Draft 

ADVISORY BOARD ON 

RADIATION AND WORKER HEALTH 

National Institute for Occupational Safety and Health 

Focused Review of Appendix C to TBD-6000 – 

Dow Chemical Company (Madison Site) 

Contract No. 200-2009-28555 

Prepared by 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, Virginia 22182 

August 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 pre-decisional 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.
TBD Appendix C Review 2 SC&A – August 24, 2009 

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TABLE OF CONTENTS 

Executive Summary.........................................................................................................................3 

1.0 Introduction..........................................................................................................................4 

1.1 Synopsis of Site Profile and SEC Issues..................................................................4 

2.0 Review of Appendix C – Dow (Madison Site)....................................................................6 

2.1 Uranium Exposures..................................................................................................7 

2.1.1 Uranium Exposures during the Operating Period........................................7 

2.1.2 Uranium Exposures during the Residual Period........................................10 

2.2 Thorium Exposures................................................................................................11 

2.2.1 Thorium External Exposures during the Operating Period........................11 

2.2.2 Thorium Exposures during the Residual Period ........................................14 

3.0 Transparency of Modeling Approach ................................................................................15 

4.0 References..........................................................................................................................16 
TBD Appendix C Review 3 SC&A – August 24, 2009 

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EXECUTIVE SUMMARY 

The Advisory Board on Radiation and Worker Health (Advisory Board) requested that SC&A 

conduct a focused review of Appendix C, Dow Chemical Co. (Madison Site), a supplement to 

Battelle-TBD-6000 (Battelle 2006). Appendix C provides site-specific dose reconstruction 

guidance to support the generic guidance included in TBD-6000. In its reviews of the Special 

Exposure Cohort (SEC) Petition Evaluation Report for SEC-00079, including Addendums 1 and 

2, NIOSH had determined that the operating period for Atomic Weapons Employer (AWE) work 

at Dow extended from January 1, 1957, through December 31, 1960, and included exposures to 

both uranium and thorium. NIOSH had also determined that the residual period for uranium 

extended from January 1, 1961, through July 31, 2000, and through November 30, 2007, for 

thorium. 

SC&A had previously reviewed the site profiles, SEC petitions, and evaluation reports pertaining 

to what is referred to as the operations period (i.e., 1957 through 1960) and the residual period 

(post-1960) at the Dow Madison facility. Subsequent to those SC&A reviews, NIOSH published 

Appendix C to TBD-6000, which provides updated information and guidance pertaining to the 

Dow facility. During a conference call of the Advisory Board Work Group on SEC issues held 

on July 24, 2009, the work group requested that SC&A review Appendix C to determine if there 

is any new information contained in that report that should be brought to their attention. 

Appendix C tabulates and consolidates data and guidance that can be used to calculate internal 

(inhalation and ingestion) and external doses from uranium exposures during both the operating 

and residual periods. Appendix C also provides data that can be used to calculate external 

thorium exposures during the operating period, and both external and internal (inhalation, 

ingestion, and thoron) exposures during the residual period. NIOSH had determined that it was 

not possible to reconstruct internal thorium doses during the operating period, and NIOSH 

recommended that SEC status be granted for AWE workers during that period. However, 

NIOSH concluded that thorium exposures during the residual period could be reconstructed by 

using the limited data available for the operations and residual period, along with bounding, but 

plausible, dose reconstruction models. 

SC&A’s findings from its review of Appendix C are as follows: 

Finding 1: NIOSH has proposed the use of geometric mean data to calculate internal uranium 

exposures during the operating period. The geometric mean is based on only two measurements 

and, since NIOSH’s stated goal is to estimate maximum doses, we believe that use of the 95th

percentile is a more appropriate metric for this situation. 

Finding 2: The resuspension factor used by NIOSH for estimating uranium dust concentrations 

in air could be low by 1 to 2 orders of magnitude. NIOSH should revisit the use of a value of 1 × 

10-6/m. 

Finding 3: NIOSH should consider developing an exponential decay function for uranium 

removal during the residual period, based on guidance in ORAUT-OTIB-0070. 
TBD Appendix C Review 4 SC&A – August 24, 2009 

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Finding 4: There appear to be data entry errors in Table C.2 for the residual period. 

Finding 5: NIOSH should focus additional attention on insuring the transparency of the dose 

reconstruction guidance. 

1.0 INTRODUCTION 

SC&A had previously performed two investigations pertaining to the Dow Madison facility. 

These include the following: 

• A Focused Review of Operations and Thorium Exposures at the Dow Chemical Company 

Madison Plant, August 2007 (SC&A 2007a). This report presents SC&A’s review of 

NIOSH’s Evaluation Report for SEC-00079 (April 13, 2007), which is concerned with 

the reconstruction of doses to workers at the Dow Madison facility during the uranium 

operations performed from 1957 through 1960. 

• A Focused Review of Addendum 2 to the Dow Chemical-Madison Plant SEC Petition 

Evaluation Report (SEC-00079), September 2008 (SC&A 2008a). This report presents 

SC&A’s review of NIOSH Addendum 2 to its evaluation report, which deals with the 

reconstruction of thorium doses during the residual period. 

