Health and Safety
Executive / Commission
Slips and trips
This report summarises the findings of the Study of the Dynamics of Pedestrian Stair Use. This work was carried out and reported in three distinct phases:
The first phase investigated the effect of varying the going size between 150mm and 450mm. The results indicate that users prefer stairs with larger goings, but that there was little change in most test variable beyond a going size of 250mm.
It is proposed that during stair descent at least part of the toes should be supported by the tread when the initial contact with the tread is made. Population data showed that a minimum going size of 250mm is required for 50% of the population to accomplish this. It is therefore recommended that the minimum going size of stair be increased as follows:
It is intended that these larger, minimum going sizes will be submitted to the relevant committees of consideration for inclusion in the appropriate British Standards and building regulations.
The second phase addressed the potential of slip on stairs of different goings and different surface materials and different contaminants. Experiments showed that slips could occur in both ascent and descent. Ascent accidents tend to be less severe in nature because the centre of gravity of the user is slightly forward and most falls are relatively small towards the higher steps. During descent accidents tend to result in more serious injuries since a fall can potentially result in the user descending the entire flight of stairs impacting any number of steps on route.
Although the slip resistance value that represents an unacceptable slip risk on stairs may differ from that routinely used for walking on a level, the pendulum test did correctly rank the anti-slip performance of the flooring materials used in the study.
In descent, as the going size is decreased and the available friction is low, the user oversteps onto the nosing and the contact area between the shoe and stair is dramatically reduced. Depending upon the contact angle the user's weight may now act to help overcome the frictional forces. This results in increased likelihood of the foot slipping off the nosing, which may lead to an irrecoverable misstep and a potentially serious fall. Further investigation is required to determine:
Results suggest that the risk of the user slipping may be reduced by:
The third phase of the project considered the effect of proprietary nosings in an overstep situation. Experiments were carried out on stairs with two different going sizes and twenty different propriety nosings.
While there are some significant differences between nosing types, most of the nosing groups considered were not significantly different from the control situation (no added propriety nosing) in terms of the number of slips, losses of balance of or heel catches observed.
The study showed that the causes of a potentially serious stumble have the following ratio:
Slips: Losses of Balance: Heel Catches
12: 4: 1
Of the nosings tested one group, the silicon carbide, stood out as having the desired effect, reducing both the number of slips and losses of balance observed. The added roughness provided across the nosing resulted in a decreased likelihood of foot movement when a large overhang occurred.
Both the PVC and Al + PVC nosings reduced the losses of balance seen; however this beneficial effect was outweighed by an increase in the number of slips. Since slips are more likely to have serious consequences than losses of balance it is considered that both of these nosing types are less safe than not adding a nosing at all.
The surface roughness and shape of the nosing, as well as the colour contrast of the nosing with the rest of the stair all appear to have some effect on the likelihood of an incident. Propriety nosings should be designed to:
Project Leader:
Dr. Steve C. Thorpe (Health & Safety Laboratory)
Author:
Dr. Marianne Loo-Morrey
HSL Report Number:
PS/03/02