Draft Report

ADVISORY BOARD ON RADIATION AND WORKER HEALTH

National Institute for Occupational Safety and Health

Assessment of the Metallurgical Laboratory

Special Exposure Cohort (SEC) Petition-00135

with Special Emphasis on the 250-Workday Criterion

Contract No. 200-2009-28555

SCA-SEC-TASK5-0007

Prepared by

S. Cohen & Associates

1608 Spring Hill Road, Suite 400

Vienna, VA 22182

June 2009

Disclaimer

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.
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S. Cohen & Associates: Technical Support for the 

Advisory Board on Radiation and Worker Health 

Review of NIOSH Dose Reconstruction Program

Document No. 

SCA-SEC-TASK5-0007

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Assessment of the Metallurgical Laboratory 

Special Exposure Cohort (SEC) Petition-00135 

with Special Emphasis on the 250-Workday 

Criterion

Page 2 of 50

Document Authors:

______________________ Date: ____________ 

U. Hans Behling, PhD 

______________________ Date: ____________

Kathleen Behling

Supersedes:

 N/A

Project Manager:

______________________ Date: ____________

John Mauro, PhD, CHP
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TABLE OF CONTENTS 

1.0 Introduction, Statement of Purpose, and Approach ..........................................................5

1.1 Introduction .........................................................................................................5

1.2 Statement of Purpose ...........................................................................................6

1.3 Approach and Methods ........................................................................................6

2.0 Relevant Background Information ...................................................................................7

3.0 The Need to Develop Radiation Control Standards and Protective Measures for 

Workers.........................................................................................................................10

3.1 Methods and Instrumentation Needed to Monitor Worker Exposure and 

Demonstrate Compliance with Tolerance Levels................................................11

3.2 Tolerance Levels for External Exposures ...........................................................13

3.3 Tolerance Levels for Airborne Contaminants.....................................................14

3.4 Tolerance Levels for Absorbed Radionuclides in Body ......................................14

3.5 Tolerance Levels for Urinary Excretion..............................................................15

3.6 Tolerance Levels for Ingestion or Inhalation ......................................................15

4.0 Comparison of Tolerance Levels to Current Standards...................................................17

4.1 Comparison of Tolerance Levels for External Exposures to Current 

Standards...........................................................................................................17

4.2 Comparison of Radon Tolerance Levels in Air to Current Limits.......................17

4.3 Comparison of the Radon Breath Conversion Value Used by NIOSH to that 

of the Met Lab ...................................................................................................18

4.4 Comparison of Air Tolerance Levels to Current Derived Air Concentrations 

(DACs) ..............................................................................................................18

4.5 Comparison of Inhalation/Ingestion Tolerance Levels to Current Organ 

Dose Limits .......................................................................................................18

4.6 Assessment of Tolerance Levels of Radiocontaminants in Body ........................19

4.7 Assessment of Tolerance Levels of Po-210 in Urine...........................................20

5.0 Evidence of Potentially High Exposures and/or Exposures in Excess of Established 

Tolerance Levels ...........................................................................................................22

5.1 Examples of External Exposures in Excess of Tolerance Levels.........................22

5.2 Potentially High External Exposures Associated with the Operation of CP-1 .....23

5.3 Air Sampling Data/Inspection Reports...............................................................24

5.4 Pu Contamination Surveys of Workers’ Residences ...........................................26

5.5 Plutonium in Fecal Samples...............................................................................32

5.6 Changes in Blood Composition ..........................................................................33

6.0 Discussion and Summary Conclusions...........................................................................34

6.1 Description of the Y-12 Accident.......................................................................36

6.2 Hematological Findings in Behalf of Eight Workers...........................................36

6.3 Estimates of Acute Doses to the Lower-Exposed Group.....................................38

7.0 References.....................................................................................................................39

Appendix A – Transcript of Advisory Board Meeting held on February 19, 2009......................42

Appendix B – March 26, 2009, Memo from Designated Federal Official ..................................50
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LIST OF TABLES

Table 1. Tolerance Levels for Neutron Flux by Energy..........................................................14

Table 2. Comparison of Tolerance Levels with Current Regulatory Values for 

Neutron Exposures...................................................................................................17

Table 3. Comparison of Air Tolerance Levels to Current DAC Values ..................................18

Table 4. Select Organ Doses Resulting from a One-Time Body Burden of 0.1 μg 

(or 0.1 μCi) of Ra-226 (Type M) as a Function of Time* .........................................20

Table 5. Select Organ Doses Resulting from an Acute Exposure and Ingestion Exposure 

that Yielded a Transient Absorbed (Body Burden) of 673 μCi of Po-210 

(Type M; f1 of 0.1) ..................................................................................................20

Table 6. Select Organ Doses Resulting from a One-Time Body Burden of 1.0 μg 

(or 6.13 × 10-2μCi) of Pu-239 (Type S) as a Function of Time*...............................20

Table 7. Organ Doses Corresponding to a Steady-State Po-210 Urine Excretion Rate of 

5,000 dpm/24-Hours for a 6-Month Exposure Period ...............................................21

Table 8. Lung Doses Associated with Acute Inhalation Exposure of Plutonium as 

Evidenced by a Positive Fecal Sample* ...................................................................32

Table 9. Original Doses Assigned to Workers F, G, and H.....................................................38

Table 10. Dose Equivalent Estimates for Y-12 Workers F, G, and H .......................................38

LIST OF FIGURES

Figure 1. Artist Depiction of First Sustained Nuclear Chain Reaction by CP-1..........................9

Figure 2. Survey Instrument Developed at the Metallurgical Laboratory.................................13

Figure 3. Hematologic Effects for Five Y-12 Workers A, B, C, D, and E................................37

LIST OF EXHIBITS

Exhibit 1. Tolerance Amounts for Ingestion, Inhalation, and Maximum Permissible 

Concentrations in Air...............................................................................................16

Exhibit 2. Portable Radiation Instruments Used at Met Lab......................................................24

Exhibit 3. Air Sampling Data from Room 11 ...........................................................................25

Exhibit 4. Survey of Worker A’s Apartment ............................................................................27

Exhibit 5. Survey of Worker B’s Apartment.............................................................................28

Exhibit 6. Survey of Worker C’s Apartment.............................................................................29

Exhibit 7. Zeuto Alpha Survey Meter.......................................................................................31

Exhibit 8. Metallurgical Project Personnel ...............................................................................35
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1.0 INTRODUCTION, STATEMENT OF PURPOSE, AND APPROACH

1.1 INTRODUCTION

On December 9, 2008, the National Institute for Occupational Safety and Health (NIOSH) issued 

its Evaluation Report (ER) of the Special Exposure Cohort (SEC) Petition SEC-00135 for the 

Metallurgical Laboratory (Met Lab) in Chicago, Illinois. The ER concluded the following:

NIOSH lacks sufficient information, which includes specific biological monitoring 

data, sufficient air monitoring information, or sufficient process and radiological 

source information, to allow it to estimate with sufficient accuracy the potential 

internal and external exposures to plutonium, radium, fission products, uranium, 

and uranium progeny to which the proposed class may have been subjected.

The NIOSH-proposed class includes all Atomic Weapons Employer (AWE) employees who 

worked at the Met Lab from August 13, 1942, through June 30, 1946, for a number of 

workdays aggregating at least 250 workdays occurring either solely under this employment, or 

in combination with workdays with the parameters established for one or more other classes of 

employees in the SEC.

An exception to the 250-workday requirement is provided in 42 CFR 83.13(c)(3)(i), which states 

the following:

For classes of employees that may have been exposed to radiation during discrete 

incidents likely to have involved exceptionally high level exposures, such as 

nuclear criticality incidents or other events involving similarly high levels of 

exposures resulting from the failure of radiation protection controls, NIOSH 

will assume for the purposes of this section that any duration of unprotected 

exposure could cause a specified cancer, and hence may have endangered the 

health of members of the class. Presence with potential exposure during the 

discrete incident, rather than a quantified duration of potential exposure, will 

satisfy the health endangerment criterion. [Emphasis added.]

During an Advisory Board (or Board) Meeting in Albuquerque, New Mexico, on February 19, 

2009, there was a brief discussion regarding the overall applicability of the 250-workday 

criterion for the Met Lab SEC class eligibility. Enclosed herein as Appendix A are pages 55–62 

of the recorded transcript that relate to the 250-workday issue, along with the Board’s directive 

for S. Cohen and Associates (SC&A) to look into this matter.

The Board’s directive to SC&A was followed up by a request by Mr. Ted Katz, the Designated 

Federal Official, in a memorandum dated March 26, 2009, which is included herein as 

Appendix B.