During the July 24 teleconference of the Advisory Board’s Work Group on SEC issues, SC&A 

was requested to conduct a focused review of Appendix C, Dow Chemical Co. (Madison Site), 

of Battelle-TBD-6000 (Battelle 2006). As described by the work group, the primary intent of the 

review is to determine if Appendix C contains any new material that is relevant to the work 

group’s consideration of exposures at Dow. This request was confirmed during the July 27–29 

meeting of the Advisory Board in Cincinnati, Ohio. This report is provided in response to that 

request. 

1.1 SYNOPSIS OF SITE PROFILE AND SEC ISSUES 

During 1957 and 1958, Dow Madison performed uranium extrusion work related to the Atomic 

Energy Commission (AEC) atomic weapons program under contract from Mallinckrodt 

Chemical Company. Subsequently, in 1959 and 1960, again under contract to Mallinckrodt, 

Dow performed uranium rod straightening for the weapons program. These activities established 

the operating period for uranium dose reconstruction as 1957 through 1960. During this period, 

the major activity at Dow Madison was the production of magnesium alloys, many of which 

contained thorium. These alloys were sold commercially for use in applications involving 

missiles and spacecraft, for example. Workers at Dow were subject to radiation exposures from 

both thorium and uranium during the operating period and the residual period. 

The following was noted by NIOSH in its SEC Petition Evaluation Report, Petition SEC-00079 

(NIOSH 2007a): 
TBD Appendix C Review 5 SC&A – August 24, 2009 

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For dose reconstructions under EEOICPA, all sources of radiation exposure must 

be considered in the assessment of dose received during AWE operational 

periods. However, exposures due to non-AEC radioactive materials are not 

included in the assessment of dose received during an AWE residual radiation 

period if they can be distinguished from exposures resulting from AEC residual 

contamination. [See 42 U.S.C. 7384 n (c)(4)(b)].

Thus, exposures to both Th and U must be considered during the operating period, but thorium

exposures can be excluded during the residual period, if they can be separated from uranium 

exposures. With regard to reconstructing doses from thorium exposures during the operating 

period, NIOSH concluded the following (NIOSH 2007a): 

NIOSH has documented herein that it cannot complete the dose reconstructions 

related to this petition where doses resulted from exposure to thoriumcontaining materials. The basis of this finding is specified in this report, which 

demonstrates that NIOSH does not have access to sufficient information to 

estimate with sufficient accuracy either the maximum radiation dose incurred by 

any member of the class or to estimate such radiation doses more precisely than a 

maximum dose estimate. Members of this class at the Dow Chemical Company 

site in Madison, Illinois, may have received unmonitored internal and external 

radiological exposures from thorium radionuclides at the plant. NIOSH lacks 

sufficient information, which includes sufficient personnel and workplace 

monitoring data and radiological source term information, to allow NIOSH to 

estimate the potential total internal thorium exposures to which the proposed class 

may have been exposed. 

With the data currently available to NIOSH, it is feasible to reconstruct with 

sufficient accuracy the external and internal doses resulting from exposure to

uranium metal during the Dow Madison AWE operational period (January 1, 1957 

through December 31, 1960), and during the residual radiation period (January 1, 

1961 through December 31, 1998). NIOSH also considers the reconstruction of 

medical dose for Dow Madison workers to be feasible. 

NIOSH determined that workers exposed to thorium during the period January 1, 1957, through 

December 31, 1960, should be defined as an SEC. Uranium exposures could be estimated using 

tools such as NIOSH guidance document, Estimating the Maximum Plausible Dose to Workers 

at Atomic Weapons Employer Facilities, ORAUT-OTIB-0004 (ORAUT 2006). However, no 

estimates of uranium exposures were reported by NIOSH until Appendix C of TBD-6000 was 

published in September 2008. 

At about the time that the initial petition evaluation report was published, NIOSH received 676 

pages of additional documentation from Dow. Results of the NIOSH review of this additional 

material were presented in Addendum 1 to SEC-00079 (NIOSH 2007b). The new material did 

not alter NIOSH’s conclusion about the inability to reconstruct internal thorium doses during the 
TBD Appendix C Review 6 SC&A – August 24, 2009 

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operating period. However, NIOSH did observe that bounding of external thorium doses was 

possible. The Addendum 1 report states the following (NIOSH 2007b, p. 3): 

NIOSH has reviewed the additional documentation provided by Dow and 

concluded that the documentation does not provide sufficient additional 

information regarding potential internal thorium dose to workers at the Madison 

site during the covered period of the SEC, which would result in a change to the 

initial conclusion that it is not feasible to reconstruct those doses. The additional 

documentation does include sufficient information to provide a bounding 

reconstruction of external dose resulting from thorium. 

It was subsequently learned by NIOSH that some Mg-Th alloys sold to AEC contractors (i.e., 

Mallinckrodt) by Dow may have been used in nuclear weapons (DOE 2008). This new 

information means that exposure to thorium must also be considered during the residual period. 

