ATTACHMENT 3 PROGRESS REPORT (JULY 1950-DECEMBER 1951) ON THE HEALTH STUDY IN THE URANIUM MINES AND MILLS During the early 1900's radioactive ores were discovered on the Colorado Plateau in the Rocky Mountain area. These were carnotite ores which contained vanadium and uranium, with a small quantity of radium. Several mines were developed during this period, but production was small as there was little or no demand for these metals. A small amount was exported to Europe, and it was reported that the Curies used American carnotite ores in their early experiments. About 1914 the U.S. Bureau of Mines established a pilot plant in Denver, Colorado, in order to determine the feasibility of producing radium in commercial quantities from the carnotite ores. This project was determined to be impractical and abandoned shortly thereafter. During World War I there was a revived interest in the carnotite ores as a source of vanadium. At least two mills were established to produce this metal, and an undetermined number of mines were opened in order to supply the demand for ore. As there was no demand for the uranium, it was discarded with the tailings. Following World War I the production of carnotite ores again became negligible; however, during this period small amounts were mined for "medicinal" purposes. A water infusion of the ore was made and sold in small bottles as a health-giving agent. This practice was eventually halted by the Pure Food and Drug Act. The development of atomic energy focused attention and interest on the carnotite deposits of Colorado and Utah. During the life of the Manhattan Project many of the old tailings dumps were re-worked for their uranium content, and it was indicated that about 10% of the uranium for the Manhattan 2 Project came from this source. Beginning about in 1946 many new ore bodies were discovered in the Colorado Plateau which caused the industry to mushroom in this area. At the present time there are an undetermined number of mines (approximately 300) mining uranium ores of various types on the Colorado Plateau. The ores are the carnotites which have been recognized for many years, roscoelite, autunite, uranite, and torbermita. The greatest production of uranium ores presently comes from the State of Colorado, with sizeable quantities also mined in Utah, New Mexico, and Arizona. New discoveries but as yet undeveloped, have been reported in Montana and Wyoming. There are eight mills engaged in the processing of the uranium ores, which produce as their final products uranium oxide and vanadic acid. The uranium oxide is shipped to other establishments controlled by the Atomic Energy Commission for refining and subsequent separation of the isotopes. It is estimated that the industry employs between 2000 and 3000 persons. However, production and total employment figures are confidential. Radioactive ores have been mined for several centuries in certain parts of Czechoslovakia and Germany. Reports that have reached this country, even prior to this Government's interest in uranium production, indicated that these European mines were high in radon gas, it having been estimated that the median level of radon was in the vicinity of 1500 micromicrocuries per liter of air. This information also indicated there was an attack rate of about 1% per year of lung carcinoma among the miners working in these mines. It was also reported that 50-70% of the deaths of the workers in these mines were due to a primary cancer of the upper respiratory system. This information, which has appeared in the medical literature of this 3 country, was the only material available which indicated the health hazards associated with uranium mining. 1. Thiele, Rostoski, Saupe, & Schmorl: Uber den Schneeberger Lungenkrebs. Munchen, med. Wechnchr. 71:24, 1924. 2. Saupe, Erich, Uber die Beziehungen zwischen Lungenkrebs und Staublungenerkrankung, Zentralbl. f. inn. Med. 1933, 54. In August, 1949, when the industry had reached a sizable production rate in the State of Colorado, Dr. Roy L. Cleere, Executive Secretary, Colorado Department of Health, appointed an advisory board to advise him and the State Division of Industrial Hygiene on the procedures that his division should use in conducting studies and surveys in this industry. Among the conclusions drawn by the first meeting of this group were that little or nothing was known of the health hazards of the uranium producing industry, and that a medical reconnaissance survey should be made by a physician from the Division of Industrial Hygiene of the U.S. Public Health Service. This reconnaissance survey was made shortly after this meeting. On August 25, 1949, Dr. Cleere called a second meeting of the Advisory Committee at which was also represented the management of the larger companies mining and producing uranium in the State of Colorado. This group concluded that in view of the dearth of information that was available with respect to the health hazards associated with this industry that the Division of Industrial Hygiene of the U.S. Public Health Service should be requested to conduct a study of the uranium mines and mills. On August 30, 1949, a formal request was made 4 to the Surgeon General by the Colorado Board of Health, the Colorado Bureau of Mines, the Colorado Industrial Commission, the Vanadium Corporation of America, the Uranium-Vanadium Producers Association, and later the U.S. Vanadium Company, to conduct a health study in this industry. Shortly thereafter the Chief, Division of Industrial Hygiene, U.S. Public Health Service, replied to these agencies expressing the desire and willingness of the Division to conduct such a study. Acknowledgement is made of the assistance which the Colorado Department of Health has given in the conduct of this study. Through grants