Human-centred approaches in slipperiness measurement

Abstract

A number of human-centred methodologies--subjective, objective, and combined--are used for slipperiness measurement. They comprise a variety of approaches from biomechanically-oriented experiments to psychophysical tests and subjective evaluations. The objective of this paper is to review some of the research done in the field, including such topics as awareness and perception of slipperiness, postural and balance control, rating scales for balance, adaptation to slippery conditions, measurement of unexpected movements, kinematics of slipping, and protective movements during falling. The role of human factors in slips and falls will be discussed. Strengths and weaknesses of human-centred approaches in relation to mechanical slip test methodologies are considered. Current friction-based criteria and thresholds for walking without slipping are reviewed for a number of work tasks. These include activities such as walking on a level or an inclined surface, running, stopping and jumping, as well as stair ascent and descent, manual exertion (pushing and pulling, load carrying, lifting) and particular concerns of the elderly and mobility disabled persons. Some future directions for slipperiness measurement and research in the field of slips and falls are outlined. Human-centred approaches for slipperiness measurement do have many applications. First, they are utilized to develop research hypotheses and models to predict workplace risks caused by slipping. Second, they are important alternatives to apparatus-based friction measurements and are used to validate such methodologies. Third, they are used as practical tools for evaluating and monitoring slip resistance properties of footwear, anti-skid devices and floor surfaces.

Figure 1

Objective, combined and subjective human-centred approaches for the measurement of slipperiness.

Figure 2

Strategies for co-ordinating legs and trunk to maintain body in equilibrium with respect to gravity during standing (adapted from Winter 1995, figure 2.15).

Figure 3

Composite pattern of young and older individual’s heel velocity 117 ms before heel contact (HV = heel velocity) and 117 ms after heel contact (SHV = sliding heel velocity) on an oily vinyl floor surface; heel contact (HC) was defined as the time when the vertical ground reaction force exceeded 10 N; the darker line expresses the average pattern of the heel velocities (Lockhart 1997).

Figure 4

Gait phases in normal level walking with typical horizontal (F_H) and vertical force (F_V) ground reaction components and their ratio, F_H/F_V, for one step (right foot). Critical from the slipping point of view are the heel contact (peaks 3 and 4) and the toe-off (peaks 5 and 6) phases (Grönqvist et al. 1989).

Figure 5

Composite view of the heel dynamics (kinetics and kinematics) during a typical slip-grip response, including adjusted friction utilization (AFU) on an oily vinyl tile floor surface (Lockhart et al. 2000b).