Prior to the availability of the information in DOE 2008, consideration of thorium exposures 

during the residual period was excluded from consideration. In response to this new 

requirement, NIOSH prepared Addendum 2 to SEC-00079, in which the feasibility of 

reconstructing thorium doses during the residual period was presented (NIOSH 2008a). NIOSH 

concluded that “...potential radiation doses received from exposure to residual thorium at Dow 

Madison from January 1, 1961 through October 31, 2006 can be reconstructed with sufficient 

accuracy.” 

SC&A’s review of Appendix C is presented in the next section. 

2.0 REVIEW OF APPENDIX C – DOW (MADISON SITE) 

In September 2008, NIOSH published Appendix C to TBD-6000. The purpose of Appendix C 

was to provide site-specific dose reconstruction information to supplement the generic 

information provided in TBD-6000. Key topics addressed in Appendix C include the following: 

• Occupational internal dose from uranium 

• Occupational external dose from thorium and uranium 

• Dose from residual contamination by thorium and uranium 

Since Dow Madison AWE employees who worked with thorium during the occupational period 

are part of an SEC, no dose reconstruction is required for any of these workers who develop one 

of the 22 types of cancer specified in Energy Employees Occupational Illness Compensation 

Program Act (EEOICPA), and who worked for at least 250 days during the period from January 

1, 1957, through December 31, 1960. In all probability, workers who handled uranium also 

handled thorium. Consequently, uranium dose reconstruction during the operational period 

would not be required, unless one needed to consider probability of causation for a cancer that 

was not one of the 22 types specified in EEOICPA. For claimants with non-specified cancers, a 

partial dose reconstruction would be performed that would include occupational internal and 

external doses from uranium and medical doses. 
TBD Appendix C Review 7 SC&A – August 24, 2009 

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

Subsequent sections of this review discuss the exposure modeling guidance in Appendix C in 

greater detail. 

2.1 URANIUM EXPOSURES 

SC&A’s report dated August 24, 2007 (SC&A 2007a), does not include a review of NIOSH’s 

dose reconstruction protocol for uranium. However, we concurred with NIOSH’s conclusion 

that such doses could be reconstructed, because of the vast amount of data available 

characterizing exposures to workers at uranium handing facilities. Our August 24, 2007, report 

concluded the following: 

We have reviewed numerous reports addressing these types of operations, 

including the reports by Harris and Kingsley (1959), Adley et al. (AEC 1952), and 

documentation in support of the Site Profile for Simonds Saw and Steel ORAUTTKBS-0032 (ORAUT 2005) and the recently issued Site Profiles for Atomic 

Weapons Employers that Worked Uranium and Thorium Metals (Battelle-TBD6000 2006). We believe that these reports, taken in combination, are 

comprehensive in describing the range of operations and the range of exposures 

that workers might have experienced during uranium metal-working operations at 

DOE/AWE facilities during the early years. We believe that the material 

contained in these reports can be used to place plausible upper bounds on the 

uranium exposures experienced by workers at the Dow Madison facility. 

Hence, the comments and findings contained in this report are new and identify issues regarding 

how NIOSH is using the available models and surrogate data to reconstruct uranium doses at 

Dow. 

2.1.1 Uranium Exposures during the Operating Period 

2.1.1.1 External Uranium Exposures 

NIOSH assumed that workers involved in uranium extrusion were exposed 168 hours in each 

year for 1957 and 1958. This assumption was based on the fact that the AEC contract called for 

12 monthly cycles of 28-hours each for the extrusion work, including clean-up (Appendix C, 

Section C.2.1.2,a). Similarly, workers involved with uranium rod straightening were assumed by 

NIOSH to spend 168 hours in each year for 1959 and 1960. Purchase orders have been 

discovered covering two monthly periods of rod straightening work in 1959 and 1960. SC&A 

believes that these estimates of exposure duration are reasonable, based on the available 

information. 

Using an annual exposure of 168 hr/yr and dose rate parameters obtained from TBD-6000, 

appropriate exposures and/or doses were calculated by NIOSH. For example, the external dose 

to an extrusion operator is listed in Table C.2 of Appendix C as 176 mR/yr. This is based on a 
TBD Appendix C Review 8 SC&A – August 24, 2009 

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photon dose rate for that job category of 5.7 mrem/calendar-day1 from Table 6.4 of TBD-6000 

plus small contributions from contaminated floor exposure and air submersion. (Making the 

assumption that the whole-body dose of 5.7 mrem/day results from a photon exposure of 

5.7 mR/day2

, then 5.7 mR/calendar-day × 365 calendar days/2,000 work hours × 

168 work-hours/yr = 175 mR/yr). 

While the traceability of the Table C.2 data in Appendix C to the data in Table 6.4 of TBD-6000 

is apparent, the provenance of the data in Table 6.4 is less clear. Table 6.2 of TBD-6000 lists the 

daily whole-body photon dose (30 to 250 keV) to an operator standing near a bare uranium metal 

shape as 5.7 mrem/d based on a 40-hr work week, which can be converted to 1.04 mrem/hr 

(5.7 mrem/calendar-day × 365 calendar-days/250 work-days × 1 work-day/8hr). TBD-6000 

further assumes that an operator spends 50% of his time 1 foot (30.48 cm) from a uranium metal 

slab. From Table 6.1, we see that the dose (photon plus bremsstrahlung) 1 foot from a 

rectangular uranium ingot is 2.08 mrem/hr, or based on exposure 50% of the time, equals a dose 

of 1.04 mrem/hr. Of the several uranium shapes listed in Table 6.1, the rectangular ingot3

generates the highest dose, so the selection of this geometry is claimant favorable. 

