Gard News has a look at problems involving cargo carried in jumbo bags and some solutions to these problems developed by the industry.
About a year ago a reefer vessel insured by Gard went down on a voyage from Europe to South-America. In the Bay of Biscay the cargo shifted in heavy weather, the vessel took a list to port, capsized and sank. Of the 24 crew, two were lost. That brought to mind a very similar case from 1997, when the reefer vessel VANESSA also capsized in bad weather and went down. Both these reefer vessels carried fertiliser in jumbo bags.
Gard has searched for other similar cases and looked at the transportation of granulated cargo in jumbo bags, first of all as a return cargo in reefers. Reefer vessels, purpose built for carrying fruit, may carry different types of available cargo when returning to the fruit producing countries. As fertiliser is in big demand by the same agricultural countries, it has become a very common return cargo. Fertiliser may be ammonium nitrate, which is also used for explosives, or other types of nitrates or phosphates, including urea. In dry, granulated form, these products may be shipped in bulk, in sacks or in large, so-called jumbo bags, both in bulk vessels and in other types of dry cargo vessels. Other names used for such cargo units are "big bag", "super sack", "bulk bag", but the proper name is Flexible Intermediate Bulk Container, or FIBC.
The Flexible Intermediate Bulk Container
More and more cargo is transported in jumbo bags, which are made in many sizes, for contents usually between 500 and 3,000 kg. They may be round or square and vary in heights between 100 and 200 cm, and are often made of an outer layer of woven polypropylene for strength and an inner layer of polyethylene. Transportation is usually done by lifting in loops, and there are bags with one, two or four loops at the top, depending on whether they are to be lifted by crane or forklift. For easy handling by fork lifts, the bags may also be transported on pallets. The jumbo bags are filled from the top, and some are arranged so they may be emptied from the bottom or are just cut open, if not of a re-usable type. They are very handy for transportation of cargo in powder, pellet or granulated form, but may also be used for nodule types of products, like potatoes, onions, etc. A lot of raw materials for the chemical industry are transported in jumbo bags, and they are commonly used for products like cement, fertiliser, salt, etc. The bags may be placed inside cargo containers and, if used for fertiliser for instance, they are easy to put on trucks for direct delivery to farmers. Jumbo bags are gaining in popularity so fast that there are now international conferences for the producers and users, and the "6th World FIBC Congress" was held in Amsterdam in September 2010.
The risk of capsizing
All vessels may sometimes face risks of grounding, collision and fire, but such accidents may to a certain extent be handled by the crew, and if not, the crewmembers normally have a chance to leave the ship. The capsizing of a vessel, however, may leave the crew no time for action and possibly not even time to save themselves. IMO and Class regulations therefore aim to provide all vessels with sufficient stability, also if the hull should be damaged to a certain extent.
Slack bunker-and ballast tanks onboard may contribute to a capsizing, but the two main initial causes will either be that the cargo has shifted or there has been massive ingress of sea water. One may eventually lead to the other.
To protect the vessel against capsizing due to ingress of water, there are the relevant IMO regulations in the International Load Line Convention and SOLAS for obtaining the International Cargo Ship Construction Certificate. To avoid the risk of shifting cargo, there are SOLAS Chapter VI, Carriage of Cargoes, and the Code of Safe Practice for Cargo Stowage and Securing.
Jumbo bags are excellent for the handling of granulated cargo like fertiliser. But during ships' motions in heavy weather, it has been found that the cargo may move within the bags and the bags may take a slightly different shape. If stored tightly together and on top of each other in a boxed cargo hold, this normally does not represent a problem. But if stored in multi-decked cargo holds, without a shoring between the bags and the deck above, the cargo may shift. The shifting of such cargo on several decks may result in the vessel taking a list and eventually capsizing. Reefer vessels are more vulnerable to such shifting of cargo in jumbo bags than others. They are usually built for speed, so they are slim-hulled and may roll considerably. They usually have four decks of a height of 2.2 metres, which allows only one bag in height per deck, leaving an empty space above. There may also be reduced friction between the material of the bags and for instance the flooring of aluminum plating often used in reefer vessels, or if plastic sheets have been placed on the decks for the purpose of cleanliness.
Loading of ammonium nitrate in jumbo bags at Yara Industrial in Koping, Sweden.
Cases from the past
There is not much guidance available on how to stow and secure jumbo bags, and there has not been much warning against non-reefer types of cargo in reefer vessels, but it is never too late to learn from cases from the past.
