). No fuel will reach the public
roadway. If an ignition source is
present, fire could develop along the channel. The closest distance from the
open channel drain to
the Angle Station is about 230m.
Aircraft Incident
The site is located at the
most southern part of the airport island with a perpendicular distance of
1.32km to the southern runway of the airport, 3.24km and 1.45km from the ends
of the southern runway. The site is further protected by a hill 68m high on the
southeast quadrant and is surrounded by a number of buildings. The physical environment provides shielding which reduces the chance of a direct hit on the
tanks farm by aircraft.
In addition, aircraft movements at HKIA are carefully controlled by air traffic controllers who will not permit any low flying aircraft from flying over or close to the tank farm, thus further reducing the possibility of aircraft striking the tanks. Aircraft taking off and landing are confined to the runways which are more than 1km away from the tank farm and the directions of taking off and landing will not take the aircrafts towards the direction of the tank farm. In accordance with the PAFF, aircraft crash is the only conceivable incident that can result in more than 10% of tank contents spilling instantly. However, as discussed above and shown in Annex G4, the estimated frequency of such accident is less than 1x10-9 per year, which is below the Societal Risk guideline frequency as stipulated in the TM, and therefore further consideration is not necessary.
Hazard of Cable Car to Tank Farm
As shown in Figure 10.1, the nearest alignment of the cable car system is about 270m from the tank farm. This separation distance is sufficient to prevent the tank farm being affected by any ignition sources that may arise during the operations of the cable car within the Angle Station. Even in the very rare case that a hill fire starts around the Angle Station, it will not affect the tank farm as it is separated by Scenic Road which serves as a fire break. In addition, fire protection systems and procedures are also in place to control fire risk and fire services will arrive the site within a few minutes.
During the construction of the cable car the work boundary will be 20m from the location of the Angle Station and Tower T2B, and activities within the construction site would be mainly at ground level and will be strictly controlled by method statements and procedures. Further, the separation distance is such that construction activities will not cause any hazards at the tank farm.
Therefore, the hazards arising from cable car construction activities need no further consideration.
Other Hazards
Other hazards such as
landslide, subsidence, typhoon, wind and earthquake, which could cause damage
to the tanks, have been addressed in the design in accordance with the relevant
engineering codes and standards adopted and therefore not considered
further.
Summary of Hazard Scenario
In summary, the hazard assessment in this report covers the following potential scenarios.
· Tank Fire;
· Fire within Inner Bund;
· Fire within Outer Bund;
·
Grass / Ditch
Fire; and
·
Pool fire at Sea Surface. .
Figure 10.4 Tank Layout
Figure 10.5 Indicative Cross Section
Flammable
liquid in the tank farm has such low vapour pressures that any hazards from
drifting vapour can be ignored. The
only possible sources of off-site risk are thermal radiation and toxic smoke
from fires.
The thermal radiation model
used in the PAFF report has
been adopted for this study. Aviation fuel fire is extremely smoky and the
clear flame is only a few metres high at ground and most is obscured by smoke.
As stated in the PAFF EIA report, modelling of pool fires incorporates the
effects of the smoke in the flame. This shows that there is a significant
reduction of transmissitivity which effectively shields persons near to the
flame. This drastically reduces the fatal effect distance beyond the edge of
the burning pool, particularly for large pools. The heat radiation from a smokye flame is 20KW/m2. Sensitivity
studies show that persons beyond 3m away from the fire are able to move away
from fire and will
survive. Hence, there is no fatality beyond 3m away from
the fire.
The smoke plume trajectories are assessed using full scale fire data(Ref. 2).
Tank fires are treated as pool fires and the base of the flame is elevated and surrounded by a metal wall. The effect of tank fire is limited to the tank radius plus 3m (i.e. 22.5m from the centre of a large tank and 16.75m from the centre of a small tank) which is confined to the site boundary. Therefore, tank fires do not impose any risk to either cable car passengers or workers.
