UNIT-1

Ventilation and control of sweat :

Cargoes requiring special ventilation due to emission of gases, absorption of oxygen, dust, release of moisture.Cargo VentilationBulk cargoes are ventilated to prevent the formation of cargo sweat or ship’s sweat which

could damage the cargo, to reduce the harmful heating of a cargo, and/or to remove hazardous gases from the cargo spaces. Ventilation in the wrong circumstances can do

considerable harm and before a decision is made to ventilate a space it is necessary to consider the requirements of the cargo, the temperature and humidity within the holds and outside and the presence or absence of sea spray. The types and positions of ventilators with which the ship is provided must also be taken into account

Hold ventilators: Most bulk carriers built since 2000 are provided with two hold ventilators set into the forward end of the hatch covers and a similar pair of ventilators set into the after end of the hatch

covers. These are easy to open or close, easy to clean, cheap to fit and maintain but are more exposed to sea water and spray on deck than are mushroom ventilators, and therefore require more attention. Ventilators of this type do not contain fans. The arrangements within the hatch cover depend upon whether the hatch panels are single double skinned.

Older bulk carrier and any bulk carriers fitted with mechanical ventilation are more likely to be provided with two or four ventilation trunks per hold, with one

or two situated at the fore end of the hold, and one or two at the after end. These ventilators pass vertically through the mast houses with the forward ventilator in each hold being on the starboard side and the after ventilator on the port side. The ventilators terminate on top of the mast houses with grilles

which face aft and are provided with watertight doors. No fans are provided, so any ventilation is natural. Some older vessels are provided with ventilators of the hinged-door type set into the hatch covers, or with portable

ventilator cowls, in addition to the mushroom or

cowl ventilators at the extremities of the hold. Such additional ventilators are required to provide surface ventilation within the hatch square when a ship is carrying a cargo which fills the hold to coaming level, thereby sealing off the hatch square from the rest of the compartment. The portable ventilator cowls have to be bolted in position on the hatch covers when blank plates have been removed.

Reasons for

ventilating bulk cargoes: A number of difficult cargoes have special ventilation requirements to prevent overheating or to remove dangerous gases. In such cases officers should be guided by any instructions provided by owners, charterers, shippers and/or the IMSBC Code.The carriage of several typical cargoes is described and these provide a good illustration of the varied reasons for ventilating. Coal is ventilated to remove hazardous gases. With

steel a major object is to avoid the formation of sweat, which would damage the cargo. Iron ore has no particular need for ventilation although it is desirable to maintain a dry and healthy atmosphere in the holds for access and to reduce corrosion.When there is no special need to remove gases, the reason for ventilating is to remove moist air and replace it with drier air to discourage the formation of sweat.

Sweat: Sweat is the name given by seamen to condensation which occurs in a ship’s cargo spaces. There are two types of sweat, ship’s sweat and cargo sweat. For sweat to occur there must be moisture in the hold atmosphere and a difference of temperature between the air in the hold and the cargo or the ship’s steel work.The temperature difference usually occurs as the ship moves from one climatic region to another or from a cold to a warm current or vice versa, and the larger the change in temperature the more likely is the formation of sweat.

Sources of moisture in cargo spaces: The most important source of moisture in a hold is the cargo. Most commodities, particularly

materials of vegetable origin, possess some natural moisture and create an atmosphere, known as the storage atmosphere, in any compartment in which they are stored. Moisture in a hold can also be the result of rainfall during loading and the air in a hold will be moist if conditions were moist when the hold was closed on completion of loading.The amount of moisture in the air is measured by its dew point, which is the lowest temperature to which a mass of air can be reduced without condensation occurring. As condensation is a ‘bad thing’ it is helpful to remember that air with a high dew point is a ‘bad thing’. Dew point is obtained from a table, entered with readings taken from the wet and dry bulb hygrometer.

Cargo sweat: Cargo sweat consists of condensation which forms on the surface of cold cargo when warm moist air comes in contact with it. Cargo sweat will form when the dew point of the air in the hold is higher than the temperature of the cargo. This is most likely to occur when the ship has loaded a cargo in a cold

region and air is

admitted to the hold as the ship is traveling towards a warmer region.To prevent cargo sweat when passing from a cold region to a warm region all ventilation should be stopped and the hold should be kept closed, with the air unchanged, as far as possible. The temperature of the cargo will only rise very slowly to equal the external atmosphere, and so long as the hold remains closed the air within it will gradually become warmer and able to hold more moisture.With an inert cargo the dew point of the air in the non-ventilated hold remains constant as it warms up. If the cargo contains moisture it will give off moisture as it warms up. However, as the heat will flow from the shell of the ship into the hold atmosphere and from the hold atmospshere to the cargo, the temperature of the hold air stays a step ahead of the cargo temperature. Any moisture given off by the cargo can be held in the air.

It will be safe and

desirable to ventilate only after the surface

temperature of the cargo has risen to equal that of the air outside the hold or when the external air is exceptionally dry, so that its dew point is lower than the temperature of the cargo.