Based on statements contained in Appendices A and B, the Board and NIOSH agreed on the 

following issues:
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(1) There were a substantial number of workers at Met Lab who were there for less than 250 

workdays.

(2) Operation of Chicago Pile Number One (CP-1) was a planned event and not an 

uncontrolled critical event/operation.

(3) In addition to the startup and operation of CP-1 as a plutonium production reactor, 

however, the Met Lab was engaged in numerous other radiochemical operations, which is 

why NIOSH established the SEC class in the first place.

(4) SC&A was directed to review and assess the OCAS Evaluation Report along with other 

available information in context with the SEC’s 250-workday criterion.

1.2 STATEMENT OF PURPOSE

The purpose of this report is to provide a preliminary assessment of the Office of Compensation 

Analysis and Support (OCAS) ER and related materials, which, in turn, may provide the 250-day 

Work Group with specific topics for future discussions/decisions regarding the applicability of 

the 250-workday criterion for the Met Lab and possibly other AWE facilities.

1.3 APPROACH AND METHODS

In addition to the SEC-00135 ER, SC&A reviewed more than five-hundred separate documents/ 

reports that were listed in behalf of the Met Lab in NIOSH’s Site Research Query Database 

(SRDB). Our review of these and other documents focused on potential information/data 

regarding the following:

Source term data and processes at the Met Lab

Personnel staffing/employment periods

Existing knowledge regarding radiological risks from external and internal radiation

Existing regulations/standards/protocols for limiting worker exposures to external and 

internal radiation

Available instrumentation and methods used to monitor workers for external and internal 

exposures

Personnel monitoring data for external and internal exposures

Radiological incidents and evidence of acute high-dose external and internal exposures

Presented in the sections that follow are excerpts in the form of quotations and exhibits from 

select SRDB documents that address each of these topics. Whenever a relevant section of a 

SRDB document is sufficiently brief, it is also enclosed herein as an exhibit.
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2.0 RELEVANT BACKGROUND INFORMATION

The Met Lab consisted of seven locations that were part of the University of Chicago campus. 

Under contract with the University, the Met Lab officially began operation on August 13, 1942,

under the direction of the Manhattan Engineer District (MED). The primary goal for the Met 

Lab was the design, construction, and operation of the world’s first nuclear reactor for the 

purpose of producing plutonium. The “Chicago Pile Number One,” or CP-1, was crudely 

constructed in an abandoned squash court under the west grandstand of the University’s Stagg 

field. Enrico Fermi, the project’s director, described CP-1 as “a crude pile of black bricks and 

wooden timbers” (CP-1 2008, SRDB Ref. ID 42824).

SRDB Ref. ID 43013 (DOE 2008), entitled The Manhattan Project: CP-1 Goes Critical,

provides the following description of CP-1 and the first sustained nuclear chain reaction: 

...The wooden timbers supported a lattice structure that contained over six tons 

of pure uranium metal, along with 34 more tons of uranium oxide. The almost 

400 tons of black bricks in the assembly were graphite, placed there to serve as 

moderators; the bricks in two of every three layers had a nodule of uranium 

inside each of them. The presence of so much "moderating" material might have 

sounded comforting to outsiders until they learned that the moderators were there 

to increase the amount of fission produced by the uranium. The only things 

preventing a fission chain reaction from growing within the pile were a series of 

cadmium rods inserted into the pile's side to absorb the free neutrons emitted by 

the radioactive uranium. Unlike most reactors that have been built since, this

first one had no radiation shielding and no cooling system of any kind. Fermi 

had convinced Arthur Compton that his calculations were reliable enough to rule 

out a runaway chain reaction or an explosion, but, as the official historians of the 

Atomic Energy Commission later noted, the "gamble" remained in conducting "a 

possibly catastrophic experiment in one of the most densely populated areas of 

the nation!"

Daily the pile grew, brick by brick. Tests on the early afternoon of December 1st 

indicated that it was very close to being ready. By that evening, the scientists

present were convinced that if they withdrew the cadmium control rods the fission 

chain reaction in the pile would be self-sustaining. Final preparations for the 

first test began. The next morning most of the observers found themselves 

crowded together onto a balcony where squash spectators had once stood, ten 

feet above the floor on the north end of the room [see Figure 1]. Fermi, Compton, 

Walter H. Zinn, and Herbert L. Anderson were grouped around an instrument 

console at one end of the balcony; from there they could operate one set of 

control rods. The only person on the floor of the squash court was George Weil, 

the man who would physically withdraw the final control rod. If the reaction 

threatened to grow out of control, Weil could re-insert his control rod, and an 

automatic control rod would also insert itself if the reaction reached a certain 

pre-set level. In case of emergency, such as Weil becoming incapacitated or 
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failure of the automatic control rod, Norman Hilberry stood on the balcony with 

an improbable nuclear safety device: an axe.

In an emergency, he would cut a rope that ran up to the balcony, releasing 

another emergency control rod into the pile. The last line of defense consisted of 

a "liquid-control squad" that stood on a platform, ready to flood the pile with a 

cadmium-salt solution. Taken together, these safety precautions were a strange 

combination of the high-tech and the ad hoc.

After rehearsals, Fermi at 9:54 a.m. ordered the electrically-operated control 

rods removed. All eyes turned to the array of instruments indicating the pace of 

the fission reaction within the pile. Shortly after 10:00, Fermi ordered the

emergency control rod removed and tied to its rope. At 10:37, Fermi ordered 

Weil to pull all but thirteen feet of the final rod out of the pile. The pace of the 

audible clicking from the neutron counters (similar to Geiger counters) increased. 

Over the next few hours, the pile inched its way toward criticality, Weil gradually 

removing more and more of the final rod while Fermi monitored his array of

instruments. ...At 11:25, Fermi ordered the automatic and emergency control

rods reinserted for a final safety check. Ten minutes later, these were both 

removed in order for the experiment to resume. The neutron counters 

immediately resumed their clicking, the pace growing and growing until a 

sudden "whrrrump!" filled the room. The automatic control rod had slammed 

home into the pile, having been set too low during the safety check. While

everyone present took a few deep breaths, Fermi calmly called for lunch.

By 2:00 p.m., everyone had resumed their places. Fermi resumed the slow 

process of inching toward criticality, more and more of the control rod appearing 

as Weil slowly withdrew it from the pile. Finally Fermi said to Compton "this is 

going to do it. Now it will become self-sustaining." ...By this time, the clicketyclick of the neutron counter had become a steady hum, too fast for the ear to 

count. At 3:25 p.m., Weil slid the rod back one more time. As Fermi completed 

one final calculation, his face broke into a broad smile and he announced "the 

reaction is self-sustaining." ...

Following 28 minutes of operation, at 3:53 p.m. Fermi ordered the emergency 

control rod replaced. [Emphasis added.]

Operation of CP-1 was terminated in February 1943, and the nuclear reactor was dismantled and 

moved to the Argonne National Laboratory, where it was reconstructed as CP-2. CP-2 began 

operation in March of 1943 for continuing research on reactor designs that led to the large 

production reactors at Hanford. These produced plutonium needed for the bombs tested at the 

Trinity site and employed in World War II in Nagasaki.
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Figure 1. Artist Depiction of First Sustained Nuclear Chain Reaction by CP-1
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3.0 THE NEED TO DEVELOP RADIATION CONTROL STANDARDS 

AND PROTECTIVE MEASURES FOR WORKERS

Before the first sustained nuclear chain reaction was demonstrated on December 2, 1942, 

radiation source terms and human exposures were largely limited to x-ray machines and radium 

sources (along with their radioactive daughter products). The introduction of the nuclear reactor, 

therefore, introduced unprecedented radiological hazards associated with exposures to neutrons, 

fission products, and activation products, whose potential health effects from external or internal 

exposure had never been studied.

Because of these uncertain dangers, Dr. A.H. Compton, who was head of the Metallurgical 

Project, considered it expedient to establish a separate Health Division, along with the Physics, 

Chemistry, and Technical Division (Stone 1945). In turn, the Health Division was organized 

into the following three separate lines of responsibilities:

(1) The Medical Section conducted human clinical tests with terminally ill patients, and 

provided routine blood and urine examinations of workers.

(2) The Biological Research Section conducted animal studies on the effects of alpha, beta, 

gamma, and neutron radiation from external sources or internally from the ingestion, 

inhalation, or trancutaneous assimilation of fission products, plutonium, polonium, and 

uranium.