from the National Cancer Institute for the years 1950-51, the Colorado Department of Health has been enabled to devote a large amount of their personnel's time to this work and to furnish considerable quantities of necessary equipment. The contributions of these agencies are gratefully acknowledged. While the negotiations referred to in the above section were underway, the Industrial Hygiene Field Station of the Public Health Service had conducted a very limited study of the mining problems in the mines located on the Navajo Indian Reservation. The preliminary information obtained in this brief study indicated that the miners were exposed to external radiation, radon gas, and a high silica dust containing an undetermined amount of radioactivity. In addition to the above enumerated factors, it appeared that the uranium and vanadium which was contained in the dust was of toxicologic importance, and also that the matter of internal radiation due to the inhalation of radioactive dust must be considered. Shortly thereafter a preliminary survey was made of a mill producing uranium oxide and vanadic acid. This information indicated that the mill 5 workers were exposed to the following environmental materials: (1) uranium and vanadium containing dust; (2) fumes and dusts of the isolated uranium and vanadium; (3) it was determined that radon was of little significance in the mills due to the large area available for dilution of the gas; (4) external radiation was not an apparent problem; (5) it would be necessary to consider the internal radiation factor, as dust control in the mills was not too effective. With this background of information it was concluded that the health study should consist of two essential and correlated phases: (1) the medical investigation, and (2) the environmental investigation. In July 1950 the study was initiated at Durango, Colorado, at which time medical examinations were made of the mill workers concurrently with an environmental study. Approximately 700 workers were given medical examinations in the first phase of the study conducted during the period from July to October 1950. During the 1951 season approximately 460 men were examined, of which 260 were miners and 200 were mill workers. During the two seasons 1200 persons have been given physical examinations, which represents the maximum amount of men that can be readily examined at this time. The remaining persons are employed at locations so remote that it would be impracticable for a medical team to get to them. However, it is believed that this represents a large enough segment of the working population to draw valid conclusions. Since the mines and mills are frequently located at extremely remote locations, it has been necessary to confine this study to the summer and early fall months in order to avoid adverse weather conditions. 6 The medical study consisted of a detailed physical examination, a chest x-ray, and clinical studies of the blood and urine. The environmental phase included the determination of the nature and concentrations of the materials to which the workers were exposed. Through a correlation of these data, it was hoped that information could be gained on the health hazards associated with the industry so that any necessary control procedures could be instituted. Of the group of miners examined only eleven were found to have had a five year exposure in the study. Environmental studies have been made in the six mills and approximately sixty mines. These studies consisted of the evaluation of the dust problem, especially with relation to the silica content of the dust; the determination of the nature and extent of exposure to toxic materials such as uranium, vanadium and mineral constituents of the ore; and the evaluation of the radon concentrations in the mines. In order to conduct this study the Division of Industrial Hygiene, U.S. Public Health Service, has cooperated very closely with the Atomic Energy Commission, especially the Division of Biology and Medicine and the Health and Safety Branch. The various State health departments concerned, i.e., Colorado, Utah, New Mexico, Arizona, have been advised of the progress of this study and in many cases have given us valuable cooperation. We also sought the assistance of the U.S. Bureau of Mines, especially on ventilation studies in the mines, and certain analytic work has been performed by the Los Alamos Scientific Laboratory, the Navy Radiological Defense Laboratory, and the U.S. Bureau of Standards. 7 The medical information has not been summarized, but it has been indicated that there were no medical findings relatable to uranium exposures. A number of cases of silicosis have been uncovered but this would be expected, as many of the workers had previous experience in hard rock mining. It is not surprising that other positive medical findings were not encountered, as the majority of these persons employed in the uranium mining and milling industry have been exposed for a period of less than five years. From experience in the European mines, it is indicated that a minimum of ten years would be required for the development of lung cancer. Cases of transitory illnesses have been encountered among workers in the mills which were apparently related to momentary high concentrations of vanadium. Chronic conditions also have been noted among the workers in the uranium mills which has been attributed to the exposure to relatively low concentrations of vanadium compounds. The workers complain of an irritation to the upper respiratory tract and a chronic cough. The physicians have also noted a green coating on the mucous membranes of the mouth and throat of the workers who complain of this chronic condition. Laboratory findings indicate a uranium level in the urine of from 0.2 to 60 micrograms per liter. It appears that the median value for the mine workers is in the neighborhood of 2.5 micrograms and for the mill workers 4.2 micrograms. Blood and urine samples of the mill workers indicate a trace of vanadium. A selected number of blood samples have been obtained for uranium determinations, but these analyses have not been completed. It is hoped that these medical studies will serve as a base line and that they can be repeated at intervals of from three to five years so that the progress of these workers may be followed. 