Hidden Contributory Factors in Slip Incidences

This article starts with a true[1] story about a tragic incident on a wet floor that resulted in severe head injuries and chronic mobility disabilities. This is a story which mirrors many incidences of the 1000-plus reported[2] slips on wet floors every year. 

Setting the Scene

The story starts in a large city hospital, and as is common with hospitals, it never stops day and night. So, in the very early hours, around 24:45, a hospital cleaner with long experience of working this shift, started to clean a 3rdfloor area that serve as a landing for 4 lifts and a thoroughfare for two main corridors and access to a large ward. For practical and safety reasons this is the only time that full floor cleaning can reasonably take place.

Even at this time in the early morning, the area must to be kept clear and ready at all times, but at this particular time the lights were dimmed to save energy and no one was in the immediate area. The cleaner, using the standard set of floor mopping equipment and cleaning product allocated for that area, adopted the standard practice of dividing the floor area into smaller and more manageable ‘zones’, and working from zone to zone. As per normal practice he positioned three slip warning signs. This particular piece of floor cleaning equipment is designed to use as little cleaning solution as possible so as to ensure the floor dries as quickly as possible. Instead of wet mopping the floor, the equipment only dampens the mop.

At around 01:00, just as the cleaner was half way (finishing zone 3) through cleaning the floor area, a nurse was attending patients as part of her normal daily routine in the ward immediately adjacent to the floor landing area. A set of large double doors separated these two people. 

15 minutes later (01:15), the nurse was finishing off her ward duties and started to make her way out of the ward and out on to the landing, with the intention of attending patients in other wards. By this time the cleaner had just finished the floor and was now helping his supervisor to dispose of black bag waste into the bin storage room. At this point in the story everything is normal and routine, nothing different from the daily routine has changed. However, as the nurse left the ward to carry on with her duties through the set of large double doors on to landing, she turned to the left took a couple of steps and slipped backwards, hitting her head on the hard floor. At this very moment of the incident the cleaner and supervisor were in the bin storage room, hospital porters were in the staffroom on a break, no one witnessed the incident. A large ‘bang’ from the impact soon aroused the attention of the cleaner, his supervisor, and the porters.   

Injuries Sustained from the Fall

As a result of the fall, the nurse suffered a post traumatic brain injury and a dislocated right shoulder. She had two epileptic seizures almost immediately and was admitted into ICU and put on a ventilator. She remained unconscious for several days and remained in hospital for a further 10 days. After leaving hospital, she would suffer blackouts lasting several hours, this lessen with medication over time. She suffered from post-traumatic amnesia during her stay in hospital and her memory, concentration and mobility remained impaired for some time afterwards. Her mobility problems contributed to a number of falls post incident that resulted in a broken tibia, damaged knee (due to altered gait) and accelerated pre-existing osteoarthritis.

What Factors Contributed to the Fall?

At first glance this story reads like a typical fall on a wet floor, but what really caused the nurse to fall backwards resulting in such severe injuries? 

In the majority of falls and slips, the primary causative factor is found to be wet or dry contamination on the floor.  Without contamination on the floor, the probability of a fall is highly unlikely. However, this idea of a slip solely due to a contaminated floor is far too simple. In our experience, it is more often than not that multiple factors are in play which combine to increase the probability and severity of a fall. The probability of a slip on a safety floor, for example, with a low to medium slip risk when wet with water, will be affected by any modification (including cleaning method employed, wear and maintenance) or addition of any coating applied to the floor. This example can be extended to any floor: It is very common for companies to ‘seal’ or apply a coating on to a surface for aesthetic reasons, or adopt a cleaning method that runs contrary to the manufacturers’ recommendations. All these modifications change the physical properties of the floor surface and therefore the slip probability.

The other factors which contribute to or exacerbate the risk of a fall are: Operations in the immediate area that either generate or fail to remove contamination, the appropriateness (type and design) of footwear, the state of mind of the individual, their range of mobility, the environmental conditions, and the physical properties of the floor surface. 

Let’s examine this story to see how multiple factors came into play that resulted in severe injuries and how the existing risk assessment failed to consider the effect of multiple factors. 

Before the incidence took place it’s important to look at the risk assessment for that specific area. The assessment determined that, because the area must be kept clear and ready to use at all times, a floor cleaning system must be chosen that leaves the floor dry within the shortest reasonable time, and that the time chosen to clean the floor must be during the quietest period. The cleaning system chosen was one of the factors in this story that contributed to the raised probability of a fall in occurring. The floor cleaning equipment was designed to lightly dampen one side of a flat double-sided microfibre-based mop. When used to clean a small section of floor, the mop head would be flipped and the dry side used to remove excess cleaning solution. Once that small section had been cleaned and the excess removed (the area would still be slightly damp, just not wet), the mop head would be replaced with a clean, dry one and the process starts again. Under standard environmental conditions (approximately 22 degrees centigrade and low humidity) the cleaning system returned a dry floor section in about one minute. 

Main Contributory Factor

The first failure in this story occurred when we consider that multiple witnesses attested to the fact the floor was still wet 15 minutes after cleaning ‘zone 4’ (from 01:00 to 01:15). The equipment – if used correctly – would have returned a dry floor by this time. However, it was discovered that the system used to regulate the amount of solution to dampen the mop head (to prevent over-wetting) was prone to easily accidental or intentional over-wetting and there was no reliable way for the cleaner to tell until the cleaning solution was on the floor. This simple hidden failure of the system contributed to the long dry time – the more solution applied to the floor the longer it takes to evaporate. Should the cleaner have made sure that the floor was dry before finishing? The obvious answer to this question is yes, but now consider the additional factors that come into play.

