PREVENTION OF MARINE
POLLUTION FROM SHIPS
Preventing Marine Pollution from Ship
• Identify various ship operations generating
• Distinguish tank operations resulting in
• State the hazards involved in handling
• Explain safety measures in handling petroleum
In order to avoid marine pollution from ships,
activities on board vessels should be taken with
extreme care. Lack of safety measures increases
the chance of spilling oil or harmful substances.
This chapter deals with ship’s operational
activities that generate marine pollution.
Emphasis on standard safety operating
procedures in the handling of petroleum cargo is
given in this chapter
SHIPS OPERATIONS GENERATING POLLUTION
The common causes of pollution from routine shipboard
operations are as follows:
• Ships taking in or transferring bunkers or disposing of or
transferring fuel, fuel residues and oily bilge water
• Tanker operations such as cargo loading/discharging, tank
cleaning, ballasting operations
• Discharge of hold bilges or ballast water on vessels other than
• Washing of decks covered with cargo remnants or hydraulic oil
which has leaked from deck machinery
• Discharge of sewage
• Disposal of galley and other garbage
-the operation of taking on board fuel.
- in most cases, bunkering is a major cause of operational oil
spills for all types of vessels. The ship’s officer-in-charge of
monitoring this task has to be alert and experienced in this field.
The areas of safety concern are as follows:
• The position of overflow and air pipes
• Overflow tank and sounding pipes
• Depth indicators of all fuel tanks
• Overflow alarm system
MEASURES TO PREVENT OIL SPILL DURING OPERATIONS
a. Fitting of scupper plugs and checking that drain plugs of
bunker, manifold and fuel tank air pipe containment “save-
alls” are in place
b. Establishing communication with supply control position and
agreeing on maximum pumping rate and pressure. Ensure that
any signals to be used are thoroughly understood
c. Checking the conditions of hoses and couplings before and
d. Checking blanks available and hose string of sufficient length
to allow for normal for normal movement of vessel.
e. Checking all valves in required position and tank vent pipes
free from obstruction before bunkering commences.
f. Taking accurate sounding of all tanks before and on
completion of bunkering in oreder to verify the amount of fuel
g) Barge/ shore tank sounding and/or meter readings should also
be checked before and after bunkering to help resolve any
problem concerning quantity.
h) Taking frequent sounding during bunkering and rate of
delivery slowed down during topping of.
i) Ample warning should be given to supplier of need to reduce
delivery rate and the final shutting off.
j) Vessel should be upright and even keel throughout the
TRANSFERRING OF FUEL
-Transferring is done either within the ship or from ship-to-ship
Ship-to-ship > transfer or lightening may occur either in a port area
or at sea
If transfer is from one ship to another ship, risk is also considerable.
Safety measures should be undertaken to prevent the release of
oil into the water. The measures are as follows:
a. Fenders are properly placed when a vessel is to be positioned
alongside the damaged vessel for the transfer of oil (in case of
b. Before transfer begins, a lightening plan must be detailed so that
vessel shall stay at even keel.
c. Clear languages or communication instructions and signals must
be adopted by both ships.
d) All pieces of equipment must be in good condition, this includes
the hoses, couplings, etc.
e) Experienced personnel who have the skills in the delicate
operations must be deployed.
f) Emergency procedures must be adopted by both vessels.
BILGE WATER DISCHARGE OPERATIONS AND
>Bilge water discharge should be done to shore facilities. However
in order to discharge water from bilges at sea, a series of
conditions are provided by technical Annex I of MARPOL
73/78. For the purpose of monitoring discharge of oily ballast
water or tank washings from cargo tanks, installations of an oil
discharge monitoring and control system is required together
with fitting of oil/water interface detector.
For the purpose of monitoring discharge of oily bilge water and
oily ballast water from fuel tanks, installation of oil filtering
equipment is required. Different equipment should be attached
to oil-filtering equipment depending on the gross registered
tonnage of the ship.
Regulation 14 of the revised Technical Annex I reuires that any
ship off 400 GT and above but less than 10,000 GT shall be fitted
with oil filtering euipment, which design is approved by the
administration. It should be noted before the revision of
technical Annex I of MARPOL 73/78, the oil filtering equipment
requirement was within Regulation 16 of Technical Annex I
The equipment requirements for oil-water separating equipment
and oil filtering equipment are as follows:
a) Oil-water separating equipment – It may include any
combination of a separator, filter, or coalescer and also a single
unit designed to produce an effluent with oil content of less than
b) Oil filtering Equipment- It includes any combintaion of a
separator, filter or coalescer and also a single unit designed to
produce an effluent with oil content no exceeding 15ppm. It is
intended to use equipment attached to oily-water separating
equipment certified for an effluent of less than 100ppm
The following are the regulations relative to fitting the filtering
• When the level of effluents discharge more than the required
15ppm, the bilge alarm system activates.
