Machines for EU safety footwear testing – part 6

Considering the requirement for perforation resistance specified in EN ISO 20345:2011.

by Peter Allen

The first five articles in this series considered SATRA test equipment that can be used to conduct the tests required to meet the 'basic' requirements for safety footwear as set out in the European safety footwear standard EN ISO 20345:2011 – 'Personal protective equipment – Safety footwear'. The test methods specified in this standard are found in EN ISO 20344:2011 – 'Personal protective equipment – Test methods for footwear'. This and subsequent articles will focus on the SATRA machines which can be used to carry out the tests associated with the 'additional requirements' specified in the standard.

These additional requirements cover a range of hazards encountered in the workplace, where additional levels of protection need to be considered over and above the protection provided by footwear conforming to the ‘basic’ footwear requirements. Products which conform to these specific additional requirements should be marked with the designated symbol appropriate to each category of hazard. These symbols allow the customer to identify the additional hazards for which the footwear is appropriate.

The specific additional hazards and the associated requirements are set out in section 6 of EN ISO 20345 and categorised into three sub-sections relating to i) whole footwear (clause 6.2), ii) upper (clause 6.3) and iii) outsole (clause 6.4).

In this article, we will focus on the SATRA test equipment required to carry out the perforation resistance test specified within the standard, which is one of the required assessments within the 'whole footwear' category. The word 'perforation' has recently been introduced by the relevant EU committee as a replacement for 'penetration', although this latter word will continue to be used in the standards until they are updated. Footwear conforming to these requirements can be marked with the symbol 'P'. Subsequent articles will cover the remaining hazards associated with whole footwear, as well as for 'upper' and 'outsole'.

It should be noted that some of the test methods specified for the penetration tests may be found in EN 12568:2010 – 'Foot and leg protectors – Requirements and test methods for toe caps and penetration resistant Inserts'.

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) footwear. Where perforation resistance is claimed for the footwear, this is applicable to both Class I and Class II products.

Perforation resistance

EN ISO 20345:2011 clause 6.2.1 (entitled 'Penetration resistance') is intended to provide the footwear user with a level of protection against a nail (pin) or other upward-facing sharp object which could penetrate the sole and injure the user in the event of the sharp object being stepped on.

Sub-clauses within clause 6.2.1 of EN ISO 20345:2011 set out a number of detailed requirements to demonstrate effective perforation resistance overall. These are i) 'determination of penetration force' (clause 6.2.1.1), ii) 'construction' (clause 6.2.1.2), iii) 'dimensions' (6.2.1.3), iv) 'flex resistance of penetration-resistant inserts' (clause 6.2.1.4), and v) 'behaviour of penetration-resistant inserts' (clause 6.2.1.5). This last clause considers the effects of some specified adverse environmental conditions on the inserts.

Clause 6.2.1.1 ('determination of penetration force') is subdivided into requirements for 'metallic anti-penetration inserts' (clause 6.2.1.1.1) and 'non-metallic anti-penetration inserts' (clause 6.2.1.1.2). For both metallic and non-metallic inserts, the test can be carried out using SATRA's STM 566 tensile testing machine, working in compression and fitted with the specified specimen support platens and 'penetration nail' – for example, the SATRA NP4 jaw assembly (figure 1). The details of the required tests are set out in EN ISO 20344:2011 clause 5.8.2 (metallic inserts) and clause 5.8.3 (non-metallic inserts).

There are some differences in how the test is conducted, depending on whether metallic or non-metallic inserts are under evaluation. In both cases, the shoe bottom is removed from the footwear upper. The complete bottom unit is then placed on a support plate mounted in the tensile testing machine (for instance, SATRA STM 566). The support plate contains a 25mm diameter hole with its centre aligned with the specified nail. This allows the nail to be pushed through the specimen during the test without coming into contact with the support plate. The specimen is positioned so the nail is applied from the underside of the sole.

The standard specifies that, for metallic inserts, the force required to perforate the sole unit shall be not less than 1,100N and, for non-metallic inserts, using a force of 1,100N, the tip of the test nail shall not penetrate through the test piece. The test methods describe the number of individual perforations required for a test specimen and some positional information related to where the perforation is positioned. It is important to note that if the footwear sole is constructed from absorbent materials (such as leather), the test specimen should be conditioned by immersion in water for a specified period prior to the test.

Clause 6.2.1.2 (construction) requires that the perforation-resistant insert must be built into the shoe in such a way that it cannot be removed without damaging the footwear. There are also some other details of construction defined, however there are no tests associated with meeting the requirements of this clause.