2.1.1.2 Internal Uranium Exposures 

Internal uranium exposures are summarized in Table C.1 of Appendix C. To calculate internal 

exposures, air monitoring data were selected from Table 7.2 of TBD-6000 for extrusion 

operations and from Table 7.7 for rod straightening operations. In Table 7.2, geometric mean 

values for the daily-weighted average (DWA) are presented for several extrusion-related 

activities. NIOSH selected the maximum DWA from within this group of activities; 992 dpm/m3

for the [redacted]. This was converted in Table C.1 to an inhalation exposure of 

551 dpm/calendar-day based on a breathing rate of 1.2 m3

/hr (992 dpm/m3 × 1.2 m3/hr × 

168 hr/yr × 1 yr/365 calendar-days). General extrusion laborers were assumed to be exposed to 

air containing 147 dpm/m3

 based on the geometric mean DWA for a “weigh man.” Supervisor 

and clerical exposures were assumed to be 50% and 10% of the general laborer, respectively 

(Battelle 2006, p. 44). 

Geometric mean air concentrations experienced by operators during rod straightening were 

assumed to be 1,690 dpm/m3, while exposures to laborers were 50% of operators, supervisors 

were 50% of laborers, and clerical personnel were 10% of supervisors (Battelle 2006, p. 47). 

It is important to note that the geometric mean values for the operators in Tables 7.2 and 7.7 of 

TBD-6000 are calculated from min/max values (i.e., two values) reported by the original authors 

and not from a multi-value population (TBD-6000, p. 44): 

 1

 This is the geometric mean for a lognormal distribution with an assumed GSD of 5. 

2

 This assumption is slightly non-conservative, based on a conversion factor of 1 mR/0.877 mrem. 

3

 The dimensions of the slab are 40.64 cm wide × 60.96 cm long × 10.16 cm thick (Anderson and Hertel 2005). 
TBD Appendix C Review 9 SC&A – August 24, 2009 

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If the value was presented as a two-value range, the two values were assumed to 

be set about the geometric mean such that the geometric mean is equal to the 

square root of the product of the two values; this lognormal distribution is also 

assumed to have a GSD=5. 

Given the very limited data used to calculate the geometric mean and the fact that the geometric 

mean is substantially less than the expected value of the lognormal distribution, we do not 

believe that the geometric mean is a claimant-favorable metric for calculating inhalation doses. 

We believe that, given the uncertainty in the data, the 95th percentile value is a more appropriate 

metric under these circumstances. We note that in its SEC-0079 Petition Evaluation Report 

(NIOSH 2007a), NIOSH specifically cited its ability to estimate maximum doses: 

NIOSH has access to sufficient information to estimate the maximum radiation 

dose that could have been incurred from exposure to uranium. Potential internal 

doses received from exposure to uranium during AEC-related uranium metal 

operations can be reconstructed using assumptions and methods such as those 

provided in the NIOSH guidance document, “Estimating the Maximum Plausible 

Dose to Workers at Atomic Weapons Employer Facilities” (ORAUT-OTIB-0004). 

We do not believe that the approach taken in Appendix C is representative of a maximum dose 

estimate or one that is claimant favorable for all workers. We question the use of “maximum 

dose,” since this is only appropriate in denial of claims. The stated approach should be to 

develop plausible bounding doses based on sound scientific principles. 

 

Finding 1: NIOSH has proposed use of geometric mean data to calculate internal uranium 

exposures during the operating period. The geometric mean is based on only two measurements 

and, since the stated goal is to estimate maximum doses, we believe that use of the 95th percentile 

is a more appropriate metric in this situation. 

 

Ingestion exposures are also presented in Table C.1 of Appendix C. These exposures are 

calculated based on OCAS-TIB-009 (NIOSH 2004). Based on the methodology in OCAS-TIB009, the daily ingested activity is assumed to equal 0.2 times the airborne activity. This is 

adjusted to a calendar-day basis in Table C.1. For example, the DWA for the extrusion operator 

of 992 dpm/m3

 is converted to an ingestion exposure of 136 dpm/calendar-day (992 dpm/m3 × 

0.2 × 250 work-days/365 calendar-days = 136 dpm/calendar-day). Notwithstanding some of our 

previously cited concerns with OCAS-TIB-009, the ingestion exposures as derived for this 

application appear to be upper bounds, because the implicit assumption is that cleanup did not 

occur after the extrusion and rod straightening campaigns, and ingestion occurred throughout the 

year. 
TBD Appendix C Review 10 SC&A – August 24, 2009 

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2.1.2 Uranium Exposures during the Residual Period 

2.1.2.1 Internal Uranium Exposures 

Guidance for estimating internal uranium doses during the residual period is presented in 

Table C.1. The only additional information provided in Appendix C is that the estimates assume 

resuspension of uranium deposited during 1960. If one assumes a uranium air concentration in 

1960 of 1,690 dpm/m3 (TBD-6000, Table 7.7), a terminal settling velocity of 0.00075 m/s, and a 

settling time of 168 hours, the uranium surface concentration is 0.767 × 10-6 dpm/m2 at the 

beginning of the residual period, which can be converted to an air concentration of 

0.767 dpm/m3 in subsequent years, based on a resuspension factor of 1 × 10-6/m. The resulting 

inhalation rate is 5.0 dpm/calendar-day, based on a breathing rate of 9.6 m3

/work-day 

(0.767 dpm/m3 × 9.6 m3/work-day × 250 work-days/365 calendar-days). This value is similar to 

the value of 5.5 dpm/calendar-day cited in Table C.1. 

