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Sampling of dangerous & noxious liquid cargo onboard chemical tankers

Why cargo sampling ? Cargo samples are evidence of the condition of the product during the various phases of transport (storage at terminal, arriving on board, loading, passage, discharging). This procedure describes sample-taking procedures and the legal background. Suitable PPE is to be worn when taking samples. Sample bottle to be flushed prior collecting sample.

For protection against possible cargo claims it is very important that cargo sampling is correctly carried out. The following is normally required ; Depending on the cargo involved, a series of samples are taken to determine the ship’s preparedness for loading. Always accompany surveyor during sampling.

How many samples are taken depends on the conditions in the charter party and the type of cargo. Unless specified otherwise, as a general rule a sealed sample should be taken for every tank carrying cargo. Samples taken by the vessel bearing no signature from the surveyor or other authorised person, unless a very good documented sample log is kept by the vessel, have no real value as evidence in legal actions.

Samples must be taken at the manifold where it is permitted, prior to releasing cargo to the tanks to ensure that Shore lines are clean and correct cargo being loaded. Whenever more than one tank is to be loaded with the same cargo, cargo is to be loaded one by one line/tank at a time to avoid contamination of whole cargo system when loading 1st foot.

After examination of the tanks, mudboxes, piping etc (as far as possible) for cleanliness it is usual to load sensitive chemicals into the ship's tanks to a level of approximately 0, 3 m and then take samples from the tanks, presuming that any previous residues in the piping are by then dissolved into the new cargo (''soak test"). Similarly samples are taken from an initial discharge into container tanks or similar located on the shore before commencing unloading at full rate to the shore storage tanks.

If a "soak test" upon loading is turned down by the surveyor or the shipper and loading stopped, the chief officer should then request sealed and identified samples of the cargo lot in question, from the ship's tanks as well as from the shore tanks. By these means the shipowner may be able to protect his interests in case of any dispute.

Sometimes drip-samples are taken from the loading manifold during loading. This method is simple, but not always fully representative. The pumping rate may vary during the transfer, whilst the sampling rate is more or less constant. Furthermore it is difficult to guarantee the proper identity of a sample taken over a long period of time. This is not meant to discourage the ship’s officers from taking a drip-sample during loading, but only to mention the weak points of the method. In fact, drip-sample during loading may be the only way to establish whether a cargo was contaminated during the pumping on board or ashore.

Before unloading cargo samples are normally taken from the ship's tanks. The cargo samples should be sealed and marked on board, particularly if no independent surveyor is present. The ship should keep one sample for future reference in case of any disputes arising. The samples should be stored in a dark and cool room especially put aside for this purpose. The room should have steel bulkheads and be open to the weather deck.





Samples of products which deteriorate or change with, time (e g styrene, vegetable oils) have a limited purposeful storage time on board. With e g phosphoric acid the samples may remain representative as regards chemical composition, but may not be so as regards contents of sediments, However, normally the samples are stored one year, which is the normal respite for making any claim.

Sampling at deep levels is carried out with containers which are lowered upside down or have valves or other means of filling themselves up at the deeper level. Sampling at various different levels is necessary for products which have a tendency to stratify, viz phosphoric acid which may contain a higher percentage of solids near the tank bottom than at top level.


Safety precautions

Sampling is risky, vapours or spray from the product may cause poisoning, caustic burns or scalding of personnel. Release of small amounts of products may also cause problems on deck or the environment (terminal, water). For these reasons, it is absolutely necessary to comply with the strictest safety regulations and the requirements of the material safety data sheets.

When samples are taken through tank openings (hatches), personnel should stay to the windward side of the opening. Depending on the properties of the cargo, suitable protective clothing should be worn as required. When taking samples from lines under pressure the risk of spray from the product should be taken into account.

Closed sampling to be carried out whenever possible except at manifold.

Sampling should not take place until 30 minutes after loading has been completed to ensure any static charges have been dissipated. Earthing requirements of the instrument must always be complied with, as per the manufacturer’s instructions. The bonding connection must be tested by ship staff prior to each cargo operation and if any abnormalities are found, the instrument is to be withdrawn from service until rectified.




