I think there are a number of questions and items here.
1. What are you wanting from the insurance/OC? Medical costs? Pain and suffering compensation? Income replacement for time off work?
Is it more a matter of OC liability, that the OC may then be able to claim back from their insurer? Was there anything that could have been negligence from the OC – eg Trench/hole not covered or marked that caused the arm break.
2. What constitutes volunteering? Did you unilaterally decide to pull up a few weeds in common property, or was it in response to a SC/OC request along the line of “We are having a working bee Saturday morning to cleanup and weed the CP garden. All owners/residents are invited to attend and help in a voluntary capacity.”
3. What would you have done had it been the same in your own Garden? Can you use your own medical/income protection etc insurance to cover