Independent Wheelchair Transfers in the Built Environment: How Transfer Setup Impacts Performance Phase 2: Final Report

Design Criteria for the Transfer Station

A custom-built modular transfer station was designed and fabricated to meet the study goals. The station was designed to investigate the impact handhelds, back rests, heights, and seat widths have on transfer performance. The design criteria for the station listed in Table 1 were derived from multiple design requirements in the standards where both adults and children are expected to transfer. 

Table 1. Transfer Station Design Criteria

Seat Heights: Transfer platforms in play areas need to be between 11 and 18 inches maximum above the ground (ADA-ABA Section 1008.3.1.2)[7]. Additionally, transfer walls at pool decks are between 16 and 19 inches above the ground (ADA-ABA Section 1009.4.2) [7].  The maximum height allowed between two transfer steps is 8 inches in play areas (ADA-ABA Section 1008.3.2) [7] and swimming pools, wading pools, and spas (Section 1009.5.4). No minimum height for steps is specified.  Based on earlier findings (Phase 1 Final Report), there was concern that the 8 inch maximum may not accommodate some wheelchair users.  Because of these concerns the station was designed to allow for adjustments in height up to, but not to exceed the 8 inch maximum height allowance. 

Seat width and depth: ADA-ABA currently requires a minimum entry point of 24 inches for transfer steps in play (Section 1008.3.1.1) [7] and pool areas (Section 1009.4.5) [7].  Additionally a 30 inch minimum width has been proposed medical diagnostic exam tables.  We selected 18 inches minimum seat width as a starting point with the potential to grow to 30 inches.  The seat depth was not a primary variable of interest and was fixed at 16 inches.  This dimension is within the range of seat depths allowed for transfer steps in play and pool areas and for proposed diagnostic equipment (14 to 17 inches).  Transfer surfaces on the station were padded with 1" foam and a vinyl cover for comfort and to protect the skin during the experimental protocol. 

Ramp: A ramped surface was designed to insert between two steps and serve as an integrated sliding board to assist with the transfers by bridging the gap between steps.  Ramped surfaces used for transferring are not currently part of the standards but are present in some real world transfer situations.  For example, some amusement park rides have sloped surfaces built into the structure of the ride vehicle to help individuals transfer into and out of the vehicle.  A ramped surface was made to attach between the two transfer platforms ('steps') and span across an 8 inch wide space.  The angle of the ramp varies as the second platform height changes and the ramp grows or shrinks in size so as to maintain a constant 8-inch gap between the two transfer steps. The ramp had a constant width of 30 inches and was 1 inch thick. The minimum length was 8 inches and the maximum length was 11 inches.

Grab bars: Section 609 of the ADA-ABA standards [7] includes provisions for grab bars in areas where transfers are expected. Grab bars can have either circular or non-circular cross-sections [7]. Circular grab bars are more commonly used and were selected for testing.  The outside diameter dimension range for circular cross-section grab bars are between 1.25 and 2 inches. A 1.5 inch diameter was chosen for the study. Section 1009.4.5 of ADA-ABA [7] describes grab bars to be used on swimming pool, wading pool, and spa transfer walls. This standard gives the grab bar height range of 4 to 6 inches from the wall to the top of the gripping surface. Two grab bar height options were designed for the study; a 6-inch and a 2.75-inch. The 2.75-inch was added to examine the effects of a handheld when located closer to the transfer surface.  A 4 inch grab bar was not made because it was felt that the differences between the 6 inch and 4 inch would be negligible. The grab bars were designed to be 16 inches long so that they could span the depth of the platforms. Section 1009.4.5 of the ADA standards also gives the dimensions for grab bars spacing [7]. When two grab bars are provided there should be at least a 24-inch clearance between them. Since transfer seat width was a modifiable variable in the study, the grab bars were designed to have a range between 18 and 30 inches. This allows for another 6 inches below and above the standard to be evaluated (note: provisions for grab bars were applied to the handhelds which are referred to in several places throughout this report).

Backrests: The backrest design for platform 1, the first surface that participants transferred to from their WMD as seen in Table 2, was based on bench seat back supports in section 903.5 of the ADA [7].  Back supports should be a minimum of 18 inches from the seat surface to the top of the support. Three different height back supports were designed for this study; a 14-inch, a 17-inch, and a 20-inch. These heights were chosen because they range from below and above the current minimum requirement. They were designed to be easily added and taken off of the station by sliding them in and out of two circular slots located in the scissor lift table top. Each backrest was also designed to have a 5^o angle for comfort.

Clear space: A grid 72 inches long by 90 inches wide was used to facilitate the recording of space requirements for each WMD user (Figure 1). This is more space than what is required in the standards.  If a person required space beyond the size of the grid, the additional distance was measured and recorded.  The grid was positioned such that it was centered with the middle of the transfer station. A coordinate system was assigned to the grid so that each cell was given an alphabetic (y-direction) and numeric (x-direction) name. The center point (0,0) was located on the line in-between the grid values A15 and A16. There were a total of 720, 3 X 3 inch cells in the grid. To calculate the space, three points were recorded for transfers to and from the platform: a point to the right of center, a point to the left of center, and a depth value (Figure 2). These points were found by recording each WMD's outermost points on the grid. When calculating both right of center and left of center values any point right of the reference line (A15/A16) was assigned a positive (+) value, while any point left of the reference line was assigned a negative (-) value. For the depth, all values were positive (+). Space data was recorded as the maximum distance away from the A15/A16 reference line to the right (right of center), the maximum distance away from the A15/A16 reference line to the left (left of center), and the maximum distance away from the front edge of the platform (depth). The angle the WMD was positioned with respect to the transfer station was measured from the front edge of the platform as shown in Figure 2. An angle of 0 degrees was given if the WMD was positioned parallel to the x-direction of the coordinate system (e.g. in parallel with the front edge of the platform). An angle of 90 degrees was given if the WMD was positioned parallel to the y-direction of the coordinate system (e.g. perpendicular to the front edge of the platform).

Figure 1. Scaled version of the 72 inch x 90 inch grid used to record position measurements

Figure 2. Location of wheelchair and measurement points for clear space calculations.  Also shown is the location of the transfer seat on the transfer station. The transfer seat had a fixed depth of 16 inches. The width of the seat was adjustable and could range from a minimum of 18 inches to a maximum of 30 inches. The minimum dimensions of the seat are depicted above.