Machines for EU safety footwear testing – part 3

Considering how to assess specific ergonomic features, slip resistance and innocuousness of safety footwear.

In this article, we continue with an overview of the SATRA test machines that can be used to conduct footwear tests to the requirements of European safety footwear, as set out in 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'. In part 2 of this series, we investigated the tests listed under 'basic requirements' which focus on whole footwear tests. All clauses relating to whole footwear were listed at the start of the previous article. The three sections not covered in detail in part 2 are now covered in this article. These requirements are ‘specific ergonomic features’ (clause 5.3.4), 'slip resistance' (clause 5.3.5) and 'innocuousness' (clause 5.3.6).

Within EN ISO 20345:2011, footwear is classified as either 'Class I' or 'Class II'. 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) products. The particular requirements covered by clauses 5.3.4, 5.3.5 and 5.3.6 – the focus of this article – are applicable to both Class I and Class II footwear.

Special ergonomic features

Clause 5.3.4 sets out the requirements for the assessment of the ergonomic performance of safety footwear, and references EN ISO 20344:2011 clause 5.1. There is no specific equipment directly required to carry out the assessments, which are subjective tests carried out by three assessors wearing correctly fitted footwear of the type under assessment. The assessors simulate typical tasks likely to be undertaken in general use – walking, climbing stairs and kneeling/crouching. Six specific questions relating to these activities need to be answered by each assessor. An affirmative answer is required for each question and from each assessor for the footwear to meet the requirements of this clause. There is one exception allowed – for footwear assessed to be rigid in accordance with ISO 20344:2011 clause 8.4.1. This stiffness assessment can be carried out using the SATRA STM 465SG stiffness guide test device. For rigid footwear, the kneeling/crouching assessment is not required.

Slip resistance

Figure 1: Applying a lubricant solution of sodium lauryl sulphate (NaLS) to the tile prior to conducting a slip test

The requirements for slip resistance testing are set out in clause 5.3.5. It specifies that, when testing in accordance with ISO 20344:2011 clause 5.11, the safety footwear shall conform to one of three test conditions whose requirements are given in EN ISO 20345:2011 clause 5.3.5.2. These are i) resistance to slip on ceramic tile with a lubricant solution of sodium lauryl sulphate (NaLS), the application of which is shown in figure 1, ii) clause 5.3.5.3 (resistance to slip on steel floor with a lubricant solution of glycerine) or iii) clause 5.3.5.4 (resistance to slip on ceramic floor with NaLS solution and on steel floor with glycerine solution). Footwear which conforms to these requirements is rated 'SRA' (clause 5.3.5.2), 'SRB' (clause 5.3.5.3) or 'SRC' (clause 5.3.5.4).

The requirements are applicable to conventionally soled footwear. They are not applicable to special purpose footwear containing spikes, metal studs or similar, nor to special purpose safety footwear to be used on soft ground (for example, sand or sludge).

EN ISO 20344:2011 clause 5.11 gives more specific details regarding the conduct of the test. It also sets out the four specific test conditions which are required to be conducted, and for which minimum levels of coefficient of friction are set out in EN ISO 20345 clause 5.3.5. The first test condition is a forward heel slip conducted using a specified ceramic tile flooring surface and lubricated with NaLS. This test is conducted with the heel set at an angle of 7 degrees to the tile surface and the heel sliding forward.

The second test condition is 'forward flat slip' (in which most of the heel and some of the forepart slide forward). It is conducted on the same surface and lubrication (ceramic tile and NaLS) as the first case. The third slip condition is a forward heel slip, also set at 7 degrees. It is conducted using a stainless steel plate of specified roughness, coated with a 90 per cent glycerine solution, which is a very slippery viscous liquid. The fourth test condition is a forward flat slip, also conducted with the same surface and lubrication (stainless steel with glycerine) as in the third case.

EN ISO 20344:2011 clause 5.11 references EN ISO 13287 – 'PPE – Footwear – Test method for slip resistance'. It does not call up all the test conditions listed in this method, but only those described above. However, a considerable amount of detail is included within EN ISO 13287, such as the requirements for the test machine which is essential for conducting these tests. SATRA’s STM 603 slip resistance tester and a number of specific accessories can be used to conduct the tests required for EN ISO 20345 clause 5.3.5.