8 The environmental investigation has probably yielded more information of immediate interest than have the medical studies. During the 1950 and 1951 seasons 132 samples for radon gas in 48 mines gave a median level of 3100 micromicrocuries per liter. The established maximum allowable concentration adopted by the American Conference of Government Industrial Hygienists is 10 micromicrocuries for an 8-hour exposure. This median level of 310 times the accepted maximum allowable concentration. The highest value encountered in this survey was a value of 80,000 micromicrocuries per liter. As indicated previously in this communication, the median level of radon in the German mines where definite pathology was found was in the vicinity of 1500 micromicrocuries per liter. The matter of external radiation received by the miners has been given serious consideration by the study team. Measurements of gamma radiation have been made using survey meters for area monitoring and pencil dosimeters for personnel monitoring and estimates of the external dose, ranging from 25 to 176 mr/day, were obtained by these methods. However, the meaning of these figures is obscure as a number of problems exist in the mines which interfere with radiation measurements. For example, radon decay products deposit on any surface and thus concentrate on survey meters and dosimeters. As a result the instrument readings are primarily functions of the surface of the instrument and the concentration of radioactive dust and not a function of the gamma field produced by the ore bodies. Radioactive dust is also concentrated in the workers' clothing and thus increases their total radiation dose. The problem of measuring external radiation require considerable study, but this inquiry has been deferred until other problems have been solved. 9 Dust control in the mines has been fairly good due to the widespread use of wet drilling and because of the fact that many of the mines are so-called wet mines. Dust concentrations encountered have ranged from 5 to 20 million particles per cubic feet, and it is believed that in view of our present knowledge the silicosis problem in the mines is not too acute. However, our investigation has revealed that the dust does not behave in accordance with the same principles as does other industrial dust. This phenomenon is presently being investigated. Appendix A discusses this point further. Internal radiation due to the inhalation of radioactive dust has been recognized as a potential health hazard due to the fact that uranium and radium both of which are contained in the dust, and radioactive lead, which is an end product of the decay series, are bone seekers. This problem has not as yet been evaluated but it is planned to undertake an investigation of this nature. Due to the extremely high concentration of radon in the mines, it was felt by the investigators that immediate attention should be given to this problem. The matter was discussed with personnel of the Health and Safety Branch of the Atomic Energy Commission and of the Atomic Energy Project of the University of Rochester. In order to assist us in the determination of radon, the Health and Safety Branch of the Atomic Energy Commission has made available an instrument for the measurement of this gas. Previously it was necessary to send the samples to the National Bureau of Standards for analysis, which involved considerable delay. By the use of this instrument, results may be obtained within a matter of several hours. 10 To date over 48 mines have been investigated for radon and almost without exception the concentration has been found to be alarmingly high. The investigation has also been extended to cover non-uranium mines in the same general area, and in general radon has been found in these mines which are producing non- ferrous metals. It was assumed that the radon gas was released into these mines from ground water and also from small amounts of radioactive materials associated with the non-ferrous metals. Only in a few cases has the radon concentration in the non- uranium mines been of sufficient magnitude to cause alarm. This phase of the problem is further discussed in Appendix 3. Before field work was begun in 1951, work by Dr. William F. Bale of the University of Rochester, and the Health and Safety Branch of the Atomic Energy Commission showed that the problem of internal radiation produced by radon would be re-examined. Experiments by these groups indicated that the decay products of radon could be concentrated in the lungs and produce much higher radiation dose than had previously been calculated. Dr. Bale spent several days with the environmental group in June 1951 evaluating the problem in mines. Following this work, it was decided that it was highly important to measure the atmospheric concentrations of radon decay products as well as radon concentrations and this was done for the remainder of the season. Generally, it was found that the ratio of radon daughters to radon was marked influenced by ventilation and that it was possible to reduce the potential hazards very significantly by ventilation. Not only was the radon removed but of even more importance the solid daughters did not have time to grow into equilibrium with their parent. 