Machines for EU safety footwear testing – part 4

In the latest part of this series, we consider the assessment of insoles and insocks.

This series of articles continues to look at the SATRA test machines which can be used to conduct footwear tests to the requirements of European safety footwear standard EN ISO 20345:2011 – 'Personal protective equipment – Safety footwear' and the associated test methods found in EN ISO 20344:2011 – 'Personal protective equipment – Test methods for footwear'. The focus of part 4 of this series is on 'Basic requirements for insoles and/or insocks' (clause 5.7).

Within EN ISO 20345:2011, footwear is classified as either 'Class I' or 'Class II'. Class I is footwear made from leather and other materials, excluding all-rubber or all-polymeric footwear. Class II footwear is all-rubber (entirely vulcanised) or all-polymeric (entirely moulded) footwear. The particular requirements for insoles and insocks are applicable to all Class I footwear. Class II footwear may or may not have an insock present, but if one is used, the requirements must be met.

Basic requirements for insoles and/or insocks

Sub clauses within clause 5.7 of EN ISO 20345:2011 cover a number of characteristics: i) thickness (clause 5.7.1), ii) pH value (clause 5.7.2), iii) water absorption and desorption (clause 5.7.3), iv) insole abrasion resistance (clause 5.7.4.1), v) insock abrasion resistance (clause 5.7.4.2), and vi) chromium VI content (clause 5.7.5). The applicability of each of these tests depends on a number of characteristics of the footwear – for example, if an insock is removable or not. Table 3 of EN ISO 20345:2011 sets out which tests are to be carried out, depending on aspects of the footwear construction. In this article, we will look at the test equipment required for each of these test categories. However, for any particular product, table 3 should be referred to for the tests required.

Insole and insock performance

Figure 1: A graduated eyepiece is used to measure the thickness of an insole or insock

'Thickness' (clause 5.7.1) sets out the requirements for a minimum thickness of the insole or insock. It references ISO 20344:2011 clause 7.1 which, in turn, specifies the use of a graduated eyepiece (figures 1 and 2) for measuring the thickness of the insole and/or insock. SATRA supplies a suitable instrument for making this assessment – SATRA STD 405M.

Figure 2: The graduation seen through the eyepiece

'pH value' (clause 5.7.2) is a requirement only for leather insoles or leather insocks. The pH value of a material is an indication of how acidic or alkaline it is, measured using the pH scale from 1 to 14. A measurement of 1 is strongly acidic and 14 is strongly alkaline. Skin irritation can occur if a material has a very high or low pH value. Clause 5.7.2 sets out the allowable pH values and also references ISO 20344:2011 clause 6.9 which, in turn, references ISO 4045 as the method to determine the pH value. SATRA's STM 145 shaking machine for leather analysis, together with SATRA STM145PH 'pH jars' can be used as part of this assessment process. In addition, a leather mill is required to finely divide the specimen before it is shaken in water using the shaking machine.

Figure 3: Water absorption and desorption is assessed using SATRA’s STM 706 Bally permeometer

'Water absorption and desorption' (clause 5.7.3) sets out the requirements for the water absorption capability of the insole and insock. The requirement defines a minimum amount of water absorption (measured as a mass per unit area) which must be achieved by the product. Also defined is its ability to release at least 80 per cent of the absorbed moisture in a conditioned atmosphere over a defined period of time. This clause references ISO 20344:2011 clause 7.2, which sets out the equipment to be used, the specimen preparation, the conditioning required and the test procedure to be followed. SATRA's STM 706 'Bally permeometer' (figure 3) can be used to conduct this test. The test comprises a 'rolling flex' action which presses the specimen onto a wet base plate under a given pressure.

'Abrasion resistance' (clause 5.7.4) specifies the requirements for the abrasion resistance of insoles and insocks. Different test methods and associated test machines are used to assess the abrasion resistance of insoles compared to insocks.

Abrasion resistance of insoles

An abrasion resistance test is specified for non-leather insoles (clause 5.7.4.1), but there is no abrasion resistance requirement for leather insoles. Tests should be carried out in accordance with EN ISO 20344:2011 clause 7.3. The assessment is conducted with a 'Veslic' type to-and-fro rub fastness tester. SATRA's STM 421 'rub fastness tester' is suitable for this assessment. When conducting a test, the specimen is rubbed with pieces of wet, white wool felt covered with an abradant fabric under a given pressure, with a number of to-and-fro motion cycles. The abrasion damage is assessed by comparison to reference test pieces which establish the pass/fail criterion. SATRA can supply the abradant fabric and the white wool felt pads used in this test.

Abrasion resistance of insocks

Figure 4: Setting up a SATRA STM 633 Martindale abrasion machine

The abrasion resistance of insocks (clause 5.7.4.2) is assessed using a Martindale abrasion method as specified in EN ISO 20344:2011 clause 6.12. This is the same test method as required to assess the abrasion resistance of linings as set out in clause 5.5.2 of EN ISO 20345:2011 (which was covered in part 1 of this series). The test can be carried out using SATRA's STM 633 Martindale abrasion machine (figure 4) and is conducted under both dry and wet conditions. As for vamp and quarter linings, the requirements are that the specimen should not develop any holes within a specified number of cycles for each of the test conditions (dry and wet).

Chromium VI content

Chromium is a transition metal, the sulphate salt of which is used in leather tanning. Chromium ions can exist in many oxidation states, two of which are chromium III (trivalent chromium) and chromium VI (hexavalent chromium). In finished leather, it is present as chromium III, which is not considered to be hazardous. However, under certain harsh conditions, chromium VI can be formed. This is a known skin irritant, potential carcinogen and environmental hazard. The requirement within clause 5.7.5 is that, when determined in accordance with test method EN ISO 17075, the quantity of chromium VI in leather should not exceed 3.0mg/kg – 3 parts per million (ppm). This is a test requirement which applies only to insoles and insocks made of leather.

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Publishing Data

This article was originally published on page 46 of the November 2016 issue of SATRA Bulletin.