Someone I went to school with very nearly died from exactly that situation. The visible scars are serious, but as I understand it, the internal damage was such that he wasn't expected to survive. Industrial site, busbar chamber, supply switched off - checked for dead and he was told to start work. Then he found the bars were live as the genny had started up. Someone told me it was 11kV, but that doesn't sound right for a customer genny on a not very large site - I know the site (a paper mill), I can't imagine them having a genny at 11kV, I'd have assumed 415V would be more like it (he was working on the customer side, not the DNO).