Segregating of dangerous goods

 

 

Segregation

General

The provisions of this chapter should apply to all cargo spaces on deck or under deck of all types of ships and to cargo transport units.

The International Convention for the Safety of Life at Sea (SOLAS), 1974, as amended, requires in regulation 6.1 of part A of chapter VII that incompatible goods should be segregated from one another.

For the implementation of this requirement, two substances or articles are considered mutually incompatible when their stowage together may result in undue hazards in case of leakage or spillage, or any other accident.

The extent of the hazard arising from possible reactions between incompatible dangerous goods may vary and so the segregation arrangements required should also vary as appropriate.  Such segregation is obtained by maintaining certain distances between incompatible dangerous goods or by requiring the presence of one or more steel bulkheads or decks between them, or a combination thereof.  Intervening spaces between such dangerous goods may be filled with other cargo compatible with the dangerous substances in question.

The following segregation terms are used throughout this Code:

“Away from”;

“Separated from”;

“Separated by a complete compartment or hold from”;

“Separated longitudinally by an intervening complete compartment or hold from”.

The general provisions for segregation between the various classes of dangerous goods are shown in the

segregation table”.

In addition to the general provisions, there may be a need to segregate a particular substance, material or article from other goods, which could contribute to its hazard.  Particular provisions for segregation are indicated in the Dangerous Goods List and, in the case of conflicting provisions, always take precedence over the general provisions.

For example:

In the Dangerous Goods List entry for ACETYLENE, DISSOLVED, class 2.1, UN 1001, the following particular segregation requirement is specified:

“separated from” chlorine

In the Dangerous Goods List entry for BARIUM CYANIDE, class 6.1, UN 1565, the following particular

segregation is specified:

“separated from” acids

Where the Code indicates a single secondary hazard (one subsidiary risk label), the segregation provisions applicable to that hazard should take precedence where they are more stringent than those of the primary hazard.

Except for class 1, the segregation provisions for substances, materials or articles having more than two hazards (2 or more subsidiary risk labels) are given in the Dangerous Goods List.

In the Dangerous Goods List entry for BROMINE CHLORIDE, class 2.3, UN 2901, subsidiary risks 5.1 and 8, the following particular segregation is specified:

“segregation” as for class 5.1 but “separated from” class 7”.

Segregation of packages

Applicability

The provisions of this subsection apply to the segregation of:

packages containing dangerous goods and stowed in the conventional way;

dangerous goods within cargo transport units; and

dangerous goods stowed in the conventional way from those packed in such cargo transport units.

Segregation of packages containing dangerous goods and stowed in the conventional way

Definitions of the segregation terms Legend

Reference package - BLUE

Package containing incompatible goods - RED

Deck resistant to fire and liquid – BOLD LINE

NOTE. Full vertical lines represent transverse bulkheads between cargo spaces (compartments or holds) resistant to fire and liquid.

Away from:

Effectively segregated so that the incompatible goods cannot interact dangerously in the event of an accident but may be transported in the same compartment or hold or on deck, provided a minimum horizontal separation of 3 metres, projected vertically, is obtained.

Separated from:

In different compartments or holds when stowed under deck.  Provided the intervening deck is resistant to fire and liquid, a vertical separation i.e. in different compartments,

may be accepted as equivalent to this segregation.  For on deck stowage, this segregation means a separation by a distance of sit least 6 metres horizontally.

Separated by a complete compartment or hold from:

Either a vertical or a horizontal separation. If the intervening decks are not resistant to fire and liquid,      then only a longitudinal separation, i.e. by an intervening complete compartment or hold, is acceptable. For on deck stowage, this segregation means a separation by a distance of at least 12 metres horizontally. The same distance has to be applied if one package is stowed on deck and the other one in an upper compartment.

Note: One of the two decks must be resistant to fire and to liquid.

Separated longitudinally by an intervening complete compartment or hold from:

Vertical separation alone does not meet this requirement. Between a package under deck and one on deck, a minimum distance of 24 metres, including a complete compartment, must be maintained longitudinally. For on deck stowage, this segregation means a separation by a distance of at least 24 metres longitudinally.

Oil Tanker 

 

A tanker is a specialized ship intended for the carriage of bulk liquid cargo. An Oil tanker

again is further divided into 2 basic types, namely Crude Oil Tanker and Product Oil

Tanker.

For both of the above the cargo of oil is carried within the tanks similar to the holds of other ships, the difference being that the bulkheads are extra strengthened to take in the load, and the hatch or rather the tank openings are very small, the sole purpose of having them is for Man Entry and for small repair work in the dry docks.

The cargo of oil is loaded on to the ships tanks by pipelines, which are fixed on the ship (permanent structure), the shore pipelines are connected to the ships pipelines at the manifold on either side of the ship. Note that some special ships also have manifolds at the bow and at the stern.

The shore pipelines may be connected using flexible steel rimmed rubber hoses (small ports/ Ship to ship transfers/ SBM) – the flexible come in small lengths are connected to each other to make them long pieces.

The shore pipelines may also be connected with rigid loading arms – also called ‘chiksons’, which are remotely controlled and take in the roll of the ship to a certain extent but the fore and aft movement of the ship has to be kept to a minimum.

The combined pipeline system of the shore and the ship deliver the oil to the cargo oil tanks directly via the drop lines. These are as the name suggests pipelines, which drop to the bottom of the tanks vertically from the pipeline on deck – thus bypassing the pump room.

There are various cross- over valves, which are opened in order to load a group of tanks.

The shore system starts to pump/ delivers by gravity (some Persian Gulf ports) at a slow rate, so that any leakages can be detected and to check whether the right tank is receiving the oil or not, once the shore and the shipside are satisfied the pumping – loading of the cargo is increased. In case of any subsequent leakages that are detected the ship valves should not be shut abruptly, rather the shore has to be informed first and then only the ship valves are to shut, this to prevent pressure surge from bursting the pipelines.

To prevent this surge from affecting the pipelines the cargo valves have set times at which they close – this depends on the size of the valves – typically a 550mm valve would shut at about 24 seconds, whereas a 250mm valve would shut at 6-8 seconds.

After the ship completes her loading the stage is set for the unloading or discharging operation.

