The most common type of surface in an outdoor staircase is grating of steel in both steps and platform. The steps have a load bearing bar and a cross bar which with different serration can increase the grip under the shoe. Even if you choose plain plate or another surface that we use it has different characteristics that affects the friction or anti-slip safety.
It is much more common with slipping accidents in a staircase then caused from trip and fall. The distance between the steps and the step depth has also an impact on how you walk the staircase and affects the risk for accidents.
In order to measure the risk for slipping it is performed tests in a laboratory environment where the material is divided according to the size of the slip risk. Generally, the friction number is affected by the applied load, the temperature and the material surfaces which means to be confident in the result the test should be performed in the real environment. The tests for R-classification is made for risk of slipping with shoes.
Property owners have a responsibility to have anti-slip surfaces and can be liable for damages if a slipping accident occurs. Therefore, it is important to have the right type of surface in the staircase or grating if there is a risk of slipping.
Oil is applicated on the ramp in the right floor type and the test person walks in small steps back and forth with shoes until they slip (the test person is wearing a safety wire to prevent slip damages). The computerized readout then determines the R-classification based on the slipping angle. The rating starts with R9 which corresponds to the worst slip resistance and continues to the best slip resistance, classification R13.