Methods of sampling

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Sampling methods for different types of goods

The following section describes the principles of sampling of products in the form of liquids, granules, powders, bulk or retail sale packages, etc. The procedures described below should be used, except for specific products where different procedures may be required. (e.g. dangerous goods)

For customs clearance purposes, take one aggregate sample consisting of an appropriate number of incremental samples chosen randomly or systematically throughout the consignment. If you are satisfied the consignment is homogeneous, one incremental sample is usually taken as representing the goods covered by the same customs declaration.

1. Sampling of Liquids

This section covers the sampling of liquid products at ambient temperatures.

Chapter General information of sampling gives some information about homogeneous and heterogeneous products. The guidance in the following sections explains how you should sample heterogenous products which will require a number of incremental samples to ensure the sample is representative.

In some cases it may be difficult or impossible to take more than a single sample, however, if you are satisfied that the product is homogenous a single sample may be taken as representative of the consignment.

You may be satisfied that the liquid can be considered as homogeneous when:

• the nature of the liquid does not allow any deposit or stratification of their components e.g. spirits; or
• the liquid product has been homogenized by mixing, shaking, or circulation through liquid pumps prior to sampling.

If the products are non-homogenous due to their nature, and homogenization is not possible, a larger number of incremental samples must be taken at various spots (depths) to ensure that a representative sample is obtained. When there are serious concerns about obtaining a representative sample consult the customs laboratory regarding the sampling plan.

1.1 Sampling from tanks

1 - liquid surface 2 - surface sample – taken from surface 3 - top sample – approx 10 cm to 20 cm from the liquid surface (depends on the volume / height of the container) 4 - upper sample – 5/6 of height from bottom to surface 5 - middle sample - 3/6 of height from bottom to surface 6 - lower sample - 1/6 of height from bottom to surface 7 - outlet sample – From the outlet valve 8 - bottom sample

Equal quantities of upper, middle, and lower spot samples are taken from positions Nos 4, 5, and 6 (shown in the picture). The minimum incremental samples required are given in the following table:

Dipping vessels (Sampling tool L02-01, L02-02) may be used to draw the samples. The sampler is lowered through the hatch of the tank until it reaches the desired level, opened and kept in position until it is filled and then finally hauled up.
In the case of very viscous or creamy liquids more incremental samples at different heights are necessary. A sampler used for cross-level sampling (Dipping vessel L02-01) can be also used to take samples from tanks.

A vacuum pump (Sampling tool L01-01) may also be used, if the depth from which the sample is to be taken does not exceed 4 m, and depending on the viscosity of the liquid. Equal quantities of upper, middle and lower spot samples should be taken.

The incremental samples from all sampling spots/levels are collected in a mixing vessel, and after they have been thoroughly mixed an aggregate sample is created. If it is certain that all tanks of the vessel contain the same lot (with identical properties), an aggregate sample can be formed for the whole consignment by combining the incremental samples taken from all tanks. The number of incremental samples to be taken is determined by the number of tanks containing the same product from the same lot. Remember that impurities and/or residual water may be present on the surface of the liquid or at the bottom of the tanks.

If it is not possible to draw representative samples from the top of a tank, sampling must be done at the time of discharge or charge (Sampling tool L06-01) (See Chapter 1.4 Sampling from moving cargo).

1.2 Sampling from ships or barges and road or rail tankers

The total capacity of a ship or barge for the transport of liquid cargo is usually divided into a number of independent reservoirs (sections, compartments), which may have different sizes. The sampling procedures and the formation of aggregate samples are the same as described for sampling from tanks. Incremental samples are taken from each independent reservoir. If we are certain that all reservoirs of the vessel contain the same lot, an aggregate sample can be formed for the whole vessel by combining the incremental samples taken from all reservoirs.

Railway and truck tankers can be considered as horizontal cylindrical tanks. If we are certain that all compartments of a railway or road tanker contain the same lot, an aggregate sample can be formed for the whole tanker by combining the incremental samples taken from all compartments. If it is not possible to draw representative samples from the top of a tank, sampling must be done at the time of discharge or charge (Sampling tool L06-01).

A single sample only is required from vehicle fuel tanks. See sampling procedure card Petroleum liquids.

1.3 Sampling from transport packages

Sampling may be carried out using a vacuum pump (Sampling tool L01-01), various pipette-type samplers (Sampling tool L03-01) or other appropriate samplers e.g. Sampling tool L04-01 or Sampling tool L05-01.

If possible, properly homogenize the content of the transport packages before sampling. If samples are to be taken from only one transport package, the final samples are poured directly from the sampler into the sample containers. When a set of transport packages are to be sampled and we are certain that they all contain the same product, incremental samples are taken from different transport packages, which are then combined in a receptacle in order to create the aggregate sample. After thorough mixing of the aggregate sample, the final sample is obtained.