Clause 6.2.1.3 (dimensions) sets out a number of dimensional requirements associated with the size and positioning of the perforation-resistant insert and references EN ISO 20344:2011 clause 5.8.1. There are no tests specified to meet the requirements of this clause.

Clause 6.2.1.4 considers flex resistance of perforation-resistant inserts. Although this type of insert is required to protect the user from nail penetration, it should also allow the footwear to flex in use. One of the failure modes for a perforation-resistant insert is a fatigue failure due to flexing. This could be, for example, due to a fatigue crack initiating from a notch on the edge of a metallic insert, or a delamination or breakdown between fibres for a non-metallic insert. This clause specifies that the inserts shall show no visible signs of cracking or delamination after being subject to one million flexing cycles when tested in accordance to EN ISO 20344:2011 clause 5.9 which, in turn, references EN 12568:2010 clause 7.2.2. This standard specifies a flexing method and a rate of flexing of 16Hz (16 cycles per second).

SATRA's STM 441 midsole flexing machine has six stations and is designed to carry out this test. It allows both straight and curved perforation-resistant inserts to be tested. The standard sets out how the flexing line is determined and where the insert can be cut. Removal of the heel part is allowed to facilitate the testing. The specimen is clamped across the flexing line between the jaws of a clamp via two elastic interlayers which are designed to protect the specimen from damage by the clamp. During the test, rollers on the flexing arm of the machine provide the flex specified in the standard. Springs assist with the rapid return of the specimen to the neutral position at the end of each flex cycle.

Clause 6.2.1.5 of EN ISO 20345 ('behaviour of penetration-resistant inserts') focuses on the effects of the environment on these components. Clause 6.2.1.5.1 covers metallic inserts and non-metallic inserts are covered in clause 6.2.1.5.2. These clauses call up clauses in EN ISO 20344 which, in turn, reference EN 12568:2010.

For metallic inserts in Class I footwear, a test is specified which exposes a specimen cut from a new insert (that is, not cut from completed footwear) to a mild salt solution and, after a prescribed time, sets out the amount of corrosion allowable. For metallic inserts in Class II footwear, the perforation-resistant insert is tested in situ within the footwear. After exposure to a mild salt solution for a specified time, the insert is removed from the footwear and inspected for corrosion.

For non-metallic inserts, a more extensive set of tests is specified. These cover the effects of high temperature, low temperature, acid, alkali and fuel oil. The same tests apply to Class I and Class II footwear. For both classes of footwear, only new (unused) inserts are used for these tests. For the high- and low-temperature tests, the specimens are conditioned for a period of time at a specified temperature before being re-tested for nail perforation, with the test being carried out within two minutes of being removed from the temperature-conditioning chamber. Likewise, after conditioning in acid, alkali or fuel oil, the conditioned specimens are subject to a repeat of the nail perforation test. It is important to note that only non-metallic inserts are subjected to the more extensive environmental tests and subsequent perforation test as described here, and as set out in clause 6.4 of EN 12568:2010.

This perforation test, applied after each type of environmental conditioning, has some differences to the tests described in clause 6.2.1.1.2 of EN ISO 20345. The main difference is that new, unused inserts are used for this test, instead of testing them when incorporated into a sole. The unused inserts are typically quite flexible and need to be clamped into position on the test platen before the perforation test is carried out. Details of the clamping device are set out in EN 12568:2010 clause 7.2.1.1.3. SATRA NP3 tensile tester jaws, which includes a clamping plate, conform to this standard (figure 2). These jaws can also be used to carry out the test specified in clause 6.2.1.1 of EN ISO 20345 by the removal of the clamping plate (in effect, then operating as the SATRA NP4 jaws). Both SATRA NP3 and NP4 jaws incorporate the nail, nail holder and support platens. The nails conform to EN 12568:2010 clause 7.2.1.1.2, which is specified for all the puncture tests called up within clause 6.2.1 of EN ISO 20345: 2011.

SATRA test equipment

SATRA test equipment is designed and manufactured in the UK and supplied to a global market. Purchasing organisations include brand owners, retailers, manufacturers, component and material suppliers, test houses, government institutions, universities and research institutes. SATRA test equipment draws on the expertise gained over almost one hundred years of history of fundamental research, development of over 400 SATRA test methods and the extensive use of SATRA machines in our own laboratories.

Click here for comprehensive information on SATRA's range of test equipment.

Publishing Data

This article was originally published on page 42 of the March 2017 issue of SATRA Bulletin.

Other articles from this issue »

---