This appendix analyzes the potential hazards identified in the HAZID session documents as part of the MQRA. This analysis was conducted by the DNV team following the MQRA HAZID session using the HAZID log sheets as well as research on specific topics as required
Hazard Registers are presented for the potential hazards. Each Hazard Register begins with a description of the potential hazard, causes, consequences and safeguards. Then a typical risk assessment potential scenario is developed. In this potential scenario development, the frequency of the scenario is considered. Where the frequency is less than the lower bound of the Hong Kong EIAO criteria (1x10-9 /year), the scenario is not considered credible. The conclusion on the credibility of the scenario is provided in the risk evaluation section of the Hazard Register. Those scenarios that are credible will then be considered in the MQRA risk analysis. The Hazard Registers are not listed in order of priority.
2.1
High-Energy
Ship Collision
A powered high-energy ship collision of a large ship at near right angles into the side of the LNG carrier is estimated to be a worst-case scenario. Breach of containment is possible if the collision energy is sufficiently high. Such a scenario could possibly lead to fire, potentially affecting populations on the water as well as onshore. The fire would be fought by existing fire fighting equipment that is standard on an LNG carrier. These include, but are not limited to, automatic fire detection and suppression, manual fire fighting equipment together with the water deluge that coats the entire deck and outer hull of a carrier in the event of an emergency.
This potential scenario will be
evaluated along the entire transit route to both Black Point and
2.2
Collisions
between Gas Carriers
Along the route of the LNG
carrier, it has been considered whether it is possible for two gas carriers to
be in the channel at the same time.
This situation is not anticipated for
Considering the volumes of LNG
to be delivered, it is not anticipated that two LNG carriers (one inbound, one
outbound) would be transiting
Considering a collision scenario between an inbound LNG carrier and an LPG vessel, traffic management safeguards are in place to assist in the minimization of vessel collisions.
The
Grounding will be addressed in the detailed analysis in the MQRA.
At Node 4 of the Black Point
route, the LNG carrier will be passing under the Tsing
Ma Bridge, a heavily traveled bridge connecting Tsing
Yi Island to Lantau and linking
When an LNG
carrier is nominated for discharge in
This scenario will be included in the detailed analysis of grounding scenarios as part of the MQRA.
2.5
Hazard
Register – Black Point
Black Point Hazard
No. H1: Grounding
Black
Point Hazard No. H2: Ship Collision - Powered Collision of
LNG carrier into another vessel
Black
Point Hazard No. H3: Ship Collision – Drifting Collision
Black
Point Hazard No. H4: Ship Collision - Powered Collision of
another vessel into the LNG carrier
Black Point Hazard No. H5: Ship Collision (Striking) – Powered
Collision of LNG vessel into obstructions
Black Point Hazard No. H6: Sinking / Foundering
Black
Point Hazard No. H7: Breach of
Cargo Containment
Black
Point Hazard No. H8: Fire and Explosion
Figure 2‑1 – Event Tree for Fire and Explosion
Black Point Hazard No. H9: Aircraft Impact into LNG Carrier During
Takeoff/Landing from
2.6
Hazard
Register –
Figure 2‑2 – Event Tree for Fire and Explosion
2.7
Events
Excluded from the Analysis
The following section details the scenarios that have been excluded from
the analysis. The scenarios have
been judged to either not result in a breach of cargo containment, have a
frequency of less than 1x10-9 per year, or do not increase the
consequence (hazard to life).
Further analysis (performed as needed) is also discussed.
2.7.1 Events without Breach of Cargo Containment
1. 750mm and 1500mm Grounding Events
For the grounding scenario, it was decided to only consider a small release (250mm inner cargo tank hole size), given that large and medium releases (750mm and 1500mm inner cargo tank hole sizes, respectively) related to grounding were considered unlikely, and are below the frequency criteria.
The Sandia
report conducted an analysis for the penetration of a double-hulled tanker, and
determined that the penetration would need to be approximately three meters
before generating a hole in the inner hull (ref. 03). The Sandia report does not consider an accidental grounding
event to result in cargo tank breach.
To date there has not been a loss of containment of LNG due to
grounding. The two grounding events
that have occurred at 12 and 17 knots did not lead to a breach of
containment. As the speed of the
LNG carrier in
2. Drifting Collision between LNG carrier and another vessel
The drifting collision between
an LNG carrier and another vessel is described in the earlier sections related
to Black Point and South Soko Hazard No. H3. The speed of the current in the
3. Breach of Containment from Pipework/Equipment on LNG Carrier
Breach of containment from pipework or equipment on the LNG carrier would occur due to spontaneous failures (material defects, construction defects, fatigue, corrosion, etc.) and/or operation errors. Any release from the carrier equipment would be localized to the carrier and would be mitigated by the safety systems on board, such as the fire water protection systems. As detailed in the Black Point and South Soko Hazard No. H8, in the 40 year history of LNG carrier transit there has not been a fire/explosion on board that resulted in a breach of containment.
2.7.2 Events with Frequency of < 10-9 per year
1. Breach of Cargo Containment
A cargo containment breach due
to material defect, fatigue, extreme environmental conditions, overfilling,
etc. is described in the earlier sections related to Black Point and South Soko Hazard No. H7.
The tank construction materials are very highly corrosion
resistant. Forecasts will be
available to assist in making any decision for avoidance of adverse weather to
limit hull stresses from sloshing and potential structural fatigue. Onboard operational procedures will
describe how to avoid overfilling of tanks. If there would be a potential for
failure, this would have occurred in the open seas given the increased load to
the carrier in these conditions and not in
2. Potential Aircraft impact into the LNG Carrier
The hazard of an aircraft impacting the LNG carrier is described in the earlier sections related to Black Point and South Soko Hazard No. H9. The frequency of this event (estimated at 4.7x10-10) showed that the likelihood of aircraft impact on an LNG carrier is below the EIAO criteria and was thus not considered further in the MQRA analysis.
2.7.3 Events without Increase to Consequence
1. Potential LNG spill / fire / explosion in the carrier void space
The
potential to have an LNG spill in the carrier void space that would lead to
breach of containment from a second LNG tank due to embrittlement
or that would lead to a fire or explosion that may also lead to a breach of
containment from a second LNG tank is addressed more fully in Appendix III,
Section III.2. The Sandia Report (ref. 03) considers several incident
scenarios and assesses the potential for and impacts of LNG carrier
damage. Sandia
draws its conclusions from “embrittlement scoping
analyses (that) were conducted to assess the potential damage to an LNG carrier
from small and large LNG spills based on available fracture mechanics data and
models”. Sandia
concludes:
· While accidental
incidents could lead to minor to moderate damage to a LNG carrier, they would
not lead to severe structural damage and the potential for cascading damage to
other tanks.
· Should there be a
secondary event, “This cascading release is not expected to increase
significantly the overall fire size or hazard ranges, but the expected fire
duration would increase.”
2. Sinking / Foundering
The sinking / foundering of an
LNG carrier is described in the earlier sections related to Black Point and
South Soko Hazard No. H6. Capsize or sinking of the LNG carrier
would most likely result from extreme weather. In the 40 years of LNG carrier
operations, a sinking event has never occurred. According to the Stolt
Nielsen Transportation Group (ref. 04), the Draught Fore at Normal Ballast for Ship Stolt Aquamarine (whose length is 176.8 meters) is 7.8
meters. This is higher than the
maximum wave height in
The carrier would avoid operating in severe weather conditions that exceeded its design criteria. Thus the low likelihood of such an event deemed the scenario not credible to include in the analysis.