The phrase was poorly written, but the idea is that the effect of radiation on the body is cumulative, and the “safe” level is one that is low enough for our cells to repair the damage. The most practical application is with the rules that apply to nuclear workers; if their total exposure reaches a certain level they are not allowed near any source of radiation. So the article is suggesting that the dose from a lightning strike is 10,000 times the “safe” level for a lifetime. I find this claim dubious because that kind of exposure would almost certainly cause symptoms of radiation sickness and would likely be fatal.
But would being struck by darkning be fatal?
Thanks for the Explanation, I was worried if I got hit by dark lighten I would turn into the hulk...