Revision to perforation resistance test

A report on the new internationally-standardised nail for testing protective inserts for safety footwear.

by Peter Doughty

Safety footwear is manufactured to provide protection against a range of hazards, one of which is from injury caused by sharp objects such as nails perforating the footwear outsole. In order to provide this necessary protection, footwear is fitted with an insert, which is typically made from a sheet of metal or from reinforced textile material.

Performance standards for safety footwear have been available for many years and include tests to assess this underfoot protection from sharp objects. In addition to the standards for the completed item of footwear, European standard EN 12568 described test procedures for evaluating the perforation-resistant insert itself when it was in isolation from the footwear.

Objections to the 2019 standard

In 2019, EN 12568 was superseded by a new international standard (ISO 22568). ISO 22568 is published in four parts – parts one and two cover testing of metallic and non-metallic safety toe caps, while parts three and four concentrate on the testing of metallic and non-metallic perforation-resistant inserts.

To test a perforation-resistant insert, a standardised nail (stylus) with a shaft diameter of 4.5 mm and a conical tip (intended to approximate a typical nail) is driven through the insert while the force needed to penetrate it is measured using a load cell.

The development work on ISO 22568 was started following proposed formal objections by two European countries to the perforation resistance test in EN 12568. The main concern raised was that the profile of the nail used in the test was too different to that encountered in the workplace. In particular, the shaft diameter was claimed to be too large. This situation was not new, but had become more critical with the invention, introduction and growing popularity of perforation-resistant inserts made from non-metallic materials.

It is recognised that metal and non-metal inserts have different advantages. However, as the insert is not visible, it is not possible without destroying the footwear for the end user to know which type is fitted in a particular shoe or boot. This was also raised as a concern, which is being addressed in the current revision of the footwear standards EN ISO 20345, EN ISO 20346 and EN ISO 20347.

The project group assigned to the revision of EN 12568 consisted of manufacturers (both of inserts and whole footwear), test laboratories and certification bodies. New test methods and prototype nails were developed. In 2017, a test method was selected including a new nail (having a 3 mm shaft diameter with a pyramidal shape tip), and EN ISO 22568-4 was published.

Refinements introduced

Problems have been encountered since that time with the repeatability of the test using the pyramidal nail, which is thought to be due to differences in the roughness of the surface of the pyramidal tip. Measurement and control of roughness on the edges and faces of the pyramidal tip is not something that can be easily done. The test has therefore now been revised to use a new design of nail that has a conical tip but a smaller 3 mm diameter shaft. A new version of ISO 22568 part 4 will now be published to include the 3 mm conical nail – the full official title being EN ISO 22568-4:2021 – ‘Foot and leg protectors – Requirements and test methods for footwear components – Part 4: non-metallic perforation resistant inserts’. This will enable manufacturers to test the non-metallic perforation-resistant insert components with either a 4.5 mm or a 3 mm diameter nail, thus providing an indication of in-use performance under a greater range of conditions.

Publishing Data

This article was originally published on page 14 of the May 2021 issue of SATRA Bulletin.

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