• The oil filtering equipment should be strongly suited for
The equipment requirements for oil-water separating equipment
and oil filtering equipment are as follows:
• It is fitted in areas where flammable atmosphere may be present
• Electrical support attachment should be equipped with safety
equipment and installed in the safe areas.
• The equipment is designed to function automatically but
manual control is also provided in case of emergency.
• The system should be able to operate at least 24 hours of
normal duty without attention.
• The bilge alarm has an oil content meter. The meter can
withstand corrosion arising from saltwater. The meter is fitted
with an alarm device, which is set automatically to alert crew of
the ship. The alarm activates when the effluent exceeds 15ppm.
The alarm also operates automatically when the meter fails to
function during a warm up period or de-energized.
Tankers carry a variety of petroleum products. Tankers are
considered as the single largest contributor of marine pollution.
The introduction of supertankers created public concerns in
both developing and advanced countries. Oil pollution from
tankers originate from two principal sources. These are as
1. Various types of tanker accidents.
2. Normal tanker operations(i.e. tank cleaning, ballasting, and
other operational activities involving discharge of oil overboard)
Aside from the tanker accidents and normal tanker operations, the
dry-docking activities of these types of ships also add to the oil
pollution. However, the normal tanker operation is considered
as the main source of marine pollution from tankers.
In this regard, it is extremely important that all loading and
unloading operations are done with all the necessary
precautions. This practice reduces the risk of unnecessary oil
release into the water that pollutes the sea but also ascertains
that lives and properties are not endangered.
STANDARD SAFETY PROCEDURES FOR TANKER
The standard safety proceduresin the following tanker operations
are normally followed to avoid accidents that may entail marine
A. Pre-loading Operations
i. Before loading, a communication and signaling system
should be agreed upon between the ship and shore
personnel. For a standard ship, a shore safety checklist is
used and the items on it are checked.
ii. A loading plan is drawn between the ship and the shore
wherein loading sequence, stoppages, etc. are stated. The
ullage is calculated to which the cargo is to be loaded
iii. Fire fighting equipment and gears are placed close to the
manifold and ready for immediate use. Measures are taken
to prevent oil from flowing overboard in case of leakage of
hose couplings, etc. the tank lids are closed gastight and the
tank vent risers are put in loading position.
iv. The ullage meters are lowered to their lowest position. The
ships cargo lines are set right as in the case with tank valves.
If only one product is to be loaded, the valves in the main
and the crossover lines may all be kept open. The suction
and discharge valves of all pumps are shut.
v. The cargo line valves in the pump room are to be set right.
The terminal will connect their lines to the ship’s manifold
by means of hoses or steel pipes. After all the checking, the
ship can indicate to terminal that their valve/s now may be
opened and loading can start. The time the ship is ready to
load is noted on time sheet. Inert gas installation should be
v. …installation should be shut off. The gases in the tanks are
blown out during loading and dislodged by cargoes.
B. During Loading Operations
i. Loading should start slowly to check if connections are oil
tight and also to avoid static accumulation. Checks should
be made if oil flows overboard via the seachests in the
pump room and the cargo in indeed flowing into the tanks.
ii. The speed of loading may rise gradually to an agreed speed
or allowable hose or chicksan pressure. Soon after loading
has begun, the terminal and ship will take samples of the
tanks that are being loaded to check the temperature of the
iii. During loading,rounds are made regularly to check the
moorings, emergency, towing wire, etc. the loading speed is
checked. The calculated ullage is checked if nearly reached.
The tank valve is closed. The regular intervals are checked
iii. if sheer forces and bending moments reach the maximum.
If so, steps are to be taken to reduce them. Near the end of
loading, speed must be reduced to diminish the chance of
an overflow from the tank, as this may entail a heavy fine on
C. POST LOADING OPERATIONS
i. After completion of loading, the ship’s manifld valves are
only to be closed after the shore valves have been closed.
The tank valve is to be closed last. After completion of
loading, the hoses or loading arms should be emptied into a
drip tray prior to disconnecting.
ii. After disconnecting the hose and loading arms, blind
flanges are to be connected to the manifold valves. All main
and crossovers valves are shut.
iii. All openings of the tanks are closed gas tight, except P/V
breakers. The whessoe gauges are to be raised up to the
D. DISCHARGING OPERATIONS
i. Of every cargo tank, the ullage, density, and
temperature of the cargo is to be taken and the tanks
are water dipped. The sip and terminal representative
or an independent cargo inspector on behalf of the
receiver does this. Thereafter, the quantity of cargo is
ii. Hoses or chicksans are connected. Then, tank
ventilators are opened and the pump room is freed of
gas. After this, the necessary valves in the pump room
can be opened. During discharge, the ventilators of the
pump room must be kept going. The necessary cargo
lines and terminal valves are opened.
iii. The inert gas is started
iv. The pumps are ordered and stand by until discharging is about
to start. After short gate valve is opened, the ship manifold
valves may also be opened and discharging can start.
v. During discharging, the same measures as in loading can be
undertaken to ensure safety.
vi. When the liquid level is low, the dischargespeed must be
slowed down to darining speed. A grumblling sound heard
from the tank means that it is nearly dry. To drain wing tanks
the ship may be given a list of the suction valves and their
vii. After all tanks are drained, tank dips are taken in the presence
of terminal inspector n behalf of the receiver of cargo and the
quantity left on board is calculated. After discharging is
completed, hoses and loading arms are disconnected and all
other connections are removed.