11 In view of the acuteness of the radon problem it was felt that it was necessary to temporarily put aside our full-scale environmental investigation of this industry and concentrate on the control of this contaminant in the uranium mines. For this reason a number of conferences were held that the operating companies, at which time the problem was explained to them and they were urged to adopt immediate steps for adequate ventilation of the mines. Most of the companies indicated that corrective measures would be undertaken and subsequent studies have shown that ventilation is now being provided in many of the mines operated by the larger companies. At the present time we are engaged in studies to determine the radon and radon degradation products after ventilation has been provided. This work has indicated that with proper ventilation it is possible to reduce the radon concentration to an order of magnitude of 1000 micromicrocuries per liter. We are tentatively urging the mines to establish 100 micromicrocuries of radon per liter as the maximum working level, but that every effort should be made to reduce this value as far below 1000 micromicrocuries as is possible through recognized engineering methods. This figure of 1000 micromicrocuries of radon per liter was not presented as a M.A.C., as there is not sufficient information available to establish any definite figure. It was believed that if sufficient ventilation was provided to meet this figure, the concentrations of radon daughters would be reduced to much lower levels and thus minimize the internal radiation hazards. The subject of internal radiation from radon and its decay products, and the effect of ventilation on atmospheric concentrations of these elements is presented in Appendix C. 12 The problem of attempting to secure adequate control measures in all of the mines by personal consultation was far beyond the ability of this staff. It was for this reason that it was felt advisable to call a conference of all of the companies concerned in order to appraise them of the findings of the mine studies and to give them more complete information on the control of radon. Prior to this conference the staff members developed a simplified technique by which the radon concentration could be estimated by means of equipment readily available to most operating companies. This consisted of drawing a sample of contaminated air through a filter paper approximately 1 inch in diameter and measuring the radioactivity deposited on this medium. By means of mathematical relationships the radon in the atmosphere may be estimated from the radioactivity on the filter paper. Although the results obtained are not true figures, the magnitude is sufficiently accurate to serve as a guide in controlling the contaminant. During the week of August 13, 1951, two conferences were held at the Salt Lake City Field Station, the first being for State and official agency personnel and the second for technical representatives of the various companies. At the State conference there were representatives from five State health departments concerned, the U.S. Geological Survey, and the Atomic Energy Commission. At the industrial conference there were 20 representatives from 8 mining companies and 3 representatives from the U.S. Bureau of Mines. These conferences appeared to be successful and the industrial group expressed a desire to hold meetings of this type at infrequent intervals so that they might be appraised of additional findings and improvements in the methods of estimating and controlling radon. The proceedings of this conference are being summarized 13 and will be circulated to all persons concerned. This communication will contain specific instructions for the estimation of radon and radon degradation products. It is our intention to assist the technical personnel of the operating companies in the establishment of control programs by individual visits to the companies concerned. It is felt that a great deal of valuable medical information could be obtained by an epidemiological study of the persons who were employed in the uranium mines and mills during the period prior to 1950. A few cases of lung carcinoma in ex-uranium miners have been refereed to this office by various persons. In most instances these have been followed up by a complete medical and occupational history. To date the number of cases referred to us in this manner have not been sufficiently great to indicate a causal relationship between illness and occupation. Preliminary investigations made by the State of Colorado have indicated that certain counties of that State, which are located on the Colorado Plateau, have a crude death rate from cancer significantly greater than those counties coated in agricultural regions. In order to obtain more information on the older workers, the State of Colorado has employed a lay epidemiological investigator. He will be expected to secure as much information as is possible regarding the fate of those persons employed in the uranium mining industry prior to 1950. This will be accomplished by obtaining records for the companies that were operating during that period, through welfare records, and death records in the counties in which the industries are located. A very important phase of his work will be to interview many persons in order 14 "illegible" first-hand knowledge of those workers associated with the industry in the years past. During the course of this epidemiological investigation cases of illness may be found, which, on the basis of information at hand, may be related to the occupation. Preliminary arrangements have been made to have these persons referred to a private physician by the Executive Secretary of the Colorado Department of Public