Machines for EU safety footwear testing – part 9

Continuing this series of articles examining SATRA test equipment which can be used to conduct the tests specified in the European standard EN ISO 20345:2011 – 'Personal protective equipment – safety footwear'.

by Peter Allen

The first five articles in this series cover ‘basic requirements’, and subsequent articles consider the test equipment that can be used to conduct the tests, as set out in clause 6 of EN ISO 20345:2011 ‘additional requirements for safety footwear’. In this issue, we are continuing to consider additional requirements for ‘whole footwear’ (clause 6.2) and, in particular, ‘metatarsal protection’ (clause 6.2.6), ‘ankle protection’ (clause 6.2.7), and ‘cut resistance’ (clause 6.2.8). All three of these tests can be applied to both Class I and Class II footwear, as defined in the standard.

Additional requirements may be necessary for safety footwear, depending on the risks to be encountered at the workplace. In such cases, safety footwear must conform to the appropriate added requirements, and can be marked with the codes set out in EN ISO 20345. These codes allow the customer to identify the additional hazards for which the footwear is appropriate.

Metatarsal protection

Figure 1: SATRA’s STM 609 safety footwear impact tester

As we have seen in an earlier article in this series, rigid toe caps in safety footwear are intended to provide a defended space for the toes against impact in the toe region. However, as accident statistics show, impacts often occur to other parts of the foot – such as the area directly behind the toe cap (known as the ‘metatarsal region’, named after the bones present in this area). To help prevent such injuries, there is the option for footwear to have a metatarsal guard, which usually rests on the back edge of the toe cap and provides protection to the top of the foot.

The requirements for assessing ‘metatarsal protection’ is set out in clause 6.2.6 of EN ISO 20345. This highlights that the metatarsal protection device must be such that, under impact, the resulting forces are distributed over the sole, the toe cap, and as large a surface of the foot as possible. Clause 6.2.6 of EN ISO 20345 further specifies that when tested in accordance with ISO 20344:2011 clause 5.16, a minimum clearance is obtained at the point of impact after the specified impact test (as set out in EN ISO 20345:2011). This test can be performed using SATRA’s STM 609 safety footwear impact tester (figure 1).

Testing the metatarsal protection provided by a safety boot in accordance with ISO 20344:2011

A striker with defined geometry and a mass of 20kg is dropped from a height to deliver an impact energy of 100J onto the footwear sample, which contains a wax foot form (figure 2) as specified in the test method. The test method defines the position where the impact striker impacts, depending on the footwear size. After the impact test, the foot form is removed and a dial gauge with a hemispherical foot is used to measure the vertical height at the maximum point of impact deformation. SATRA can provide a suitable height gauge (STM 609HF). When conducting this impact test, the most complex aspect is the preparation of the wax foot form, using either a production last or an identical footwear sample to the one being tested. In order to assist this process SATRA can provide a vacuum moulding machine (the SATRA STM 329 vacuum former) and suitable plastic formable sheets which are used in part of the process of creating the foot form (figure 3). Footwear which meets the requirements of this test can be marked with the symbol ‘M’.

Figure 2: A wax foot form that was placed inside a test sample, showing damage caused by a striker delivering an impact energy of 100J

Figure 3: A plastic foot form being made on a SATRA STM 329 vacuum moulding machine

Ankle protection

The ankle is another part of the foot/leg which can be protected against impact. This is covered in ‘additional requirements for special applications’ within EN ISO 20345:2011 clause 6.2.7 – ‘ankle protection’. This specifies that, when tested in accordance with EN ISO 20344:2011 clause 5.17, the mean value of the force transmitted through the sample must not exceed 10kN, and no single value is to exceed 15kN.

The apparatus required to carry out this test consists of a 5kg guided, falling mass delivering an impact energy of 10J to the test specimen which rests on a defined anvil. The anvil is connected via a force transducer to a solid mass of at least 600kg. The test method sets out, by means of a user trial, the centre of where the ankle protection should be positioned in the footwear and the size of the specimens to be cut from the footwear. Specimens are taken from the inner and outer ankle protectors from three sizes of the footwear, giving a total of six specimens. Footwear which meets the requirements of this test can be marked ‘AN’.

Cut-resistant footwear

Another of the ‘additional requirements’ set out in EN ISO 20345:2011 clause 6.2.8 is ‘cut resistance’. The standard sets out the areas on the footwear upper where cut resistance should be provided. Clause 6.2.8.3 specifies that, when tested according to ISO 20344 clause 6.14, the cut resistance index (see EN 388) must be not less than 2.5. The cut resistance tests can be carried out using SATRA’s STM 611 circular blade cut resistance tester (figure 4).

Figure 4: The SATRA STM 611 circular blade cut resistance tester

Specimens are taken from each of one pair of three sizes (SML), with two specimens being cut from each pair (a total of six specimens). Cut-resistant footwear also needs to comply with the perforation resistance requirements (previously called ‘penetration resistance’) set out in clause 6.2.1 of EN ISO 20345:2011. See part 6 of this series (published in the March 2017 issue of SATRA Bulletin) for the equipment required to conduct the tests associated with perforation resistance.

Footwear which meets the requirements of cut resistance (including the associated requirement of perforation resistance) can be marked ‘CR’

SATRA test equipment is designed and manufactured in the UK and supplied to a global market. SATRA’s range of over 300 test machines and devices draws on the experience gained over its 99-year history, from fundamental research, development of over 400 test methods and the extensive use of SATRA machines in our own commercial laboratories.

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Please e-mail test.equipment@satra.com for further information on SATRA test equipment.

Publishing Data

This article was originally published on page 42 of the November 2018 issue of SATRA Bulletin.