Tank cleaning and installation of fittings for tankers
Tankers are equipped with tank washing machnes. These may be
portable or mounted in the cargo tanks. The conductivity must
be checked every time before it is used and lowered to a butter
hole into a tank. Some of the regulations concerning
installations pertain to the following:
A. Slop tanks
>the purpose of the slop tank is to separate, as much as possible,
water that has been introduced into tank washing during and
during ballast voyage, from the oil that is removed from tank.
The contents of slop tank, after tank washing and pumping out
unpolluted water, consist of oil, water-oil emulsion and some
Load on Top- when the cargo is loaded while the hold still contains
slops. Introduced in 1960, which contributed significantly to the
reduction of oil pollution from tankers. The load on top
regulation was made mandatory under MARPOL 73/78.
The following procedures are followed when loading on top:
a. The tanker arrives at the port of destination fully laden and
ready to discharge its cago.
b. After discharging the cargo, quantities of oil remain clinging to
the sides of the tanks.
c. The ship has to fill some of its tanks as ballast water return
d. These tanks has to be washed and the slops are pumped into a
e. Ballast water is pumped into some of the cleaned tanks. The
dirty ballast tanks are cleaned and the slops are pumped into the
f. While on return voyage, the oil and water in the slop tank
separates. The oil floats to the top and water under the oil is
carefully pumped into the sea.
g. At the loading port, oil is loaded into the cargo tanks on top of
oil remaining in the slop tank.
MARPOL 73/78 requires that oil tanker of 150 tons gross tonnage
and over be provided with oil-water interface detectors for use
in slop tank and other tanks, where separation of oil and water
is effected for discharge to the sea.
B. CRUDE OIL WASHING (COW) and the Inert gas System
MARPOL 73/78 requires crude oil washing for tankers of
20,000 deadweight and over to be equipped with COW system.
COW was introduced in 1970s. This system allows the cleaning
of tank from sludge with crude oil itself. Thus, under COW
system, tanks are washed not with water but with crude oil or
the oil cargo itself because the best solvent for sludge is the
COW was used as an alternative to the Segregated Ballast Tank or
SBTs for existing tankers at that time, as required by MARPOL
73/78. if the ship has COW, it must also be equipped with an
inert gas system before washing begins, the tank must be
monitored for the quantity of gases and oxygen. During
operation, the pressure on inert gas system must be higher than
the suction pressure of pump with which the tank is discharged
It is noted thatinstead of using seawater,tank cleaning is done by jet
spraying the cargo tanks with crude oil itself, which has been
proven by experts as a better cleaning agent than water alone.
The consignee of cargo also benefits from this technique
because no oil wasted in cleaning the tank. In the previous
technique, when oil and water mixture is used a proportion of
oil cargo is wasted when mixed with water
C. Sewage treatment plant
>sewage is one of the marine pollutants coming from ships.wastes
and fuel residues consists mainly of contaminated water.
Modern ships are fitted with holding tanks, which allows
overboard discharge in allowable sea areas. Specific standard
discharge connections are required to enable pipes of reception
facilities to be connected with ships in case discharge of sewage
is performed at shore reception facilities.
Chapter 3 regulation 9 of the revised Technical Annex IV of
MARPOL 73/78 requires that a ship has to be equipped with
any of the following equipment for prevention of marine
pollution from sewage coming from ships:
1. A sewage treatment Plant
2. A sewage comminuting and disinfecting system approved by the
3. A holding tank
C. Sewage treatment plant
the sewage treatment plant or comminuter or the holding tank
should be in accordance with standards set by the IMO.
D. Garbage Disposal System
>garbage is another source of marine pollution from ships. The
Technical Annex V to MARPOL 73/78 provided regulations
concerning the disposal of garbage. Ships are required to be
fitted with comminuter or grinder. Discharge regulations for
garbage and wastes, which are either comminuted or grounded
are also required.
i. There are various operations on board ships that generates
marine pollution. These are bunkering, cargo loading, cargo
discharging, tank cleaning, garbage disposal system, and sewage
treatment and disposal operations.
ii. Since bunkering operations are the main source of marine
pollution from ships, extreme care are to be exercised by
shipboard personnel during the performance of these activities.
Particularly important is tanker operations because og the
nature of cargo that are carried on board ship.
iii. Precautionary measures are supposed to be ensured to avoid
hazards to life and marine environment in every performance
of particular activities involving the handling of oil or petroleum
iv. MARPOL 73/78 provides important regulations covering the
equipment to be used and the conditions when the discharges
may be permitted