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1 INTRODUCTION
The safety of port manoeuvres of chemical tankers is
particularly important due to the risks associated with
the transport of dangerous cargoes.
Due to the features of dangerous cargo onboard a
margin for unnecessary risk is much lower in
comparison to ships carrying other cargoes. The
gravity and consequence of an accident is much
higher in comparison to other vessels due to character
of cargo onboard which can be:
− flammable/volatile/explosive,
− corrosive,
− self-reacting ,
− reacting with other substances (e.g. water )
− involving serious pollution in case of spill/release.
The explosion of a chemical tanker as a result of a
violent self-reaction of styrene monomer shown in
Fig. 1 illustrates the scale of hazards associated with
cargo on chemical tankers.
Figure 1. Chemical tanker explosion due to vigorous self-
reaction of Styrene Monomer [12] .
The usual consequences of an accident, such as
damage to the ship and port infrastructure, in this
case can lead to further consequences, usually not
expected for other types of vessels - fire, explosion,
environmental pollution or poisoning and can be
fatal.
Risk Assessment of Port Manoeuvres of a Chemical
T
anker Vessel
T. Abramowicz
-Gerigk, A. Hejmlich & M. Randak
Gdynia Maritime University, Gdynia, Poland
ABSTRACT: The development of smart port systems and autonomous navigation is related to the growing
interest in the systemic approach to risk assessment of port operations especially for the vessels transporting
dangerous cargo. The paper presents the general risk model of port manoeuvres of a chemical tanker vessel.
The risk model is based on Bayesian influence diagram allowing to determine the risk dependent on the
decisions made with respect to the applied safety options. The conclusions are based on real life near miss
examples and discussion of experienced Ship Masters.
http://www.transnav.
eu
the
International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 17
Number 4
December 2023
DOI: 10.12716/1001.17.04.
08
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Ports and terminals determine the precautions for
chemical tankers operation. The international
regulations and guidance for safe carrying hazardous
chemicals at sea are provided by a number of
conventions and codes i.e.: the consolidated editions
of international conventions Safety of Life at Sea
(SOLAS) and International Convention for the
Prevention of Pollution from Ships (MARPOL –
73/78), International Code for the Construction and
Equipment of Ships carrying Dangerous Chemicals in
Bulk (IBC Code), Code for the Construction
Equipment of Ships Carrying Dangerous Chemicals in
Bulk (BCH Code), International Safety Guide for Oil
Tankers and Terminals (ISGOTT), Tanker Safety
Guide (Chemicals), Ship to Ship Transfer Guide
(Petroleum), Safety in Oil Tankers, Safety in Chemical
Tankers, The International Maritime Dangerous
Goods (IMDG) Code, Supplement to IMDG Code
Medical First Aid Guide for Use in Accidents
Involving Dangerous Goods (MFAG) and Emergency
Response Procedures for Ships Carrying Dangerous
Goods Guide (EmS), Ship Oil Pollution Emergency
Plan SOPEP, Clean Seas Guide for Oil Tankers,
FOSFA (for Oils, Seeds and Fats), Prevention of Oil
Spillage through Cargo Pumproom Sea Valves,
Chemical Hazards Response Information System
manual (CHRIS Guide USCG), Chemical Data Guide
for Bulk Shipment by Water (Condensed CHRIS),
Material Safety Data Sheet (MSDS) for particular
cargo.
The ship master is responsible for understanding
and complying with local regulations.
The priorities of precautions that are taken by
chemical tankers before, during, and after cargo
operations have been previously studied by Arslan
[3], who proposed to use AHP (Analytic Hierarchy
Process) method. The study presented in this paper
concentrates on the safety of port manoeuvres
performed by a chemical tanker close to the terminal.
The ship-port-environment system has been
considered in the risk assessment study and formal
approach has been used in the development of a risk
model, including: hazards identification, possible
accidents related to the identified hazards, their
probability, consequences, risk prevention and risk
reduction options [7].
Taking into account the high level of uncertainty,
probabilistic knowledge about possible accidents or
knowledge based on experts opinions, the Bayesian
influence diagram was proposed for modelling the
risk [1,4].
The proposed general model can be further
developed with respect to its implementation in smart
port systems, autonomous integrated transport
infrastructure [8,14] and control systems of
autonomous ships [10].
The examples of dangerous and near miss
situations during port manoeuvres are presented. The
risk control options are analysed from the point of
view of the experienced ship master of a chemical
tanker.