While loading the cargo had by passed the pump room, now however the cargo from the tanks is allowed to flow to the pump room through the bottom pipelines. Just within the pumproom and at the pumproom bulkhead are situated isolation valves known as ‘Bulkhead Master valves’, by opening the valves the oil is led to the pump suction valve and on opening that the oil flows to the centrifugal pumps. Turbines, which are situated

in the Engine Room, commonly drive these pumps; the shaft penetrates the ER bulkhead and drives the pump situated at the bottom of the pumproom.

The pump accelerates the flow of the oil into the discharge pipeline and this oil is thus led on the deck pipelines and to the manifold from where it flow through the flexible pipeline or the hard loading arm to the shore pipeline system.

The Pump Room

This is a cofferdam kind of space – in fact it is accepted as a cofferdam, which begins on main deck and ends at the keel.

It may have more than 2 decks, however these decks are not normally solid decks but are partial decks made of expanded metal, so you are able to see right to the bottom.

There would be a companionway leading from the top to the next deck and so on right to the bottom.

At the lowermost deck are situated the Cargo Oil Pumps (COP’s). The numbers of pumps vary in number – for crude oil tankers it is normal to have 4 pumps, three being used at any one time.

For product oil tankers the number of pumps depend on the number of grade of oil that the ship is capable of carrying.

So if the ship can carry 4 grades of oil then she would be having 4 pumps.

Once the gravity flow to the COP’s is not possible the stripped pumps are started, these pumps are of the reciprocating type and have great capacity to create partial vacuum to suck out the remaining oil from the tanks. Again on a product oil tanker the number of stripped pumps would be equal to the number of grades of oil that it can carry.

Earlier on Crude oil carrier there would be stripper pumps of the reciprocating type however today largely eductors are used to remove the remaining oil from the tank. Generally 2 eductors are provided on each crude oil tanker. However 1 stripper pump is always provided to strip the cargo lines of any residual oil and to pump the same to the shore system.

The pumproom is a hazardous area as such the light fittings are gas tight and only tanker safety torches are used. The ventilation system is of the exhaust type and has intakes from all the levels with the intakes being fitted with closing devices so that if required only a certain level can be evacuated.

Hydrocarbon gases being heavier than air tend to settle at the bottom of the pumproom as such the main exhaust are always from the bottom level.

The pumproom lighting is devised in such a way that the lights do not come on unless the ventilation has been started and is kept on for 15 minutes.

AT the top of the pumproom a harness and lifting arrangement is provided to lift out a person from the lowermost deck, for this reason a clear passage is left vertically from the top to the bottom of the pumproom.

Fire man’s outfit are also placed at the top of the pumproom, the pumproom may have different types of fixed fire fighting appliances such as total flooding by CO2 or by foam applicators fitted in the bilges (below the floor plates under the lowermost deck).

Bilge alarms are fitted which give alarms when the bilges are filled – a high level and a low level alarm is fitted which gives indications in the Engine room as well as in the Cargo Control room.

Picture shows the main deck layout of a Product tanker (capable of carrying 4 grades of oil):

The same tanker – with the tank layout.

And part of the pump room layout of the same tanker.

The above shows the location of the drop valves; drop lines, line master, bulkhead master and the bottom lines.

Cargo Oil Pumps (COP)

A centrifugal pump, in the pumproom bottom platform. The dark green pipeline is the discharge line. The pump consists of an impeller which rotates within the casing. Due to this rotation which is generally about 1000 – 1700 rpm the oil is speeded up and this increase in velocity causes the oil to flow out at a great pressure. These pumps are capable of delivering a very high rate of discharge (up to 4000 m3/hr). With this type of pump the level of oil has to be above the pump – as such the pump is situated at the bottom of the pump room.

Another detail of the same centrifugal pump.

The earlier centrifugal pump situated in the pumproom is driven by a shaft which is connected to the steam turbine – situated in the ER. The shaft passes from the ER to the pumproom through the pumproom bulkhead via a gas and oil tight gasket.

The turbines are driven by superheated steam from the boiler in the ER.

Positive displacement pumps such as the reciprocating pump work on the principle of a hand pump – the movement of the piston creates a vacuum which sucks out the fluid. However the size of the pump is dependent on the size of the piston and the length of the strokes so for discharging at a high rate is practically impossible. In general these pumps are used to discharge small quantities of oil such as the strippings – the balance that the centrifugal pump cannot discharge due to the oil going below the level of the pump. The pump is used today on crude tankers to strip out the pipelines after discharging and then collecting these line content (small) and then pumping them to shore.

Eductors

Eductors work on the principles of Bernoulli’s Principle.

A driving fluid is pumped down the main line, with very high velocity, through a constriction, and past a relatively smaller opening, thus creating a vacuum.

When eductors are used for clean ballast, the driving fluid is seawater.

When used for stripping crude oil, the driving fluid is the cargo itself- delivered by means of a bypass from one of the main cargo pumps.

When used for stripping tank washings, the driving fluid is from the secondary slop tank and then re-circulated back to the primary slop tank. In the latter case the driving fluid is either crude oil or seawater, depending on the tank cleaning method.

 Eductors are simple and rugged, have no moving parts, and do not become air locked like other type of pumps. They are widely used on tankers of all types and sizes.

 

Tank layout of a crude oil tanker:

The Pipeline system:

Pipeline systems on tankers differ in their degree of sophistication, depending on employment of the tanker. 

ULCC’s and VLCC’s have relatively simple pipeline systems usually the direct line system.

Some product (parcel) tankers may have very sophisticated piping systems. This could be the ring main system or in case of a chemical product tanker it could mean an individual pipeline and an individual pump for every tank on board.

Basically there are three systems of pipelines found on tankers, and the fourth system being the free flow system found on large crude carriers

Ring Main System

Direct line system

Single line to Single tank system (Chemical/Product ship)

Free Flow system

Ring Main System:

It is generally of a square or circular layout.

It is used mostly on product tankers, as segregation of cargo is required.

Though the system is expensive, as more piping, and extra number valves are used.

However if the vessel is carrying many grades of cargo, the advantages compensate for the extra cost of the original outlay.

Direct Line System:

This system is mainly found on crude oil carriers where up to 3 grades of cargo can be carried as most of the direct pipeline systems is fitted with three direct lines.

This system is cheaper to construct. The disadvantages over the ring main system, is that line washing is more difficult, the system has fewer valves which make pipeline leaks difficult to control, as the system lacks versatility there is problem with line and valve segregation.

This system provides the vessel to carry as many grades as there are tanks.

