Has anyone gotten hurt while wearing a fall safety harness while in a confined entry/space work environment?

I got hurt wearing a fall safety harness while doing confined entry/space work on my hands and knees or crouching. My job had me doing this for 8-12 hours plus for 2 days. There was absolutely no threat of me falling anywhere being that I was working on the floor of a crude oil tank. I feel that a confined space safety system would have prevented this because that is what it is designed to do. I feel that a "Fall Safety Harness" was not the proper equipment and resulted in my injury. Anyone here know anything about this industry and can help me figure this out? Thank you!!!