On 13th December 1981, the Ecuadorian reefer vessel BONITA, with P&I cover with Gard, was hit by a hurricane in the English Channel, on a voyage from Hamburg to Panama and Ecuador. The vessel was of the Clipper-type, 8,400 GT and built in Norway in 1971. She rolled considerably, being of a slim hull and powered for a speed of 22 knots. The cargo from Hamburg was fertiliser in plastic sacks, stowed manually on the reefer decks. In nine-metre-high waves, the vessel rolled tremendously and got a list of 25 degrees, which increased to 60 when the crew left her. Of the 37 people on board 35 survived, rescued under very difficult conditions by British helicopters and a rescue boat from Guernsey. The case is still one of the major rescue operations of the Royal National Lifeboat Institution and is referred to at the Marine Museum of St. Peter Port in Guernsey.
The vessel, which sank the following night, was not loaded with jumbo bags, which were not much in use at that time. But the plastic sacks of fertiliser were not shored against the decks above the cargo, and one may also suspect insufficient stowing in the extreme wings of the cargo holds. The vessel had Ecuadorian flag in order to profit by obtaining very cheap Ecuadorian fuel and did therefore also leave Hamburg with some bunker tanks empty. Later, sister vessels used drilling mud as added ballast in some of the bottom tanks.
On 26th February 1986 the six year old general cargo ship ANGELA SMITS went down after meeting heavy weather in the Bay of Biscay. As the cargo shifted, the vessel developed a severe list and eventually sank. The cargo was ammonium nitrate in jumbo bags, loaded at a Norsk Hydro plant in Porsgrunn, Norway, and destined for Australia.
A major disaster with a vessel carrying jumbo bags happened on 9th December 1994, when the Ukrainian SALVADOR ALLENDE went down in the North Atlantic. On a voyage from Freeport, Texas to Helsinki, she encountered a storm 750 miles off Nova Scotia, took a list to port, capsized and went down stern first. Waves were said to be 50 feet, or around 15 metres high. A major search and rescue operation took place with spotter planes and helicopters, as well as six diverted cargo ships. The two helicopters of the 106th Rescue Group of the New York Air National Guard worked under very difficult conditions, had to refuel in mid-air no less than ten times and were later recognised for the "longest over-water rescue with helicopters in aviation history". One of the helicopters picked up one survivor from the sea and a German vessel another. The Atlantic Ocean claimed the lives of the rest of the crew, no less than 29 persons.
The SALVADOR ALLENDE was a general cargo vessel, but had similarities to a reefer vessel, both in having a hull form designed for a speed of 19 knots when new and in having upper and lower tween decks in the cargo holds. She was loaded with 7,300 tons of rice, in jumbo bags of 1.7 m3, weighing about one ton each. Rice will have the same tendency to move within the jumbo bags as other granulated cargo, and the investigation showed that the stow had not been as tight as it could have been. The bags were carried in the lower holds, lower and upper tween-decks, in tiers two to five-high, depending on headroom. There had been considerable free space in incomplete rows and around obstructions such as columns and web frames at the flare to the ship sides forward. Rubber tiers and pallets had been used to fill voids, a questionable procedure. Ropes of 14 mm synthetic and natural fibre had been used for lashing, not steel wires. The lashings only covered part of the cargo, and as the ropes were merely looped through the straps, the bags could move along the lines.
During the heavy rolling motions of a ship, the bags will seek to fill the voids between them, and during sideways pressure the cargo may be compressed and also rise within the bags, creating even more slackness in the transverse direction. In the case of SALVADOR ALLENDE, it was found that the bodily shift of cargo could have amounted to thousands of tons, and even by movements as little as 2cm per bag, with 24 bags across, this would have caused a dangerous heeling moment, resulting in a list and the vessel eventually taking in water and capsizing.
The SALVADOR ALLENDE was not a Gard-covered vessel, but the reefer VANESSA was. She was a Bahamas-flagged, 4,000 GT vessel making 16 knots. On a voyage from Koping in Sweden to Puerto Bolivar in Colombia, she sank in rough seas 435 miles east of St. John's, New Foundland on 23rd October 1997. Six lives were lost. The cargo on board the VANESSA was ammonium nitrate, carried in jumbo bags. Ammonium nitrate was becoming a popular return cargo for reefer vessels trading to South America, used either as a fertiliser in fruit farms or as an explosive, for instance for use in the mines of Colombia.
