SATRA updates slip resistance test method

Introducing the latest version of the SATRA TM144 test method, which continues to provide a key tool to footwear suppliers in demonstrating due diligence towards a safety critical property and to developers seeking high performance.

SATRA has recently completed a periodical review of one of its most important test methods – SATRA TM144 – ‘Friction (slip resistance) of footwear and floorings’. First published in 1992, it was last revised in 2011 and, during the last three decades, has become firmly established as the world’s preeminent method in assessing the most important property that a footwear sole has – its ability to grip the floor and enable the wearer to move safely without slipping. The method is now embedded in countless specifications and the associated SATRA STM 603 test machine into dozens of test laboratories around the globe. The method is widely accepted as a valuable and fair test, more than capable of identifying low-performing materials or tread designs, as well as highlighting the best.

It is therefore important to reassure the many users of this tried and trusted method that its fundamentals remain unaltered. The equipment and the manner of its use remain the same, and footwear tested by the 2021 update will give the same results as when tested by the 2011 version.

The revisions

So, what has changed? Two further annexes have been added to the existing five: Annex F – ‘Assessing resistance to slip on mud’ and Annex G – ‘Assessing slip resistance of leather soles’. Furthermore, all references to testing on ice are now given in a more self-contained Annex E. The purpose of the annexes (now seven in number) remains the same – to remove the wealth of fine detail from the main body of the method in order to help keep it concise and understandable. Nevertheless, the many technical aspects to this method still require it to be a long document, so to assist with navigation, a contents page has been included inside the front cover. Section headings and subtitles have also been made more prominent and all the illustrations have been redrawn in colour. There have been many editorial changes to improve clarity and meaning, and clause numbers have inevitably changed as sections of text have migrated – for example, from Annex B to Annexes E and F.

In addition, there are a few technical amendments, mostly of a minor nature. Firstly, the original standard reference surface quarry tile (referenced SATRA STM 603 C in the 2011 method) has been deleted and now the only permitted reference quarry tile is SATRA STM 603 AC (introduced in 2011). The original tile ‘C’ had been discontinued commercially, but the parallel use of both the ‘C’ and the ‘AC’ tiles was permitted in the 2011 method for those users who still had stocks of tile ‘C’. However, in the intervening ten years, those stocks have surely been used up, so there is no longer any need to include use of tile ‘C’.

The method now also says more about ensuring that the plane of the test floor is in line with the horizontal friction-force measuring load cells, to within ±5 mm vertical tolerance. Some users may need to insert packing plates beneath their test floor surfaces to raise them to the correct height.

The moment in time at which the friction measurement is taken for the report remains at 0.10 ±0.01 seconds. Zero time is now explicitly given as the moment that the relative motion between footwear item and test floor commences – ‘the start of horizontal movement of the driven item, either footwear or test floor’. However, it is now also made clear that the friction recorded may also be the time averaged value during the time window 0.09 to 0.11 seconds, rather than necessarily a truly instantaneous value taken somewhere between those limits.

The setting wedge for the seven-degree heel contact test mode is now also more tightly defined to assist with the set-up procedure. This is a small detail, but it also keeps SATRA TM144 aligned, in that respect, with EN ISO 13287 – ‘Personal Protective Equipment – Footwear – Test Method for Slip Resistance’. We have also introduced guidance on setting up contact modes for ‘unconventional’ sole bottom profiles, such as rocker soles. In addition, more information is provided about the possible origins and forms of test specimens, if they are not whole footwear or whole soles – for instance, sliders cut from sheet material or moulded plates. Samples of finished whole shoes are preferred, but it remains useful to be able to test candidate materials in pre-production, in order to get a fair idea of likely final performance.

In ice testing (Annex E), the number of test runs and which run is to be reported has been updated dependent upon the ice surface condition, smooth ice, frosted ice with smeared or undisturbed frost. Leather soles (Annex G) have been separated out as a special case, because the new surface of leather is so unrepresentative of the bulk of the wear life, and because leather is water absorbent. Annex F (assessing resistance to slip on mud) gives a standardised procedure for those soles, perhaps with deep cleats, which also need to provide grip on soft surfaces, not just on man-made hard surfaces. Finally, in ‘Related Standards’ under clause 8, reference is made to the US ASTM derivation of SATRA TM144, which is ASTM F2913 – first released in 2011 and most recently updated in 2019.

Publishing Data

This article was originally published on page 12 of the April 2021 issue of SATRA Bulletin.

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