48V (and some more when batteries are full) are slightly below the limit of non harmfull voltage.
I suspect you have never seen the pictures of a wrench that "exploded"/"splattered" all over someones body. 50V may not (usually, but your mileage will vary) be able to produce enough current in a body to kill via fibrillation, but as usually deployed it has enough joules to kill in other ways. 50V is the number in the regs below which certain controls are not required. In some jurisdictions, it also allows those that are not "electricians" to perform work. Anyone regularly working around that many joules, no matter the voltage, has either been properly trained in a safety regimen, or is extremely lucky. It is no different than people who work around high pressure compressed air/steam. There is a lot of stored energy there, and you need to treat it with respect (same with heavy weights suspended above your head, or lots of other examples). Gary