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

Clear Space Evaluation

nlike [sic] the first phase of the transfer study, subjects in this study were not impeded by any obstacles on the floor that limited the manner of which they approached the transfer station (e.g. subjects in the previous study could not transfer to the station face on).  As a result subjects positioned themselves in a wide variety of locations about the transfer station.  Both the physical size of their WMD, where they positioned it with respect to the station and at what angle they positioned their WMD were all factors that weighed into the space analysis.  Graphical techniques were used to better understand the relationships between these factors.  As can be seen in Figures 7 and 8 more participants set themselves up on the right side of the transfer station compared to directly in front of or to the left of the station.  This may be explained in part by the effects of hand dominance on transfer ability and preferences.  The majority of study participants were right handed and likely their right side was stronger than their left side.  Positioning themselves to the right of the station allows them to use their right side as the trailing arm which carries more of the force during a transfer than does the leading arm when moving toward a new surface.  

Additionally, from Figure 7 it can be seen that some study participants did not transfer entirely within the boundaries of the transfer station. The space needed by the study participants was compared to a turning space dimension as described in the ADA-ABA standards (60x60 inch space). All of the study participants were able to transfer within the 60 inch depth, in fact the largest depth dimension required by anyone subject was 55.5 inches.  However, when looking at Protocol A for the maximum height transfer only 65% of the population could transfer entirely inside of the 60 x 55.5 inch defined space. For the transfer to a lower platform that number decreased to 53% when moving to the station and 56% when coming back to the station. (Protocol A).  A similar trend for participants requiring more space to transfer lower versus higher was found for the other protocols as well (B and C).  The reason that subjects may have used more space to transfer lower than higher may be that they needed more clearance space to accommodate the pivoting swing of the buttocks and increased knee and hip flexion that occurs when moving their body closer towards the ground than when moving their body further from the ground (e.g decreased knee and hip flexion).  Increasing the width of the clear floor space an additional 12 inches to 72 inches would accommodate 75-77% of users who would be expected to transfer higher or lower than their seat to floor height.  In order to accommodate 95% of the study population transferring higher and lower than their mobility device seat, the total width would need to be increased to 92 inches total.

As mentioned previously, the right side of the transfer station was preferred by the study participants. Shifting the clear floor square area requirement more towards the right may accommodate more people and minimize the overall amount of space required around transfer elements.   Like the previous study, subjects were not restricted to transferring from a certain direction (e.g. to their left or right) or within certain predefined clear floor spaces.  This was done to better assess limitations associated with transfer heights and to limit the number of transfers that each subject needed to perform.  Had subjects been limited by a certain direction or standard space dimension, it’s possible that fewer subjects could have completed the transfers at all or as high or as low as they did due to a lack of function or inadequate space available to position their WMD and themselves. 

For the angle of WMD positioning, participants had the option to align themselves parallel to the station (at 0 degrees), perpendicular to the station (at 90 degrees) or at any angle in between. When transferring to and from the station, the 50th percentile study participants preferred an orientation angle of around 30 degrees. It’s important to note that the angle of positioning can increase the amount of space required (e.g. in either the width or length dimensions) and should be accounted for in the future when planning the amount of clear floor space to design for around transfer elements.