On dosage level, my recollection is that we worked on a WED of 75 roentgen for purposes of estimating the worst case usefulness of rescue staff - or the potential for use of various routes for evacuation.
We understood at the time that the armed forces uses the same or similar values; I recall quite a lot of discussion amongst the scientists - almost all the staff were research scientists, some impressively eminent and well known (spending time listening to them was a major upside for an impressionable youth!) - as to how the limits had been derived, and what the experimental evidence backing it up was. The suspicion was that medical tests after Hiroshima and Nagasaki were probably important, plus much extrapolation given the uncontrolled nature of the 'experimental conditions' !
Form what I have seen much more recently, those dosages would have dramatically reduced life expectancy and lifespan, to say the least. Hmm.
Back in the early eighties, I often worked on the CT Scanner at a well known Hospital in Surrey. Among their specialties was a form of radiation therapy which 'killed' diseased bone marrow immediately prior to bone marrow transplant. Stay with me on this, I think there is a connection.
One of the problems with their technique was that repeated doses to various parts of the body had the obvious effect of making the patient very ill indeed, sometimes too ill for the treatment (replacement bone marrow) to have any great effect. So, they reasoned that if they could irradiate the patient's
whole body in 'one go', they would be in better shape to take immediate benefit. I knew the man who designed the machine they were building and it was scary.
To give an idea of scale, the 'source' for their previous system which irradiated individual limbs and body areas was, the size of a pencil eraser. (The little rubber thing on the end of a pencil?) This was transported in the back of a Land Rover - just that in its containment! The source they would need for the whole body irradiator was the size of a 'D' Cell battery and would need a twelve ton flat bed to transport it.
Now the guy who designed it did admit that when he rang Aldermaston to discuss the delivery of the source, he was told "Not over an open line!" Furthermore, the MOD wanted to install monitoring equipment in the room where the patients would be. When he asked why, they told him they wanted to know what happened when real people got close to an Atom Bomb.
It didn't take Sherlock Holmes to answer your question; "...as to how the limits had been derived, and what the experimental evidence backing it up was. " Probably not much Hiroshima/ Nagasaki, more the Royal XXXXXXX Hospital in Surrey.
Landroger