Health. If, in the opinion of the private physicians, there is a relationship between the illness and occupation, arrangements will be made for further clinical studies to be conducted either at the University of Utah, or Colorado, Medical School. It is believed that this phase of the project may yield valuable information. In pursuing this study many facets of research and investigation have arisen, many of which are directly related to health conditions in the mines and mills and many others which are of academic interest. In planning our future work in this investigation, every attempt has been made to pursue only those angles that are of importance in the health aspects. Within recent months a technical advisory committee has been created within the Division of Occupational Health to guide the study and advise the investigators in the methods of study. The January, 1952, meeting of this advisory committee and its consultants has been called primarily to consider the following points: -15- 1. To review the findings of the study to date and to formulate comprehensive plans for its future conduct. 2. To determine which phases of the study would best be handled as field investigations and which should be studied as research problems. Decisions should also be made on where research work should be done and by what groups. 3. To advise on feasible methods for estimating the internal and external radiation to which the miners are exposed. 4. To determine maximum concentrations of radon and its decay products that should be permitted in mine atmosphere. 5. To advise on the desirability of issuing a progress report to the interested operators and Governmental agencies and to decide what information should be included in such a report. APPENDIX A BEHAVIOR OF URANIUM DUST SAMPLES DURING SETTLING IN 1 MM COUNTING CELLS During the course of the current health study of the uranium mining and milling industry, it has become apparent that collected dust does not behave in accordance with certain recognized principles as does other industrial dust. This phenomenon was first noticed during the 1950 study season while counting dust by standard light field techniques. At this time, it was observed that the particle count in prepared counting cells increased alarmingly after a standard settling time of 20- 40 minutes. The Subcommittee on Standard Methods of the American Conference of Governmental Industrial Hygienists recommend at least 30 minutes settling time for the 1.0 mm counting cell before counting. Presumably, all dust particles visible by light field counting technique will settle to the view plane just above the counting cell surface during a 20 minute settling time. Dust samples from the Durango Mill, Durango, Colorado, were counted with a microprojector. After 30 minutes settling time of the counting suspension, it was found that the count increased with each succeeding field during the counting period. Therefore, the settling time was changed to 60 minutes, with some stabilization of count for succeeding fields noted. It has been noted that generally the second counting cell prepared from each sample has higher count than the first cell, as the suspension is allowed to settle for some minutes longer in the second cell. During the 1951 study season, it was decided that representative dust samples from mines and mills should be counted and this phenomenon observed periodically throughout a long period settling time. Representative samples were prepared according to the standard technique, utilizing Dunn cells with a depth of 1.0 mm. The same prepared dust suspension was used and counted throughout the counting period. In the table below, a series count of dust from a mine is indicated. These counts represent the particles counted per 1/4 mm in the Dunn cell. The sample was taken in a dead end raise during drilling for a sample period of 10 minutes. Carnotite ore is extracted from this mine. Settle time Particles counted/ 1.4 mm field 40 minutes 72* 80 118 87 128 92 166 95 184 156 254 180 338 243 545 292 820 2 This sample was counted 7 days after sampling. The 40 minute count in the above table is the same as the 40 minute count 12 hours after sampling. Apparently, holding of samples for longer than 72 hours does not affect the sampled dust characteristics. Recently, a representative sample from the Rifle Mill at Rifle, Colorado was counted periodically throughout a long settling period. Again, the same procedure was used. The periodic counts were made on the same prepared counting cell. The table below indicates the results of this series count of mill dust. Settling time Particles counted/ 1/4 mm Field 20 minutes 59 230 " 214 330 " 233 360 " 255 15 1/2 hours 287 Representative dust samples from mills handling (1) lead- zinc ores, and (2) copper ores were prepared in the same manner and counted periodically over long settling periods. This experiment was performed to see if the above mentioned phenomenon presented itself in counting these typical industrial dusts. The tables below indicate the results of this experiment. Lead-Zinc Ore Settling Time Part. counted/ 1/4 mm Field 40 minutes 65 90 " 71 93 " 72 95 " 76 97 " 61 102 " 80 105 " 77 Copper Ore Settling Time Part./ 1/4 mm. 34 minutes 125 38 " 135 44 " 161 81 " 146 93 " 162 97 " 149 102 " 156 172 " 132 176 " 164 248 " 179 291 " 180 295 " 130 These determinations have all been plotted on the attached graph. These graphs may illustrate more clearly the phenomenon mentioned. APPENDIX B RADON IN NON-URANIUM MINES In May 1950, before field work on the uranium study was begun, our attention was directed to a report of an investigation of the Hillside Mine in Arizona. This was an old mine which had been operated for over 50 years and had recently been surveyed for uranium. No