Are there special considerations for locating securement points on wheelchairs with tilt-in-space seating systems?
For non-WC19-compliant tilt-in-space wheelchairs, the four (i.e., two front and two rear) securement points should either all be attached to the seat or all attached to the base of the wheelchair frame. This practice minimizes the chance for significant slack developing in the tiedown straps during a crash, which would result in large wheelchair movements, or the wheelchair coming free from one or more of the tiedown straps. This slack could develop, for example, if the securement points at the front are on the base and those at the back are located on the seat behind the pivot point. In a frontal crash, the forces on the back of the seat would be likely to cause the seat to tilt further rearward, thereby reducing the distance between the rear securement points and the rear anchor points, resulting in slack in a tiedown system that depends on tension to function effectively.
If four securement points are available on the seat such that the two front securement points are forward of the seat pivot point and the two rear securement points are rearward of the seat pivot point, this approach is generally recommended, over using four securement points on the base. Securement points on the seat are likely to be higher and thereby result in more optimal tiedown strap angles between 30 and 45 degrees to the horizontal. More importantly, the tension between the front and rear tiedown straps will stabilize the seat about the seat pivot point and maintain the orientation of the seat without depending on the strength of the tilt locking mechanism.
If four suitable securement points cannot be found on the tilt-in-space seat, then all four should be located on the strongest available points on the frame of the wheelchair base. Although the rotational stability of the seat will be completely dependent on the tilt-in-space locking mechanism when the base is secured, there is less chance for movement between securement points on the base and anchor points in the vehicle, and therefore a better chance for effective wheelchair securement.
If the wheelchair complies with WC19, use the securement available as directed by the manufacturer. For WC19-compliant wheelchairs, it is not as important that all four securement points are on the seat or on the base. This is because WC19-compliant wheelchairs are dynamically tested in a 30-mph frontal impact using the securement points provided by the manufacturer. Thus, whether the securement points are on the base or the seat, the wheelchair will have demonstrated that it can be effectively secured in a severe frontal crash test.
There is, however, a potential problem if all four securement points are not located on either the base or the seat, even for WC19-compliant wheelchairs. If, after securing the wheelchair and adding tension to the tiedown straps, the seat tilt angle is manually adjusted, the tension in the tiedown straps may be lost. This would be the case, for example, if the rear securement points are on the seat and the front securement points are on the base, and the seat is tilted rearward after the four-point strap system has been tightened. Unless the attendant notices the reduced tension, and readjusts the tiedown straps, this additional slack will reduce the tiedown effectiveness and could potentially result in the wheelchair being released from one or more tiedown straps during transit.