Machines for safety footwear testing – part 1

The use of test equipment to assess vital components used in safety footwear.

This short series of articles will examine SATRA test equipment which can be used to test safety footwear to the requirements of EN ISO 20345:2021 – ‘Personal protective equipment – safety footwear’ and the associated test methods found in EN ISO 20344:2021 – ‘Personal protective equipment – test methods for footwear’.

In this month’s article, we look at the test machines and devices used to test uppers, linings and tongues, as set out in EN ISO 20345 under basic requirements for safety footwear. Future SATRA Bulletin articles will consider other basic requirements and additional requirements for special safety applications.

The fine print

Basic requirements for safety footwear are defined in clauses within section 5 of EN ISO 20345 – ‘Basic requirements for safety footwear’. These clauses cover the following: ‘general’ (5.1), ‘design’ (5.2), ‘whole footwear’ (5.3), ‘upper’ (5.4), ‘lining’ (5.5), ‘tongue’ (5.6), ‘insole, insock and footbed’ (5.7), and ‘outsole’ (5.8).

The detailed requirements within each of these clauses are covered by a series of sub-clauses. Table 2 of EN ISO 20345, entitled ‘Basic requirements for safety footwear’, sets out these sub-clauses and identifies which of them are applicable to either Class I, Class II or hybrid footwear types.

Class I footwear is made from leather and other materials, excluding all-rubber or all-polymeric footwear. Class II footwear is all-rubber (that is, entirely vulcanised) or all-polymeric – entirely moulded, for instance from polyvinyl chloride (PVC) or polyurethane (PU). Hybrid footwear is footwear that cannot be classified as footwear of class I or II. Within this article we are considering the test equipment required to carry out the tests for uppers (5.4), linings (5.5) and tongues (5.6).

Class I footwear

For Class I footwear, the requirements for uppers (within EN ISO 20345) are summarised here, along with details of the relevant SATRA test machines and other devices.

General (clause 5.4.1): This sets out minimum heights for five styles of uppers, below which the properties described overleaf need to apply. In order to carry out these height assessments, only a few simple measuring tools are required.

Tear strength (clause 5.4.3): Clause 5.4.3 references EN ISO 20344 clause 6.3, which sets out tear test requirements for leather (ISO 3377-2:2016 – ‘Leather – Physical and mechanical tests – Determination of tear load – Part 2: Double edge tear’) – known as the ‘Baumann tear test’, and for coated fabric and textiles (ISO 4674-1:2016 – ‘Rubber- or plastics-coated fabrics – Determination of tear resistance – Part 1: Constant rate of tear methods’, method B), which is a ‘trouser tear’ method. These tests can be conducted with SATRA’s STM 566 tensile tester fitted with Baumann jaws (STM 566ST) for the leather tear test (figure 1), and with standard flat jaws (STM 566F) for the coated fabric or textile trouser tear test. Quick-release flat jaws (STM 566QR) are also available. For both types of test, a specimen cutting knife is recommended (and essential for the Baumann tear test) to ensure that accurate test specimens are produced.

Tensile properties (clause 5.4.4): Referencing EN ISO 20344 clause 6.4, this clause sets out the tensile test requirements for leather splits according to the ISO 3376:2020 – ‘Leather – Physical and mechanical tests – Determination of tensile strength and percentage elongation’ test method. This test can also be conducted with SATRA’s tensile tester STM 566 fitted with STM 566F jaws or STM 566 QR jaws. A specimen cutting knife is again essential to accurately prepare the test specimen.

Water vapour permeability, absorption and coefficient (clause 5.4.6): This clause references EN ISO 20344 clauses 6.6, 6.7 and 6.8. To carry out these assessments, three key pieces of SATRA test equipment can be used: i) STM 701 Bally flexometer – shown in figure 2, ii) STM 473 water vapour permeability tester (figure 3) – used to determine the water vapour permeability (WVP) required by the method (EN ISO 20344 clause 6.6), and iii) STD 478 water vapour absorption test device – used to determine the required water vapour absorption (WVA) as set out in clause 6.7 of EN ISO 20344.

The STM 701 test machine is used to pre-condition the specimens by repeated flexing prior to conducting the WVP test. From the values obtained for WVP and WVA, clause 6.8 sets out the method of calculating the water vapour coefficient for the specimen. In addition to the equipment listed, simple measuring equipment, specimen cutting knives and a precision balance are required. It is important to note that the water vapour permeability test must be carried out (in its entirety) only in an accurately controlled atmosphere of 23 ±2°C and 50 ±5 per cent relative humidity (RH).

pH value (clause 5.3.6): Used to determine the pH value of all leather parts (uppers, linings and tongues), this clause references EN ISO 20344 clause 6.9, which specifies ISO 4045:2018 – ‘Leather – Chemical tests – Determination of pH and difference figure’ as the method to be utilised. The pieces of equipment required are a leather grinder (also known as a ‘cutting mill’) and a shaking machine, which is used to extract soluble elements from the leather. SATRA produces an STM 145 shaking machine and the associated plastic containers reference STM 145PH.

Chromium VI content (clause 5.3.6): Clause 5.3.6 sets out the maximum quantity of chromium VI allowable in all footwear leather parts (uppers, linings and tongues), using one of the test methods described in ISO 17075 – either part 1: 2017 (‘Leather – Chemical determination of chromium (VI) content in leather – Colorimetric method’) or part 2:2017 – ‘chromatographic method’).

Depending on which of these methods is selected, the following are required: cutting mill, shaking machine, analytical balance, special filters, a high-performance liquid chromatograph (HPLC), assorted general laboratory glassware, consumables and chemicals.