commercial uranium was found, but radioactive dust was located on ventilating fans. Consideration of this information developed the thought that it was probable that uranium mineralization would occur to some extent in areas where other non-ferrous metals were deposited. Available information on the Schneeburg mines also indicated that high uranium content of the ores was very low and yet high atmospheric radon concentrations were prevalent. Thus, it appeared that it was possible that significant amounts of radon would be present in many mines besides those that were operated primarily for uranium. As the opportunity arose, a few mines were investigated to test this hypothesis. It has only been possible to do a limited amount of this work, but the results are interesting and are presented below: Area Mine Station Radon uuc/1 Front Range Silver Plume Mendota Tunnel 24 " " " " " 400 level 27 " " " Terrible 1300 level 26 " " " " Main haulway 17 " " " Cold Springs 435 level 40 " " " Boulder City 15 " " " Consolidated 3,637 in from Caribou portal 14 " " " " " 1040 D2 level 575 " Aspen Smuggler #2 800 from portal 440 " " " " 1300 from portal 250 " " Durant 3000 from portal 320 " Tunnel Seven mines in the Marysvale area were surveyed with field instruments as no radon flasks were available. These readings are at best, semiquantitative, but radon decay products were found in all of the mines. In two cases, a two cubic foot sample taken through a respirator pad gave readings of 17 mr/hr when placed on the probe of a Geiger survey meter. This limited investigation indicates that over a large area of the Intermountain states radon concentrations exceeding 10 uuc/1 will be found in practically any mine. In some areas, it is probable that many thousand miners have been exposed to atmospheric concentrations of radon of several hundred uuc/1 during the last 70 years. This phase of the general problem should be investigated further, as it is likely that many additional individuals are exposed to radon than those who are presently working in uranium mines, and that a study of selected groups might yield information that would be useful in determining a M.A.C. for radon and its daughters. APPENDIX C - PART "Illegible" Digest of Dr. Bale's memorandum on "Hazards Associated with Radon and Thoron" The M.A.C. for radon used by the New York Operations Office is 10-10 curies of radon per liter of air, while Dr. Robley Evans has suggested a value of 10-11 curies per liter. Before the A.E.C. adopts an M.A.C. of 10-11 curies per liter it appears worthwhile to reevaluate the levels at which danger from radon and thoron would be come significant. According to Evans, a malignant disease of the lungs, attributable to radon exposure is always carcinoma of bronchial origin, and therefore due to radiation of the epithelial lining of the bronchi. These assumptions are made: The radiation dose is due to the alpha radiation from radon, in equilibrium with radon, in the outside air, plus the alpha radiation from RaA and RaC1 which are considered to exist in the bronchi in equilibrium with radon; and that the adult right lung has 9.8 g. of live epithelial tissue and 5.3 cc of air per g. of such tissue. Referred to a level of 10-10 curies per liter the average dose for a 40-hour week to the epithelium is 0.86 x 10-3 rep/week or 1.7 x 10-2 rem/week. This is 5.7% of the 0.3 rem/week tolerance. Therefore, if these assumptions are valid, it appears either that a radon level of 1 x 10-10 curies per liter is acceptable and a level of 1 x 10-9 curies per liter can exist without appreciable hazard, or that bronchial epithelium is very much more radiation sensitive than other body tissues. II. Additional hazards associated with Radon The vital fact seems to have been neglected that the radiation dose from the air-borne daughters of radon present under most conditions where radon itself is present is likely to far exceed the dosage due to radon and its disintegration products which are formed while the radon is in the bronchi. This additional dosage is due to the fact that the solid decay products are absorbed on dust, remain suspended in the air and are inhaled and concentrated in the lungs. The following calculations of radiation dosage delivered to the bronchial epithelium are based upon the assumption that 40% of the radon disintegration products attached to dust entering the lungs is removed and retained for an hour or so in bronchi, with an internal diameter of 0.2 mm and larger. On this assumption, where the radon concentration is 1 x 10-10 curies per liter the dosage from the alpha particles of radon and equilibrium amounts of its daughters products is 2.6 x 10-4 mev per hour, and the dosage from dust-borne RaA and RaC1 is 2.9 x 107 mev per hour. Using Evan's figures the average alpha radiation dose to the bronchial epithelium turns out to be 1.13 rep for a 40-hour week. assuming that 1 rep equals 20 rem, this dosage is 22.6 rem per week. -2- It may be pointed out that if the above assumptions are justified, the direct dosage contribution from radon plus its daughters formed in the lungs is less than one-thousandth of the total ionizing radiation dosage to the bronchial epithelium. In the Schneeburg and Joachimstahl mines an increased incidence of lung cancer seems to have been associated with a prolonged exposure to radon concentrations of the order of 10-9 curies per liter. According to the above concepts the radioactive dust associated with such concentrations might produce a weekly radiation dose to the bronchial epithelium of 11.3 rep or 226 rem. It is not surprising that the exposure of bronchial epithelium to radiation doses of this magnitude should produce malignancies. APPENDIX C - Part "illegible" Collection and Measurement of RaA and RaC1 After the importance of RaA and RaC1 in producing internal radiation had been pointed out to us, this question was investigated in several uranium mines. Preliminary experiments showed that large amounts of short-lived, alpha-emitting substances did exist in mine atmospheres and work was begun to develop a field method, utilizing available instruments, that would evaluate the atmospheric concentrations of these elements. In its present stage of development the method consists essentially of the following steps: 1. Air is drawn through a one-inch diameter circle of Whatman 41 filter paper at a measured rate (14-23 liters per minute) by a hand-cranked pump for either a 5 or 10 minute period. 