Reaction times under the effect of crushing forces

Status:

completed 08/2002

Aims:

The BG expert committee for structural objects reports that power-operated windows are increasingly being installed in buildings. Such windows present a greater hazard than windows which are opened and closed manually. During automatic closing of the windows, crushing or shearing points arise between the window and the frame, depending upon the window's design. A particular risk exists here of injury, such as bruising, crushing, and possibly even broken fingers. Safeguards must therefore be provided against pinch and shear points on power-operated windows. In addition to solutions involving force limiters or cutouts, one possible means of reducing the potential hazard to a minimum is to reduce the velocity of the moving element. This measure is based upon the notion that if the closing velocity is sufficiently low, adequate time is always provided to remove upper limbs from the hazard area, even where contact may already have been made with the moving window. At the initiative of the expert committee for structural objects, the velocity is to be identified at which a gap between moving window element and frame may close whilst still allowing persons to remove their fingers or hands from the gap without risk of injury. Based upon the known deformability of the fingers as the body part at the greatest risk, the measured reaction times may form the basis for a proposal for a maximum closing speed which is deemed permissible.

Activities/Methods:

A test arrangement simulating a vertically closing window is fabricated for performance of the experiments. The measurement facility on the test arrangement permits measurement of the time required for a person to withdraw his or her hand from the danger zone as soon as contact with the closing window is sensed. The reaction times are determined at a range of closing speeds. As it can be assumed that under real-world conditions, persons whose hands are resting within the window opening are distracted, a distraction condition is also implemented. The subjective strain upon the test subjects is also recorded in the measurements to be performed.

Results:

The reaction times decreased with increasing closing velocity until a threshold was reached beyond which the volunteers were clearly unable to react more quickly. When the subjects were distracted, the reaction times were substantially longer than without the distraction component. The subjective strain increased with rising closing velocity, and was greater in the presence of the distraction component than in its absence. No significant differences were noted between the sexes, either in reaction time or in strain level. On the basis of the studies performed, a permissible closing velocity of approximately 300 mm/min is proposed for power-operated windows in order to avoid crushing or shearing injuries.

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