The disadvantage is the cost factor having a multitude of pumps on board.               

Free flow Tanker:

This system is usually found on large crude carriers, where the cargo piping is not used for the discharge of cargo.

Instead, gate valves are provided on the bulkheads of the tanks which when opened; allow the oil to flow freely in the aft most tank and into the COP.

The advantages of this system are primarily the cost factor, it allows for fast drainage and efficient means of pumping the cargo tanks. Disadvantages are of single crude being shipped.

Independent System:

This layout is not very common in the tanker trade.

This system is quite normal on chemical ships.

There are some Product Tankers that have this system fitted on the ships.

This is a single line servicing an individual tank through an independent pump that could be either a submersible pump or a deep well pump.

Enclosed Space Entry

An enclosed space is one with restricted access that is not subject to continuous ventilation and in which the atmosphere may be hazardous due to the presence of hydrocarbon gas, toxic gases, inert gas or oxygen deficiency. This definition includes cargo tanks, ballast tanks, fuel tanks, water tanks, lubricating oil tanks, slop and waste oil tanks, sewage tanks, cofferdams, duct keels, void spaces and trunkings, pipelines or fittings connected to any of these. It also includes inert gas scrubbers and water seals and any other item of machinery or equipment that is not routinely ventilated and entered, such as boilers and main engine crankcases.

Many of the fatalities in enclosed spaces on oil tankers have resulted from entering the space without proper supervision or adherence to agreed procedures. In almost every case the fatality would have been avoided if the simple guidance in this chapter had been followed. The rapid rescue of personnel who have collapsed in an enclosed space presents particular risk. It is a human reaction to go to the aid of a colleague in difficulties, but far too many additional and unnecessary deaths have occurred from impulsive and ill-prepared rescue attempts.

Respiratory hazards from a number of sources could be present in an enclosed space. These could include one or more of the following:

Respiratory contaminants associated with organic vapours including those from aromatic hydrocarbons, benzene, toluene, etc.; gases such as hydrogen sulphide; residues from inert gas and particulates such as those from asbestos, welding operations and paint mists.

Oxygen deficiency caused by, for example, oxidation (rusting) of bare steel surfaces, the presence of inert gas or microbial activity.

Hydrocarbon Vapours

During the carriage and after the discharge of hydrocarbons, the presence of hydrocarbon vapour should always be suspected in enclosed spaces for the following reasons:

Cargo may have leaked into compartments, including pumprooms, cofferdams, permanent ballast tanks and tanks adjacent to those that have carried cargo.

Cargo residues may remain on the internal surfaces of tanks, even after cleaning and ventilation.

Sludge and scale in a tank which has been declared gas free may give off further hydrocarbon vapour if disturbed or subjected to a rise in temperature.

Residues may remain in cargo or ballast pipelines and pumps.

The presence of gas should also be suspected in empty tanks or compartments if non-volatile cargoes have been loaded into non-gas free tanks or if there is a common ventilation system which could allow the free passage of vapours from one tank to another.

Oxygen Deficiency

Lack of oxygen should always be suspected in all enclosed spaces, particularly if they have contained water, have been subjected to damp or humid conditions, have contained inert gas or are adjacent to, or connected with, other inerted tanks.

Other Atmospheric Hazards

These include toxic contaminants such as benzene or hydrogen sulphide, which could remain in the space as residues from previous cargoes.

ATMOSPHERE TESTS PRIOR TO ENTRY

General

Any decision to enter an enclosed space should only be taken after the atmosphere within

the space has been comprehensively tested from outside the space with test equipment

that has recently been calibrated and checked for correct operation.

It is essential that all atmosphere testing equipment used is:

Suitable for the test required;

Of an approved type;

Correctly maintained;

Frequently checked against standard samples.

A record should be kept of all maintenance work and calibration tests carried out and of the period of their validity. Testing should only be carried out by personnel who have been trained in the use of the equipment and who are competent to interpret the results correctly.

Care should be taken to obtain a representative cross-section of the compartment by sampling at several depths and through as many deck openings as practicable. When tests are being carried out from deck level, ventilation should be stopped and a minimum period of about 10 minutes should be allowed to elapse before readings are taken.

Even when tests have shown a tank or compartment to be safe for entry, pockets of gas should always be suspected. Hence, when descending to the lower part of a tank or compartment, further atmosphere tests should be made. Regeneration of hydrocarbon gas should always be considered possible, even after loose scale has been removed. The use of personal detectors capable of continuously monitoring the oxygen content of the atmosphere, the presence of hydrocarbon vapour and, if appropriate, toxic vapour is strongly recommended. These instruments will detect any deterioration in the quality of the atmosphere and can provide an audible alarm to warn of the change in conditions.

While personnel remain in a tank or compartment, ventilation should be continuous and frequent atmosphere tests should be undertaken. In particular, tests should always be made before each daily commencement of work or after any interruption or break in the work.

Sufficient samples should be drawn to ensure that the resulting readings are representative of the condition of the entire space.

Hydrocarbon Vapours

To be considered safe for entry, whether for inspection, cold work or hot work, a reading of not more than 1% LFL must be obtained on suitable monitoring equipment.

Benzene

Checks for benzene vapour should be made prior to entering any compartment in which a cargo that may have contained benzene has recently been carried. Entry should not be permitted without appropriate personal protective equipment if statutory or recommended Permissible Exposure Limits (PEL’s) are likely to be exceeded. Tests for benzene vapours can only be undertaken using appropriate detector equipment, such as that utilizing detector tubes. (Benzene causes cancer, and has a delayed action which may be up to 20years)

Detector equipment should be provided on board all vessels likely to carry cargoes in which benzene may be present.

Hydrogen Sulphide

Although a tank which has contained sour crude or sour products will contain hydrogen sulphide, general practice and experience indicates that, if the tank is thoroughly washed, the hydrogen sulphide should be eliminated. However, the atmosphere should be checked for hydrogen sulphide content prior to entry and entry should be prohibited in the event of any hydrogen sulphide being detected. Hydrogen sulphide may also be encountered in pumprooms and appropriate precautions should therefore be taken.

Oxygen Deficiency

Before initial entry is allowed into any enclosed space, which is not in daily use, the atmosphere should be tested with an oxygen analyzer to check that the normal oxygen level in air of 21% by volume is present. This is of particular importance when considering entry into any space, tank or compartment that has previously been inerted.

