Whereas there is only slight evidence for a genetic damage threshold, there is good evidence for a threshold for somatic effects. It is just over 20 rem (Fig. 5.2). Below this level no somatic effects or bodily effects to the individual himself occur and above this the level of damage rises until for acute exposures, it is possible to talk of the percentage of fatalities at certain whole body doses above 100-200 rem.

A scale of values for damage in terms of doses for an average individual is the following: less than 20 rem causes no observable reactions; 30-50 rem bring detectable changes in the blood; 50-100 rem produces nausea and vomiting; 400-500 rem gives an individual a 50-50 chance of survival without medical care; and 600-1000 rem may be lethal.