Additional Contributory Factors

This leads to the next part of the story: the environmental conditions at the time were dictated by the hospital in the effort to save energy, and the aesthetic requirements of the floor.  Every night the lights are dimmed in the main corridors and landing areas to save energy, including the lift landing area where the fall occurred was included.  There was also a requirement to maintain ‘shiny’ floors purely for aesthetic requirements, but also to reduce the cleaning demand on high and very high foot traffic areas; a Polyurethane coating was selected that met both these requirements and was applied.

The floor and the coating were completely smooth and the floor beneath the coating could reasonably be described as medium dark in colour. This degree of detail of the environmental conditions and surface detail are very important to remember as a third factor is introduced: the cleaning solution used. The cleaning solution (water and cleaning product mixture at the recommended dilution) selected and used was completely clear, non-foaming and odourless when used. As shown in the technique description of how cleaning products work, the cleaning solution ‘spreads out’ over the surface as a film rather than forming ‘beads’, this makes it much more difficult to see wet patches on the floor. 

The ability of surfactants in a cleaning solution to reduce surface tension (‘spread out’) has another consequence when you consider the point at which a rubber heel makes contact with a floor. By reducing the surface tension, the cleaning solution can penetrate (called ‘wetting’) tiny crevices and gaps and this includes the gap between a shoe and floor surface, even when full downward weight is applied. This film reduces the ability of the shoe to generate friction between the shoe and floor, thereby increasing the risk of a fall.

If we now reintroduce the other factors, the dimmed ambient lighting, shiny floor and dark coloured flooring, we can see that in the reduced light it would be difficult to see wet patches on a dark floor surface that already looks wet due to the highly reflective coating. This does not take away from the fact that the floor was wet for longer than it should have, but what if the cleaner had missed a patch of floor with the dry side of the mop head? All these factors were not considered in the original risk assessment for cleaning operations in that area, but they have such a huge bearing in the probability of a fall. 

Test Results and Observations

To determine the probability of a fall from the effect of the cleaning equipment (and method employed), cleaning solution and floor surface (including coating), a quantitative slip resistance test was conducted on the area of floor where the fall occurred. Ambient light levels could not be tested.  

The slip resistance test equipment was used under the following conditions: Dry, damp and wet. The dry condition was the floor as presented at approximately 13:00 with no prior cleaning conducted, and acted as a frame of reference with which the damp and wet test results can be compared to. 

The damp condition was the floor presented immediately after cleaning according to the equipment and product manufacturers’ recommendations. Testing of the damp condition was conducted immediately after cleaning and every 10 secs until the slip rating matched the dry condition. 

The wet condition was the floor presented immediately after cleaning using excess solution (over-wetting of the mop), within the capability of what the cleaning equipment can apply to the floor. Testing of the wet condition started immediately after cleaning and repeated every 10 secs until the slip rating fell into the low slip risk band. 

Figure 1 – The SlipAlert Test Graph
Figure 2 – SlipAlert Test Kit

The following results were obtained:

Figure 3 – Slip Resistance Results

We can see that when the equipment was used according to manufacturer’s instructions the floor dried very quickly to a dry state in approximately 50 seconds. However, should the equipment be misused (accidently or intentionally), the floor presented a very high slip risk for just over 2 minutes, and over 3 minutes until dry. In our experience, the initial slip resistant readings were the highest recorded in a number of years, and came as a surprise to all parties in this story. 

In this story, the floor was wet for 15 minutes which indicates that the floor was grossly over-wet, which would have ensured the floor stayed in a dangerous state for a long period of time.

During testing it was observed that: 

  • Even when using the equipment as per recommendations, the floor dried unevenly, leaving wet patches 
  • During the damp cleaning test, the cleaner using the dry side of the mop head to remove the excess solution accidently missed wet patches. 
  • From the cleaner point-of view the wet patches were virtually indistinguishable from the rest of the floor, due to the completely clear and non-foaming solution, dark floor and shiny floor coating.


Why were the wet floor readings so dangerously high and persistently high for so long? The original flooring supplied would have typically come with a set of laboratory slip resistance test results (for dry and wet), but the moment a coating or any surface modification is applied, those slip resistance values no longer apply, as the coefficient of friction has changed – this was not considered in the risk assessment. In this case, the coating was designed to prevent soiling (oils and greases) and other dirt from adhering to the floor, to make cleaning easier and less of a demand. This had the unfortunate consequence of allowing the combination of soiling and water, aided by the cleaning solution (reducing the surface tension), to slide more easily. 

This story highlights the often-missed fact that many different factors come together to turn a manageable situation into a dangerous situation. It also highlights the fact that a risk assessment that does not consider multiple factors, consequences of failures (intentional or accidental), and changes made to any one part to the system (e.g. coatings, environmental changes or methodology) must be considered a serious over-sight and therefore inadequate. An inadequate risk assessment is a recipe for future incidences. 

[1] Names, dates, parties, and location have been removed or changed to protect against identification; all other details are true and correct as pertaining to the case

[2] http://www.hse.gov.uk/food/slips.htm – For major and 3-day absence injuries reported to the HSE “…1,300 injuries per year, of which approximately 80% are slips…”. Date: 30/08/2017

Slip warning sign during cleaning
Slip warning sign during cleaning