It would be hard to consider that a volunteer ED tech position exists. There will be certain skills and procedures that you will be expected to perform, activities that come with an inherent liability. I can't see a hospital not paying for these services.
Volunteer EMS services are different; they are a municipal service, not a healthcare organization (different liability issues and rules)
Sorry. Maybe someone knows better, but what you write of is quite rare, if not non-existent. Your options are probably either to function as a general volunteer or to get a job as an ED tech.
- senior medical student / retired ED tech