(3) The Health Physics Section was tasked with developing new instrumentation that could 

be used to qualify and quantify workplace radiation fields and monitor workers for 

external and internal exposures.

Early emphasis of establishing exposure limits by the Biological Research Section of the 

Plutonium Project was based on “tolerance levels” for external radiation, as well as for internal 

exposures, as described by Dr. Robert Stone, Associate Project Director for Health of the 

Metallurgical Project, in a 1945 report (Stone 1945):

When the Health Division of the Plutonium Project was called into existence in 

1942 there were established tolerance doses, or maximum permissible exposures, 

for x- and gamma-rays, but it was evident that these rested on rather poor 

experimental evidence. There was little knowledge of the tolerance for fast 

neutrons, and none for slow and thermal neutrons, or for alpha or beta rays. 

Except for radiophosphorus and radiostrontium nothing was known of 

tolerances of artificial radioactive materials in the body and the knowledge of 

these two was sparse. Comparatively little was known even about radium which 

had caused considerable havoc among radium dial painters. Consequently while 

the hazards were being estimated, experiments were started to check the 

calculations and to determine the behavior in the body of the multitudinous 

radioactive isotopes that were to be created. [Emphasis added.]
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The term “tolerance level” was generally defined as that amount of exposure below which 

deleterious health effects were unlikely. However, deleterious health effects for consideration 

were largely those currently defined as non-stochastic effects that principally included changes 

in the cell composition of the peripheral blood. Other indicators included changes in urine 

constituents, and even changes to or loss of fingerprint patterns that may have resulted from beta 

radiation to the hands.

3.1 METHODS AND INSTRUMENTATION NEEDED TO MONITOR WORKER 

EXPOSURE AND DEMONSTRATE COMPLIANCE WITH TOLERANCE 

LEVELS

The term “Health Physics” was first introduced by the MED to define that discipline in which 

physical methods are used to determine the hazards to the health of personnel. In a 1945 report 

entitled Health Protection Activities of the Plutonium Project, Dr. Robert Stone, Associate 

Project Director for Health of the Metallurgical Project, stated the following (Stone 1945, SRDB 

Ref ID 7693):

 On the Use of Pocket Ionization Chambers (PICs) (pp. 7–10):

Before the war such hazards as existed were relatively easily controlled. The 

most wide-spread ones existed in those locations where x-rays and radium were 

used for medical purposes. In most cases the radiation sources were fixed and 

protection was built-in...

In 1942 when the Health-Physics section was organized, there was still no pile. 

There were no accumulations of extremely radioactive fission products...

It was realized that with a new industry working in unexplored fields with new 

equipment, it would probably be impossible to keep all possible sources of 

radiation behind sufficient shielding. ... Hence it was necessary to set up 

personnel monitoring such that some measurement of the amount of radiation 

reaching each individual could be made. There were in the market at the time of 

the beginning of this project a few small ionization chambers that were shaped 

like fountain pens and could be worn in the pocket.

... These instruments are satisfactory for measuring x-rays with an energy of 

about 200 kv, but the calibration is not entirely accurate for gamma rays. ... A 

great deal of difficulty was found with the— the principle was simple enough,

but the application was somewhat complicated. ... these instruments were 

useless for quantitative measures of beta rays, weak x-rays and neutrons.

[Emphasis added.]

On the Use of Film Dosimeters (pp. 10–11):

The photographic film method of registering exposure to radiation has long been used. 

Films have varying responses to rays of different energies and therefore are impossible 
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to calibrate for rays of all energies and types. ... [however] after many trials a 

reasonably satisfactory film meter was evolved. ... These films thus acted as a good 

check against the pocket ionization meters and those who were routinely exposed had to 

carry both kinds of meters.

 On the Use of Instruments (pp. 11–14):

... special apparatus had to be developed for rapidly measuring hands and shoes 

in such a way as to indicate whether dangerous amounts of material were 

present. Geiger-Mueller counters, scaling circuits and registers are used in such 

a way that the fronts and backs of both hands and the soles of the feet are placed 

in a fixed geometry and counted for an automatically controlled time.

... In addition to ionization chambers, Geiger-Mueller counters and proportional 

counters were used in the work area monitoring, and some warning instruments 

were placed to detect people with contaminated clothes.

Since it was impossible to have fixed monitoring at all points in all buildings, 

routine surveys of benches, desks, floors, sinks, hoods, etc., were necessary. A 

group of people had to be specially trained for this job of surveying. Instruments 

were developed for measuring the alpha radiations for surfaces, the beta and

gamma radiations and the radioactive materials in the air. Survey instruments of 

these kinds had not been needed on any such scale before and hence had to be 

developed before they could be used. This in itself was a tremendous problem.

If anyone should wonder how contamination could get around to such an extent 

as to indicate a need for such surveys, let him think how small a droplet of a 

saturated solution of radium chloride it would take to contaminate a whole 

laboratory, and then image working with beakers, tubs and vats full of similar 

material. 

Instrument development problems that faced the Health-Physics section were 

numerous and were not all solved, because it was felt that if we could with 

reasonable assurance keep the radiations in working areas down to low levels 

that the talents of those capable of developing such instruments would be better 

applied to instruments for the operation and control of piles and chemical 

extraction plants.

... Many problems have not been solved, or solved only in a crude way. The 

measuring of fast, slow and thermal neutrons and of alpha radioactive materials, 

in terms that will indicate their effectiveness on living tissue, is still in the 

development stage. ... [Emphasis added.]

One instrument developed at the Met Lab was the Zeus by W. P. Jesse in 1945. It was an 

ionization chamber with a sliding thin aluminum or plastic shield over the 5” × 6” detector 

window located on the bottom of the unit for measuring alpha, beta, and gamma, as shown in 

Figure 2 below. 
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Zeus Mark 1, Model 21-A 1945

Figure 2. Survey Instrument Developed at the Metallurgical Laboratory

3.2 TOLERANCE LEVELS FOR EXTERNAL EXPOSURES

For external photon exposure, the MED adopted the value of 0.1 R per day (or 30 R/year), 

which had previously been identified by the National Bureau of Standards in Handbook 20

(NCRP 1936). For persons handling uranium, beta radiation to the skin of the hands was limited 

to 0.5 R/day (or 150 R/yr). 

The tolerance level of 0.1 R per day (or 30 R/year) also became a reference value for other 

types of radiation (including external and internal sources that emitted neutrons, protons, and 

alpha particles). Because it was recognized that for a given dose, high-linear energy transfer 

(LET) radiation posed greater hazards than photons, the tolerance levels for neutrons (and alpha 

radiation) were adjusted to reflect their relative biological effectiveness.

For neutrons (and alpha particles), the higher LET values reduced the daily photon exposure 

value of 0.1 R/day to 0.025 Roentgen Equivalent Physical (REP). Implicit in this tolerance 

level for external neutrons was a quality factor of 4. 

Based on LET considerations and calculated on the energy required per ion pair, the MED

derived the following theoretically derived tolerance levels for neutron exposure, as defined in 

Table 1:
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Table 1. Tolerance Levels for Neutron Flux by Energy

(Source: Wirth 1945)

Fast Neutrons (3 MeV to 0.5 MeV)

3 MeV: 200 η/cm2/sec

2 MeV: 200 η/cm2/sec

1 MeV: 250 η/cm2/sec

0.5 MeV: 360 η/cm2/sec

Slow Neutrons (0.5 MeV to 0.1 eV)

0.5 MeV: 360 η/cm2/sec

0.1 MeV: 1,000 η/cm2/sec

<0.3 eV: 2,500 η/cm2/sec

Thermal Neutrons (0.1 eV to 0.01 eV)

0.1 eV: 15,000 η/cm2/sec

0.03 eV: 25,000 η/cm2/sec

3.3 TOLERANCE LEVELS FOR AIRBORNE CONTAMINANTS

For tolerance levels of airborne contaminants, the MED selected radon levels of 100 pCi/l, 

which represented one-tenth of the exposure that was thought to have produced harmful effects 

of Czechoslovakian miners. For Po-210, a tolerance level of 5 × 10-4 micrograms per cubic 

meter (or 2.245 μCi/m3) was derived from animal data. For plutonium, an air concentration 

tolerance level of 0.35 μCi/m3 was adopted, which was based purely on computational 

comparisons of radiation emissions between plutonium and radium. (At the time, it was 

assumed that radium per unit activity was 10 times more hazardous than plutonium.) And 

for uranium (assumedly natural uranium), the MED assigned a tolerance level of 150 μg per 

cubic meter of air (or 1 × 10-5μCi/m3) (USERDA 1946, Bonsib 1942).

