Wheelchair casters are a common point of failure in adverse environments due to rough terrains, inclement and debris. Failures can lead to injuries of the wheelchair users, and are often difficult to repair or replace. The World Health Organization has indicated that ISO 7176 may not be sufficient to confirm the reliability of wheelchairs in less-resourced settings, and that has been echoed at consensus conferences and by a working group of wheelchair product experts. These experts have furthermore ranked caster failure as one of the most critical areas for testing and test development.
The ISWP Caster Test, also called as the “Chakra”, has been developed to address the testing requirements for casters used in less-resourced settings. It consists of a turntable on which test casters are suspended from arms which are clamped to the test equipment (see figure below). The Chakra is able to test casters against straight and angular impacts as seen in the field. Corrosion seen in humid environments and wear experienced on rough surfaces are integrated into the caster testing protocol. The exposures of testing factors included in the protocol are based on outdoor exposures seen in less-resourced settings.
The protocol includes a two-cycle testing process. Each cycle consists of two steps as follows:
Step 1. Casters are tested for an interval of 100 hours in the corrosion chamber as per standardized corrosion testing methods.
Step 2: Casters are tested against bumps and abrasive surfaces based on the caster wheel size. Caster direction of rolling is reversed following a certain number of test cycles.
The cycle is repeated again until there is a physical failure, deformation, tire wear or loss of functionality. If the samples complete the two cycles of testing, the manufacturer can choose to test the product further.
Manufacturers should report the test results and the following details should be reported:
- Castor model and wheelchair model.
- Whether the castor model meets the strength requirements specified in this document.
- If the castor was tested beyond the strength requirements, report total corrosion testing hours and number of test cycles (low-shock and high-shock exposure conditions separately).
- Castor load.
- Reference to this standard.
- Castor failure modes seen during the test.
- Any confounding factors that may have influenced the test results and failures.