The Goldilocks Principle in Slip Safety

We’re all familiar with the story of Goldilocks, either from reading it as children or reading it now to children of our own. In the tale, Goldilocks is presented with three bowls of porridge. One is just too cold for her. The other is far too hot. But the third is just the right temperature, being neither too hot, nor too cold.


The Goldilocks Principle is something that can be applied in many walks of life. There are plenty of scenarios where it is helpful to have just enough of something (not too little, certainly not too much). This is certainly applicable in the world of slip safety.


Over the last decade we have seen a move from little to no idea about slip resistance (for example, not having heard of the pendulum test, or using R ratings instead of PTV) to an exponentially greater knowledge. Saying that, there is still a way to go: it’s not often in a room of facility managers, safety or risk managers, of even insurers, that more than 5% recognise the pendulum test when shown a photograph of it.


However, as the saying goes, a little knowledge can be dangerous.


Instead of getting it wrong by under-specifying (so we had lots of slippery-wen-wet floors), I am now seeing a fair chunk of people over-specifying incredibly slip-resistant surfaces in cases where this is not appropriate. This is particularly the case in certain architecture practices.


It seems this is driven in part by the lack of a comprehensive understanding of the subject and in part by the desire not to be sued or held accountable should any accidents occur in a building once handed over.


The Pendulum Test is the only slip resistance measurement recognised by HSE and in the courts. Legally, a Pendulum Test Value (PTV) of 36 is the only benchmark that tends to be recognised. Yet I often see specifications of PTV 50+.


If you look at the classification of risk according to the UK Slip Resistance Group Guidelines and the HSE, you’ll see that there’s no such thing as very low slip potential. You have high slip potential (most slippery) moderate slip potential and low slip potential (least slippery). 36+ PTV gives you low slip potential.


Furthermore, if you review the accident risk exposure, a PTV of 24 gives a 1 in 20 risk exposure; a PTV of 36 gives a 1 in 1,000,000 risk exposure, so there is an exponential curve here. But higher than this and there is no further reduction in the published risk guidance. Realistically, once you get to a 1 in 1,000,000 risk, how much lower risk can you get?


It’s not feasible to eliminate the risk of a slip (other than by keeping floors perfectly clean and dry), so in that context, if we can achieve a 1 in 1,000,000 risk, surely that is pretty good.


Now, there is evidence that the slip resistance of an installed floor can fall in use for a variety of reasons. Primarily these falls in slip resistance will come from ineffective cleaning. But to have an out-of-the-box wet PTV of 45+ you require a very textured surface. If you add a very textured surface to an ineffective cleaning regime, the drop in slip safety is only going to be faster and more dramatic.


So designing-in or building-in some headway is pragmatic. But remember: just enough, not too much!


In my experience, it’s best, if you are aiming for a sustainable slip resistance of PTV 30, to achieve this by starting life at PTV 36; factoring in some slight deterioration. Whereas if you started life at a PTV or 45, my experience tells me that quite rapidly that floor could be performing at significantly under PTV 25.


In the real world, day-to-day cleaning practices are simply not robust or effective enough to maintain floors in a safe, clean condition, particularly if those floors are textured. This isn’t to criticise cleaning contractors: typically, their scope of works includes nothing about maintenance of slip safety.


So, specifiers should be choosing materials that are slightly above the threshold they wish to maintain… but only slightly above. The Goldilocks principle should apply.


Coupled with specifying the right level of slip resistance, both specifiers and facility managers should ensure that a robust plan is in place around the maintenance of that floor surface and that the slip resistance is monitored over time, to double check that everything is working as it should. It’s no good having a safe surface if you polish it, or apply a layer over the top of it, or allow contamination to build up on the surface.


Be aware here that cleaning and maintenance (O&M) guidance provided by floor suppliers is often not designed to maintain slip resistance. Don’t just blindly rely on this guidance: check that it works for yourself by using a pendulum test to monitor slip safety over time.


Additionally, the other factors within the CHIMES model must be considered. If you have a floor in the middle of an office building, where there is the most minute risk of a spillage, but no other realistic chance for the floor to get wet (other than perhaps during cleaning), the level of slip resistance of that floor surface is almost irrelevant. You can choose whatever you like in that environment because the risk of that floor posing a slip problem, according to the CHIMES model, is incredibly low.


The other key challenge of the over-specification of textured, anti-slip surfaces is that their aesthetics will also be compromised. Again, a textured surface is going to see dirt clinging to it and becoming embedded within the pores. That’s going to influence the colour shade and overall aesthetic of that material, and it won’t actually fit the criteria that the specifier was seeking to achieve. An architect choses materials in good part for how they look, so they want them to maintain that appearance.


An effective, periodic deep clean could be a good way of helping to maintain standards. Consider undertaking sealing work to the surface, which can be done without compromising the slip resistance (but make sure that you consult a specialist and that they perform dry and wet slip resistance tests to confirm that the sealant used does not make the wet slip resistance worse) but will make the surface easier to clean and maintain on a day-by-day basis.


This isn’t to say, though, that we should be going the other way and under-specify slip safety. Far from it.


If you start life with a slip resistant surface, then you’ve got half a chance of keeping it that way. If you start life with something that is inherently very slippery when wet, you’re fighting an uphill battle.


If you inherit a slippery-when-wet floor in an area that is likely to become wet or contaminated, your options limited to replacement or retroactive anti-slip treatment. Treatment can be very effective indeed and is a more cost-effective and less disruptive option. However, it is an additional cost and potential complication.


When you’re installing a new floor, seek to get it right from the outset.


Typically, when we are anti-slip treating new floors nowadays, it is when a shiny aesthetic is sought but a certain level of slip safety is also needed. Technology now allows us to achieve a safe surface (based on the pendulum test) whilst maintaining sheen. So there are proven ways of making floor surfaces sufficiently slip resistant, but again, these should be done with care: treating a floor to PTV 40 when wet will produce an easier floor to maintain than treating a floor to PTV 60 when wet.


To summarise: asking for a 45, 50 or 55 wet PTV will, actually, only bring problems in my experience. These include:

  • Inability to keep the floor aesthetically clean
  • That poor cleanliness filling up the pores of the floor and causing a slippery film to appear on top of the surface
  • Faster wear
  • Trip hazards in extreme cases
  • Injuries such as cuts and grazes from falling on the floor


So, over-specification of slip resistance is something of a vicious circle.


Use the Goldilocks Principle and get things “just right”. In the long run, this is the only way to achieve sustainable slip safety.

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