As a kid in a campment I saw a monitor/counseror be possibly saved by wearing a life vest when he jumped from an old "romanic" bridge, I don't really know how high, but it would be between 10 to 15 meters. I believes he was saved by the vest because he jumped... and floped on his back. His vest was split in two all along his back, fabrick and foam both. I imagine that if he had jumped without a vest he might at least have been gravely injured. He was dazed a bit but oterwise was OK.