ATTACHMENT 8


Chairman, Biochemical Advisory Committee     February 25, 1952
 for the Uranium Study
Duncan A. Holaday, Senior Sanitary Engineer

Proposed Working Level for RaA and RaC1.

     In the interim report on the uranium study which has been
sent to you, 172 micromicrocuries of RaA plus RaC1 is suggested
as the atmospheric concentration of those elements which should
be permitted in the atmosphere.  This value was selected without
sufficient information on which to base a scientific standard. 
However, the best available data was used in order to arrive at a
figure which the operators could use for control purposes.  The
reasoning back of this figure is presented below.

     At the Advisory Committee meeting in Cincinnati, Dr. Austin
Brues said that it was his opinion that a dose of 2000 rem per
year to the lungs could be expected to be carcinogenic in a
fairly short period of time (a definition of short time was not
given).  This opinion is the first tangible evidence that we have
had indicating the radiation dose that might be expected to be
dangerous.  It therefore appears necessary to adopt as a working
level a concentration of alpha emitters that would deliver
somewhat less than 2000 rom per year to the lungs.

     A concentration of 100 micromicrocuries of RaA plus RaC1 is
equivalent in radiation dosage to a concentration of 50
micromicrocuries of radon per liter.  This is assuming that the
radon is in equilibrium with its immediate daughters.  Using Dr.
Balc's assumptions that 40 percent of the respired activity is
retained in the bronchials for the lungs and that the relative
biological effectiveness of an alpha particle is 20, the
radiation dose to the bronchial epithelium will be 555 rom for a
50-week year if the atmospheric concentration of RaA plus RaC1 is
100 micromicrocuries per liter.  These are rather pessimistic
assumptions and it is probable that the actual radiation dose
which a worker will receive will be somewhat less than this
figure.  For example, instead of a 40 percent retention of
activity, we use an 8 percent retention such as was obtained by
Dr. Holanger in his experiments using uranium dust, we reduce the
assumed radiation "illegible" by a factor of 5.  A relative
biological effectiveness of 20 for alpha is probably high. The
first could be as low as 5.  Using these more favorable
assumptions, we arrive at a calculated case to the lungs of 27
rom per year.  This latter figure is certainly a very safe one,
whereas the "illegible" rom per year dose would undoubtedly be
frowned upon by many health physicists.  However, it is
approximately 25 percent of the dose which Dr. Brues considered
immediately dangerous.  It is probable that the true radiation
dose to the lungs will be somewhere between the two note
of figures which have been given above.

     At this time we are taking cascade impactor samples in each
mine we visit in order to determine the distribution of the
activity and see what fraction of it is absorbed on the material
that is in the respircule range.  It is our hope that a
sufficient amount of such data will enable us to reduce the
{illegible illegible} factors that are now present in all our
calculations.

				1

     May I say that I am not at all happy about the necessity of
selecting a supposedly safe working level for radioactive dust on
the basis of the manner information that is available.  However,
it is my opinion that we must have such a level in order to
institute a control program and that the figure which we have
proposed has a good possibility of being safe.  Our work on
"illegible" ventilator has shown that such a level is not an
impossible one to attain.  In fact, it appears that it would be
easier for the operators to reduce the atmospheric concentrations
of RaA plus RaC1 to 100 microcuries than it would be for them to
reduce the radon concentrations to 1000 micromicrocuries per
liter.

"illegible"

cc:  Washington