he means health, not HP points, the distinguishing thing would be that health is a measure of how healthy in general you are.
the toxic and hazardous waste dumps are an EXCELLENT source of FREE radiation, i would need to check but i seem to recall both are fairly radioactive and sewage is a usable source as well of rads.
now that i think about that again… i should actually test if sewage will help mutate, i believe i had success in the past with it, i’m sure that at the dump variation that contains sewage there is also radiation, i’m just having trouble remembering if sewage itself was of any use.
as far as how safe, very unsafe, but it also varies a TON, i’ve had plenty of characters who either simply shrugged off “fatal” doses of radiation or were actually outright actively healed by being radiated in a few cases, i think you do still have a fatal dose of some sort in the latter case but it’s insanely high.
if you’re serious about rolling around in radiation, which, you should be if you want mutations, find a geiger counter and always keep it turned on and with spare batteries and if you’re feeling lucky, when you get a hit indicating a “hot” tile, curl up and have a sleep, it’s a gamble for sure either way really, you can save a lot of purifier by doing both radiation and cooking as well.