Americans typically tolerate 0.3 rem* annually from background radiation, and 0.01 rem from industrial operations without complication. Workers who deal with radioactivity can be exposed to 5 rem to their entire bodies and 50 rem to their extremities, as stated in the Code of Federal Regulations
, Title 10, Part 20, Standards for Protection Against Radiation
Similarly, protective action guidelines values have been developed by the U.S. Environmental Protection Agency. For workers performing emergency
services, these rem limits include:
* Protecting valuable property: 10
* Life-saving or protection of large populations: 25
* Life-saving or protection of large populations when rescuer fully understands the risks involved: >25
In a recent publication of the Health
Physics Society, mention is made of real life, survivable doses of 25 rem and that doses reaching 50 rem may be acceptable under life-saving situations.
* The REM (Roentgen Equivalent, Man)
is a unit of equivalent dose. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Rem relates the absorbed dose in human tissue to the effective biological damage of the radiation. It is determined by multiplying the number of rads by the quality factor, a number reflecting the potential damage caused by the particular type of radiation. The rem is the traditional unit of equivalent dose, but it is being replaced by the sievert (Sv), which is equal to 100 rem.
The RAD (Radiation Absorbed Dose)
is a measure of the amount of energy absorbed by the body. The rad is the traditional unit of absorbed dose. It is being replaced by the unit gray (Gy), which is equivalent to 100 rad. One rad equals the dose delivered to an object of 100 ergs of energy per gram of material.
Doses that induce clinical responses to radiation overexposure begin roughly at about 70 to 100 rad. At 100 rad, radiation fatalities are minimal, but become more probable as the whole body dose increases. The estimated dose that will kill 50% of exposed individuals within 60 days (no medical
care) is about 350 rad.