Generally nearly all substances have been assigned Permissible Exposure Limits (PEL) and /or Threshold Limit Values (TLVs). The term Threshold Limit Value (TLV) is often expressed as a time weighted Average (TWA).  The use of the term Permissible Exposure Limit refers to the maximum exposure to a toxic substance that is allowed by an appropriate regulatory body.

The PEL is usually expressed as a Time Weighted Average, normally averaged over an eight-hour period.

Short Term Exposure Limit (STEL), is normally expressed as a maximum airborne concentration averaged over a 15-minute period.

The values are expressed as parts per million (PPM) by volume of gas in air. Toxicity can be greatly influenced by the presence of some minor components such as aromatic hydrocarbons (e.g. benzene) and hydrogen sulphide. A TLV of 300PPM, corresponding to about 2%LEL, is established for gasoline vapours.

Entry Procedures

General

A responsible officer prior to personnel entering an enclosed space should issue an entry permit. An example of an Enclosed Space Entry Permit is provided in ISGOTT.

Suitable notices should be prominently displayed to inform personnel of the precautions to be taken when entering tanks or other enclosed spaces and of any restrictions placed upon the work permitted therein.

The entry permit should be rendered invalid if ventilation of the space stops or if any of the conditions noted in the checklist change.

No one should enter any cargo tank, cofferdam, double bottom or other enclosed space unless an entry permit has been issued by a responsible officer who has ascertained immediately before entry that the atmosphere within the space is in all respects safe for entry. Before issuing an entry permit, the responsible officer should ensure that:

The appropriate atmosphere checks have been carried out, namely oxygen content is 21% by volume, hydrocarbon vapour concentration is not more than 1% LFL and no toxic or other contaminants are present.

Effective ventilation will be maintained continuously while the enclosed space is occupied.

Lifelines and harnesses are ready for immediate use at the entrance to the space.

Approved positive pressure breathing apparatus and resuscitation equipment are ready for use at the entrance to the space.

Where possible, a separate means of access is available for use as an alternative means of escape in an emergency.

A responsible member of the crew is in constant attendance outside the enclosed space in the immediate vicinity of the entrance and in direct contact with a responsible officer. The lines of communications for dealing with emergencies should be clearly established and understood by all concerned.

In the event of an emergency, under no circumstances should the attending crew member enter the tank before help has arrived and the situation has been evaluated to ensure the safety of those entering the tank to undertake rescue operations.

Regular atmosphere checks should be carried out all the time personnel are within the space and a full range of tests should be undertaken prior to re-entry into the tank after any break.

The use of personal detectors and carriage of emergency escape breathing apparatus are recommended.

Reference should be made to ISGOTT for additional guidance on entry into pumprooms.

 

Cargo Measurement 

Tank quantities are measured by noting the level of the fluid in the tank and then referring to the tank calibration tables and noting down the quantity specified against that level.

Thus we take the sounding of a tank – water and fuel on all type of ships and then follow the above practice. Note that prior to referring to the tables the tank level has to be corrected for error due to trim and list. These corrections are generally given in the tank calibration tables.

The above method though fine by all are turned upside down on a tanker. A tanker loads oil and it is not feasible to take a sounding every now and then – besides it is very messy. On tankers therefore instead of sounding the reverse is measured – that is the vacant level to reach the top of the tank – or the ullage.

Thus ullage tables are nothing but the sounding table reversed.

Note the following:

The maximum sounding of a tank is 24.35m the maximum ullage is also 24.35m.

When the sounding is 10m the ullage would be 24.35 – 10 = 14.35m

Thus when a tank is filling up the sounding increases, whereas the ullage reduces.

Once the liquid level is obtained the same is seen for the quantity (Volume) in the calibration book.

This is the Gross volume at Natural Temperature GVn (observed temperature being taken of the liquid at three levels and then averaged)

The sounding of any water which may be present in the tanks is now taken (some water is usually present in crude oil and also sometimes in product oil). The calibration tables are again referred and the volume of Free Water is obtained.

Thus the Net Volume at Natural (NVn) is found by subtracting the water form the GVn.

This NVn is now converted to a volume at 15˚C by looking up the correction in the ASTM tables – a factor is found, which converts the Volume at Natural temperature to a volume at 15˚C.

This would then be the Net volume of oil loaded.

The conversion is required since the loading temperature may be 40˚C whereas the temperature of the oil after a voyage of 30 days would drop to about 30˚C or so. Obviously the volume would then contract, so a standard temperature correction is done to 15˚C at both the load as well as the disport.

For weight calculations the volume at 15˚C is taken and this is multiplied by the density at 15˚C of the oil (actually a factor which is 0.0011 less than the density at 15˚C is used)

Bale Capacity:

This is the cubic capacity of a space when the breadth is taken from the inside of the cargo battens, the depth from the wooden ceiling to the underside of the deck beams and the length from the inside of the bulkhead stiffeners or sparring where fitted.

Grain Capacity:

This is the cubic capacity of a space when the lengths, breadths and the depths are taken right to the ships side plating. An allowance is usually made for the volume occupied by frames and beams.

Stowage Factor:

This is the volume occupied by unit weight of cargo. Usually expressed as cubic metres/ tonne. It does not take into account space, which may be lost due to broken stowage. However it obtained by multiplying the greatest length by the greatest breadth with the greatest height.

Example:

A bale of Hessian has the following dimensions: L – 1.2 M, B – 1.2 M and H – 1.5 M. The bale weighs 800 KGS.

The SF then would be obtained by:

Volume: L x B x H = 1.2 x 1.2 x 1.5 = 2.16 CBM

So, 2.16 CBM would weigh 0.8 MT

Or 1 MT of the cargo in bales would occupy 2.7 CBM

 

Broken Stowage:

The space between packages which remains unutilized. This is generally expressed as a percentage and the amount that is to be allowed varies with differ rent cargo and the shape of the hold. It is greatest when large cases have to be loaded in a n end hold, where the after end narrows down considerably.

BS is generally not given in any of the booking lists, but is a ship/ hold experience factor or a sister ship experience factor for that particular cargo. The most commonly accepted figure is about 10%, thus with a BS of 10% the available cargo space that may be loaded would be 90%.

Example: Given to load a quantity of light packaged cargo having a SF at 2.7 CBM/MT, the hold space (bale capacity) is given as 885 CBM. To find the amount of cargo that may be loaded in the hold.