There are two issues that should be addressed relative to this approach—the resuspension factor 

and the assumption of a time-independent air concentration during the residual period. SC&A 

had previously questioned the use of a resuspension factor of 1 × 10-6/m (SC&A 2007b, 

Section 7.1). In our review of TBD-6000, we noted the following: 

Resuspension factors are highly uncertain and variable in time and location, and 

that the resuspension factor adopted in the TBD might be too low by at least 1 

order of magnitude, especially if it is to be used to place a plausible upper bound 

on exposures. 

SC&A also provided a comprehensive review of ORAUT-OTIB-0070 (ORAUT 2008), where 

similar concerns about the use of a resuspension factor of 1 × 10-6/m were raised (SC&A 2008b). 

These concerns were summarized in Finding No. 13 from SC&A 2008b: 

Finding #13: NIOSH’s Recommended Resuspension Factor of 10-6 m

-1 is 

Inappropriate. 

Indoor resuspension factors cited in the scientific literature that involve 

substantial industrial activities (as would be expected in an AWE facility that may 

continue to operate after operations were performed for the MED or AEC) may 

experience air concentrations corresponding to RF values of 10-4

 m

-1 to 10-3 m-1. 

The recommended RF value of 1 × 10-6

 m

-1 by the NRC is limited to facilities that 

have previously been subjected to extensive decontamination efforts in 

anticipation of license termination. A principal objective of such 

decontamination efforts is to minimize any removable surface contamination that 

would contribute to the resuspension of surface contaminant. NRC’s criteria that 

include the recommended RF value of 10-6 m

-1 have only recently been 

established, and have limited relevance to AWE facilities that operated decades 
TBD Appendix C Review 11 SC&A – August 24, 2009 

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ago and were never subjected to the stringent D&D criteria that separated the 

AWE’s operational period from its post-operational period. 

The second concern is the use of a time-invariant uranium air concentration during the residual 

period. While this approach is claimant favorable and will, in part, offset a low resuspension 

factor, it is inconsistent with the guidance in ORAUT-OTIB-0070 (ORAUT-2008), where an 

exponential decay function is recommended. It is also inconsistent with the exponential decay 

approach taken for thorium air concentrations during the residual period, as discussed 

subsequently in Section 2.2.2.1.1. 

Finding 2: The resuspension factor used by NIOSH for estimating uranium dust concentrations 

in air could be low by 1 to 2 orders of magnitude. NIOSH should revisit the use of a value of 1 × 

10-6/m. 

Finding 3: NIOSH should consider developing an exponential decay function for uranium 

removal during the residual period based on guidance in ORAUT-OTIB-0070. 

2.1.2.2 External Uranium Exposures 

Guidance on estimating doses from external pathways during the residual period is presented in 

Table C.2. Appendix C does not provide any information as to how the external exposures and 

doses were calculated, except to state that they are based on “Contamination Only” from 

Table 6.4 of TBD-6000. We note that the data entries on the last line of columns 4, 5, and 6 in 

Table C.2 are the same as those on the last line of columns 4, 5, and 6 in Table C.1. We believe 

that typographical errors exist in Table C.2, since we have been able to reproduce the data in 

Table C.1. If we assume that the “Contamination Only” exposure from Table 6.4 of TBD-6000 

is 1.384 × 10-3 mR/calendar-day (geometric mean), then the annual exposure would be 

0.505 mR, not 5.5 mR, as reported in Table C.2. 

Finding 4: There appear to be data entry errors in Table C.2 for the residual period. 

2.2 THORIUM EXPOSURES 

2.2.1 Thorium External Exposures during the Operating Period 

Consistent with the position developed in Addendum 1 to the petition evaluation report for SEC00079 (NIOSH 2007b), NIOSH does not attempt to reconstruct internal thorium doses during the 

operating period, but they do develop bounding external doses based on data received after the 

initial petition evaluation report was published on April 13, 2007. 

Before describing the NIOSH approach to external thorium dose reconstruction during the 

operating period, it is useful to review the available data. This review is presented in the 

following paragraphs. 
TBD Appendix C Review 12 SC&A – August 24, 2009 

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Silverstein (1957c) observed that, based on a film badge survey, the average weekly external 

exposure to workers involved in a variety of production operations, including foundry activities, 

inspection, and shipping, was less than 10 mR, with the maximum exposure being about 30 mR. 

The film badge survey data, which were taken at the Dow Bay City Plant, where operations 

similar to those at Dow Madison Plant were performed, are summarized in Table 1 (Silverstein 

1957b). The data are based on exposures for 13 working days. 

