1 General
The aim of these Guidelines is to introduce some technical
improvements for further consideration in the design and equipment
of tankers to reduce the exposure of seafarers to benzene vapours,
be it on deck, in the engine-room or in the accommodation, in
particular during loading and gas-freeing.
Further use of closed cycle
loading and unloading is also encouraged for cargoes other than
those required by the IBC Code. Other technical solutions such as
vapour recovery or vapour filtering that may be developed in the
future should also be taken into account.
2 Ventilation in the accommodation
In accordance with standard operational procedures, ventilation
should be closed down or shut down during loading and gas-freeing,
all internal and external doors should be kept closed and passage
through doors to open deck should be restricted to a minimum.
Nevertheless, experience has shown that it has proven impossible to
keep the measured vapour concentrations below acceptable levels.
Some restricted ventilation will also have to be maintained in
certain areas such as the galley
and bathrooms.
2.1 Air intake
Consideration should be given to the location of
the air intakes to minimize the entry of harmful vapours.
Traditionally, these are normally located on the boat deck connected
to the engine-room casing or in the exhaust stack. Bearing in mind
that vapours are normally heavier than air, other higher locations
may be considered to avoid the vapour envelope around the
tanker.
2.2 Air filtering and
monitoring
A chemical or mechanical filter where the incoming
air is continuously monitored for its concentration of harmful
vapours should be provided.
3 Ventilation in the engine-room
3.1 Special air ducts
Combustion engines require large volumes of
atmospheric air. Therefore, most engine-rooms are provided with
overpressure in relation to the accommodation. To reduce the
overpressure and, thereby, the risk of harmful vapours entering the
accommodation, special air-ducts could be fitted to the air intake
for combustion engines and boilers.
3.2 Other ventilation
Apart from the air intakes to the engines,
additional ventilation in the engine-room is also required to remove
heat and to avoid the risk of explosion. Therefore, the presence of
harmful vapours cannot be completely avoided. The presence of
personnel in the engine-room during loading and gas-freeing should
therefore be kept to a minimum. In the engine control room and
engine workshops the same ventilation principle as in the
accommodation should be applied.
4 Airlocks
Airlocks should be provided to allow crew members to pass from
contaminated areas (such as the engine-room and open deck) to the
accommodation through a double set of doors where one must be closed
before the next can be opened. The space between these doors should
be supplied with filtered air with a slight overpressure. One
airlock between the open deck and accommodation and one between the
engine-room and accommodation is considered acceptable.
5 Washing and changing facilities
Washing and changing facilities and toilets should
be located with a possibility for the crew to enter directly from
the cargo area without passing through any other part of the
accommodation. Preferably it should be arranged in such a manner
that passage to the accommodation can only take place from the
changing room for soiled work clothes through the washing facilities
and through the changing room for clean clothes. Lockers and washing
machines for soiled working clothes should as well be located
separate from the accommodation.
6 Work o deck
6.1 Spill trays
In new tankers, the design of spill trays should be
such that the surface of any liquid in the spill tray is reduced to
the minimum extent possible and thus the evaporation minimized. One
way of achieving this could be by designing spill trays with sloping
sides. Other constructions with similar effect may also be
acceptable. Drainage facilities for the spill trays and the disposal
of their content should be installed (e.g., slop tanks and disposal
arrangements).
6.2 Purging air capability
There should be adequate purging air capacity to
ensure efficient and complete purging of all pipes and hoses used
for cargo handling to the terminal after unloading. Whether
compressed air or inert gas should be used for purging purposes
depends on the carriage and unloading requirements of the cargo.
7 Cargo measurements and sampling
To allow all cargo related measurements, including
ullage, temperature measurements and sampling to be carried out in a
closed mode, permanently fitted equipment should be installed.
8 Gas-freeing
Gas-freeing should be undertaken using permanently
fixed blowers with a piping system, which fits closely to the cargo
tank hatches. Each blower should have sufficient capacity and
pressure to ensure that the expelled vapours are let with sufficient
velocity well clear of the ship through adequate riser
arrangements.
9 Tank washing and stripping
Tank washing machines should be permanently mounted in the cargo
tanks. Efficient stripping arrangements to drain the suction wells
as much as possible should be provided.
10 Controlled tank venting system
Whenever a vapour emission control system is available ashore,
vapours displaced from the tank during loading should be returned to
that system (vapour return). Ships should therefore be fitted with
piping systems suitable for vapour return.