The bale capacity is 885 CBM but since the BS is 10% the available space would be 885 x 90% Or 796.5 CBM Thus the cargo that can be loaded would be 796.5/ 2.7 = 295 MT (about).  However this BS that is given is for a proper stow as per earlier estimates, the final stow should also be a good stow or the BS that would be obtained on final completion would vary.

Thus on final completion of loading if the ‘tween deck was loaded with only 275 MT then the BS that was obtained would be:

Full capacity 885 CBM at 2.7 CBM/ MT could take in 885/ 2.7 = 328 MT

But it finally took in only 275 MT thus had a shortfall was 53 MT which was due to BS.

Thus,

328 MT – 275 MT = 53

And 53  / 328 = 0.16

Expressed as a percentage = 16% was lost due to BS instead of the earlier estimated figure of 10%.

Example-101

Given to load No. 1 Lower Hold

Bale capacity – 962 m3

Max Height – 11.945m

Permissible Load – 9.2 t/ m2

Forward Breadth – 4.5m

After Breadth – 11.5m

Mean Breadth – 8m

Length – 10.5m

 

Area of the hold – Length x Mean Breadth

A = 11 x 8 = 88m2

Permissible Load density – 9.2 t/m2

Therefore the load if evenly spread all over the hold would enable the hold to be loaded with:

88 x 9.2 = 809.6 MT

Example-102

Given to load No. 1 Lower Hold

Bale capacity – 962 m3

Max Height – 11.945m

Permissible Load – 9.2 t/ m2

Forward Breadth – 4.5m

After Breadth – 11.5m

Mean Breadth – 8m

Length – 10.5m

Cargo – SF 2.7 m3/t

Volume – 962 m3

Cargo can load – Volume/ SF

Cargo to load – 962/ 2.7

Cargo to load – 356 MT

 

Example-103

Given to load No. 1 Lower Hold

Bale capacity – 962 m3

Max Height – 11.945m

Permissible Load – 9.2 t/ m2

Forward Breadth – 4.5m

After Breadth – 11.5m

Mean Breadth – 8m

Length – 10.5m

Cargo – 150 MT, SF 2.7 m3/t to load only in after half of the hatch space

After breadth – 11.5m

Mid Breadth – 8m

Mean breadth – 9.75m

½ Length – 5.25m

Area of ½ hold as above – 51.2 m2

Volume of above – 611 m3

Max permissible load on 51.2 m2 – 9.2 x 51.2 = 471 MT

Since the cargo has a SF of 2.7 m3/t the volume occupied by the cargo would be:

Volume/ SF

611/ 2.7 = 226 MT

So the after half of the hold would take in 226 MT of the cargo and would remain within the permissible load density.

Let us now fill up the forward half of the hold with a cargo having a SF of 0.8 m3/t (heavy cargo)

Cargo – ?? MT, SF 0.8 m3/t to load in forward half of the hatch space

After breadth – 4.5m

Mid Breadth – 8m

Mean breadth – 6.25m

½ Length – 5.25m

Area of ½ hold as above – 32.8 m2

Volume of above – 392 m3

Permissible load would be: 32.8 m2 x 9.2 (SF) = 302 MT

Cargo that could be loaded as per SF – Volume/ SF = 392/ 0.8 = 490 MT

But the permissible load is – 302 MT, so the cargo could not be loaded right up to the top of the hold. So there would be a height restriction.

First we find the Volume as required for the permissible load of 302 MT

Load 302 = Volume/ 0.8

Or Volume = 302 x 0.8 = 242 m3

Since we know the area as 32.8 m2 we can find the height,

Volume/ Area or 242/ 32.8 = 7.4 m

Thus the cargo of 302 MT could be loaded only up to a height of 7.4m.

 

Securing Cargo 

 

Need for solid stow and securing of all cargoes

Cargo onboard a ship will tend to shift with the motion of the ship. This necessitates the

cargo to be lashed (secured) to the ship structure. However the lashing with ropes/ wire

ropes/ iron restraining bars is not very effective because of the fact that the tightened

lashings have a tendency to work loose with the motion of the ship.

On shore any nut which is fitted tightly on a bolt works loose with vibrations as such - spring washers are used together with check nuts and split pins to prevent the working loose of such nuts. This is not practical on shipboard lashings - except for turnbuckles and bottle screws with restraint bars. Below deck lashings further are not attended to during sailing and if they work loose it is practically impossible to do a very effective job to re-secure them. Temporary measures are often adopted and these may not be very effective as stated earlier.

Thus the only way to prevent the lashings from working loose is to stow the cargo very close to each other and then to shore the cargo with timber. This would prevent the cargo from acquiring momentum while swaying with the ship and thus prevent to a large extent the working loose of the lashings.

 

For bagged cargo if the same is not stowed solidly and thus allowing too much of broken stowage, would tend to shift with the motion of the ship, thus shifting the centre of gravity laterally and inducing a list to the ship. This coupled with the heeling of the ship would make the weather deck of a ship too close to the water line and thus endanger the safety of the ship.

Bulk cargo on general cargo carriers are therefore saucered with the same cargo, in order to prevent the cargo from shifting to one side.

Deck cargo due to the high KG is especially vulnerable lateral shifting and the lashings work loose and also to part lashing. Especially since the transverse momentum gained by such cargo during the rolling of a ship is liable to part lashings. Thus all deck cargo has to be definitely shored and then also lashed to deny the cargo from gaining any momentum.

Deck cargo - Lashed

                                                Deck Cargo - Shored and Lashed

Cargo liable to slide during rolling, such as steel rails, should be Stowed fore and aft

All long cargoes such as steel rails, pipes, long steel plates as well as steel coils are stowed with their ends in the fore and aft direction. This again is necessary due to the fact that most of theses cargo cannot be individually lashed they rather grouped into bundles and the bundles are lashed to make many small bundles of pipes or rails as the case may be. This prevents the individual pipes from sliding and since as mentioned the transverse momentum is quite large when the ship is rolling, and the pipes are thus prevented from damaging the sidewalls of the hold. This is severe since repeated banging has resulted in tearing holes in the shipside plates below the waterline and the ship capsizing due the inflow of water.

If the pipes / rails are stowed in the fore and aft direction this is prevented.