Table 1. Film Badge Survey of HK31 Casting Production 

during 13 Working Days 

Job Exposure (mR) 

Pour Off #1 10 

Pour Off #2 75 

Pour Off #3 10 

Knockout #1 10 

Knockout #2 <10 

Sandblast #1 10 

Sandblast #2 <10 

Bandsaw #1 10 

Bandsaw #2 50 

Chipper #1 <10 

Chipper #2 10 

Machine Trim 10 

Inspection (Rough) 10 

Pickler <10 

Rotary File #1 50 

Rotary File #2 10 

Buffer 10 

Heat Treat 10 

Wheelabrator <10 

Pickler <10 

Inspection (Final) 10 

Touchup <10 

X-ray <10 

Fixture <10 

Shipping 50 

Metal Reclamation 10 

External radiation exposure had been measured by Dow for a stack of Mg-3.5% Th alloy 

(HK31A) slabs.4

 The β/γ dose at the surface was 4.2 mR/hr, 1.8 mR/hr at 1 foot, and declined to 

0 at a distance of 7 ft from the alloy stack. Dow estimated that a worker with his hands in 

contact with the alloy stack and his body 1 foot from the stack would receive an exposure to the 

hands of 168 mR/week and exposure to the body of 72 mR/week, based on a 40-hr week 

(Silverstein 1956c). 

 4

 This was a 9-ft high stack of slabs with dimensions of 10 in × 26 in × 76 in (Dow 1956). 
TBD Appendix C Review 13 SC&A – August 24, 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. 

Exposure to thorium pellets measured 35 mR/hr on contact and Dow estimated that at the normal 

working distance from the pellets, the worker’s exposure was less than 1 mR/hr (Silverstein 

1956a). 

In addition, Dow estimated that a single worker handling all the thorium pellets required for a 

100,000 lb run of Alloy HK31 would receive an external exposure of 53 mR (Levy 1957). 

Based on 2 to 3 such runs per year, the annual exposure would be 0.10–0.16 R. Companion 

estimates using 26% Th hardener yielded values of 0.25–0.38 R/yr. A worker who continuously 

handled HK31 for 40 hours per week would receive a weekly whole-body dose of 0.07R (Levy 

1957). 

Stein (1982) reported on external exposure measurements made during the casting of Alloy 

HK21A by CONALCO (a successor operator of the Madison Plant). While these measurements 

were made during the residual period, they should be representative of external exposures during 

the operating period. Other than exposures to thorium hardener, the highest exposure reported 

by Stein (1982) was 0.7 mR/hr measured at a distance of 1 foot from HM scrap slabs. 

Extrapolating this measurement to a full year results in an exposure of 1,400 mrem. Most of the 

other measurements reported by Stein (1982), except those involving hardener exposures, were 

at least an order of magnitude lower. Exposures to a barrel of thorium hardener (38% Th) were 

15–20 mR/hr, values similar to those reported by Silverstein (1956a) for Th pellets. 

These various thorium external exposure estimates are summarized in Table 2. 

Table 2. Annual Estimates of External Thorium Exposures 

Activity Annual Exposure 

(mR/yr) Reference 

Alloying with 26% Th hardener 250–380 Levy 1957 

Alloying with Th pellets 100–160 Levy 1957 

Casting HK31 at Bay City <500–1,450 Silverstein 1957b 

Continuously handling HK31 3,500 Levy 1957 

Continuously handling Th pellets 

(at worker’s normal distance from Th) 

<2000 Silverstein 1956a 

Standing one foot from a stack of HK31A alloy slabs 3,600 Silverstein 1956c 

Standing one foot from HM alloy scrap slabs 1,400 Stein 1982 

It should be emphasized that all the annual exposure estimates in Table 2 except casting of alloy 

HK31 at Bay City are based on meter readings, not time-integrated measurements. 

NIOSH used the film badge data in Table 1 of this report to develop external photon exposures 

for thorium. They developed a lognormal distribution for the data and assumed that operators’ 

exposures would be defined by the 95th percentile exposure of 1,095 mR/yr. Laborers’ 

exposures were set at half of the value for operators (548 mR/yr). Supervisors’ exposures were 

set at half the laborers’ exposures, and clerical and other workers’ exposures were set at the 5th

percentile. NIOSH assumed that beta doses were the same as photon doses at all distances. 

SC&A checked the NIOSH analysis but, as can be seen from Table 1, all but three of the photon 

exposure measurements are 10 mR (or less). This results in a poor fit to a lognormal distribution 
TBD Appendix C Review 14 SC&A – August 24, 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. 

and creates considerable uncertainty as to the 95th percentile value. By fitting the data points to a 

regression line for a lognormal distribution, SC&A calculated that the 95th percentile was 

788 mR/yr. However, fitting the data to an empirical cumulative distribution function resulted in 

a value of about 1,000 mR/yr for the 95th percentile. This is in reasonable agreement with the 

value of 1,095 mR/yr cited by NIOSH. 

2.2.2 Thorium Exposures during the Residual Period 

The beginning date for the residual period was fixed as January 1, 1961. The end date for 

thorium exposures during the residual period was fixed at November 30, 2007, since the final 

shipments of thorium-contaminated material were made during November 2007 (Pangea 2008). 