2 PORT OPERATIONAL LIMITATIONS
2.1 Safe manoeuvring space
With a ship size similar to the size of the design ship
for a given port, safe manoeuvring space also depends
on the dimensions of the berths and locks with limited
access for tugs. Vessel size can be just on the limit for
compulsory use of tug or tugs and it may also leave
some hesitation in view of Ship Masters decision to
take a tug or not. This is related to commercial
pressure associated with demanding and competitive
market in order to reduce idle days of ship in
operation. In this case, the human factor is of great
importance [2].
Most common factor for compulsory use of tug
imposed by port authorities will be the size of a ship,
whether or not dangerous cargo is onboard and
whether the weather conditions, mostly wind force,
are within port limitations.
The manoeuvring areas limited horizontally by
narrow channels, berths and jetties too small to
accommodate the ship, tight turning areas, narrow
locks without fenders and small ratio of the water
depth to the ship's draught results in a very limited
UKC (under the keel clearance) when approaching
and mooring to the pier.
An example of a chemical vessel with corrosive
Sodium hydroxide solution cargo onboard, leaving a
small (23 meters wide compared to 19.8 m ship
breadth) Runcorn lock from Runcorn channel
(England) and entering bigger lock, stern first, port
side alongside, in order to get into Eastham dock, is
presented in Fig. 2
Figure 2. Runcorn – Eastham vessel shifting during the
night – upper figure, proceeding astern to Runcorn jetty
with 2 tugs on narrow bend, kicks ahead needed with
rudder in purpose to correct drift from the wind. ( cargo
onboard – Sodium hydroxide solution, cat Y, corrosive).
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The local knowledge about water levels is required
in order to fulfil UKC margins and safety
requirements. In case that a vessel is not complying
with regular company requirements (e.g. UKC=10 %
of dynamic draft), thorough risk assessment must be
performed and decision must be consulted with DPA
(Designated Person Ashore).
At times it is better to take less cargo onboard
during loading then later wait few days for water
level to rise just a few centimetres, what happens for
example in Swedish ports, with water level
fluctuations, it may be recommended to leave few
centimetres allowance during loading stage in port for
possible drop of water level on arrival at discharge
port.
2.2 Deck operations affecting navigation
Due to busy and complex character of cargo handling
activities on chemical tanker, some activities on deck
may still be performed even during pilotage stage of
navigation.
Mopping, steaming, checking of cargo tanks,
ventilation of tanks and works on deck may be still
present just before mooring. However some activities
are strictly forbidden in ports when the pilot is
onboard. For example ventilation of toxic and smelly
cargoes (e.g. containing benzene) which can be easily
smell by pilots. These operations shall be stopped at
this stage.
In case of steaming, in some conditions this
operation may affect maneuvering by limiting Ship
Master visibility on approach to a jetty. In this case
steam shall be stopped.
Steaming of mooring systems and equipment in
case of sub-zero conditions (e.g. Finland and Sweden
during winter season) shall be done well in advance.
Tank cleaning operations shall be limited in
confined waters to a minimum in purpose to reduce a
risk of black out. Power consumers like bow thrusters
shall have priority.
3 GENERAL RISK MODEL OF PORT
MANOEUVRES OF A CHEMICAL TANKER
VESSEL
In the ship-port-environment anthropo-technical
systems both the technical aspects and human factors
are considered [2, 6, 13, 15]. The factors considered in
the hazards identification and risk reduction options
processes are related to the ship, port and
environment.
3.1 Factors considered in hazards identification
The factors considered in hazards identification
related to technical aspects are as follows.
Factors related to the ship:
− chemical and physical properties of the ship's
cargo,
− technical condition of ship hull construction,
− technical condition of ship cargo systems,
− technical condition of ship handling systems,
− technical condition of the deck equipment –
mooring, towing, emergency towing and
anchoring systems,
− age of the ship,
− availability of ship handling aid systems,
− communication with the terminal,
− emergency equipment.
Factors related to the port:
− communication with the terminal,
− reliable weather forecast,
− current and tide information,
− pilotage,
− towing assistance,
− technical condition of cargo handling facilities,
− technical properties and condition of berthing
facilities, fendering and mooring systems,
− decision support systems: docking systems,
pilotage aid system,
− dangerous operations carried out close to the
vessel,
− availability of emergency services:
− firefighting services,
− emergency towing services,
− pollution response services,
− emergency medical services.
Factors related to the environment:
− shallow water conditions,
− wind,
− current,
− waves,
− fog,
− ships’ congestion in the port.