3.4 TOLERANCE LEVELS FOR ABSORBED RADIONUCLIDES IN BODY

For tolerance levels of radioactive contaminants in the body/tissues, tolerance levels for 

absorbed quantities of select radionuclides were based on animal data and extrapolation to man. 

The MED established the following radionuclide-specific tolerance levels (i.e., permissible body 

burdens):

Radium: 0.1 μg (or ~0.1 μCi)

Polonium: 0.15 μg (or 673 μCi)

Plutonium: 1.0 μg (or 6.13 × 104pCi)
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3.5 TOLERANCE LEVELS FOR URINARY EXCRETION

For urinary excretion, tolerance levels had been established only for polonium at 5,000 dpm 

for a 24-hour urine volume.

3.6 TOLERANCE LEVELS FOR INGESTION OR INHALATION

Lastly, tolerance amounts for the ingestion or inhalation and the maximum permissible

concentrations in air that can be breathed without exceeding the tolerance concentrations in a 

specified tissue [i.e., bone (B), lung (L), thyroid (T), and external whole body (E)] were derived 

for mixed fission products, strontium, iodine, and xenon, as shown in Exhibit 1. Important to 

note is that tolerance levels were not only specified for continuous daily intakes/exposure, but 

also for a single 1-day intake/exposure. For example, as much as 135 μCi of I-131 could be 

inhaled or ingested in a single day as a “one-time” tolerable intake.
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Exhibit 1. Tolerance Amounts for Ingestion, Inhalation, and Maximum Permissible 

Concentrations in Air 

(Source: Radiation Standards, undated, SRDB Ref ID: 40381)
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4.0 COMPARISON OF TOLERANCE LEVELS TO CURRENT 

STANDARDS

Tolerance levels established in behalf of Met Lab workers and others were based on limited 

scientific data that over the past 60-plus years have exponentially increased and revised our 

understanding of the dose response relationship with regard to human health risks. Perhaps 

equally significant was the shift from tolerance levels associated with non-stochastic effects to 

regulatory standards that are largely based on stochastic health risks. As summarized below, 

current exposure limits are well below those of tolerance levels applicable to Met Lab workers.

4.1 COMPARISON OF TOLERANCE LEVELS FOR EXTERNAL EXPOSURES TO 

CURRENT STANDARDS

For penetrating whole-body photon exposures, the tolerance levels of 0.1 R/day (or 30 R/yr) is 

approximately 6 times the current yearly regulatory dose limit of 5 rem.

For skin exposures to the extremities from betas, the 0.5 R/day (or 150 R/yr) is about 3 times the 

current regulatory limit of 50 rem/yr.

Table 1 in Section 3.2 cited neutron flux values by energy that were considered tolerance values 

for continuous neutron exposures. Table 2 compares these values to current regulatory values 

defined by the Nuclear Regulatory Commission (NRC)/Department of Energy (DOE). On 

average, tolerance values permitted workers to be exposed to neutron flux dose equivalents that 

were more than 10 times the current values given in the last column of Table 2.

Table 2. Comparison of Tolerance Levels with Current Regulatory Values for 

Neutron Exposures

Neutron Energy Tolerance Levels 

(η/cm2/sec)

Current Standards*

(η/cm2/sec)

Tolerance Level/ 

Current Standard

3 MeV 200 20 10

2 MeV 200 20 10

1 MeV 250 18 14

0.5 MeV 360 30 12

0.1 MeV 1,000 80 12

0.3 eV 2,500 670 4

0.1 eV 15,000 670 22

0.03 eV 25,000 670 37

* Current values are flux values corresponding to 100 mrem per 40 hours or 

5,000 mrem/2,000 workhours.

4.2 COMPARISON OF RADON TOLERANCE LEVELS IN AIR TO CURRENT 

LIMITS

Section 3.3 identified a tolerance level of 100 pCi/liter of air for radon for continuous exposure. 

This value was specified without consideration to the equilibrium fraction between radon and its 

short-lived daughter products.
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If radon is assumed to be in full equilibrium with its short-lived progeny, continuous exposure at 

100 pCi/l is about 3 times the current exposure limit of 4 working level months per year 

(4 WLM/yr). At 50% equilibrium, the tolerance level is 1.5 times the current limit.

4.3 COMPARISON OF THE RADON BREATH CONVERSION VALUE USED BY 

NIOSH TO THAT OF THE MET LAB 

An assessment of radium body burden by means of radon breath analysis requires a conversion 

factor by which the activity of Rn-222 in exhaled air is converted to activity of Ra-226 in the 

body. By means of experimental data and their interpretation, Met Lab personnel derived a 

conversion value of 1 pCi/l of radon in exhaled air to correspond to 0.1 microgram (or ~0.1 μCi 

or 1 × 105pCi) of Ra-226 in the body (Tybout 1945).

The Met Lab conversion factor is 2.52 times lower than the conversion factor assumed/employed 

by NIOSH, as given in ORAUT-OTIB-0025 (ORAUT 2005). OTIB-0025 cites a conversion 

value of 252,000 pCi of Ra-226 in body for each pCi/l of radon in exhaled air. In brief, the Ra226 body burden of Met Lab workers assessed by radon breath analysis would have been 

underestimated by a factor of 2.52.

4.4 COMPARISON OF AIR TOLERANCE LEVELS TO CURRENT DERIVED AIR 

CONCENTRATIONS (DACs)

When compared to present-day derived air concentration (DAC) values, the air tolerance levels

for continuous 8-hour per day exposure levels varied dramatically, as shown in Table 3. Because 

uranium was regarded as primarily a chemical toxin, the ratio between the tolerance level and 

DAC was lowest at 2. Most serious discrepancies between tolerance levels and DACs were for 

Po-210 and Pu-239/240, which differed by factors of 7,483 and 50,000, respectively.

Table 3. Comparison of Air Tolerance Levels to Current DAC Values

Radioelement Tolerance Level 

(μCi/m3)

DAC (μCi/m3)

Ratio of

Tolerance Level/DAC

Sr-90 1.6 × 10-22 × 10-38

I-131 0.3 2 × 10-215

Po-210 2.245 3 × 10-47,483

U-238/234 1 × 10-52 × 10-52

Pu-239/240 0.35 7 × 10-650,000

4.5 COMPARISON OF INHALATION/INGESTION TOLERANCE LEVELS TO 

CURRENT ORGAN DOSE LIMITS

Of significance to inhalation ingestion tolerance levels, as shown in Exhibit 1, are quantities of 

radionuclides that could be either inhaled or ingested on a “one-time” basis, with the assumption 

that no additional intake would be permitted for a 1-year period.
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For example, Exhibit 1 shows a maximum air concentration of 0.028 μCi/l of I-131 that a person 

may breathe for 8 hours as a one-time inhalation exposure. This air concentration converts to a 

total inhalation of 269 μCi of I-131.

Inhalation of I-131 (μCi/day) = (0.028 μCi/l)(1000l/m3)(1.2 m3/hr)(8 hr/day)

= 269 μCi

By means of the Environmental Protection Agency (EPA) dose conversion factor of 

1.08 rem/μCi inhaled (EPA 1988), the one-time inhalation of 269 μCi of I-131 translates to a 

thyroid dose of 290 rem that is delivered over about a 1-month period.

Equally, Exhibit 1 shows that an individual may continuously breathe air levels of 0.0003 μCi/l 

of I-131 (or 0.3 μCi/m3). For a year consisting of 2,000 work-hours and a breathing rate of 

1.2 m

3

/hr, the annual tolerance intake of 720 μCi of I-131 is estimated, which yields an annual 

thyroid dose of 777 rem.

These values must be compared to the current regulatory limit of 50 rem to the thyroid.

4.6 ASSESSMENT OF TOLERANCE LEVELS OF RADIOCONTAMINANTS IN 

BODY

The Manhattan District History, Book I, Volume 7, Medical Program (USERDA 1946), stated 

the following on page 2.12:

It is obvious that people working with these radioactive substances would 

inadvertently ingest and inhale these substances to some degree. It was 

necessary, therefore, as an additional precautionary measure, to monitor the 

personnel to make certain that they had not accumulated more than the maximum 

allowable concentration of these substances in their body tissues. Tolerance 

levels for absorbed quantities of these radioactive materials were therefore 

derived from animal experimentation and extrapolated from these values to 

man... [Emphasis added.]

As summarized in Section 3.4, the MED defined tolerance body burdens for radium, polonium, 

and plutonium of 0.1 μg (or 0.1 μCi), 0.15 μg (or 673 μCi), and 1.0 μg (or 6.13 × 10-2μCi), 

respectively.