Class II footwear

For Class II footwear, the requirements for uppers (within EN ISO 20345) are summarised below, along with relevant SATRA test machines and devices.

Thickness (clause 5.4.2): This specifies the minimum thicknesses for the rubber or the polymeric material used in the upper. The relevant test method is referenced in EN ISO 20344 clause 6.1. In turn, this specifies that the test should be carried out in accordance with Method A in ISO 23529:2016 – ‘Rubber – General procedures for preparing and conditioning test pieces for physical test methods’ clause 7.1, using a flat presser foot of 10 ±0.1mm diameter and a load of 1 ±0.1 N. SATRA can supply a suitable thickness gauge to carry out this assessment.

Tensile properties (clause 5.4.4): Clause 5.4.4 references EN ISO 20344 clause 6.4.2.1, which sets out the tensile test requirements for rubber upper materials according to the requirements of clause 6.4.2.2, and for polymeric upper materials to the requirements of ISO 4643:1992 – ‘Moulded plastics footwear – Lined or unlined poly(vinyl chloride) boots for general industrial use – Specification’. Clause 5.4.4 (of EN ISO 20345) specifies a minimum breaking force for a rubber material, whereas for a polymeric material, it specifies a range for the modulus of elasticity at 100 per cent elongation and a minimum elongation at break. These tests can be conducted with SATRA’s tensile tester STM 566 fitted with STM 566 QR jaws (other jaw types are available). In order to conduct the polymeric material tests, an extensometer is required for the tensile tester. A specimen cutting knife is again essential to accurately prepare the test material prior to evaluation.

Flexing resistance (clause 5.4.5): This clause references the tests specified in EN ISO 20344 clause 6.5. This then specifies clause 6.5.2.2, which sets out the details for a flexing test for rubber materials. For polymeric materials, clause 6.5 specifies ISO 4643 Annex B for the flexing test, which is conducted at -5°C. For testing polymer uppers to this test standard, the SATRA STM 101F vamp flexer (low temperature) can be used. For testing rubber uppers, an STM 168 rubber flex tester can be used. Press knives should be used when preparing the test specimens.

Hydrolysis (clause 5.4.7): This clause references EN ISO 20344 clause 6.10 – 'Determination of resistance to hydrolysis of upper', which requires the determination of the upper hydrolysis with the flex test specified in Annex B of ISO 5423:1992 – ‘Moulded plastics footwear – Lined or unlined polyurethane boots for general industrial use – Specification’. This test is conducted after preparation and conditioning in accordance with Annex E of ISO 5423, for which a heated humidity chamber is required. SATRA produces the STM 601 upper material vamp flexer (figure 4) suitable for the flexing test. A specimen preparation knife is recommended.

Vamp and quarter linings

As can be seen from the descriptions above, the only common test for uppers on Class I and Class II footwear is a requirement for a tensile strength test (although even here the requirements for Class I and II differ). In comparison for vamp and quarter linings, the requirements for Class II footwear are the same as for Class I, although Class II footwear is not required to have linings. The only exception is the requirement for water vapour permeability, which is a requirement only for Class I footwear. For simplicity, both Class I and Class II footwear will be covered in the same section in this article for linings.

For both Class I and Class II, the requirement for vamp and quarter linings (within EN ISO 20345:2021) are contained within section 5 of the standard. The requirements are summarised below, along with relevant SATRA test machines and devices.

Tear strength (clause 5.5.2): This clause references EN ISO 20344 clause 6.3. It is the same test method as referenced for the tear requirements for vamps (see the test equipment listed against clause 5.4.3 of EN ISO 20345). Although the test methods are the same, the strength requirements are different for linings compared to the upper.

Abrasion resistance (clause 5.5.3): Clause 5.5.3 references EN ISO 20344 clause 6.12, and the SATRA STM 633 Martindale abrasion machine (figure 5) can be used to carry out this test. The specimens are retained in the specimen holders (perhaps with a specified backing for the specimens) and are abraded against a specified woven fabric with a felt underlayer. Tests are conducted under both dry and wet conditions. It is important to ensure the correct combined mass of holder, spindle and weight is used, along with the correct geometry of the specimen holder. A cutting knife should be used to prepare the test specimens. The test should be conducted in a temperature and humidity-controlled atmosphere of 23 ±2°C and 50 ±5 per cent RH.

Water vapour permeability, absorption and coefficient (clause 5.5.4): This references EN ISO 20344 clauses 6.6, 6.7 and 6.8. This is the same test method as referenced for the water vapour permeability, absorption and coefficient requirements for uppers. Thus, the same test equipment should be used as required for determining these requirements for the upper (see the test equipment listed against clause 5.4.6 of EN ISO 20345). The performance requirements for linings are contained in EN ISO 20345 clause 5.5.3. It is important to note that this clause does not apply to Class II footwear.

Other requirements for tongues

These are only a requirement for Class I footwear and are only applicable if a tongue is present.

Tear strength (clause 5.6.2): This clause references EN ISO 20344 clause 6.3. The same test method is used as referenced for the tear requirements for uppers (see the test equipment listed against clause 5.4.3 of EN ISO 20345). Although the test methods are the same, the strength requirements are different for the tongue compared to the upper.

Additional testing

This article is not intended to give a detailed description of the application of EN ISO 20345 or EN ISO 20344. However, it has been set out in order to highlight the main pieces of test equipment needed to assess uppers, linings and tongues required by EU safety footwear legislation. Future articles will consider the test equipment needed for the assessment of other components and whole footwear, as well as additional requirements for special applications.

Publishing Data

This article was originally published on page 26 of the February 2022 issue of SATRA Bulletin.

Other articles from this issue »

---