firmness and stability
firmness and stability
Beneficial Designs has learned that the greatest barrier to accessibility on trials is the firmness and stability of the trail surface itself. The greatest barrier for accessibility in playgrounds is also firmness and stability of the surface. All surfaces must be firm and stable enough to roll on, but must also be safe, providing head impact attenuation. Playground surfacing has to prevent head injuries if children fall off of the highest pieces of playground equipment. As a result, BD developed the Wheelchair Work Measurement Method to measure the accessibility of outdoor recreation surfaces.
This test procedure was created using an instrumented wheel on a wheelchair. An operator pushes the wheelchair and the wheel measures the torque being applied to the hand rim on the wheelchair. The wheelchair is propelled in a straight line across a level playground surface for a distance of 2 meters. The force over time is measured to calculate the total work per meter to roll on the surface of the playground. This measurement is then compared to the force per meter to roll up a 7.1% ramp. To be accessible, the effort to roll on the level playground surface must be less than the work to roll up the 7.1% ramp. This relates to the firmness of the playground surface.
Then, the wheelchair is pushed 90 degrees around a turn on the level playground surface. The force over time is measured to calculate the total work to roll through a 90-degree turn on a level surface. This measurement is compared to the force to push the wheelchair through a 90-degree turn on the 7.1% ramp. This relates to the stability of the surface.
The Rotational Penetrometer, an instrumented surface indenter, was developed to make field measurements of playground surfacing that correlates to the Wheelchair work measurement method. This device uses a precision spring to push an indenter into the surface to measure firmness. The indenter is then rotated back and forth to see how stable the surface is. The additional penetration of the indenter into the surface is a measurement of the stability of the surface.
Both the Wheelchair Work Measurement Method and the Rotational Penetrometer are illustrated and explained in chapter 10 of the U.S. Access Board’s Guide to the ABA Accessibility Standards. Under “4. Assess During the Planning, Installation and Maintenance Phases,” the Wheelchair Work Measurement Method is shown being performed in a laboratory setting while the Rotational Penetrometer is shown being used in the field. Research on firmness and stability of exterior surfaces may be found in the Accessible Exterior Surfaces report authored by Beneficial Designs and funded by the U.S. Access Board.