1.4 Sampling from moving cargo

If possible, the most representative sample of liquid product transported in bulk can be obtained when they are being moved, e.g. by using of Sampling tool L06-01. Before the sample is drawn, the sampling equipment, tap and tube must be rinsed with the sampled product. As a minimum three incremental samples should be taken, at the start, in the middle and near the end of the discharge or charge, but you should take account of the total quantity of the consignment and the speed of movement when determining the number of incremental samples required and the interval between sampling. The aggregate sample is created by mixing the incremental samples. The final samples can be obtained from the aggregate sample.

2. Sampling of solids

This section describes the sampling of solid goods in the form of powders, coarse or fine particles, granules and other types of solid bulk products. Bulk products may be transported in packages or in the free bulk state.

If the products are non-homogenous due to their nature, and homogenization is not possible, a larger number of incremental samples must be taken at various spots (depths) to ensure that a representative sample is obtained. When there are serious concerns about obtaining a representative sample consult the customs laboratory regarding the sampling plan.

2.1 Sampling of bulk products

In case of bulk products transported in the unpacked state, equal quantities of incremental samples are taken from five or more positions throughout the bulk consignment. The number of incremental samples to be taken is dependent on the quantity of the goods, the container in which they are stored and the practical possibilities for sampling.

The incremental samples are collected in a mixing vessel and after they have been thoroughly mixed an aggregate sample is formed. The final sample is obtained using the sample division system.

An overview of the amount of the consignment and the amount of the sample to be taken is specified in the sampling procedure cards for each product type. For goods not covered by a sampling card this table can be used:

Where bulk goods are transported in wagons or lorries, samples are drawn from each wagon or compartment. In this case specific points are chosen to ensure a representative sample is taken from all parts of the consignment.

In certain locations where bulk products are regularly handled an Automatic Sampler may be installed. These samples may be accepted for official purposes provided the sampling is supervised throughout by a customs officer. See Sampling Tools A01-01.

Wagons or lorries up to 15 tonnes – 5 sampling points (middle and approx. 500 mm from sides):
Wagons from 15 to 30 tonnes – 8 sampling points
Wagons from 30 to 50 tonnes – 11 sampling points

If we are certain that all compartments of the lorry contain the same lot, an aggregate sample can be formed for the whole lorry by combining the incremental samples taken from all compartments.

2.2 Sampling of bulk products from transport packages

Depending on the product and the transport method, different tools may be used for sampling: spear-type sampler (Sampling tool S01-01) for piercing the package, various zone samplers (Sampling tool S02-01), sampling trowels (Sampling tool S03-01), etc.

Take note of the different lot numbers or production runs or production data when you take samples. You may take fewer incremental samples when the marks and numbers on all transport packages are the same.

You should ensure that the goods being examined consist of a single consignment. If there are several consignments, they must be identified separately. Check whether the goods to be sampled come from the same production lot. If there are different lots, they must be sampled separately. An aggregate sample may be formed only from packages from the same lot. Equal quantities of incremental samples are taken from different transport packages found at different positions in the transport vehicle or in the storage facility. They are collected in a mixing vessel and after they have been thoroughly mixed an aggregate sample is formed. The final sample is obtained using the sample division system.

Damaged packages should not be used as part of the aggregate sample. They should be set aside and may, if necessary, be subject to a separate examination and report.

2.3 Sampling from moving cargo

If possible, the most representative sample of bulk goods can be obtained when they are being discharged or moved.
As a minimum three incremental samples should be taken, at the start, in the middle and near the end of the discharge or charge, but you should take account of the total quantity of the consignment and the speed of movement when determining the number of incremental samples required and the interval between sampling.

Where the goods are being mechanically moved using conveyors or other equipment there may be diverter valves or chutes that allow samples to be drawn at regular intervals from the moving stream. The aggregate sample is created by mixing the incremental samples. The final sample is obtained using the sample division system.

In certain locations where bulk products are regularly handled an Automatic Sampler may be installed. These samples may be accepted for official purposes provided the sampling is supervised throughout by an officer. See Sampling Tools A01-01. 

3. Sampling of products in retail sale packages

A retail package should be considered to be any pack specifically prepared for sale to an individual for domestic use.

Practical considerations may mean that you would treat a larger package as a retail package even though it is not classified as such in the Combined Nomenclature/TARIC.

This will apply particularly in the case of heterogeneous products where it will be necessary to take whole packages in order to obtain a representative sample.

For more information see specific card Retail packages and finished articles. 

4. Sampling of articles

Where the goods are found to be piece goods (e.g. timber, stone and ceramic products, metal castings or sheets or products such as electronic devices and apparatus) you should generally take whole items. If a single item is large the representative piece may be separated (using appropriate tool such as saw, axe, and tongs) and sent to the laboratory for examination. Large articles (such as metal tubes or sheets) can be tested immediately using a mobile laboratory or by means of mobile diagnostic equipment. In some cases technical data sheets and photographic evidence may be a satisfactory alternative to sampling. However sampling might still be necessary in some cases for complete classification.