By assuming a body burden defined by these tolerance levels for even a brief period of time, 

SC&A derived the following organ doses by means of IMBA (Integrated Modules for Bioassay 

Analysis), as shown in Tables 4, 5, and 6.

Inspection of Tables 4, 5, and 6 shows that even the transient absorbed quantities (or body 

burdens of tolerance levels) of Ra-226, Po-210, and Pu-239 yield organ doses in the tens, 

hundreds, and thousands of rem. Because tolerance levels were not restricted by a duration of 

exposure, derived organ doses in Tables 4, 5, and 6 could, therefore, be the result of a single 

acute exposure event.
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Table 4. Select Organ Doses Resulting from a One-Time Body Burden of 0.1 μg 

(or 0.1 μCi) of Ra-226 (Type M) as a Function of Time*

Year Organ Doses (Rem)

Lung Bone Surface RBM

1 293 23 2.6

5 302 63 7.2

10 302 96 10.1

20 302 123 11.3

 * The body burden of 0.1 μCi was the result of an acute inhalation exposure as determined by a WBC.

Table 5. Select Organ Doses Resulting from an Acute Exposure and Ingestion 

Exposure that Yielded a Transient Absorbed (Body Burden) of 673 μCi of Po-210 

(Type M; f1 of 0.1) 

Year Organ Doses (Rem)

Lung Bone Surface RBM

1 32,280 63,400 2660

5 32,833 63,464 2661

10 32,833 63,646 2661

Table 6. Select Organ Doses Resulting from a One-Time Body Burden of 1.0 μg

(or 6.13 × 10-2μCi) of Pu-239 (Type S) as a Function of Time*

Year Organ Doses (Rem)

Lung Bone Surface RBM

1 124 0.4 2.9

5 177 5.2 6.5

10 193 14.3 8.3

20 205 35.7 10.5

* The body burden of 6.13 × 10-2

μCi of Pu-239 was the result of an acute inhalation exposure as 

 determined by a chest count.

4.7 ASSESSMENT OF TOLERANCE LEVELS OF Po-210 IN URINE

Until December 31, 1946, the MED defined tolerance values for uranium excretion for only 

Po-210 at 5,000 dpm in a 24-hour urine sample.

Under a steady-state of daily urine excretion of 5,000 dpm representing a 6-month inhalation or 

ingestion exposure period, SC&A derived the following organ doses using IMBA.

Inspection of Table 7 shows that for a 6-month exposure to Po-210 that resulted in a steady-state 

excretion rate of 5,000 dpm per day, organ doses as high as 1,500 rem would have resulted.
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Table 7. Organ Doses Corresponding to a Steady-State Po-210 Urine Excretion Rate 

of 5,000 dpm/24-Hours for a 6-Month Exposure Period

Organ Cumulative Dose (Rem)

1 Year 2 Year 3 Year

Inhalation

 Lung 1,581.00 1,590.25 1,590.42

 Kidneys 209.30 215.85 215.95

 LLI 108.10 111.48 111.54

Ingestion

 Liver 101 102 102

 Kidneys 196 198 198

 LLI 8.25 8.25 8.25
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5.0 EVIDENCE OF POTENTIALLY HIGH EXPOSURES AND/OR 

EXPOSURES IN EXCESS OF ESTABLISHED TOLERANCE 

LEVELS

Our review of the more than 500 reports/documents identified in the SRQD for the Met Lab 

largely confirmed the fact that available individual monitoring data are insufficient for dose 

reconstruction, as concluded by NIOSH in the Petition SEC-00135 ER.

However, among some of the reports reviewed, there exists a substantial number of documented 

incidents in which Met Lab personnel either received doses in excess of tolerance levels or were 

exposed to radiological conditions that are of relevance to the 250-day criteria. Presented below 

are examples of such incidences.

5.1 EXAMPLES OF EXTERNAL EXPOSURES IN EXCESS OF TOLERANCE 

LEVELS

From Nickson 1943: Notes of Meetings in Regard to Radiation Hazards of Project Personnel, 

dated October 28, 1943, the following statements appear:

In this meeting some of the hazardous points on the Project were discussed. By 

and large the hazards referred to were those of radiation. ... [Employee’s]

group was discussed. It was discovered that a total of 5 grams of radium was in 

their possession... Examination of [this group’s] badge reading for the past six 

weeks on these individuals showed some had exceeded 0.6 r during any week ... 

[Employee X] has recently started work in a room in Ryerson with a 1 gram 

source. [The employee’s] last recorded [blood] count is 9-28-43 at which time 

[the employee’s] white blood count was 6700, with no abnormalities of the reds 

or differential. [The employee’s] hemoglobin is 13.5 grams. An interview with 

[the employee] revealed that [the employee’s] source to date with which [the

employee] has done a little work, is inadequately shielded, so much so that a 

tolerance dose is received in the room above which [the employee] is working, 

in two hours. The problem of more adequate shielding for both [employee] and 

those in the room above [the employee] has been considered and is at present 

being constructed. However, in the course of [the employee’s] problem [the 

employee] will be required to move the source from the experimental apparatus 

to a place of adequate storage several times a day. At present [the employee] is 

planning to move the source with an arrangement which does not get it more than 

arm’s length from [the employee’s] body. The question of devising and using 

tongs has been discussed with [employee]. [The employee] agreed to do so. It 

was pointed out to [the employee] that with [the employee’s] present procedure 

it can be calculated that [the employee’s] body will receive on the order of an r 

for each removal from the apparatus or from its place of storage.

In view of the nature of [the employee’s] experiments and in view of the 

inadequate shielding at present it is my feeling that [Employee X] should 
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receive weekly white counts, differentials, platelet counts, and total counts 

including a reticulocyte count along with the above every two weeks.

... [Employee] is known to have been working with a hot solution... and it was revealed 

[the employee’s] so-called dirty room, in which highly active materials were kept, is now 

being revised with the installation of a lead safe ... [Emphasis added.]

These statements suggest that “Employee X” was expected to move a 1-gram radium source 

several times in a single day. This would have resulted in an external exposure of several 

roentgens in a single day. Lesser doses of 100 mR every 2 hours would also have been received 

by personnel working in the room above.

5.2 POTENTIALLY HIGH EXTERNAL EXPOSURES ASSOCIATED WITH THE 

OPERATION OF CP-1

Although SC&A found no specific data regarding external photon and neutron dose rates/

exposures associated with the operation of CP-1, a search regarding instrumentation developed 

and employed during the early period of the Manhattan Project cited the need for instruments 

capable of measuring the very high dose rates with open experimental ports in the pile to which 

scientists/engineers may have inadvertently exposed themselves, as noted in Exhibit 2 and 

quoted below.

... It turned out that the scientist and engineers were so interested in their work 

that they often overlook the radiation hazard. Uranium, which is used in the 

piles, was not very radioactive. However, when irradiated it produced fission 

products and plutonium, which cause a more series [sic] radiation hazard. It was 

also noted that a worker walking by an experimental hole in the pile would not 

suffer an immediate reaction, but could receive a high dose which would show 

up a few days later. [Emphasis added.]
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Exhibit 2. Portable Radiation Instruments Used at Met Lab

Zeuto 1940s

The Oak Ridge pile at the Clinton Engineer Works (later became the Oak Ridge National Laboratory) began 

operating on November 2, 1943. It turned out that the scientist and engineers were so interested in their work that 

they often overlook the radiation hazard. Uranium, which is used in the piles, was not very radioactive. However, 

when irradiated it produced fission products and plutonium, which cause a more series radiation hazard. It was also 

noted that a worker walking by an experimental hole in the pile would not suffer an immediate reaction, but could 

receive a high dose which would show up a few days later. As such, instrumentation needed to be developed that 

could measure higher and higher exposure rate levels. The exposure rate levels were increasing rapidly from mR/h 

from basic studies to 100's or 1,000's of R/h for fission products in plutonium production reactors.

5.3 AIR SAMPLING DATA/INSPECTION REPORTS

Uranium metal production was a major part of the Manhattan Project. In order to determine the 

potential hazards in the handling of materials, various facilities linked to the Project were visited 

and evaluated regarding worker safeguards, as described in a December 1942 report (Bonsib 

1942). In behalf of the Met Lab, the report provided the following observations: 

Practically all of the work in the shops and laboratories visited is concerned with 

the metal. The shop in Eckhart Hall is in the basement and is very crowded. The 

ventilation, which is dependent solely upon any air that might come through or 

around tightly closed windows and a single door, is exceedingly bad. It is urgent

that this shop be moved out of its present location so that the health of those

engaged in this work may be better safeguarded. If this is not feasible then 

adequate ventilation should be PROMPTLY installed. ... It is undesirable for 

men milling or working on the metal to smoke without first washing their hands

as some of the metal may be ingested. [Emphasis added.]

