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Assessment of cool bags

Testing of insulated bags and boxes.

In this article, Simon Courtney looks at the testing of insulated bags and boxes against BS EN 12546-2:2000 – 'Materials and articles in contact with foodstuffs – insulated containers for domestic use – Part 2: Specification for insulated bags and boxes'.

Insulated bags and boxes are popular functional items used for temporary storage and transport of foodstuffs and incorporate insulation properties to keep the contents cool (and sometimes hot) prior to consumption. They can vary in size from small lunch bags for individuals through to larger boxes and bags intended for family picnics.

Insulated bags and boxes intended primarily for use with cold food and/or drinks are often referred to as cool bags or boxes and those intended primarily for hot food and/or drinks as hot bags or hot boxes. BS EN 12546-2000: Part 2 applies to both types of container.

Part 2 of this specification is applicable to all types of portable domestic food and/or drink insulated containers such as boxes, chests and bags, intended to contain generally wrapped or packaged food and/or drinks in their containers. The specification does not apply to insulated bags designed specifically for short-term transportation of frozen foods, containers for industrial or catering uses, or insulated flasks and jugs.

‚Äč Figure 1: Determining thermal conductivity of a cool bag

Figure 2: Pictogram for insulation performance

The specification defines an applicable container as one consisting of an inner container and an outer protective case with an insulant between them in order to reduce to a minimum the transfer of heat to or from the contents of the inner container. Although this specification refers to containers that may be used to keep the content hot or cold, it contains only an assessment for the storage of cold items. The specification does not assess the effectiveness of containers for hot storage.

BS EN 12546-2000: Part 2 comprises six tests: capacity, insulation performance, impact resistance, handle strength, ease of cleaning and seepage.

The specification requires that a container ‘shall be designed in such a way that it shall be possible to easily and completely clean the item’ but does not describe how this should be assessed. However, SATRA does this by inspecting the item to ensure that it is possible to access all internal surfaces of the container with a hand-held cleaning cloth

Checking capacity of containers

In the capacity test, the actual capacity of the items is measured and compared with any declarations made, whether this is on a swing tag attached at the point of sale or permanently attached to a product. The capacity is determined by filling rigid boxes with water. Flexible containers are filled with small polystyrene spheres of known low density, rather than water, as the weight of the water could cause the container to collapse, spilling its contents. The weight of the water or spheres which are used to fill the container is measured and this weight is used to calculate the internal volume of the container in litres.

Figure 3: Cool bag undergoing physical strength testing

The specification requires that the nominal capacity of the containers is quoted to the user to an accuracy of ± 5 per cent for rigid containers and ±10 per cent for flexible containers. No explanation for the different levels of accuracy is given in the specification. SATRA considers that the level of accuracy for measurement for flexible containers is lower than that for rigid containers due to the ease with which the container will distort and the compressible nature of the polystyrene spheres.

Determination of thermal conductivity properties

In the insulation test, the thermal conductivity of the container is assessed in order that it can be declared to the user. The container is half filled with water at 5ºC and the time taken for the water to rise to a temperature of 15ºC is calculated when it is placed in a warm environment (figure 1). To do this, the container is half filled with domestic tap water which has been bought to a temperature of 5±1ºC and a thermocouple is secured in the water so that it is held at a position of approximately half the depth of the water. The lid of the container is sealed and the whole container is placed in an oven at a temperature of 32±1ºC. The temperature of the water in the container is measured every 15 minutes until it rises to 15ºC. The insulation performance of the bag is quoted as the time taken for the water to rise from 5ºC to 15ºC (to the nearest whole hour). The specification requires that this information is declared to the user by means of a pictogram, which is shown in figure 2. Again, this information can be included on a swing tag or permanently attached to the container itself.

The specification does not quote any requirements for the insulation properties or capacity, only that the correct information is provided to the user.

Physical strength testing

In the impact test, the container is loaded with 0.25kg of sand per litre of calculated capacity. The container is raised to a height of 500mm above a flat concrete floor surface and allowed to fall freely so that it impacts against the flooring, simulating a loaded bag being dropped. The damage to the container is assessed against a requirement of ‘not more than superficial damage which does not impair its function’. The test is repeated, angling the container so that each of the container’s corners impact against the surface in turn.

Most cool bags and boxes have one or more carrying handles and these require assessment of strength. The container is loaded with 0.5kg of sand per litre of capacity and attached to a fixed support. It is then dropped from this position and the fall arrested by an inelastic support such as a canvas strap. This procedure is repeated for a total of ten falls per handle and any damage is assessed. The requirement for this test is that the handles remain effective after testing (see figures 3 and 4).

Water seepage testing

In the seepage test, water is introduced into the container to determine whether there is a risk of liquids seeping through from the inner container to the insulant. This test is not applicable to designs which have a continuous inner container (such as moulded plastic boxes), but is applicable to non-continuous designs such as bags which contain a stitched seam through which liquids may pass. To perform the test, the container is filled to 25 per cent of its capacity with water containing a water-soluble dye and a wetting agent. Once filled, the container is sealed and shaken 25 times to agitate the dyed water inside. The container is emptied, dried and, for all machine-washable products, a single wash is carried out in accordance with the washing instructions for the item. The container is allowed to dry prior to assessment. The specification does not specify how the container is to be dried but SATRA allows the container to air dry overnight at a temperature of 23ºC before the container is dismantled to inspect for any signs of seepage. The specification requires that no traces of coloured water seeps through the seam.

Figure 4: Failure of fabric at seam resulting from physical strength test

SATRA testing services

Using BS 12546-2, SATRA is able to assess all styles and designs of insulated bags and boxes to ensure they are satisfactory for placement on the market and to assist with the declaration of information that should be available to the user at the point of sale.

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