2.2.2.1 Internal Exposures 

Inhalation Exposures 

The approach used to bound thorium exposures during the residual period was originally 

presented in Addendum 2 to SEC-00079 Petition Evaluation Report (NIOSH 2008a). The same 

approach was adopted for use in Appendix C of TBD-6000. As a starting point for the internal 

exposure analysis, it is assumed that the airborne thorium concentration at the beginning of the 

residual period was 8.44 pCi/m3

. This value is based on the highest value (actually the highest 

minimum detectable concentration) of any general area air sample taken between 1957 and 1959 

at Dow Madison. Process and breathing zone samples were excluded, based on the premise that 

general area samples would be representative of resuspension and dispersion processes. SC&A 

agrees with this basic approach for this type of problem. 

The limiting sample was cited by Dow as <0.076 mg/m3

 of Th, which was converted to 

8.44 pCi/m3. When annualized using a breathing rate of 9.6 m3/day, the resulting exposure is 

20,256 pCi/yr. In its focused review of Addendum 2 (SC&A 2008a), SC&A raised questions 

regarding the definition of the sample population from which the maximum value of 

<0.076 mg Th /m3

 was selected. Although these questions have not been answered, their 

resolution will probably not change the bounding value significantly. 

To establish the rate at which this initial (1961) concentration would decay, NIOSH selected data 

obtained during clean-up operations conducted by Pangea in 2006 (Pangea 2008). Pangea 

measured airborne Th concentrations of 9.94% of the derived air concentration for Class Y 

Th-232 in perimeter monitoring stations. (The DAC for Class Y Th-232 is 1 pCi/m3 per 10 CFR 

20, Appendix B, Table 1.) The initial air concentration and the 2006 air concentration were then 

fitted to an exponential decay function based on guidance provided in ORAU-OTIB-0070 

(ORAUT 2008), and year-by-year air concentrations were calculated. The annual inhalation 

intakes in pCi/yr of Th-232 from Table 3-2 of Addendum 2 to the SEC-00079 Petition 

Evaluation Report were converted to units of dpm/calendar-day in Table C.3 of Appendix C. 

For example, for 1961, 20,256 pCi/yr × 2.22 dpm/pCi × 1 yr/365 calendar-days = 

123 dpm/calendar-day. The calculations in the two documents are clear and correct. The 

approach of using air concentrations made during clean-up is clearly a bounding approach. 
TBD Appendix C Review 15 SC&A – August 24, 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. 

NIOSH notes that the values in Table C.3 should be used for Th-232, Th-228, and Ra-228, and 

that twice the Table C.3 values should be used for Th-230. The basis for the Th-230 assumption 

is assays of materials (soil, slag, and debris) removed during decontamination of the Dow 

Madison facility in 1992. A total of 100,614 tons containing 11.4 Ci of Th-230 and 5.7 Ci of 

Th-232 was shipped to Envirocare in Utah for disposal (Baker 1992, p. 3-1). SC&A believes 

that, at a facility such as this, it would be unlikely that Th-230 exposures would be greater than 

Th-232 exposures. However, the approach taken by NIOSH is certainly bounding. 

Thoron Exposures 

In Addendum 2 to the SEC-00079 Petition Evaluation Report, NIOSH analyzed thoron (Rn-220) 

measurements made in December 1959 during the melting and casting of HK31 alloy. From the 

selected dataset, NIOSH calculated that the 95th percentile thoron concentration was 0.182 pCi/L. 

When SC&A reviewed Addendum 2, we determined that the correct value for the 95th percentile 

was 0.247 pCi/L (SC&A 2008a). NIOSH used the corrected value of 0.247 pCi/L in 

Appendix C of TBD-6000 as the beginning thoron concentration for the residual period. The 

thoron concentration was then allowed to decay at the same exponential rate as was used for 

thorium in air (see Section 2.2.2.1.1). NIOSH also reported thoron exposures in WLM, although 

they did not define the units of measurement (presumably WLM per year), nor how units of 

pCi/L were converted to WL. We note in UNSCEAR 2000 (Annex B, p. 103) that for thoron, 

1 Bq/m3

 equals 3.64 mWL (0.135 WL per pCi/L) at equilibrium. NIOSH cites essentially the 

same value (0.133 WL per pCi/L) in OCAS-TIB-0011 (NIOSH 2008b). 

It appears, although not so stated, that NIOSH made the claimant-favorable assumption of 

equilibrium between Rn-220 and its progeny. DOE cites a default value for the thoron progeny 

equilibrium factor of 0.04 (DOE 1999, Table 4), while UNSCEAR cites a somewhat higher 

value of 0.1 (UNSCEAR 1993, Annex A, Para. 120). Both values are well below the 

equilibrium factor apparently assumed by NIOSH. 