A review of air sampling data reported in 1946 (or more than 3 years after these documented 

observations) indicates numerous locations and times where air concentrations were well above 

tolerance levels (Air Sampling 1946, SRDB Ref ID: 16801). For example, Exhibit 3 shows that 

Room 11 had an air concentration of 229% of tolerance levels on February 28, 1946, and 140% 

on February 26, 1946.
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Exhibit 3. Air Sampling Data from Room 11
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5.4 PU CONTAMINATION SURVEYS OF WORKERS’ RESIDENCES

In April and May of 1946, the personal residences of three workers (designated herein as 

Workers A, B, and C) were surveyed by the Health Physics Section for plutonium contamination

(Crain 1946). Results of these surveys are enclosed as Exhibits 4, 5, and 6. Inspection of 

Exhibit 4 identifies that Worker A “...had been working with large quantities of Pu and [the 

employee’s] face, hands, and clothing had shown unusually high levels of contamination 

(~104d/m) ...” [Emphasis added.]

The survey of Worker A’s apartment on May 22, 1946, with a portable alpha counter yielded 

variable levels of surface contamination reported in the undefined unit of “M.” Among the 

highest levels of contamination was an assortment of clothing items, shoes, wristwatch, and a 

magazine.

Lower, yet substantial, levels of alpha contamination were also found in the personal residence 

of Worker B and Worker C on May 11, 1946, and April 29, 1946, respectively, as shown in 

Exhibits 5 and 6.
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Exhibit 4. Survey of Worker A’s Apartment
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Exhibit 5. Survey of Worker B’s Apartment
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Exhibit 6. Survey of Worker C’s Apartment
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SC&A Comments

A substantial investigative effort was made by SC&A to identify the type of portable survey 

instrument used, in the hope of decoding the undefined surface contamination unit of “M” 

reported in Exhibits 4, 5, and 6.

Based on the times of the three surveys (i.e., April 29, May 11, and May 22, 1946), SC&A

believes that it was the “Zeuto” Alpha Meter developed at the University of Chicago’s Met Lab 

and used from 1943 to 1946 (see Exhibit 7).

Inspection of Exhibit 7 also identifies the fact that the “Zeuto’s” readout scale of 1–5 and 10–50 

were unitless and required the use of a calibration curve for interpretation, as given by the 

following statements cited in Exhibit 7:

...A calibration curve dated March 26, 1946, is taped on the left end of the 

instrument. It converts the unitless reading on the meter into disintegration per 

minute. [Emphasis added.]

Without the benefit of the instrument’s specific calibration curve, a definitive interpretation of 

the “M” unit is not possible. However, in comparing the general reference value of ~104d/m 

contamination levels to Worker A’s face, hands, and clothing to the itemized contamination 

levels listed at the bottom of Exhibit 4, an approximate conversion is that 1 M ≈ 1,000 dpm.

A more difficult challenge, however, is to further extrapolate the converted “M” value into the 

conventional units of dpm/unit area, such as dpm/100 cm2. This is especially true for those 

measurements in which the individual items represented a contaminated surface area that was 

substantially less than the instrument’s sensitive area assumed to represent 3” by 5”.

Lastly, these high levels of contamination found in the private residences of these workers can 

only serve as indirect evidence of the potentially large quantities of plutonium that were likely 

inhaled/ingested.
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Exhibit 7. Zeuto Alpha Survey Meter

(Source: ORAU 1999)

"Zeuto" Alpha Meter from the Metallurgical Laboratory (1943-1946)

The Zeuto seems to have been the second survey instrument designed exclusively for measuring alpha contamination (the 

first was the "Pluto"). It was developed by Francis Shonka at the University of Chicago's Metallurgical Laboratory during 

World War II. "Zeuto" is a combination of the names "Zeus" (another survey instrument developed by Shonka) and 

"Pluto." 

The identification towards the lower left of the photo reads "An Instrument Section Product, Metallurgical Laboratory, 

Univ. of Chicago." A calibration curve dated March 26, 1946 is taped on the left end of the instrument. It converts the 

unitless reading on the meter into disintegrations per minute.

The original description of the Zeuto is found in MDDC-117.

Chamber: 1" × 5" × 3", thin plastic window protected by wire screen on bottom (ca. 3" × 5")

Range: 0–5 (no units)

Size: 5.5" × 10.5" × 4.5"

Donated by [Redacted]
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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

5.5 PLUTONIUM IN FECAL SAMPLES

In a monthly summary report dated June 20, 1946, the Biochemical Survey Section provided the 

following information (Russell 1946).

In a preliminary survey of a few persons of the Metallurgical Laboratory, single 

fecal specimens were found to contain as much as 200 α c/min. Some of these 

individuals were removed from contaminated areas for at least one week and a 

fecal analysis at the end of this showed only a slight decrease. Even at the end of 

two weeks one individual having an initial count of ~200 α c/min in a single 

specimen decreased to only 30 α c/min . . .

The question as to whether the plutonium detected in the feces was coming from 

the lungs or if there was a slow elimination of the ingested material is one which 

could not be answered since no experiments had been conducted along this line...

The continued presence of plutonium in fecal samples even up to two weeks following the 

workers’ removal from contaminated areas suggests that (1) inhalation was likely the dominant 

exposure pathway, and (2) plutonium originally deposited in the upper regions of the respiratory 

tract continued to be transferred upward and into the GI tract over several days.

By unconservatively assuming that (1) a “single fecal specimen” represented a full 24-hour 

sample, and (2) sample processing and sample counting resulted in a counting efficiency of 50%, 

SC&A derived the following lung doses shown in Table 8. Derived doses correspond to a single 

24-hour fecal sample with an activity of 400 dpm and obtained 1 week following an acute 

airborne exposure.

Table 8. Lung Doses Associated with Acute Inhalation Exposure of Plutonium as 

Evidenced by a Positive Fecal Sample*

Year Lung Dose (Rem)

1 7.2

5 10.0

10 11.3

20 12.0

* Doses were derived in behalf of a 400 dpm Pu activity in a 

24-hour fecal sample obtained 1 week after exposure.
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5.6 CHANGES IN BLOOD COMPOSITION

In a report entitled Health, Radiation and Protection – Report for Month Ending May 7, 1943

(Stone 1943; Ref ID 40751), the following observations were briefly cited:

Three workers showed blood changes due to overexposures to radiation.

Blood effects due to handling of radium sources appeared in two workers 

during the past month. The cyclotron was responsible for a third worker with a 

low blood count. [Emphasis added.]

The report provides no additional data that describe or quantify the “blood effects” in behalf of 

the five workers. It may be assumed, however, that the observed blood effects and the decision 

to assign an overexposure to radiation as the underlying cause was based on criteria defined in 

Nickson 1943 (Ref ID 44786).
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6.0 DISCUSSION AND SUMMARY CONCLUSIONS

The potential impact of granting a waiver to the 250-workday criterion to Met Lab workers was 

not exhaustively addressed in this report. However, a preliminary sampling of data suggests that 

this may include a substantial number of workers.

In a report entitled Metallurgical Project Personnel (Compton 1943, SRDB Ref ID: 44477) 

dated February 26, 1943 (or less than 7 months after facility operation commenced), all Project 

personnel are identified by name in various categories that include scientists, research associates, 

research assistants, technicians, craftsmen, laborers, etc.

Pages 6 and 7 of the Metallurgical Project Personnel report also identified a total of 169 

individuals who were classified as “Resigned or Cut Off,” as shown in Exhibit 8. A reasonable 

conclusion is that, during the first 7 months of facility operation, about 169 individuals had either 

resigned or were terminated with employment periods of less than 7 months. 

The regulatory requirement of a minimum of 250 workdays for SEC class eligibility was most 

likely not an arbitrary decision in terms of the time period. It is reasonable to assume that this 

time period was selected, because it represents a standard work-year consisting of 50 weeks and 

5-day work weeks. Additionally, for workers whose exposure was either not monitored or 

whose records are incomplete/unavailable, regulators may have assumed that radiation exposures 

of less than 1 year were highly unlikely to have resulted in compensable organ doses under the 

Energy Employee Occupational Illness Compensation Program Act (EEOICPA).