Bundling of long cargo (pipes/ rails):

This is the first tier. It is important to place the dunnage to spread the load as well as to

facilitate the passing of slings at the disport. The lashing wires are also placed prior to

loading the cargo. The size of the bundles should be to the capacity of the derrick/ crane

that would be used to discharge the cargo. The number of lashing wires is dependent on

the weight of the bundles as well as the length of the cargo.

As each bundle is completed the lashings are closed and tightened. And subsequently dunnage is again placed and the lashing wires again spread on top of the earlier cargo.

Stowage and securing for vehicles and trailers

Vehicle lashing on deck

Force parallel to and across the deck = 1.0 W

Force normal to the deck = 1.4 W

Force in the longitudinal direction = 0.3 W

The above forces are intended to represent the total force to be applied in each direction i.e., the aggregate of the static and the dynamic forces.

Case 1 – Vehicle stowed in Fore and Aft direction:

The forces preventing tipping of the vehicle are the vertical downward force and the lashings holding the vehicle (FLT)

Taking moments about A (the outer edge of wheel i.e., fulcrum position)

FLT x L = (1.0 W x 2/3 H) – (1.4 W – X)

FLT x (X + Y) sin = W (0.67 H – 1.4 X)

FLT = (W (0.67 H – 1.4 X) / ((X + Y) sin)

Note the importance of the fulcrum position (A),

The height of the centre of gravity, normally taken as 2/3 H

 is the angle of inclination of the lashings

To examine the force causing the vehicle to slide sideways:

For this example a trailer is supported by wheels on the one end and with a trestle at the other end.

 

 

          

 

In both cases sliding is resisted by the frictional resistance ‘’ between the tyre/ deck and the trestle/ trailer frame and also lashings (FLS).

Case 1 – Effect at the trestle end of trailer.

Note: Assuming ½ total forces act at each end of trailer then effective sliding force = 0.5 W – 0.7 W x Ls (assume 0.2)

= 0.5 W – 0.14 W

= 0.36 W then the force in the lashing resisting sliding = FLS = 0.36 W / cos

 

Case 2 – Effect at wheel end of trailer.

Effective sliding force = 0.5 W – 0.7 W x  (assume 0.4)

= 0.5 W – 0.28 W

= 0.22 W

then the force in the lashing resisting sliding = FLS = 0.22 W / cos 

Note the importance of ‘’ the coefficient of friction and  the angle of inclination of the lashings. In the above it can be seen near vertical lashing is great to prevent tipping but is useless for sliding whereas a near horizontal is great for sliding but is useless for tipping. So a correct angle of inclination should be fixed appropriate for the cargo.

In general the safe working load (S.W.L.) of lashing wires is taken as 1/3 the Breaking load.

If chain is used for lashing then:

If made of H.T. steel then the SWL would be 40% of the Breaking load.

And if made of ordinary steel then the SWL would be 33% of the Breaking load.

Efficient securing of cargoes is essential for the safety of the ship as well as the cargo

Securing of cargo is of prime importance not only for the cargoes themselves but also for the ship as a whole including the crew that sail on her.

Improperly secured cargo will shift in a seaway and can endanger the cargo as well as the ship.

In the worst cases the cargo may fall overboard and may endanger other ships such cargoes like logs and containers have been noted to have floated and come within the sea-lanes.

When a container falls overboard it must be remembered that it does so in spite of it being secured on the ship as well as the opposition to this being offered by the ship structure. Thus when it does go overboard it does after causing a great amount of structural damage.

There are many instances of cargo improperly secured breaking the lashings and punching a hole at or below the waterline and the ship having been lost with casualties.

Deck cargos if they part their lashings are liable to cause extensive damage, which can endanger the watertight integrity. Even minor movement of heavy cargoes has been known to shear off air pipes and sounding pipes resulting in water entering the tanks or other spaces below deck. Fire lines have also been damaged due to inadvertent movement of cargo.

Accommodation ladders as well as companionway can be damaged due to the cargo movement on deck in a seaway.

Even if the ship is not lost the damage such heavy cargoes can bring upon the structure of the ship is very heavy. Crew has often been sent to re-secure such cargo in rough weather with the crew suffering loss of limbs and other injuries.

Stowage and securing of deck cargo should be adequate for the worst conditions which could be experienced

Good stowage and good securing arrangement should be foreseen prior loading the cargo. If it is required extra lugs and eyes on deck have to be welded to provide lashing points for the cargo- this is generally done for heavy lifts or cargoes of odd sizes.

Securing should be always for the worst weather that would be encountered. Many a ship have suffered damage to cargoes and to their own structure by neglecting good and adequate lashing while on a short voyage, failing to take into account diversions and anchorage at open roadstead and cyclonic weather.

Hatches should be securely closed and cleated before loading over them

Once the cargo below deck has been loaded and all securing has been completed (securing can continue after the hatches are secured provided there is adequate space for

the crew to enter and to lash), the hatches are closed and battened down and all cleats and centre wedges should be in place.

Only after the above have been completed should any cargo be loaded on to the hatch tops.

If this is not done, and the hatch is battened down after the cargo has been loaded on to the hatch tops the battening down and the fitting of the cleats as well as the centre wedges would be ineffective since the weight of the cargo would not permit the hatch covers to be correctly in place and the hatch would leak in a seaway or even in rain.

Container Cargo 

 

Sea Containers were invented in the mid 1950s by Malcolm McLean, a North

Carolina trucking owner who grew tired of wasting his trucking company’s time with

trucks standing idle in line as ships were unloaded bit by bit by dockworkers. 

McLean developed sealed truck trailers and the concept of loading and unloading the trailer interiors only at the points of origin and destination. 

The first ship modified to accept these “containers” on deck, sailed with 58 of them from New York to Houston in April 1956. This was the start of McLean’s company, the Sea-Land Corporation. 

The Matson Line (Hawaii) put the first fully containerized ship into service in 1960. 

The International Standards Organization (ISO) first established container standards in 1961.  The ISO standard is not prescriptive and instead simply stipulates tests that the containers must pass.

Modern container ships have only one problem – when the ship arrives in port, the object is to unload the containers quickly to get them on to their final destination and to get the container ships back out to sea fully loaded heading for the next port. 

To accomplish this, container ships are equipped with steel skeletons called “cell guides”.

A special lifting fixture is used with remote actuators, which engage the corner blocks on the top of the container. 

A recent survey indicates that port crane operators can execute full crane cycles to remove and position containers at rates of between 30 and 60 boxes per hour.