The cargo lost with the VANESSA had to be replaced, and that was done by the sistership NYANTIC, which soon after loaded at the same port. In bad weather, on 15th November 1997, this vessel also developed a list, but the master managed to take her to a port of refuge in the Azores, where the cargo was re-stowed. The NYANTIC had P&I cover with Gard at the time, but the event did not result in a claim. As the vessel survived, the observations of the shifted cargo gave the shippers valuable information about the behaviour of cargo in jumbo bags.
There have been other cases as well, over the years, of vessels capsizing with a cargo in jumbo bags, or having to seek a port of refuge due to listing. Often, in cases of capsizing, it has not been possible to establish a clear cause, other than assuming a shifting of cargo. When KONGSTIND, a small Norwegian freighter disappeared with a crew of four at Hustadvika on 4th January 2003, no cause was found, but it was assumed that a shifting of cargo had taken place. Almost half the cargo was fertiliser in jumbo bags; other cargo was fertiliser in sacks on pallets. This type of cargo had been regularly carried by the vessel many times, without problems. However, it was mentioned at the inquiry that the vessel had at times arrived in port with some list, and that this was caused by jumbo bags being pressed together on voyage. The vessel was a tween-decker and was normally loaded by stevedores of the shippers, supervised by the crew.
IMO's advice on FIBCs
SOLAS Chapter VI, Carriage of Cargoes, Part A Reg.5.1 deals with stowage and securing of
cargoes and requires: "Cargo, cargo units and cargo transport units carried on and under deck shall be so loaded, stowed and secured as to prevent as far as practicable, throughout the voyage, damage or hazard to the ship and the persons on board, and loss of cargo overboard". Regulation 5.6 further requires an approved "Cargo Securing Manual", for all types of ships engaged in the carriage of all cargoes other than solid and liquid bulk cargoes. IMO has also issued Guidelines on the preparation of the cargo securing manual (MSC/Circ.745). As for other vessels, reefer vessels are to have a Cargo Securing Manual on board, and if there are other types of cargo to be carried than the customary reefer cargoes, the manual should also make reference to that.
The Code of Safe Practice for Cargo Stowage and Securing has some advice on particular types of cargoes, and Annex 10 deals particularly with Flexible Intermediate Bulk Containers. It is pointed out that "The ideal ship for the carriage of FIBCs is one with wide hatches so that the FIBCs can be landed directly in the stowage positions without the need for shifting" and that "The cargo spaces should, where practicable, be rectangular in shape and free of obstructions". That is also in line with Gard's experience: no problems have been noted with the transportation of jumbo bags in box-shaped cargo holds, where the bags are loaded tightly together and on top of each other. The problem is first of all one for ships with relatively narrow hatch openings and multiple decks.
The Code of Safe Practice for Cargo Stowage and Securing seems to acknowledge the problems of vessels with teen-decks, advising that "when FIBCs have to be stowed in deep hatch wings, easy access and sufficient manoeuvring space for suitably adapted fork-lift trucks should be available". For jumbo bags in reefer vessels this may be a bit of wishful thinking, as normal fork lifts may not have enough space under the decks to move the bags by lifting them by the loops. Major shippers may have invested in purpose-built fork lifts, or they use a technique of placing the fork lift so the fork extends in the way of the hatch opening to receive a bag onto the fork. The bottom of the bag then takes a shape that will allow the fork to be extracted once the bag is in position and lowered to the deck for stowing.
The Code also advises that when FIBCs are stowed athwart ships, one should start the stowage from both sides of the cargo hold, so any void space will be at the centre and not in the wings. That void space should then be chocked off. In cases where a tween-deck or lower hold is only partly filled with FIBCs, the bags must be shored off and wire lashings should be used from side to side of the cargo hold to secure the bags. The Code does well in asking for wire lashings, too often it has been seen that synthetic ropes may stretch or are of insufficient strength to secure heavy cargo in heavy weather.
Yara's solution for loading reefer vessels
The reefer vessel VANESSA, which capsized in 1997, had loaded ammonium nitrate in jumbo bags from Koping in Sweden. Yara Industrial, Technical Nitrates, at that time Hydro Chemicals AB, is a major shipper of prilled ammonium nitrate and ships it in jumbo bags. Following the capsizing of VANESSA, and the cargo shifting of NYANTIC soon after, Yara decided to investigate the behaviour of jumbo bags filled with ammonium nitrate. The firm MariTerm, a specialist firm on the securing of cargo for transportation, was engaged to do the job and gained valuable information from the case of the NYANTIC, when it was reported that the jumbo bags had been compressed to one side, leaving an open free space of as much as 1 to 1.5 metres on the other. Following the shifting of cargo on board NYANTIC, Yara decided to use other types of vessels for their cargoes, until they had developed the so-called "Chain Lashing Method" for reefer vessels. It was decided that all reefers, to load ammonium nitrate in jumbo bags, would have to have an addendum to the Cargo Securing Manual and to have the cargo secured in a way that would avoid the risk of shifting.