For a bund fire, the effective distance will be limited to 3m from the bund wall which again is within the site boundary. Thus, bund fires do not impose any risk to either cable car passengers or workers.
As shown in Annex G3.4, fuel
will be contained in the open drainage which will go to underground at a point
which is 230m from the Angle Station.
Although there is unlikely to be an ignition
source near the drainage channel is unlikely,
fire may still occur along the ditch (length of the ditch is approximately 130
metres fire would be about 20m). Therefore, the closest distance from the
possible fire in the
ditch this location to the Angle Station is
230m. Applying the r+3 model again
shows that no risk is posed to cable car passengers, staff and workers.
The pool fire would be is
about 700m from the Angle Station and would not impose any risk to either cable
car passengers, staff or workers.
A smoke plume generated from
the fire will initially follow the tilt angle of the flame due to its high
temperature. An illustration of the
flame tilt angle is shown in Figure 10.6.
In the study report by HSE (Ref. 2),Research Report
No. 96/1996) Development of Pool Fire Thermal Radiation Model, a number of full scale fire experiments
were used for model validation. These provide a good reference on the actual
tilt angles and flame length under different scenarios. The data set contained different type of
fuels and pool diameters. Data relevant
to this study havebeen extracted from the HSE report and tabulated in Annex G5. It
can be seen in Annex G5 that the maximum recorded tilt angle is 60o and any fire at distance greater than 75m the smoke should pass
over the cable cabin. A summary of the
distance from fire from cable cabin is summarized in Table 10.8.
Figure 10.6 Illustration of Tilt Angle
Table 10.8 Summary of Distance from Fire
Fire Scenario |
Minimum Distance from Cable Car (m) |
Safe |
Tank Fire |
280 |
75 |
Inner Bund Fire |
270 |
75 |
Outer Bund Fire |
200 |
75 |
Ditch Fire |
230 |
75 |
Sea Fire |
700 |
75 |
According to Annex G5, the maximum recorded tilt angle of a flame is
60o.and
the safe distance from the fire is 75m.
By comparing with Table 10.8, it is concluded that the smoke plume will pass
over the cable car and the passengers will not be engulfed by the smoke.
As shown in the previous
section, no scenario is expected to result in any harm to passengers, workers
or staff. Therefore, the risk to passengers, staff and workers are zero, lying
below the lowest frequency of the acceptable region of the TM Annex 4..
Hazards associated with the
Fuel Storage facilities on the HKIA adjacent to the alignment of the
Cable Car System have been identified and analysed.
Four major
hazards Fivre
scenarioss-
tank fire, inner
bund fire, and outer
bund fire, ditch
fire and pool fire on the sea surface have
been considered.
In all scenarios, the
distance from the fire to the cable car cabin are all over 200m and based on
the heat radiation model developed for the PAFF, the resulting risk to life is
zero. In regard to the smoke effect, the plume will rise well above the cable
car cabin and therefore has no impact on
passengers, staff or workers. In
conclusion, the tank farm will pose no individual and societal risk to
passengers, staff or workers. Therefore,
the risks are acceptable when compared with the Risk Guidelines in the EIAO -
TM (Annex G-16).
Any emergency plan Effective communication channels should
be established developed between
the cable car operators,
the and tank farm operator, the Airport
Authority and emergency services to ensure passengers can be evacuated from the cable car that the former be immediately informed of any tank
farm events so that emergency procedures can be carried out in a
timely manner in the event of an
tank
farm incident.
Communication
andeEvacuation procedures
should be agreed
between the cable car operator, developed with the
tank farm operator, the Airport Authority and emergency services.
The emergency plan should be tested and reviewed annually.
1. Environmental Impact Assessment Report for Permanent Aviation Fuel Facility, Mouchel, 2002.
2. Development of Pool Fire Thermal Radiation Model, HSE Contract Research Report No. 96/1996.