 

Containers come in two basic sizes – 20 Footer and 40 Footer and are commonly known as TEU (Twenty Equivalent Units) and FEU (Forty Equivalent Units).

The external body of the container is made of corrugated sheet metal and is not capable of taking any load. The four corners have shoes and are strengthened to take in load.

The inside bottom has a wooden ceiling. There are weather-insulted vents provided to facilitate venting.

The weights marked on the containers are TARE weight and LADEN weight. TARE weight is the weight of the empty container and is usually 2200KGS for a TEU, while the LADEN weight may be anything from 20000KGS to 32000KGS (strengthened steel construction).

The container shoes fitted at the corners are hollow with 5 oval slots to facilitate the

fitting of container fittings as well as for lifting the container – either by using

conventional wire slings or by spreaders.

Since the containers are concentrated weights the loading of the same require special heavy dunnaging to spread the load evenly over the deck – if carried as deck cargo on conventional general cargo ships.

However the carriage of containers are primarily on container ships or on ships, which have been built to take in general cargo as well as containers to a limited extent.

Lashing of containers on purpose ships are supplied from reputed lashing makers and have been tested for the loads they are to lash. Various fittings are used and all of these are generally carried on board.

                    

Base stacker                             Twist Lock                                           Double Stacker

 

               

Corner Eye Pad                                                Side Stack Thrust                                 Bridge Fitting

        

Twist Lock                               Rod Lashing Bar                                               Spacer Stacker

A spacer stacker is used where there is a difference between adjacent containers as loaded in their heights, one being the 8ft and the other 8.5FT.

On normal ships where these fittings may not be available wire ropes are used however the number of ropes to be used would be decided by the weight of the container.

On GC ships with no provision for built in shoes only single height loads are carried.

However on container ships the hold stacks may extend to 7 high and on hatch top/ deck to 5 high.

The hold and the deck/ hatch top being strengthened.

The lashings to be done are specified in the container-lashing manual supplied to the ship from the building yard. This is not to be reduced since the stresses have been calculated and the number of lashings incorporated.

The containers are loaded onto a container ship in a specified manner. The ship is divided into BAYS or ROWS. Looking from the side the bays are marked from forward to aft.

The containers are stacked in tiers and are in general called the stacks.

This way ensures that any container can be located very easily – knowing the bay number and the row number isolates the location and the stack height give the exact position of the container.

On container ships the containers are lowered onto slots inside the holds, the holds bottom is provided with sunken shoes, twist locks/ stackers are fitted onto these and the container is lowered onto them.

Cell Guides on Deck – Open hatch concept:

Some containers are designed to carry refrigerated cargo, these special containers have their own cooling plant in built on one end of the container, and all that is required for the ship to provide is a power point for the electricity. The containers come with their own recording device and card, the ships officers has to renew the card on the expiry of the same, and is to see that the cooling plant does not stop functioning, manuals are provided whereby ships staff can do some minor repairs to the plant.

Today a variety of cargo which previously was thought could only be loaded onto a general cargo ship, is transported on container ships. An example is a tank, thus small parcels of liquid is carried on container ships.

Lashing of containers is very important since a typical container ship has a low GM(F), consequently the ship rolls quite a bit and the stresses developed by the cargo swaying is liable to break the lashings and put the containers into the sea.

             

All lashings are to be done following the ships lashing manual. In general the following is

a typical lashing system, others may also be accepted if permitted by the manual.

The planning of loading of a container ship is normally undertaken ashore, but the officer in charge of the watch should keep an eye on the loading to detect errors in stowage which may occur. A particular watch should be kept for containers with dangerous goods placards to see that their stowage satisfies segregation requirements as laid down in the IMDG code.

Other things to watch for are that container marked for underdeck stowage do not end up on deck – this is serious since the container may be for second port by rotation, also the heavier containers are generally loaded underdeck to increase the GM. Thus in addition to a loss of GM the ship would also have a mess up at the disport.

Refrigerated containers should be loaded where they can be connected to the ship’s power supply and the duty officer is to ensure the same. While loading a slight slackening of watch can become a liability since the gantries load very fast and to unload or to shift is expensive and time consuming – even if the fault actually is of the port.

Sometimes containers are loaded which due to the nature of the contents have to be overstowed, in this case the container is loaded and the container is then blocked off so that there would be no chance of any pilferage – such containers may carry – currency/ coins, drugs, and mail or other high value cargo.

Enclosed Space Entry 

An enclosed space is one with restricted access that is not subject to continuous ventilation and in which the atmosphere may be hazardous due to the presence of hydrocarbon gas, toxic gases, inert gas or oxygen deficiency. This definition includes cargo tanks, ballast tanks, fuel tanks, water tanks, lubricating oil tanks, slop and waste oil tanks, sewage tanks, cofferdams, duct keels, void spaces and trunkings, pipelines or fittings connected to any of these. It also includes inert gas scrubbers and water seals and any other item of machinery or equipment that is not routinely ventilated and entered, such as boilers and main engine crankcases.

Many of the fatalities in enclosed spaces on oil tankers have resulted from entering the space without proper supervision or adherence to agreed procedures. In almost every case the fatality would have been avoided if the simple guidance in this chapter had been followed. The rapid rescue of personnel who have collapsed in an enclosed space presents particular risk. It is a human reaction to go to the aid of a colleague in difficulties, but far too many additional and unnecessary deaths have occurred from impulsive and ill-prepared rescue attempts.

Respiratory hazards from a number of sources could be present in an enclosed space. These could include one or more of the following:

Respiratory contaminants associated with organic vapours including those from aromatic hydrocarbons, benzene, toluene, etc.; gases such as hydrogen sulphide; residues from inert gas and particulates such as those from asbestos, welding operations and paint mists.

Oxygen deficiency caused by, for example, oxidation (rusting) of bare steel surfaces, the presence of inert gas or microbial activity.

Hydrocarbon Vapours

During the carriage and after the discharge of hydrocarbons, the presence of hydrocarbon vapour should always be suspected in enclosed spaces for the following reasons:

Cargo may have leaked into compartments, including pumprooms, cofferdams, permanent ballast tanks and tanks adjacent to those that have carried cargo.

Cargo residues may remain on the internal surfaces of tanks, even after cleaning and ventilation.

