1 Introduction
1.1 This document is intended to provide guidance on the safety aspects of ballast water
exchange at sea. The different types of ships which may be required to undertake ballast
water exchange at sea make it presently impractical to provide specific guidelines for each
ship type. Shipowners are cautioned that they should consider the many variables that
apply to their ships. Some of these variables include type and size of ship, ballast tank
configurations and associated pumping systems, trading routes and associated weather
conditions, port State requirements and manning.
1.2 Ballast water exchange at sea procedures contained in relevant management plans
should be individually assessed for their effectiveness from the environmental protection
point of view as well as their acceptability in terms of structural strength and stability.
1.3 In the absence of a more scientifically based means of control, exchange of ballast
water in deep ocean areas or open seas currently offers a means of limiting the probability
that fresh water or coastal aquatic species will be transferred in ballast water. Two
methods of carrying out ballast water exchange at sea have been identified:
.1 the sequential method in which ballast tanks are pumped out and refilled with
clean water; and/or
.2 the flow through method in which ballast tanks are simultaneously filled and
discharged by pumping in clean water.
2 Safety precautions
2.1 Ships engaged in ballast water exchange at sea should be provided with procedures
which account for the following, as applicable:
.1 avoidance of over and under pressurization of ballast tanks;
.2 free surface effects on stability and sloshing loads in tanks that may be slack
at any one time;
.3 admissible weather conditions;
.4 weather routing in areas affected by cyclones, typhoons, hurricanes, or heavy
icing conditions;
.5 maintenance of adequate intact stability in accordance with an approved trim
and stability booklet;
.6 permissible seagoing strength limits of shear forces and bending moments in
accordance with an approved loading manual;
.7 torsional forces, where relevant;
.8 minimum/maximum forward and aft draughts;
.9 wave induced hull vibration;
.10 documented records of ballasting and/or de-ballasting;
.11 contingency procedures for situations which may affect the ballast water
exchange at sea, including deteriorating weather conditions, pump failure, loss
of power, etc.;
.12 time to complete the ballast water exchange or an appropriate sequence thereof,
taking into account that the ballast water may represent 50 % of the total
cargo capacity for some ships; and
.13 monitoring and controlling the amount of ballast water.
2.2 If the flow through method is used, caution should be exercised, as:
.1 air pipes are not designed for continuous ballast water overflow;
.2 current research indicates that pumping of at least three full volumes of the
tank capacity could be needed to be effective, when filling clean water from
the bottom and overflowing from the top; and
.3 certain watertight and weathertight closures (e.g. manholes) which may be
opened during ballast exchange, should be re- secured;
2.3 Ballast water exchange at sea should be avoided in freezing weather conditions.
However, when it is deemed absolutely necessary, particular attention should be paid to the
hazards associated with the freezing of overboard discharge arrangements, air pipes, ballast
system valves together with their means of control, and the accretion of ice on deck.
2.4 Some ships may need the fitting of a loading instrument to perform calculations of
shear forces and bending moments induced by ballast water exchange at sea and to
compare with the permissible strength limits.
2.5 An evaluation should be made of the safety margins for stability and strength
contained in allowable seagoing conditions specified in the approved trim and stability
booklet and the loading manual, relevant to individual types of ships and loading
conditions.
2.6 The ballast water management plan should include a list of circumstances in which
ballast water exchange should not be undertaken. These circumstances may result from
critical situations of an exceptional nature or "force majeure" due to stress of weather or
any other circumstances in which human life or safety of the ship is threatened.
3 Crew training and familiarization
3.1 The ballast water management plan should include the nomination of key shipboard
control personnel undertaking ballast water exchange at sea.
3.2 Ships' officers and ratings engaged in ballast water exchange at sea should be trained
and familiarized as follows:
.1 with the ship's pumping plan which should show ballast pumping arrangements,
with positions of associated air and sounding pipes, positions of all compartment
and tank suctions and pipelines connecting them to ship's ballast pumps and, in
the case of use of the flow through method of ballast water exchange, the
openings used for release of water from the top of the tank together with
overboard discharge arrangements;
.2 with the method of ensuring that sounding pipes are clear, air pipes and their
non-return devices are in good order;
.3 with the different times required to undertake the various ballast water exchange
operations;
.4 with the methods in use for ballast water exchange at sea if applicable with
particular reference to required safety precautions; and
.5 with the method of on-board ballast water record keeping, reporting and
recording of routine soundings.