Accessories required to carry out these tests include the following:

mechanical feet specified for the flat forward slip tests (articulated devices which balance the applied force across the footwear, heel to toe) – see figure 2
the wedge required to set the 7 degree angle
specified lasts (supplied in a range of sizes) required for the forward heel tests.

Figure 2: Available accessories include these mechanical feet, which balance the applied force across the footwear

For product development purposes, the STM 603 device can be used to evaluate the slip resistance of footwear on a special surface

SATRA also supplies the consumable items required to conduct these tests, including the specified ceramic tiles and the stainless steel surface, the slider 96 specified rubber used to calibrate the ceramic tile, and the roughness meter required to calibrate the stainless steel surface. After a period of use, the tiles will need to be replaced when they fall outside of the band of coefficient of friction (0.18 to 0.22). This is determined with the slider 96 rubber when tested in accordance with BS EN ISO 20344:2011 clause 5.11.2.4. The stainless steel surface should be checked for surface roughness and, if outside the requirement, either replaced or the surface roughness re-established.

The SATRA STM 603 slip resistance tester can also be used to assess against SATRA TM144 and ASTM F2913-11

To obtain meaningful slip resistance testing outcomes, both an accurate and reliable test machine is required, which performs the test in line with the standard. A well-trained technician will also be needed to prepare the specimens and the floor surfaces correctly, and accurately mount and position the test material. The SATRA STM 603 slip resistance tester is by far the most widely used and most respected slip resistance tester used in the global footwear industry. Along with the supply of the test machine, SATRA offers a range of different training options, which we believe is important to ensure the test is conducted accurately. The STM 603 slip resistance tester also allows tests to be carried out to SATRA TM144:2011 – 'Friction (slip resistance) of footwear and floorings', which is a more appropriate test method for general footwear than the safety footwear standard covered in this article. In addition, tests on the STM 603 include the ASTM F2913-11 test method which was derived largely from SATRA TM144 in agreement with the ASTM committee responsible for the development of the ASTM method.

As well as compliance testing with carefully defined surfaces and lubricants (where required), the STM 603 is also suitable to carry out development testing using application-specific flooring surfaces and the associated footwear – for instance, sports footwear with the appropriate playing surface. SATRA also produces an additional accessory, STM 603ICE, for preparing an ice surface to allow slip resistance tests to be carried out on various forms of ice. The ice temperature is maintained for the duration of the test using this test accessory.

Innocuousness

This requirement – highlighted in clause 5.3.6 – states that safety footwear shall not adversely affect the health or hygiene of the user. Safety footwear shall be made of materials such as textiles, leather, rubbers or plastics that have been shown to be chemically suitable. The standard references an ISO technical report (ISO/TR 16178:2010), which provides information about possible critical substances in footwear. There is no specific SATRA test equipment associated with this requirement, although SATRA offers a comprehensive testing and advice service relating to chemical innocuousness of PPE and restricted substances in general. It is worth noting, however, that SATRA does make a range of test equipment which allows the water resistance and breathability of materials and completed footwear to be assessed. These can be important considerations for the maintenance of hygienic foot conditions.

In conclusion

This article is not intended to give a detailed description of the application of EN ISO 20345:2011 or EN ISO 20344:2011. However, it has been set out in order to highlight the main pieces of test equipment needed to assess the basic requirements for whole footwear as set out in EN ISO 20345:2011, under the headings of ergonomic features, slip resistance and innocuousness.

SATRA test equipment is designed and manufactured in the UK and supplied to a global market, including to brand owners, retailers, manufacturers, component and material suppliers, test houses, government institutions, universities and research institutes. The organisation draws on the expertise gained over its long history, including fundamental research, development of over 400 SATRA test methods and the extensive use of SATRA machines in our own laboratories.

Photograph at top of page shows the assessment of safety footwear on the SATRA STM 603 slip resistance tester.

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How can we help?

Please email test.equipment@satra.com for further information on SATRA test equipment. Contact chemistry@satra.com for assistance with SATRA’s services in relation to chemical innocuousness testing of personal protective equipment or restricted substances in general.

Publishing Data

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