Sludge and scale in a tank which has been declared gas free may give off further hydrocarbon vapour if disturbed or subjected to a rise in temperature.

Residues may remain in cargo or ballast pipelines and pumps.

The presence of gas should also be suspected in empty tanks or compartments if non-volatile cargoes have been loaded into non-gas free tanks or if there is a common ventilation system which could allow the free passage of vapours from one tank to another.

Oxygen Deficiency

Lack of oxygen should always be suspected in all enclosed spaces, particularly if they have contained water, have been subjected to damp or humid conditions, have contained inert gas or are adjacent to, or connected with, other inerted tanks.

Other Atmospheric Hazards

These include toxic contaminants such as benzene or hydrogen sulphide, which could remain in the space as residues from previous cargoes.

ATMOSPHERE TESTS PRIOR TO ENTRY

General

Any decision to enter an enclosed space should only be taken after the atmosphere within the space has been comprehensively tested from outside the space with test equipment that has recently been calibrated and checked for correct operation.

It is essential that all atmosphere testing equipment used is:

Suitable for the test required;

Of an approved type;

Correctly maintained;

Frequently checked against standard samples.

A record should be kept of all maintenance work and calibration tests carried out and of the period of their validity. Testing should only be carried out by personnel who have been trained in the use of the equipment and who are competent to interpret the results correctly.

Care should be taken to obtain a representative cross-section of the compartment by sampling at several depths and through as many deck openings as practicable. When tests are being carried out from deck level, ventilation should be stopped and a minimum period of about 10 minutes should be allowed to elapse before readings are taken.

Even when tests have shown a tank or compartment to be safe for entry, pockets of gas should always be suspected. Hence, when descending to the lower part of a tank or compartment, further atmosphere tests should be made. Regeneration of hydrocarbon gas should always be considered possible, even after loose scale has been removed. The use of personal detectors capable of continuously monitoring the oxygen content of the atmosphere, the presence of hydrocarbon vapour and, if appropriate, toxic vapour is strongly recommended. These instruments will detect any deterioration in the quality of the atmosphere and can provide an audible alarm to warn of the change in conditions.

While personnel remain in a tank or compartment, ventilation should be continuous and frequent atmosphere tests should be undertaken. In particular, tests should always be made before each daily commencement of work or after any interruption or break in the work.

Sufficient samples should be drawn to ensure that the resulting readings are representative of the condition of the entire space.

Hydrocarbon Vapours

To be considered safe for entry, whether for inspection, cold work or hot work, a reading of not more than 1% LFL must be obtained on suitable monitoring equipment.

Benzene

Checks for benzene vapour should be made prior to entering any compartment in which a cargo that may have contained benzene has recently been carried. Entry should not be permitted without appropriate personal protective equipment if statutory or recommended Permissible Exposure Limits (PEL’s) are likely to be exceeded. Tests for benzene vapours can only be undertaken using appropriate detector equipment, such as that utilizing detector tubes.

Detector equipment should be provided on board all vessels likely to carry cargoes in which benzene may be present.

Hydrogen Sulphide

Although a tank which has contained sour crude or sour products will contain hydrogen sulphide, general practice and experience indicates that, if the tank is thoroughly washed, the hydrogen sulphide should be eliminated. However, the atmosphere should be checked for hydrogen sulphide content prior to entry and entry should be prohibited in the event of any hydrogen sulphide being detected. Hydrogen sulphide may also be encountered in pumprooms and appropriate precautions should therefore be taken.

Oxygen Deficiency

Before initial entry is allowed into any enclosed space, which is not in daily use, the atmosphere should be tested with an oxygen analyzer to check that the normal oxygen level in air of 21% by volume is present. This is of particular importance when considering entry into any space, tank or compartment that has previously been inerted.

Generally nearly all substances have been assigned Permissible Exposure Limits (PEL) and /or Threshold Limit Values (TLVs). The term Threshold Limit Value (TLV) is often expressed as a time weighted Average (TWA).  The use of the term Permissible Exposure Limit refers to the maximum exposure to a toxic substance that is allowed by an appropriate regulatory body.

The PEL is usually expressed as a Time Weighted Average, normally averaged over an eight-hour period.

Short Term Exposure Limit (STEL), is normally expressed as a maximum airborne concentration averaged over a 15-minute period.

The values are expressed as parts per million (PPM) by volume of gas in air. Toxicity can be greatly influenced by the presence of some minor components such as aromatic hydrocarbons (e.g. benzene) and hydrogen sulphide. A TLV of 300PPM, corresponding to about 2%LEL, is established for gasoline vapours.

Entry Procedures

General

An entry permit should be issued by a responsible officer prior to personnel entering an

enclosed space. An example of an Enclosed Space Entry Permit is provided in ISGOTT.

Suitable notices should be prominently displayed to inform personnel of the precautions to be taken when entering tanks or other enclosed spaces and of any restrictions placed upon the work permitted therein.

The entry permit should be rendered invalid if ventilation of the space stops or if any of the conditions noted in the checklist change.

No one should enter any cargo tank, cofferdam, double bottom or other enclosed space unless an entry permit has been issued by a responsible officer who has ascertained immediately before entry that the atmosphere within the space is in all respects safe for entry. Before issuing an entry permit, the responsible officer should ensure that:

The appropriate atmosphere checks have been carried out, namely oxygen content is 21% by volume, hydrocarbon vapour concentration is not more than 1% LFL and no toxic or other contaminants are present.

Effective ventilation will be maintained continuously while the enclosed space is occupied.

Lifelines and harnesses are ready for immediate use at the entrance to the space.

Approved positive pressure breathing apparatus and resuscitation equipment are ready for use at the entrance to the space.

Where possible, a separate means of access is available for use as an alternative means of escape in an emergency.

A responsible member of the crew is in constant attendance outside the enclosed space in the immediate vicinity of the entrance and in direct contact with a responsible officer. The lines of communications for dealing with emergencies should be clearly established and understood by all concerned.

In the event of an emergency, under no circumstances should the attending crew member enter the tank before help has arrived and the situation has been evaluated to ensure the safety of those entering the tank to undertake rescue operations.

Regular atmosphere checks should be carried out all the time personnel are within the space and a full range of tests should be undertaken prior to re-entry into the tank after any break.

The use of personal detectors and carriage of emergency escape breathing apparatus are recommended.

Reference should be made to ISGOTT for additional guidance on entry into pumprooms.