TO: Advisory Board on Radiation and Worker Health Work Group on TBD-6000 

FROM: Robert Anigstein and John Mauro, SC&A 

SUBJECT: Review of NIOSH Estimates of Internal Exposures at GSI 

DATE: April 24, 2013 

Review of NIOSH Estimates of Internal Exposures at GSI 

On April 1, 2013, David Allen (2013) transmitted a White Paper on GSI providing details on (1) 

how NIOSH intends to estimate doses from external radiation to nonradiographers prior to 1963; 

(2) how individual cases will be assigned to different job categories; and (3) how internal doses 

will be estimated. The same day, Ted Katz, Designated Federal Official to the Advisory Board, 

sent an e-mail message asking SC&A review this report. In our previous memo (Anigstein and 

Mauro 2013), we addressed the NIOSH estimates of external exposures and the assignment of 

doses to different workers. This memo is our response to the discussion of internal exposure in 

Allen’s White Paper. 

In a table at the end of the White Paper, Allen (2013) lists the inhaled and ingested activities 

during various periods of the operational and residual periods. The inhaled activity is greater 

than the ingested activity during most of the period of AEC operations at GSI. Furthermore, the 

effective dose coefficients for inhalation are one to two orders of magnitude greater than the 

corresponding coefficients for ingestion. We will therefore address intakes of uranium via 

inhalation, which constitute the major source of internal exposure for the reasons stated above. 

According to Allen (2013), the inhaled activity has two sources: exposure to dust generated 

during the handling of uranium while setting up the radiographic exposures, and resuspension of 

the airborne dust that had settled on the floor of the facility. The work group, NIOSH, and 

SC&A have all agreed that the uranium aerosol concentrations generated by the handling of 

uranium metal can be represented by a lognormal distribution with a geometric mean or median 

(M) of 17.54 dpm/m3

 and a geometric standard deviation (GSD) of 2.29, which yields a 95th 

percentile value of 68.7 dpm/m3. Allen assumed that the workers were exposed to the uranium 

dust at the 95th %ile concentration only during the 15 minutes they spent setting up a betatron 

shot, and spent the next 60 minutes in the control room, where they were protected from the 

uranium aerosols. Thus, they inhaled an aerosol concentration of 68.7 dpm/m3

 during 20% of 

the time allotted to uranium radiography by the purchase orders GSI received from the 

Mallinckrodt Chemical Works (MCW) over various time periods. 

Allen (2013) next derived a surface contamination level by assuming that this airborne activity 

settled over a period of 30 days, with a settling velocity of 7.5 × 10-4 m/s. He thus derived a 

surface activity concentration of 1.34 × 105 dpm/m2. He calculated the airborne activity 

concentration by applying a resuspension factor (RF) of 10-5 m-1, obtaining a concentration of 

1.34 dpm/m3. 

We disagree with this approach for several reasons. Our main problem is with the method of 

calculating the surficial activity by deposition of uranium aerosols. The assumptions about the 

Review of NIOSH Internal Exposure Estimates at GSI -1- SC&A –April 24, 2013 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

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. 
 

 

 

 

deposition velocity and settling time are based on TBD-6000 (Allen 2011). However, these 

parameters and methods apply to a steady-state situation in which the aerosol generation is 

continuous and equilibrium between airborne and surficial activity concentrations is achieved 

over 30 days. In the case of GSI, the aerosol generation was highly intermittent and took place at 

unknown intervals. According to the MCW purchase orders, the uranium radiography was to be 

performed during the day shift on weekdays (presumably to avoid paying premium rates for 

night or weekend shifts). Assuming, as Allen does, 337.5 h/y of uranium radiography from 

1/1/1953 until 6/30/1961, this work would take ~8.4 weeks if performed continuously, or an 

average of 6.75 h/week if performed intermittently, as is more likely. If, as Allen postulates, the 

uranium was handled for only 15 min per shot, then the generation was even more intermittent. 

A 30-d settling period has two implications. If the dust were to settle for even one week 

(assuming weekly uranium radiography), the column of contaminated air would have to extend 

~454 m above the floor, which is not possible, given that the betatron shooting room is ~10 m 

high. More important, workers would be exposed to the inhalation of this dust during the entire 

settling period. That is, they would be inhaling it for 65 h, the length of the average work week, 

following each uranium radiography campaign. If the campaigns took place weekly, or even 

monthly, the workers would be exposed to this concentration for the entire year. To put it 

succinctly, one cannot postulate a 30-d settling period without anyone breathing the initial dust 

concentration during this time. 