Human factors related to the following ship
personnel:
− Ship Master,
− Officer of Watch,
− deck personnel.
Human factors related to the following ashore and
port personnel,
− tug boat master,
− port pilot,
− VTS operator,
− harbour master office operator,
− berth personnel,
− designated person ashore.
3.2 Risk model of port manoeuvres of a chemical tanker
The risk model developed in form of the Bayesian
influence diagram includes decisions made by ship
personnel with respect to use of risk reduction options
having impact on the probability of events, cost of the
risk reduction options and consequences related to the
identified accidents.
The events in the model are random variables
represented by the nature nodes in the directed,
acyclic graph. The arcs of the graph show the causal
relationships between the dependent nodes. The
conditional dependencies between the linked events
are represented by probability tables assigned to the
nodes.
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Based on the conditional independence of
variables and the chain rule, Bayesian belief network
allows to determine the joint probability distribution
of the variables.
The decision nodes represent the risk control
options and their costs. The utility nodes represent
risks of possible accidents, including costs related to
their consequences.
The events – nature nodes of Bayesian influence
diagram considered in the general model are
presented in Tables 1-3.
Table 1. Definition of the events – berthing, mooring,
moored ship and unberthing
________________________________________________
Node Description of probability States
________________________________________________
Berthing Probability of an accident Safe
during berthing ALARP
Unsafe
Mooring Probability of an accident Safe
during mooring operations ALARP
Unsafe
Moored Probability of an accident Safe
Ship related to the moored ship ALARP
Unsafe
Unberthing Probability of an accident Safe
during unberthing ALARP
Unsafe
________________________________________________
Table 2. Definition of events - ship and port technical
conditions
________________________________________________
Node Node description States
________________________________________________
Ship Probability of failure on board ship Safe
ALARP
Unsafe
Port Probability of failure in port Safe
ALARP
Unsafe
________________________________________________
Table 3. Definition of events – external conditions
________________________________________________
Node Node description States
________________________________________________
Wind Probability of a dangerous wind Yes
speed and direction No
Current Probability of a dangerous current Yes
speed and direction No
Passing Probability of a dangerous impact Yes
vessel of a passing vessel No
________________________________________________
Table 4. Definition of risk reduction options – decision
nodes
________________________________________________
Node Node description States Cost keuro
________________________________________________
Tug Decision of tug boat Yes 1-1.5
boat assistance No
Leaving Decision on emergency Yes 103–105
port leaving the port No
Mooring Decision on application of Yes
lines additional mooring lines No
________________________________________________
Risk reduction options are related with decisions
to employ tug boats, leave the port and use additional
mooring lines. The costs of tug assistance during
berthing and costs related to emergency leave can be
estimated for the particular port and vessel [5].
For example the cost of slight impact with jetty is
up to 200 keuro e.g. touching dolphin as a result of a
failure to shift controls from central console to bridge
wing. Cargo spill , pollution can cause severe financial
loss – millions of euro, loss of reputation of a
company, in severe case could face bankruptcy. Fire
can cause severe financial loss – millions of euro.
The casualties mainly relate to accidents during
mooring operations, such as broken mooring lines or
structural damage to mooring equipment. There is
also a risk of an accident in the event of a collision or
collision with another object or vessel.
The definition of decision nodes of Bayesian
influence diagram are presented in Table 4.
The utility nodes of Bayesian influence diagram
presenting the risk of possible accidents are presented
in Table 5.
Table 5. Risk of possible accidents – utility nodes
________________________________________________
Node Node description
________________________________________________
RP Risk of port facility damage / delay in port
operation
RI Risk of people injuries
RF Risk of fatalities
RE Risk of environment pollution
RS Risk of ship damage
________________________________________________
The most important for development of the risk
model is the design of the network structure and then
input of the dependent probability values for the
defined nodes which allows for calculations of the
joint probability distribution for the nodes. The model
presented in the paper was developed using a
commercial tool for Bayesian belief network
development - Hugin Researcher - the computer
program with graphical interface, compiler and
system for design and use of knowledge base.
Bayesian network allows to dynamically assess the
probability of accidents. The information about the
occurrence frequency of the top event propagates
backwards through the network, changing the
probability of the primary events [9].
In the presented network, in the events of ship
damage or port facility damage, risks are calculated
on the basis of the joint probability distribution of
accidents and their costs dependent on states of the
events which can be negligible, minor, moderate,
major or catastrophic. In case of further results of ship
damage and port facility damage accidents like fire,
explosion and toxic leakage the consequences can be
personnel injuries, fatalities and environment
pollution.