Ship’s sweat: Ship’s sweat is the condensation which occurs when warm moist air in the hold comes into contact with the cold steel work which forms the deck and shell plating of the ship. Ship’s sweat will form when the dew point of the air in the hold is higher than the temperature of the ship’s steel work, conditions most likely to be met when the ship has loaded in a warm region and is steaming towards colder climates. Ship’s sweat caused by a low external air temperature is most likely to be deposited first in the vicinity of the hatch coaming and the fore and after ends of the hold amidships, as the topside tanks or double hull, even when empty, provide an insulating layer which delays the penetration of cold from the external air to the plating forming the tank/hold separation.When a cold current is met, causing a low sea temperature, the side shell plating between the topside and lower hopper tanks will be cooled, providing conditions favourable for the formation of ship’s sweat in those areas.

When passing from a warm region to a cold region full

ventilation should be continued whenever possible in order to withdraw moist air from the hold and replace it by drier external air. If the cargo contains moisture, the air in the hold will continue to be moist and will condense upon the ship’s cold steel work unless it is continually extracted, and replaced by drier air.

General guidelines for ventilation: Ventilation should be stopped, by stopping fans when in use and closing the ventilators, when the vessel is shipping spray in the vicinity of ventilator intakes. Times of interruption of ventilation should be logged.On short voyages in small ships it is normal to carry out no ventilation and to keep ventilators tightly sealed. With a low free board and regular rough weather the danger of shipping spray into open ventilators is usually found to be far

greater than the potential benefits from ventilation.On longer voyages if the cargo requires ventilation cargo holds should be ventilated when the dew point of the external air is lower than the dew point of the air in the hold. This will put drier air into the hold, forcing out wetter air and reducing the possibility of sweat forming. Dew point readings should be logged. However, dew point in the hold may be difficult to measure. The hold may be full or unsafe to enter and when it is safe to enter any airflow will be the result of ventilation, meaning that the true temperature within the hold is not being measured. Another way of deciding when ventilation is needed for hygroscopic cargoes (agricultural cargoes such as grain, timber, animal feed stuffs and wood pulp that have a moisture content that can interact with air) is to use the three-degree rule.

The three-degree rule: says that a hygroscopic cargo should be ventilated when the temperature of the outside air is at least 3°C below that of the cargo temperature taken at loading. This rule avoids the need to take readings in the holds after the voyage has commenced and relies on the fact that the temperature of hygroscopic cargoes, except at their boundaries, changes very slowly during a voyage. However it should be noted that one authority advises that the ventilation of grain cargoes is likely to do more harm than good.

Ventilation practice: When natural ventilation is being used with open ventilators at both forward and after ends, the air in the hold tends to travel from aft to forward. When forced ventilation is used it is normal to take advantage of this tendency and to drive the air from aft to forward.Air forced into a hold by a fan will seek the shortest and easiest route through the hold. If the only route by which the air can leave the hold is through a ventilator at the far end of the hold, the air will tend to flow directly to that ventilator across the surface of the cargo. If an access hatch or other opening close to the inlet vent is left open, the air will leave the hold by the access hatch without traveling the length of the hold. This is known as ‘short cycling’ and is an inefficient form of ventilation. Short cycling should be prevented by ensuring that only ventilators are left open when the hold is closed.When a hold is loaded with a bulk cargo the ventilation provided is usually surface ventilation, with air flowing over the surface of the cargo from ventilators at the after end of the hold to ventilators at the fore end of the hold or, in newer ships, from ventilators in the after end of the hatch covers to similar ventilators in the fore end of the hatch covers.Ventilators situated at the hold ends can provide surface ventilation only for the nearby hold ends when the cargo is a low-density one topped up in the hatch square and preventing a flow of air

from one end of the hold to the other. When the hold is filled the hatch square requires separate ventilation. Through ventilation of a bulk cargo, when air is forced into the body of the cargo, is not normally required and is difficult to achieve. Some through ventilation can be provided aboard ships in which ventilator trunks extend to the bottom of the hold bulkheads. Through ventilation of coal is likely to cause heating and must be avoided.The capacity of a ship’s hold ventilation fans is normally expressed in the number of air changes that can be achieved in an empty hold per hour. When a cargo is carried the number of air changes per hour will be increased, because the quantity of air which the hold contains is reduced.

Contents of Cargo Securing ManualGeneralShip Data. DefinitionsGeneral InformationPrincipal sources of dangerDevices and ArrangementsSpecification of Fixed Cargo Securing DevicesSpecification of Portable Cargo Securing DevicesInspection and Maintenance Schemes Stowage and Securing of cargo Handling and safety instructionsGeneral principles of cargo securingSafe handling of cargo securing devices Evaluation of forces acting on cargo units Forces acting on typical cargo unitsCalculation of forces in semi- and non-standardised lashing arrangementsMSLs for different securing devicesSafety factorSimplified method – Rule of thumbApplication of portable securing devicesSupplementary Requirements for General Cargo/Container vessel/Bulk CarriersExtracts from various Timber Deck CodesContainer CarriersHandling and Safety InstructionsStowage and Securing InstructionsStowage and Securing Plan Safe stowage and securing of coiled sheet steelLog for maintenance of cargo securing equipmentManual procedure for calculation of lashingsApplicable Annexes from the CSS Code

LASHCONTM IMO USER GUIDECertification for fixed cargo securing devices Certification for portable cargo securing devices.

