Would you provide a link to the source of this average instrument specific rate?
I'm interested in knowing which instruments designed to detect low-to-medium-level radiation sources on a human are configured so that five detections per second would equate to a "You're fucking dead; there's really no hope for you" dose.
(Did you ask an LLM to "convert counts per minute to mSv" and fail to sanity-check the confident-sounding result it gave you?)
> ...everything emits...
Given that the crust and sea and air of this planet are chock full of radioactives, and that every living thing on the planet builds itself out of that material, that goes without saying.
PS 300 CPM is nothing. There are places where people live where the natural background radiation is higher than that. Also, background radiation is mostly Gamma rays which is more dangerous than what comes off of fission products or nuclear fuel.
That depends on the instrument. It's an instrument-specific rate. I'd say that saying "300 CPM is nothing" absent any information other than the CPM is foolish.
As I indicated earlier, given all of the other context we have, we can reasonably suppose that 300 CPM from whichever instrument was used in this incident is nothing to be concerned about.