For more information see specific card Retail packages and finished articles.

5. Sampling of waste

Sampling and analysis of waste can only give evidence of the composition of the goods. It does not provide evidence that the sampled material is considered to be waste, further checks or administrative research into the circumstances of the goods should be performed to confirm the classification as waste.

For specific environmental purposes a more detailed sampling procedure is necessary. See for these cases specific environmental sampling procedures or ask an expert for advice.
For more information see specific card Waste.

6. Sampling of gases

This section describes the sampling of miscellaneous chemicals, chemical products and preparations in gaseous form.

Gaseous products and liquefied gases are not usually sampled by customs officers. If sampling is really necessary these products should be sampled by, or under the supervision of, persons familiar with the necessary safety precautions. They must be properly trained and equipped to sample gases. If in doubt consult your Customs laboratory.

In certain locations (pipelines and pumping stations) where bulk gasses are regularly handled an Automatic Sampler may be installed. These samples may be accepted for official purposes provided the sampling is supervised throughout by a customs officer. See Sampling Tools A01-01.

For information about the sampling of LPG, see specific card Liquified Petroleum Gases (LPG).

6.1 General comments

The sampling container (M10 Gas Cylinder) should be conditioned by rinsing with the gas to be sampled and must not be exposed to pressure. The number of incremental samples is to be agreed to by all parties involved unless continuous automatic sampling is applied. If the composition is not completely homogeneous, homogeneity can be increased with a static mixer. The suitability of the materials used in a sampling system depends on the gas sampled. Generally the use of stainless steel is recommended. Valve seats and piston seals must be made of a material (elastic) suitable for its intended use. It is recommended that the sampling cylinders used for corrosive gases are coated with polytetrafluoroethylene (PTFE) or epoxy resin.

Generally, the materials that come into contact with the samples must have the following characteristics:

• impermeable to all gases;
• minimum absorption;
• chemical inertia towards the constituents which are transferred.

Compatibility of different materials with the components of the gas is shown in the following table:

Glass is a very inert material, but subject to breakage and unsafe for the sampling above atmospheric pressure.
PTFE is inert but may have adsorbent properties. It is permeable, for example, to water, to helium and to hydrogen.

The handling and packaging of samples should be carried out in a well-ventilated place. When no information is available or the information (labelling, hazard and safety symbols, SDS, documents) diverges from what you would expect you should treat the goods as dangerous. The containers must be made of a material suitable for the safe storage of gases and should be sealed to prevent leakage or the absorption of moisture. Sample containers must be clean and free from all substances which might contaminate the material being sampled. Glass cylinders must not be exposed to pressure. The cylinders must be labelled with the volume, pressure and test pressure. The cylinders must be capable of withstanding, without bursting a pressure of at least 1.5 times the working pressure. The cylinders and associated equipment must be inspected and tested periodically to ensure they do not leak. Please refer to your national legislation and guidelines on health and safety.

In general:

• do not use naked flames;
• do not smoke;
• do not use equipment and tools which can create sparks;
• do not use spark ignition engines;
• do not use equipment that operates at temperatures greater than the flashpoint of gas mixtures;
• do not use chemicals which may react violently with gas;
• Ventilation must be sufficient to prevent the formation of a flammable atmosphere.

6.2 Sampling from tanks

If a sample is to be taken from a tank it should be fed directly from the sampler into the sample container (M10 Gas Cylinder) through the system of fittings, connectors, valves and tubing (G01-01). When a set of tanks are to be sampled representing one identical lot, incremental samples are taken from several randomly chosen tanks, which are then combined in order to create the aggregate sample. This way of sampling will give a sample that is representative at one point in time only.

6.3 Sampling from cylinders and similar containers

You should ensure that the goods being checked consist of a single consignment. If there are several consignments, they should be sampled separately. An incremental sample is drawn from each container chosen randomly or systematically throughout the consignment. If a sample is to be taken from only one container it should be fed directly from the sampler into the sample container (M10 Gas Cylinder) through the system of fittings, connectors, valves and tubing (G01-01). When a set of cylinders are to be sampled representing one identical lot, incremental samples should be taken from several randomly chosen cylinders, which are then combined in order to create the aggregate sample.

6.4 Sampling from a pipeline or when gas is being moved

Where the product is being moved using pipelines or other equipment there may be diverter valves or by-pass samplers mounted adjacent to the pipeline or mounted directly on the pipeline, which will allow samples to be drawn at regular intervals determined by the moving speed.
Incremental samples are then collected in a sample cylinder (M10 Gas Cylinder) over a period, for later analysis in a laboratory. Samples must be drawn during the whole time the lot is flowing past the sampling point to ensure that the aggregate sample is representative. Whichever probe you use, the most important thing to remember is to make sure the tip of the probe must be placed in the middle of the pipeline or, if that is not possible in the center, in 1/3 of the diameter of the pipe.

Examples of probes for sampling from pipelines (from EN ISO 3170)