Labels

The labels of the cargo samples must at least contain the following information:
  1. Name of the vessel
  2. Port of loading
  3. Cargo
  4. Tank
  5. Date and time
  6. Signature, voyage no. of Chief Officer and where possible, the surveyor.
Storage and Disposal of Samples

All samples that remain onboard are to be properly stored in the sample locker. A list of all samples stored, the method of disposal of all samples (including a record of receipts when these are disposed of ashore) is to be maintained by the Chief Officer.

The storage space should be made of materials fully resistant to the different chemicals intended to be stowed and to be cell divided in order to avoid shifting of the bottles at sea. Samples that may react with each other dangerously are not to be stowed close to each other. Incompatible cargo samples to be stowed separately following a cargo compatibility chart as per 46CFR. Adequate ventilation (not necessarily mechanical) is to be provided at the storage space.

It is prohibited to store Chemical / Oil samples (even for brief periods) in rooms or lockers not intended for this purpose.

The Chief Officer is to maintain a record of all samples with the date, grade, source and disposal date / method.

In general, samples can be disposed off three (3) months after discharge of the cargo, unless: There is a cargo claim, or There are special instructions from Charterers.

Propylene Oxide (PO Mixtures) and Acrylic Acid samples, due to their hazardous nature, must not be stored onboard.

The Chief Officer has to preventively authorise any cargo sample disposal. Cargo samples may be disposed of in the following manner.

a) Delivered to a shore reception facility and a certificate of receipt issued.

b) Added to either:

i) Tank cleaning waters of a similar grade having the same pollution category and chemical compatibility (MARPOL Annex 2 cargo) or

ii) Slops (MARPOL Annex 1) As soon as the cargo sample is disposed of accordingly, the log book should be up-dated with the required information.

Sampling on land

Samples from the land tank and line are always taken by the independent surveyor, without a ship’s representative being present.

Sampling on board

Sampling on board should always be witnessed by an officer. All personnel involved in sampling operations must wear the appropriate protective equipment for the Chemicals to be sampled prior to the commencement of the operation.

Sampling cargo under nitrogen blanket

In case of cargoes loaded and transported under permanent nitrogen blanket, the samples must not be taken through tank openings, since otherwise the moisture and/or oxygen in the air might react with the cargo. Sampling can only be done by means of a suitable valve and pumping around or with help of the closed sampling device or at pump stack running cargo pump. All safety regulations applicable for the situation and the cargo must be complied with.

Release of samples to third parties

Samples must only be released to third parties under direct instructions from Charterers and/or Management Office and a detailed receipt has to be obtained for each sample. Samples relating to a cargo claim may only be handed over to a representative of a P&I Club and after getting a receipt for the same.

Disposal of samples

Samples should only be disposed of to approved shore reception facilities and receipts for the disposal must be obtained and maintained onboard.

Sampling programme

A complete sampling programme consists of the following elements:
  1. Sample from the shore tank/line
  2. Manifold sample
  3. Sample from the ship’s line and/or pump stack.
In the latter case the valve(s) to the tank i.e. drop-valve and delivery remain closed. i) First Foot sample ii) Sample from completed tank At least enough cargo should be in the tank to fill a sample bottle. ‘First Foot sample’ refers to filling the tank approximately at one foot innage level.

Line Flushing

If a product is to be loaded into several tanks, either a certain amount of cargo is transferred from tank to tank until in the last a foot sample can be taken, or all tanks will receive ‘one foot’ cargo. Circulation rinsing with product may be required to wash lines Washing of tanks using re-circulated cargo to obtain satisfactory samples is not to be undertaken without direct management office approval and special safety precautions.



Related Info:

Practical example of determining specific gravity & density of chemical cargo

How to clean cargo tanks prior loading noxious liquid chemicals ?

Checklist for handling dangerous liquid chemicals in bulk

Following reference publications provide useful guidance and international regulations for carrying hazardous chemicals at sea.



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