These underlying assumptions/presumptions for the 250-workday criterion are not unreasonable, 

provided that there is sufficient assurance that radiation exposures (external and internal) to the 

worker were within radiation exposure limits as defined currently or in more recent years.

As summarized in Section 2 of this report, the operation of the Met Lab represented the very 

beginning of the nuclear era, and there was little information and few existing standards and 

methods for monitoring and protecting workers against the unprecedented radiological 

environments associated with the introduction of a nuclear reactor.

Section 3 of this report described the evolution of tolerance levels for external and internal 

exposures. These tolerance levels were based on limited historical data that had to be hurriedly 

supplemented by animal experiments and human clinical studies involving terminally ill patients. 

Moreover, tolerance levels were exclusively based on the dose-response relationships that govern 

radiation-induced deterministic (or nonstochastic) effects over relatively short time periods. 

Examples of determininstic effects that served as reference points for tolerance levels included 

skin erythema; alterations in blood-cell composition; cell death in select tissues/organs; changes 

in urine constituents; dermal changes, such as the loss of fingerprints; etc.
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Exhibit 8. Metallurgical Project Personnel

(Source: Compton 1943)

[Exhibit 8 has been redacted in its entirety, due to Privacy Act concerns]

Not surprisingly, the limited knowledge and/or availability of data pertaining to latent stochastic

health risks and the complex biokinetic behavior of internalized nuclides led to tolerance levels 

(as discussed in Section 4) that were scientifically flawed and inadequate for protecting the 

health of workers. When compared to present-day regulatory standards, tolerance levels for 

external doses, air concentrations, intakes by inhalation or ingestion, and sustained body burdens 

were many times higher. By far, the largest discrepancies between tolerance levels and presentday limits involved internal exposures to select radionuclides, as shown above in Tables 3, 4, 5, 

6, and 7. In some instances, such short-term/acute exposures correspond to committed organ 

doses in the thousands of rems.

In the absence of available monitoring data for individual Met Lab workers, the extent to which 

doses of this magnitude occurred may be concluded on the basis of general, but site-specific, 

documentation and their interpretation. In Section 5, SC&A identifies documented instances of 

worker exposures in excess of tolerance levels, as well as radiological circumstances that must 

reasonably be assumed to have resulted in high exposures. Equally relevant to this report is that 

these high exposures were the result of either acute or short-term exposures (i.e., << 1 year 

duration). For example, positive fecal samples are likely the result of a recent inhalation 

exposure; similarly, significant changes in the cellularity of circulating blood commonly reflect 

substantial doses received over a relatively brief period of time.

At the time of facility operation at the Met Lab, our understanding of the dose-response of 

hemopoietic tissues to either acute or chronic radiation exposure was extremely limited, as 

acknowledged in a 1947 report entitled Blood Changes in Humans Following Total Body 

Irradiation (Nickson 1947):

A major problem facing the Manhattan Project was the protection of workers 

against damage resulting from either acute or chronic exposure to external 

radiation. It was anticipated that the total dose sustained by personnel and the 

rate of administration could vary widely. Further, there was the problem of 

assessing the damage, either transitory or permanent, which might arise from 

such exposures. The problem of detecting evidence of damage following exposure 

to total radiation led to this study (Nickson 1947, pg. 1). [Emphasis added.]

In “this study,” Nickson identified three groups (i.e., Group I, II, and III) of human subjects that 

were exposed to various doses of external radiation. Group I and Group II were patients with 

either non-curable cancer or other debilitating medical conditions who received doses up to 

several hundred rem.
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Group III consisted of three normal adult volunteers from the Met Lab who were given a total 

dose of 21 R (with 7 R given on 3 consecutive days). Based on the same clinical criteria used to 

assess blood changes of other Met Lab workers, Nickson (1947) provided the following 

summary conclusions:

Group III. No evidence of change in the cellular elements of the blood was 

noted in any of these cases. It will be remembered that the individuals were all 

normal males insofar as could be demonstrated. These cases were of particular 

interest to use inasmuch as they indicated that acute exposure to far more than 

the maximum permissible level of 0.1 r per working day could not be expected to 

produce diagnostic changes in the elements of the peripheral blood which were 

studied. [Emphasis added.]

Given the facts that (1) blood changes were noted among some Met Lab workers, and that (2) the 

21 R dose received by Group III study subjects produced no evidence of change, suggest that 

acute doses well in excess of 21 R were not uncommon among Met Lab workers. 

Just how high radiation doses may have been for Met Lab workers whose blood changes were 

considered significant may be estimated from other human data. Among the most relevant and 

best documented data are those involving workers exposed during the criticality accident in 1958 

at the Y-12 facility. A brief summary of events and salient observations that are relevant to this 

report are presented below.

6.1 DESCRIPTION OF THE Y-12 ACCIDENT 

The Y-12 accident occurred on June 16, 1958. An employee of the Union Carbide Nuclear 

Company was filling a 55-gallon drum with water in order to dissolve a residue of enriched 

uranium. Apparently, this is a normal procedure in the uranium-recovery operation, since the 

same operation had been done many times before by this particular employee. On this particular 

occasion, however, there was a sufficient amount of enriched uranium that as the water was 

added, a geometric configuration was reached that allowed the enriched uranium to reach 

criticality and the drum began to act as a reactor. As it reacted, the power level increased, the 

amount of heat produced increased, and the volume of water quickly began to “boil.” However, 

the boiling destroyed the necessary geometrical configuration for criticality. The reaction 

ceased, and it stopped boiling. As it cooled off, a critical conformation was again reached. The 

drum again went critical, causing it again to boil and to automatically shut itself off. This 

oscillation was repeated every few seconds. Both neutrons and gamma rays were produced and 

the fission products resulted in a continuous buildup of gamma-ray intensity. Since water was 

continuing to flow into the container, it soon diluted the material beyond that required for a 

critical configuration.

6.2 HEMATOLOGICAL FINDINGS IN BEHALF OF EIGHT WORKERS

At the time of the accident, two groups of workers were subject to intense clinical evaluation. 

By virtue of distance to the source, the first group consisted of five “highly exposed” workers 

identified as workers A, B, C, D, and E.
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Highly Exposed Workers. Figure 3 shows that there is a rapid loss of lymphocytes from the 

peripheral blood that is the result of the direct killing of the highly sensitive mature and fully 

differentiated peripheral blood lymphocytes. Specifically, this dramatic drop from about 1,800 

lymphocytes per mm3to about 1,100 per mm3occurred in the first few hours post-exposure. 

Other cellular changes involving white blood cells and platelets largely reflect damage to the 

immature hemopoietic stem cells of the bone marrow. Since injury to stem cells prevents the 

normal and continuous replacement of aged white blood cells, platelets, and red blood cells, the 

perturbations in peripheral blood cellularity have distinct timelines that for sublethal doses are 

most pronounced 4 to 8 weeks post-exposure.

Figure 3. Hematologic Effects for Five Y-12 Workers A, B, C, D, and E

(Source: Andrews et al. 1961)

Lower Exposed Workers. In addition to the five highly exposed workers (who are not the focus 

of this discussion), there were also three other workers in the area at considerably greater 

distances. These lower exposed workers were identified as Workers F, G, and H.

As was the case for the five highly exposed individuals, Workers F, G, and H had pre-accident 

clinical baseline hematological data on file, which served as reference values for studying the 

impacts of their exposures. Results of the clinical investigation were summarized in the 

following statement (Sitterman 1959):

The findings in these three low-dose patients can be summarized with the 

statement that there are no definite changes clearly attributable to radiation. 

[Emphasis added.]
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This statement implies that in behalf of these three workers, no significant hematological 

changes were observed in spite of their exposures to substantial acute doses of photon and 

neutrons as discussed below.

6.3 ESTIMATES OF ACUTE DOSES TO THE LOWER-EXPOSED GROUP

For Workers F, G, and H, original estimates of the absorbed doses for photons and neutrons are 

given in Table 9.

Table 9. Original Doses Assigned to Workers F, G, and H

(Source: Sitterman 1959)

Worker Dose (rads)

Photons Neutrons Total

F 50.5 18 68.5

G 50.5 18 68.5

H 16.8 6 22.8

Original doses, however, assumed a relative biological effectiveness (RBE) of 2 for the neutron 

component of the first collision absorbed dose based on deterministic effects relative to 

lethality. 

Because Y-12 workers are eligible for compensation under EEOICPA, NIOSH reassessed the 

criticality doses in ORAUT-OTIB-0057, which was issued May 15, 2006 (ORAUT 2006). 