CODE OF SAFE PRACTICE FOR CARGO STOWAGE AND SECURINGTable of contentsForewordGeneral principlesChapter 1 - GeneralChapter 2 - Principles of safe stowage and securing of cargoesChapter 3 - Standardized stowage and securing systemsChapter 4 - Semi-standardized stowage and securingChapter 5 - Non-standardized stowage and securingChapter 6 - Actions which may be taken in heavy weatherChapter 7 - Actions which may be taken once cargo has shiftedAnnex 1 - Safe stowage and securing of containers on deck of ships which are not specially designed and fitted for the purpose of carrying containersAnnex 2 - Safe stowage and securing of portable tanksAnnex 3 - Safe stowage and securing of portable receptaclesAnnex 4 - Safe stowage and securing of wheel-based (rolling) cargoesAnnex 5 - Safe stowage and securing of heavy

cargo items such as locomotives, etc.Annex 6 - Safe stowage and securing of coiled sheet steelAnnex 7 - Safe stowage and securing of heavy metal productsAnnex 8 - Safe stowage and securing of anchor chainsAnnex 9 - Safe stowage and securing of metal scrap in bulkAnnex 10 - Safe stowage and securing of flexible intermediate bulk containersAnnex 11 - General guidelines for the under-deck stowage of logsAnnex 12 - Safe stowage and securing of unit loads

FUNDAMENTAL SECURING PROCEDURES. Shifting cargo presents hazards such as damage to the vessel or explosions. It is important that all precautions be taken to protect cargo from shock, fire, high temperature, moisture, or any other hazards that could lead to a catastrophe. In transit, repairs to dunnage or resecuring shifted cargo are difficult and dangerous. Securing is done to resist forces generated by vessel response to sea conditions and includes various wooden structures. It also includes any straps or webs that are used to restrain cargo stowed in the holds and on the weather deck of a ship. The terms blocking and bracing describe more specifically the securing process. The terms are closely related, although each function is distinctly different.

Blocking. Blocking is the act of attaching solid pieces of wood, or blocks, to a deck, bulkhead, or overhead, so that these pieces lean directly against the cargo to prevent its movement. Blocking must be braced, shored, or tommed to be effective. Figure shows the basic technique of blocking from which more complex securing structures are developed. Additional bracing would be required to secure

the item adequately. Pieces of wood measuring 2 by 4 inches are doubled instead of using single 4- by 4-inch pieces to make nailing and securing to the deck possible. The 2- by 6-inch blocking extends the full width of the unit load. Since blocking may be nailed directly into the wooden deck, the load may be secured in any location in the hold without the need for extending pieces to permanent ship's structures for bracing. Since it is very difficult to drive nails into a metal deck, 4- by 4-inch lumber must be extended to the bulkhead to provide necessary bracing.

Bracing. Bracing is the act of installing a wood piece or structure so that it extends from a deck, bulkhead, or overhead to the stow. This technique

strengthens the blocking by supporting it in a horizontal direction. Figure shows a basic method of bracing. Kickers are relatively short lengths of lumber nailed horizontally. They add rigidity to the uprights and braces and are either nailed to the deck or wedge-fitted to a bulkhead. In both cases, the structure extends slightly higher than the unit load and along its full width.Shoring and Tomming. Shoring, which includes blocking and bracing, is the process of securing cargo to prevent side-to-side movement by supporting it from the side. Shoring may also be used to prevent downward movement by supporting cargo from below. Tomming is the securing of cargo to prevent upward movement. Personnel secure the cargo by running lumber from the ship's overhead structure down to the cargo either vertically or at an angle.

Precautions prior to loading packaged goods1. Correct description of the goods including at least

a. the mass of each load unit b. the mass of the load c. position of the center of gravity if not in the middle d. enveloping dimensions of each load unit e. limitations for stacking and orientation to be applied during transport f. all additional information that is required for proper securing2. Goods a.are safe and suitable for transport, are loaded b. are suitably packed c. within load units are adequately secured to prevent damage to the packaging and to prevent movement in the packaging during transport d. are ventilated so that any noxious or harmful gases are permitted to vent off 3. Dangerous goods a. are correctly classified, packed and labeled b. transport document is completed and signed C. meets the requirements of the load securing plan d. is in sound and clean condition 6. Anti slip mats, dunnage materials, blocking bars and all other securing equipment that should be fixed during loading, are properly applied in accordance with the securing plan 7. All lashing equipment is properly applied in

accordance with the load securing plan 8. All equipment necessary for load securing is available when starting to load visual inspection of the outside of the vehicle and of the load if accessible to check for evident unsafe situations 9. Fitting marks and placards as required by dangerous goods regulations 10. No unwanted interaction between goods of different types or risk class can occur 12. Lashing equipment, lashing protection material and anti slip mats are provided in sound condition 13. All current valid certificates for load restraint points used for the securing of the load, are available 14. Measures are put in place to prevent pests

Need for solid stow and securing.