2-10. MAXIMUM PERMISSIBLE DOSE
a. In 1946, the remnants of the pre-war advisory committee were called
together for the purpose of examining the nature and magnitude of the new radiation
protection problems that we were obviously facing. This resulted in an immediate
enlargement of the group and the establishment of seven specialized committees to
deal with what were then the more clearly recognized problems facing us.
b. Immediately prior to this and as a part of the work carried on during the
Manhattan project, a great many radiobiological and biomedical experiments had been
carried out--probably more in two or three years than in the preceding two or three
decades. This was done primarily to ensure protection of radiation workers and, in the
process, the studies essentially upheld the 1936 permissible dose for x and gamma
rays and the 1941 permissible body burden for radium.
c. The first major change in our permissible dose standards was introduced in
1949, at which time the basic value for radiation workers was lowered from 0.1
roentgen per day to 0.3 roentgens per week, or the equivalent of about 15 roentgens
per year. This was essentially a reduction by a factor of two over the value established
d. The introduction of this new value has been the source of a great deal of
misinterpretation and misunderstanding. The reason for lowering the level at this time
was not based on any new biomedical information that showed that the radiation was
more harmful than we had thought before. It was lowered purely and simply in
recognition of the fact that there would probably be much larger numbers of people
exposed; many different kinds and quantities of radiation involved; and that lowering the
permissible levels by a factor of two was technically feasible and would not involve
unreasonable costs or restrictions. The decision was made in spite of the fact that
there was no new evidence for injury at the previously accepted levels.
e. The NCRPM report putting forth the new permissible dose levels was
completed in 1949, but not published until 1954. This was primarily because it was
recognized as a very large and important step in radiation protection philosophy and it
was felt that the report should be tried out on the scientific and technical public for an
extended period before publication. During the five-year period, the 1949 report was
issued as important input and basis for much of the discussion in the tri-partite
conferences between England, Canada, and the United States in 1949, 1950, and
1953. It also provided the first input to the ICRP beginning in 1950 and at least through
its 1956 meetings.
f. Many of the features of the 1949 report are still reflected in our present day
philosophy and, in only a few areas, has our increase in knowledge been sufficient to
necessitate any appreciable change in our philosophy.