2. The alpha activity on the filter paper is measured by a field instrument (the Juno and the Mark II Alpha Radiac have both been satisfactory for this purpose) at measured times after collection. These instruments are calibrated against a methane flow proportional counter to obtain disintegrations per minute, using radon daughter products collected on a filter paper as a source of alpha radiation. 3. The calculation of alpha emitting radon daughters in the atmosphere is based upon a mathematical treatment by Dr. John H. Harley, Chief, Analytical Branch, Health and Safety Division, AEC. He presents three derivations, namely: (1) "The build-up of activity on the filter paper from the start of sampling until equilibrium is established between the rate of deposit and the rate of decay of the activity." (2) "The decay of the equilibrium activity after sampling is stopped." (3) "The decay of the activity present when sampling is stopped at any time before equilibrium is reached." From the equations in(3) above, theoretical decay curves were plotted for 5 and 10 minute samples. Data obtained from mine filter paper samples were plotted on the same graphs, which are attached. (Figures 1 and 2). As these data appeared to agree with the theoretical curves, the decay curve were used as the basis for construction of correction curves (Figure 3) to correct the observed dpm at time t to dmp at time 0 (time 0 is the moment at which sampling was stopped. From the equations presented in (1) above, the activity on the filter paper at the end of any sampling time may be expressed as percentage of final or equilibrium activity. This turns out to be 10% and 18% 2 for 5 and 10 minute samples, respectively. "For an equilibrium sample, if we can determine the initial activity (at the end of sampling) this activity may be substituted into the expression, (16) curies/liter x 5.95 x 10-15 (dpm) __________________ v (v x sampling rate in lpm) to obtain the radon concentrations." For our work it appeared that expressing the alpha activity in terms of RaA and RaC1 would be more useful than expressing it as radon, especially as we are certain that in the mines radon is not in equilibrium with its decay products. Therefore, by multiplying by 2, and dividing by the fraction of final activity, we obtain for a 5 minute sample uucuries of RaA - RaC1 = 0.12 (dpm) and for a 10 minute sample __________ v uucuries of RaA - RaC1 = 0.066 (dpm) __________ v The following is an example of the method: A sample was taken from 10:03 to 10:13 at a sampling rate of 18.5 liters per minute and at 10:45 the Juno read 25 x 100. From the calibration curve, disintegrations per minute = 640,000. The correction factor for 32 minutes (10:45 - 10:13) was 1.8, so the alpha activity at 10:13 was 1.8 x 640,000 dpm. Substituting into the above formula micromicrocuries of RaA - RaC1 = 0.066 (1,152,000) = 4100. __________________ 18.5 The preceding method of calculating is based on the assumption that RaA and RaC1 are in equilibrium with each other. This assumption is probably not entirely valid in mines with good ventilation, but from the data obtained thus far, it does not seem that it introduces serious error. APPENDIX C - PART IV VENTILATION OF URANIUM MINES The essential requisites for ventilation in the working of uranium mines should be the same as those for working in any siliceous ores. These requisites are planned methods of mine ventilation to provide each work place with an adequate amount of fresh air, wet drilling where practicable, the rapid removal of contaminated air from the workings, and common sense dust control practices to be followed by the miners. For operations in rock, emphasis is usually placed on wet drilling, copious use of water to spray down the surfaces of the workplace and the muck pile during loading, and providing forced ventilation to the work face. The basic problem associated with uranium mining is not to suppress siliceous dusts, but rather to lower excessively high concentrations of radon and radon daughter products. Perhaps dust concentrations are physiologically significant if the dust is respired since it will be contaminated with radon and its daughters, but from the standpoint of silicosis production, the dust in most uranium mines is thought not to be significant. Dust counts in uranium mines have been low considering the appalling lack of dust control procedures. This fact may be explained by the lack of activity in the mines, as the mines are small and usually only one face is worked at one time. Wet drilling is generally practiced and the mines are usually abandoned overnight to allow powder smoke and dust to be cleared out. With but few modifications, it is believed that by complying with accepted mine ventilation practices, the concentration of radon and radon daughters can be lowered to an acceptable level in most uranium mines. In uranium mining, it appears more practicable to place the mine under positive pressure rather than employment of a suction system for general ventilation. This would have several advantages, namely: 1.) Churn drill holes to the surface from a point close to the breast of development drifts and stopes or rooms are becoming more in evidence in uranium mines. With the mine under positive pressure, radon would be forced from the working area through churn drill holes without distribution throughout the mine. 2.) Positive mine pressure would tend to "hold" the radon in worked out areas or force it from the mine through surface openings. 