We would like to propose an alternate approach which is consistent with the agreed-upon 

surrogate data and which avoids the problem discussed above. We assume that the upper bound 

to the uranium aerosol concentration during the operational period is given by the lognormal 

distribution discussed previously. This assumption does not require us to specify the mechanism 

by which this concentration is achieved and maintained. However, it is unrealistic to assume that 

workers would be exposed to the 95th percentile concentration during their entire work year. It 

would be more appropriate to utilize the entire distribution during dose reconstruction to all 

workers. This also avoids postulating the detailed duration of exposure of the betatron teams to 

handled uranium, since it is likely they would have spent some time in the betatron shooting 

room while the uranium was brought into and removed from the room, released from the crane, 

etc. This intake would be applicable to both betatron operators and other workers. The exposure 

of operators performing uranium radiography would actually be slightly less, since they would 

have some measure of protection in the control room. However, since the control room was not 

airtight, and since the workers would have tracked the uranium dust into the room while walking 

in and out, the degree of protection cannot be ascertained. 

Although there is no simple method for calculating the inhaled activities from the entire 

lognormal distribution, an approximate value can be obtained from the arithmetic mean. Using 

this value, the inhaled intake during the operational period is estimated to be ~264 dpm/cal. day. 

In comparison, Allen (2013) estimates a range of 15.01–34.37 dpm/cal. day,1

 while Allen and 

Glover (2007) assigned inhaled intakes of 5.2–128 dpm/cal. day. 

1

 He lists the values as dpm/d; based on earlier DCAS reports, we assume this refers to dpm/ cal. day—we did not 

verify his calculations. 

Review of NIOSH Internal Exposure Estimates at GSI -2- SC&A –April 24, 2013
 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

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. 
 

 

 

To calculate the doses during the residual period, we first calculate the areal activity 

concentration. The arithmetic mean (μ) of the airborne concentration is 24.72 dpm/m3

. If we 

divide this by an RF of 10-5 m

-1, we obtain an areal activity concentration of 2.47 × 106

 dpm/m2. 

This surficial concentration is assumed to decrease at the rate of 6.7 × 10-4 d-1 (Sharfi 2012). The 

airborne concentration during the residual period can be calculated by applying this RF to the 

decreasing surficial activity. Thus, the inhaled intakes would be 264 dpm/cal. day at the end of 

AEC operations (June 30, 1966), decreasing exponentially with time after that date. Allen 

estimated an inhalation of 1.44 dpm/cal. day at the start of the residual period, using an RF of 10­

6

 m-1 and the previously cited surficial contamination level. He stated that the exponential 

removal rate cited by Sharfi would be applied to subsequent times. 

We do not agree with Allen (2013) that an RF of 10-6 m-1 is applicable to the residual period. As 

Allen correctly points out, this RF value is applicable to aged activity in a quiescent setting. 

Although the contamination gradually aged, the setting—the betatron shooting room and other 

areas of GSI—was hardly quiescent. 

References 

Allen, D. 2011. “Site Profile for Atomic Worker Employers that Worked Uranium Metals,” 

Battelle-TBD-6000 Rev. 1. http://www.cdc.gov/niosh/ocas/awedocs.html#b6000. 

Allen, D. 2013. “GSI White Paper: Issues Raised in February 21, 2013 Work Group Meeting.” 

http://www.cdc.gov/niosh/ocas/pdfs/dps/dc-gsiwgiss-0413.pdf 

Allen, D., and S. Glover. 2007. “Site Profiles for Atomic Weapons Employers That Worked 

Uranium and Thorium Metals - Appendix BB: General Steel Industries,” Battelle-TBD-6000, 

Appendix BB, Rev. 0. http://www.cdc.gov/niosh/ocas/pdfs/tbd/b-6000-apbb-r0.pdf. 

Anigstein, R., and J. Mauro. 2013. “Review of NIOSH Estimates of External Exposures at GSI.” 

Memo to Advisory Board on Radiation and Worker Health Work Group on TBD-6000. 

Sharfi, M. M. 2012. “Dose Reconstruction During Residual Radioactivity Periods at Atomic 

Weapons Employer Facilities,” ORAUT-OTIB-0070, Rev. 01. 

http://www.cdc.gov/niosh/ocas/pdfs/tibs/or-t70-r1.pdf. 

Review of NIOSH Internal Exposure Estimates at GSI -3- SC&A –April 24, 2013
 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

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.