In 2004 a practical test with the jumbo bags in use by Yara was carried out by MariTerm for vessels of Seatrade, in order to determine the expected compression of ammonium nitrate in jumbo bags due to accelerations on board vessels, angle when tilting, angle when sliding occurred and coefficient of friction. For the test a truck with a tilting platform was used, covered with gratings in use by reefer vessels of Seatrade. The results have thereafter been used for dimensioning cargo securing arrangements for reefer vessels loading jumbo bags for Yara. It is required that the loaded cargo should not be subjected to accelerations above 0.6 g and to achieve that the metacentric height, GM, is to be below a maximum value individual for each vessel.
To secure the jumbo bags in block stow from side to side of the cargo hold, one high, two methods were designed, both using the bags to create two longitudinal boundaries or "bulkheads". This is achieved by either stretching steel chains above the bags, across the cargo holds at three to five metre distance, and securing to these the longitudinal rows of bags by web straps, or by chaining the longitudinal rows of bags to fixed points of the under deck structure. Solid fixed attachments for the chains are needed, and if such are not fitted already, the cargo hold lining and insulation have to be cut for the welding of solid lugs to the side-framing of the hull. All chains, shackles and turnbuckles are required to have a minimum breaking load of 20 tons and the web lashings one of four tons. All the lashing equipment is supplied by Yara, so the cargo shipper has full control over the quality of the gear. Lashing of bags are also required at sides, to avoid tilting, if the ship sides are not vertical. All open spaces between bags or between bags and ship structures are to be filled with air bags, etc. The bags must be protected from sharp edges and damaged bags are not allowed to be loaded. Another consideration is not to exceed the permissible deck load.
This drawing shows the lashing pattern of how jumbo bags are secured by chains and web lashings using D-ring attachments of the underdeck structure.
(Drawing courtesy of MariTerm, Sweden)
Even if the bags are secured in accordance with the above requirements, they will have a certain freedom, although limited, to move in the transverse direction. In a vessel loaded with for instance a row of 16 unsecured bags in the transverse direction, the compression of the bags could, according to tests, result in a movement of the centre of gravity by as much as 1.28 metres. Yara also requires therefore that the vessels loading their cargo fulfil the following stability criteria:
1. The angle of heel due to the shifting of the jumbo bags should not be greater than 12 degrees.
2. In the static stability diagram, the net or residual area between the heeling arm curve and the righting arm curve up to the angle of heel of maximum difference between the ordinance of the two curves, or 40 degrees or the angle of flooding (θ), whichever is the lesser, shall in all conditions of loading be no less than 0.075 metreradians.
3. The initial metacentric height, after correction for the free surface effects of liquids in all tanks, shall be not less than 0.30 metres.
These criteria are taken from the IMO International Code for the Safe Carriage of Grain in Bulk", which does not formally apply to cargo in jumbo bags, but sets a reasonable survivability criterion for vessels loading such cargo.
Finally, Yara also strongly advises vessels loading their cargo to subscribe to meteorological consulting services and navigate according to the forecasts and the advices on route planning delivered by such firms. This praxis was initiated by Seatrade as a standard procedure on all their vessels carrying ammonium nitrate in jumbo bags. Gard's experience is that ship managements adopting such services for their vessels are well pleased by the reduced risks of meeting adverse weather, and find it worthwhile to perform a slightly longer voyage.
Yara Industrial, Technical Nitrates has expressed that the tests carried out and the requirements they have established for the securing of jumbo bags are only valid for the type of bags they use and the ships they load. Last year as many as 40 to 50 reefers were loaded with such cargo, and since 1997 around 500 vessels have carried cargo in jumbo bags from Yara, all arriving at their ports of destination without problem. The principles established by Yara are therefore well worth studying by other shippers and shipping lines.
We thank Yara Industrial, Seatrade Reefer Chartering and MariTerm for providing the information on how to lash jumbo bags with prilled cargo on board reefer vessels.