NIOSH’s re-evaluation principally involved the substitution of the neutron RBE value of 2 for 

the deterministic lethality effect with the 1990 ICRP Publication 60 neutron weighting factors for 

stochastic effects applicable to cancer induction. 

NIOSH’s revised dose estimates for Workers F, G, and H, as given in Table 7-3 of ORAUTOTIB-0057, are reproduced herein in Table 10.

Table 10. Dose Equivalent Estimates for Y-12 Workers F, G, and H

Worker Dose (rads)

Neutrons Photons Total

F 242 55.6 297.6

G 242 55.6 297.6

H 79.7 18.5 98.2

In summary, whole-body single acute exposures of up to 300 rem dose equivalent were 

experienced by three Y-12 workers, but resulted in no discernable hematologic changes. Yet, 

hematological changes were noted among some Met Lab workers that were attributed to 

radiation exposure. In combination, these data, therefore, suggest that some Met Lab workers 

may have experienced doses ±300 rem delivered acutely or over short periods of time.

Important to note here is that evidence of hematological injury has been a topic of discussion 

among the Board’s 250-day Work Group members.
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7.0 REFERENCES

42 CFR 83. 2004. Procedures for Designating Classes of Employees as Members of the Special 

Exposure Cohort Under the Energy Employees Occupational Illness Compensation Program Act 

of 2000, Final Rule; May 28, 2005.

ABRWH (Advisory Board on Radiation and Worker Health). 2009. Transcript of Advisory 

Board Meeting in Albuquerque, New Mexico, on February 19, 2009.

Air Sampling 1946. Air Sampling Results New Chemistry 1946 (SRDB Ref ID: 16801).

Andrews, G.H., Sitterson, B. W., Kretchman, A. L. and Brucer, M. 1961. “Criticality 

Accident at the Y-12 Plant,” in Diagnosis and Treatment of Acute Radiation Injury, pp. 27-48, 

World Health Organization, Geneva.

Bonsib, R.S. 1942. Metal Production Operations of the University of Chicago Metallurgical 

Laboratory Project (October 30 to December 12, 1942), December 22, 1942 (SRDB Ref ID: 

17124).

CP-1. 2008. Critical Pile-1 http://www.dark-legion.org/F/MJW/01-27-08/Chicago Pile-1.htm 

(SRDB Ref ID: 42824).

Compton, A.H. 1943. Metallurgical Project Personnel, February 25, 1943, Metallurgical 

Laboratory, University of Chicago (SRBD Ref ID: 44477).

Crain, S.M. 1946. Special Surveys, Three University of Chicago, Metallurgical Laboratory 

internal memos from S.M. Crain to J.E. Rose, dated May 22, 1946; May 11, 1946; and April 29, 

1946 (SRBD Ref ID: 16798).

DOE (U.S. Department of Energy) 2008. The Manhattan Project: CP-1 Goes Critical. USDOE 

Office of History and Heritage Resources, http://www.cfo.doe.gov/me70/manhatten/cp1_critical.htm (SRDB Ref. ID: 43013).

EPA (U.S. Environmental Protection Agency) 1988. Limiting Values of Radionuclide Intake and 

Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion, 

Federal Guidance Report 11, U.S. Environmental Protection Agency, Office of Radiation 

Programs, Washington, DC.

ICRP (International Commission on Radiological Protection). 1991. 1990 Recommendations of 

the International Commission on Radiological Protection, Publication 60, Pergamon Press, 

Oxford, England.

Katz, T. 2009. Subject: Met Lab Follow-up. E-mail from T. Katz (NIOSH) to J. Neton 

(NIOSH) and J. Mauro (SC&A). March 26, 2009.
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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

NCRP (National Council on Radiation Protection and Measurements). 1936. X-Ray Protection. 

NCRP Report No. 3, National Bureau of Standards Handbook 20. Washington, DC: U.S.

Government Printing Office.

Nickson, J.J. 1943. Notes of Meetings in Regard to Radiation Hazards of Project Personnel, 

letter from Dr. J.J. Nickson (University of Chicago, Metallurgical Laboratory), to Dr. L.O. 

Jacobson (University of Chicago, Metallurgical Laboratory), dated October 28, 1943 (SRDB Ref 

ID: 44786).

Nickson, J.J. 1947. Blood Changes in Humans Following Total Body Irradiation, Metallurgical 

Laboratory, University of Chicago (SRDB Ref ID: 29944).

NIOSH (National Institute for Occupational Safety and Health) 2008. SEC Petition Evaluation 

Report SEC-00135 for the Metallurgical Laboratory, December 9, 2008.

ORAU (Oak Ridge Associated University) 1999. “Zeuto” Alpha Meter from the Metallurgical 

Laboratory (1943–1946), http://www.orau.org/ptp/collection/surveymeters/zeutochi.htm.

ORAUT 2005. Estimation of Radium-226 Activity in the Body from Breath Radon-222 

Measurement, ORAUT-OTIB-0025. Oak Ridge Associated University Team: Cincinnati, Ohio.

ORAUT 2006. External Radiation Dose Estimate s for Individuals Near the 1958 Criticality 

Accident at the Oak Ridge Y-12 Plant, ORAUT-OTIB-0057. Oak Ridge Associated University 

Team: Cincinnati, Ohio.

Radiation Standards, undated. An Overview of Research in Radiation Biology and Protective 

Measures in the Manhattan Project during the War Years 1942-1946, VII. Development of 

Radiation Standards and Protective Measures (SRDB Ref ID: 40381).

Russell, E.R. 1946. Biochemical Survey Section Report for the Month June 1946, June 20, 1946 

(SRDB Ref ID: 48389).

Sitterman, B.W. 1959. "Clinical Report." The Acute Radiation Syndrome: A Medical Report 

on the Y-12 Accident June 16, 1958, M. Brucer, Ed., Oak Ridge Institute of Nuclear Studies, 

Inc., Oak Ridge, Tennessee.

Stone, R.S. 1943. Health, Radiation and Protection Report for Month Ending May 7, 1943,

Associate Project Director for Health for the Metallurgical Project, (SRBD Ref ID: 40751).

Stone, R.S. 1945. Health Protection Activities of the Plutonium Project, Associate Project 

Director for Health for the Metallurgical Project, Nov. 2, 1945. (SRDB Ref ID: 7693).

Tybout, R.A. (1

st Lt., Corps of Engineers, Medical Section) 1945. Memo on Results of Breath 

Analyses to The Area Engineer, Chicago Area, Chicago, Illinois (Attn: Dr. J.E. Rose). February 

21, 1945 (SRBD Ref ID: 4715).
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Health for factual accuracy or applicability within the requirements of 42 CFR 82.

USERDA (U.S. Energy Research and Development Administration) 1946. Manhattan District 

History, Book I – General, Volume 7 – Medical Program. December 31, 1946 (SRDB Ref ID: 

40434).

Wirth, J.E. 1945. Tolerance Values for Neutrons, Fast, University of Chicago, Metallurgical 

Laboratory internal letter from J.E. Wirth, M.D. to Dr. J.J. Nickson dated January 9, 1945 

(SRDB Ref ID: 13791).
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APPENDIX A – TRANSCRIPT OF ADVISORY BOARD MEETING HELD 

ON FEBRUARY 19, 2009

(Pages 55–62)
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Appendix A (Continued)
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Appendix A (Continued)
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Appendix A (Continued)
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Appendix A (Continued)
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Appendix A (Continued)
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Appendix A (Continued)
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Appendix A (Continued)
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APPENDIX B – MARCH 26, 2009, MEMO FROM DESIGNATED

FEDERAL OFFICIAL

From: Katz, Ted (CDC/NIOSH/OD) [mailto:tmk1@cdc.gov] 

Sent: Thursday, March 26, 2009 12:45 PM

To: Neton, Jim (CDC/NIOSH/OD); John Mauro

Cc: melius@nysliuna.org

Subject: Met Lab Follow-up

Jim Neton and John:

In going through some of the transcripts from Albuquerque I noted there was discussion of whether or not 

OCAS would be able to bound doses associated with the planned criticality and, by inference, if not, 

whether it would be considered a "discrete incident" defined by presence rather than exposure for a 

minimum of 250 work days. I don't think this is a live petition issue since Met Lab was an 83.14 defined 

around other exposures but the sense of the discussion was that OCAS might look into the question of 

bounding the related doses and SC&A was asked specifically to become familiar with the OCAS 

Evaluation Report and related materials to allow for a discussion of this as one of the case examples to

be considered by the 250-day Board Work Group.

Just a reminder. The transcript for this issue, which was discussed on February 19th, should be up on 

the OCAS Web Site today or tomorrow.

--Ted

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