The Bayesian risk model of port manoeuvres of a
chemical tanker is presented in Figure 3.
4 RISK CONTROL OPTIONS OF POSSIBLE
ACCIDENTS DURING PORT MANOEUVRES
The risk control options include proper exchange of
information between the vessel and terminal before
berthing, proper weather information, tug assistance
during navigation in difficult to manoeuvre and
dangerous areas, tug assistance during berthing,
unberthing, emergency port leave and proper
prediction and control of mooring forces [3].
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Figure 3. Bayesian risk model of port manoeuvres of a chemical tanker.
A layout, access and dimensions of approach area
relative to own ship and port itself with its
arrangements and aids must be safe at every stage of
approach and mooring.
With modern commercial pressure Master must
pay attention that a port of call chosen by a charterer
fulfils all criterions and all information about port and
weather conditions and that they are easily accessible
and comprehensive well in advance.
Master has overriding authority to refuse calling a
port if in his judgement it is not safe for navigation.
For example when not enough room is provided
during turning vessel in narrow waters with limited
UKC. Master may also refuse entering port if there is
no tug boat provided on demand of the Master as for
some ports, notice for a tug boat is long and a tug
must arrive from another port nearby.
4.1 Tug assistance
Tug assistance is an effective measure of reducing risk
in restricted waters and port approaches. In some
ports due to horizontal (tight bends, narrow channels)
and vertical (UKC) limitations tug assistance is
compulsory and tug is made fast before entering
rocky and narrow fairway. Tug boat is usually
connected but idle (Fig. 4).
Figure 4. Tug assistance near rocky bottom with limited
horizontal and vertical allowance.
4.2 Mooring forces prediction
Chemical tanker should be equipped with modern
winches providing tension and storage drums with
capacities equivalent to her size, displacement and
designed for expected weather conditions during her
lifetime. A brake of a winch shall be properly adjusted
to rope’s SWL with regular brake tests performed
onboard (Fig. 5), with the rendering point properly set
and brakes adjusted with use of torque wrench (Fig.
6).
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Figure 5.Winch brake test and calibration performed on
chemical tanker.
Figure 6. Torque wrench used for mooring in purpose to
apply correct force on a brake related to SWL of mooring
rope.
When this is done, before a rope brakes (possibly
causing damages and fatalities), a properly adjusted
brake will slack a rope avoiding parting of a rope. A
proper estimation and marking of snap back zones is
needed onboard chemical tankers in order to avoid
serious injuries cause by parting ropes.
A mooring lines number and service meaning
quantity and orientation of ropes, shall take into
account:
− loading condition of a ship (windage, inertia,
underwater section area) in case of currents,
− wind speed and direction relative to ship’s
windage area – present and predicted,
− speed and direction of current,
− special weather conditions like high swell (e.g
Portuguese ports like Sines ) requiring higher
number of ropes and spare ropes to be ready in
case of breaking,
− traffic conditions and passing-by vessels (deeper
draft vessels when going at higher speeds may
create moored ship surge, sway and yaw which
may break mooring ropes [10].
4.3 Emergency procedures
An example of emergency procedure for so called
‘break away from jetty ‘ shall be well known and
displayed among other contingencies. Engineers shall
be informed about possible adverse weather
conditions and possible need for power on short
notice. A minimum number of crew should be always
onboard during port stay.
Break away from jetty procedures should be
trained periodically. An example of a near miss
during unmooring on Thames river – under strong
current when the aft spring fail to let go is presented
in Fig. 7.
Figure 7. Example of a near miss during unmooring under
strong current.
5 CONCLUSIONS
The age of the fleet worldwide as a pursuit for savings
is caused by commercial pressure. However we need
to mention that most Oil Majors - chemical companies
have a limit of 20 years for chemical tanker but
shipowners are constantly trying to push the limit up
to 25 years as it has to be admitted that with
systematic and well planned maintenance system it is
possible to keep vessel suitable for busy trade for few
years more. In this case, it is particularly important to
analyse the risk of possible failures and their impact
on the occurrence of accidents.
The risk model proposed in the paper can be
implemented in decision support tools which can be
used by the ship owner, ship master, vessel traffic
services or harbour master, planning the port
operations.
The implementation of Bayesian network helps to
dynamically assess the system’s safety and to predict
probability and the risk of accidents.
ACKNOWLEDGEMENT
This work was supported by the project of Gdynia Maritime
University No. WN/2023/PZ/03.
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