3.) Positive mine pressure may bend to hold radon in the fissure and rock openings of newly developed areas while miners are in the area. Perhaps the radon would diffuse out when the fan is shut off for the night, and subsequently be expelled before the men return to the area. Results of ventilation in uranium mines. G-1 Incline. This mine has two levels. The first level is reached by incline from the surface, and the two levels are connected 2 by means of a second incline. At the time of the ventilation study of this mine, there was approximately 2800 ft. of 8' x 10' drift or tunnel. A 3000 cfm fan forced air through a 10" churn drill hole to the lowest level. This air exhausted to the upper level by way of the incline, providing an air velocity through the drift and incline of 37 fpm. Approximately 7000 cfm fresh air moved down the main incline to the upper level, mixed with the 3000 cfm rising from the lower level and exhausted from the upper level through a 4' x 6' ventiliation raise in which a 10000 cfm exhaust fan had been installed. Samples of radon were taken at the foot of each incline. Initial samples were taken when the fans had been inoperative for a period of 14-30 hours. The fans were then turned on and series samples taken over a period of time to observe the effectiveness of ventiliation in reducing the radon and radon daughter concentrations. The table below is a tabulation of this data: Sample Location Radon Conc. Foot #1 incline 12,300 uuc/1 Foot #1 incline 7,080 uuc/1 Foot #1 incline 112 uuc/1 Foot #2 incline 12,500 uuc/1 Foot #2 incline 7,900 uuc/1 Foot #2 incline 290 uuc/1 Radon Daughters Remarks 7860 uuc/1 Fans off 20 hrs. 4720 uuc/1 Fans off 30 hrs.* Less than 10 Fans on 4 hrs. 5370 uuc/1 Fans off 20 hrs. 5260 uuc/1 Fans off 30 hrs.* Less than 10 Fans on 4 hrs. *This decrease was caused by the inflow of cold outside air overnight. The King #2 Mine consists of two separate workings in the same ore body. Both workings are reached by incline, Incline #1 and Incline #2. The workings of Incline #1 are provided only natural ventilation and poor ventilation was observed. Incline #2 workings were under pressure from a 2000 cfm fan which provided 3-6 air changes throughout the workings each hour. The table below indicates results of radon samples in these workings. King #2 Mine Sample Location Radon Radon Daughters Remarks Foot #1 incline 22,700 uuc/1 19,000 uuc/1 No ventilation Foot #2 incline 825 uuc/1 150 uuc/1 Good ventilation The Whitney Mine, Long Park Area, is provided with a fan supplying air to the workings through an 8" churn drill hole. Air is supplied at a rate of 320 cfm, which is not adequate as evidenced by the determined radon and radon daughter concentrations of 2000 uuc/1 and 850 uuc/1 respectively. The concentrations have been obviously lowered by existing ventilation as unventilated mines in the Long Park area have much higher concentrations of radon and its daughters. 3 The Long Park #1 Mine on Long Park Mesa, Colorado, was ventilated by a fan which supplied 1700 cfm of air to the main drift. Samples taken in a raise about 75 ft. downstream from the vent pipe showed a radon concentration of 4,600 uuc/1 and a radon daughter concentration of 1600 uuc/1. The supply of air to this working area was quite inadequate, as most of the fresh air went up the entrance shaft without passing into the rise. However, the effect of even this meager amount of ventilation was apparent when these samples were compared with those in another raise in the same ore body. This was a dead-end, isolated area with only thermal air currents present, and the radon concentration was 41,500 uuc/1 while the concentration of radon daughters was 11,500 uuc/1. On the basis of available information, it is suggested that the following ventilation procedures be included in subsequent data regarding good ventilation practice in uranium mining to reduce radon concentrations. 1.) Each uranium mine will present a special problem in ventilation due to such factors as the grade of the ore, amount of radon carried in by ground water, and exposed area. However, it is probable that 2500 cfm is a minimum amount of ventilation for a small mine. 2.) Each pair of men working in a raise, stope or small dead end raise, should be supplied 1000 cfm or more from a tube outlet located within 30 feet of the breast. 3.) A supply of not less than 2000 cfm of fresh air should be supplied to the breast of an average 8 by 10 ft. drift. (i.e., 2000 cfm was supplied the breast at King 2, Incline #2 and the radon concentration was 856 uuc/liter). 4.) In drifts of large cross section the quantity of air supply should be calculated to produce a velocity of air flow of not less than 30 fpm. 5.) Natural ventilation or uranium mines cannot be relied upon as a suitable means of removing contaminants from the working area. Information "illegible" "illegible" "illegible" Canada No uses to date "illegible" 200 "illegible 10 "illegible" AEC Good "illegible" Hardy Health & Safety Director Ore Procurement Div. -- no cooperate A.E.C. takes over -- ore shipped from mine to mill process it -- store it -- then "illegible" to "illegible "illegible" their it is stored. AEC "illegible" over health resp. No health or safety officer concerned with Div. of Ore Procurement. "illegible" it Co. in on foreign shipments not on domestic. "illegible" 1/2M in Utah.