Ingestion Exposures 

Estimates of thorium ingestion during the residual period are provided in Table C.3 of 

Appendix C. Thorium ingestion rates were calculated based on the concepts provided in OCASTIB-0009 (NIOSH 2004). Assuming a thorium air concentration of 8.44 pCi/m3

 in 1960, the 

ingestion rate in 1961 was 2.57 dpm/calendar per Table C.3 (8.44 pC/m3 × 2.22 dpm/pCi × 0.2 × 

250 work-days/365 calendar days. Ingestion exposures followed the same exponential decay 

rate as inhalation exposures. As discussed above for uranium, this approach appears to be 

claimant favorable. 

3.0 TRANSPARENCY OF MODELING APPROACH 

Numerous instances are included in the above discussion regarding how the dose reconstruction 

guidance was developed. It is often difficult to trace the assumptions to their source or to 

understand how the cited assumptions were actually implemented. In some cases, units of 
TBD Appendix C Review 16 SC&A – August 24, 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. 

measurement are not clear. With minimal effort, NIOSH could significantly enhance the 

transparency of the dose reconstruction guidance. 

Finding 5: NIOSH should focus additional attention on insuring the transparency of the dose 

reconstruction guidance. 

4.0 REFERENCES 

10 CFR 20. Code of Federal Regulations. Title 10 – NRC Regulations. Part 20: Standards for 

Protection Against Radiation. 

 

42 U.S.C. §§ 7384 et seq., Energy Employees Occupational Illness Compensation Program Act 

of 2000; as amended; OCAS website. 

AEC (U.S. Atomic Energy Commission) 1952. Adley, F.E., Gill, W.E., and Scott, R.H., Study of 

Atmospheric Contamination in the Metal Melt Building, HW-23352 (rev.), New York Operations 

Office, New York. April 4, 1952. 

Anderson, J.L. and N.E.Hertel 2005. “Bremsstrahlung Doses from Natural Uranium Ingots.” 

Radiation Protection Dosimetry. v. 115, No. 1-4, pp. 298-301. 

Baker, K. 1992. Madison Site Cleanup, Final Report, prepared by Ken Baker, Environmental 

Restoration Group, December, 1992; SRDB Ref ID: 43582 

Battelle 2006. Site Profiles for Atomic Weapons Employers that Worked Uranium and Thorium 

Metals. Battelle-TBD-6000. Battelle Team Dose Reconstruction Project for NIOSH. 

DOE 1999. DOE Standard – Internal Dosimetry. DOE-STD-1121-98. U.S. Department of 

Energy, Washington, DC. 

 

DOE 2008. Letter from Department of Energy to Department of Labor, January 8, 2008.

(SRDB Ref. ID 105199). 

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TDC 000004. 

Harris, W.B. and I. Kingsley, 1959. The Industrial Hygiene of Uranium Fabrication. A.M.A. 

Archives of Industrial Health, Vol. 19, May 1959. pp. 76–101. 

Levy, D.J. 1957. Memo to G. Ansel, Technical Director: Current Exposure to Radioactivity.. 

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NIOSH 2004. Estimation of Ingestion Intakes. OCAS-TIB-0009. Rev. 0. Office of 

Compensation and Support. 
TBD Appendix C Review 17 SC&A – August 24, 2009 

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. 

NIOSH 2007a. SEC Petition Evaluation Report Petition SEC-00079, National Institute for 

Occupational Safety and Health, April 13, 2007. (SRDB Ref ID: 39873). 

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ORAUT 2005. Site Profile for Simonds Saw and Steel, Rev. 00 PC-1. ORAUT-TKBS-0032. Oak 

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Employer Facilities, ORAUT-OTIB-0004, Rev. 3 PC-2, Oak Ridge Associated Universities 

Team: Cincinnati, Ohio. December 6, 2006. 

ORAUT 2008. Dose Reconstruction During Residual Radioactivity Periods 

at Atomic Weapons Employer Facilities. ORAUT-OTIB-0070, Rev. 00. Oak Ridge Associated 

Universities Team: Cincinnati, Ohio. 

Pangea 2008. Project Closure Report for the Spectrulite Consortium Inc. Madison, IL Facility.

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SC&A 2007a. A Focused Review of Operations and Thorium Exposures at the Dow Chemical 

Company - Madison Plant. Contract No. 200-2004-03805, Task Order No. 5. August 2007

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that Worked Uranium and Thorium Metals. Contract No. 200-2004-03805, Task Order No. 3. 

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SC&A 2008a. A Focused Review Of Addendum 2 To The Dow Chemical – Madison Plant SEC 

Petition Evaluation Report (SEC-00079). Contract No. 200-2004-03805, Task Order No. 5, 

SCA-SEC-TASK5-0057. S. Cohen and Associates, Inc., Vienna, Virginia. 

SC&A 2008b. Review of ORAUT-OTIB-0070: Dose Reconstruction During Residual 

Radioactivity Periods at Atomic Weapons Employer Facilities. Contract No. 200-2004-03805. 

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29, 2008. 

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and Casting HM21 Alloy at the Madison Division. File: T2.1-6-1. Biochemical Research 

Department, The Dow Chemical Company. August 23, 1956. TDCC 000005-000013. 
TBD Appendix C Review 18 SC&A – August 24, 2009 

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. 

Silverstein, L.G., 1956c. Magnesium-Thorium Alloys: Industrial Health Experience in 

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York. TDCC 000109-000148. 

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Ref ID: 40440. 

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