Slip Testing for Polished Finishes on Stainless Steel
Slip resistance is a crucial consideration in environments where polished stainless steel is used, particularly in sectors like architectural design, food and beverage, marine, and pharmaceutical industries. Polished stainless steel finishes, while durable and visually appealing, can pose a risk of slips and falls if not properly assessed for safety.
It’s easy to generalise and say ‘Coarse is Good, Smooth is Bad’ but this doesn’t take into account the coarser grain, or pattern if treadplate is being used, and areas where contaminates can sit. In clean room areas, contaminates are the last thing we want trapped in the polished stainless steel grain.
We were recently asked what the slip rating on our 240 silicon (2K) finish is with regard to the PTV. The Pendulum Test Value (PTV) is the preferred method of HSE and their guide is available on their website.
They summarise it as:
- High Slip Potential: PTV 0-24
- Moderate Slip Potential: PTV 25-35
- Low Slip Potential: PTV 36+
And returning to our 240 silicon which has an RA of less than 0.5µm we could confirm to our customer that based on the surface microroughness classification table, a finish with 0.5µm Rz would fall under the "High Slip Potential" category (Rz < 10 µm).
Why Slip Testing Matters
Slips and trips are among the most common causes of workplace injuries accounting for over a third of major injuries. Polished stainless steel surfaces whilst chosen for their durability and can become hazardous when contaminated with water, grease, or other substances. Proper slip testing ensures that the finishes meet safety standards, reducing the risk of accidents and ensuring compliance with regulations with Health and Safety regulations.
Slip Testing Methods
Slip resistance can be assessed using several methods such as the PTV mentioned earlier but it is important to note there are other way slip testing methods.
- Pendulum CoF Test or PTV Test
A rubber slider, mimicking a standard shoe sole, swings across the surface to measure friction. The result, known as the Pendulum Test Value (PTV), indicates the slip potential.
Slip Potential Classification:
- High Slip Potential: PTV 0-24
- Moderate Slip Potential: PTV 25-35
- Low Slip Potential: PTV 36+
- Surface Microroughness Measurement
A hand-held roughness meter measures the Rz parameter, which represents the total surface roughness. This data is particularly useful for predicting slipperiness in water-contaminated conditions. You may be used to seeing the surface finish measured in Ra rather than Rz if you specify polished finishes, however the meters can be calibrated to read either Ra or Rz or can read both at the same time.
Slip Potential Classification (Rz microroughness):
- High Slip Potential: Below 10 µm
- Moderate Slip Potential: 10-20 µm
- Low Slip Potential: 20+ µm
- HSL Ramp Test
Test subjects walk on a ramp with increasing inclination until slipping occurs. The angle of inclination determines the CoF. This method is beneficial for simulating real-world conditions but of course requires a mock-up built and a way for the ramp to be inclined.
Challenges with Polished Stainless Steel Finishes
Polished finishes such as those we produce are widely used in applications requiring durability and hygiene. But with the smooth polished finishes can reduce surface friction, increasing the risk of slips and the coarser finishes whilst they may reduce slipping may also reduce the hygienic properties so it’s a balancing act!
Common Factors Influencing Slip Resistance
- Contamination: Water, grease, or talc can drastically reduce friction on polished surfaces.
- Surface Roughness: Finishes with lower microroughness values may require additional testing to ensure safety.
- Maintenance and Wear: Improper cleaning or long-term wear can alter the slip resistance of the surface.
How can you ensure the right finish?
Here at Professional Polishing Services Ltd, safety and quality are integral to the production process. We employ advanced quality control measures, including RA meters, gloss meters, and ultrasound thickness testing, to ensure that all finishes meet rigorous standards. Both Rz (surface microroughness) and Ra (average surface roughness) parameters can be measured, ensuring precise evaluation of slip resistance and compliance with industry standards. We would then suggest you carry out PTV testing on samples based on real life scenarios involving any contaminates. This will give you not only the metrological data but practical data as well. Remember, the coarser the finish the more you are expanding the area of the surface.
Practical Recommendations for Slip Resistance
- Choose the Right Finish:
For environments prone to contamination, opt for finishes with moderate to high microroughness values to enhance slip resistance.
- Conduct Regular Testing:
Periodic slip testing ensures that surfaces maintain their slip resistance over time, especially after installation or maintenance.
- Implement Effective Cleaning Regimes:
Proper cleaning removes contaminants that reduce friction. Use cleaning agents compatible with the specific finish to avoid damage – soap and water (clean with the grain direction) is suitable for the majority of cleaning but you may need specialised cleaning materials if grease etc is involved.
- Consider Environmental Factors:
Evaluate the conditions where the polished finish will be used. Is it inside? Outside? Will there be exposure to water, oil, or other substances? Is the environment urban or marine? All of these together can help you select the safest option.
Conclusion
Slip testing is an essential process for ensuring the safety and functionality of polished stainless steel finishes installed as floors or walkways. By employing reliable methods like the PTV Test and surface microroughness measurement we can work together to mitigate slip risks and comply with safety regulations. At Professional Polishing Services Ltd, we are committed to delivering high-quality, polished finishes that are not only durable but also safe and reliable for their intended applications.