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NIOSH Response to SC&A’s Metals and 

Controls Corp. Exposure Pathway 

Evaluation and Dust Loading Commentary

Response Paper

National Institute for Occupational

Safety and Health

January 12, 2022

Pat McCloskey, CHP, CIH and Mutty Sharfi, CHP, CIH 

Oak Ridge Associated Universities Team

Reviewed by LaVon Rutherford, CHP and Timothy Taulbee, Ph.D., CHP

Division of Compensation Analysis and Support 

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.
Response Paper NIOSH Response to SC&A’s Metals and Controls Corp. 

Exposure Pathway Evaluation and Dust Loading Commentary

January 12, 2022

Page 2 of 7 

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

BACKGROUND: EXPOSURE PATHWAYS 

Since the National Institute of Occupational Safety and Health (NIOSH) presented the Special 

Exposure Cohort (SEC) Petition SEC-00236 Metals and Controls Corp (M&C) Evaluation 

Report (ER) [NIOSH 2017] at the August 2017 Board meeting, NIOSH, SC&A, and the M&C 

Work Group (WG) have spent considerable efforts refining the exposure bounding models. At its 

March 18, 2021 meeting, the M&C WG tasked SC&A to review each of the exposure models 

that NIOSH presented in its January 21, 2021 paper, Response to Comments from the Metals and 

Controls Corp. Work Group Meeting Held on September 2, 2020 [NIOSH 2021]. On October 25, 

2021, NIOSH received the SC&A report Metals and Controls Corp. Exposure Pathway 

Evaluation [SC&A 2021a], which provides SC&A's evaluation of the six exposure pathways 

NIOSH developed in support of SEC-00236. Since SC&A and NIOSH have reached a general

agreement regarding the exposure pathways, this response paper will briefly describe NIOSH's 

understanding of SC&A’s review and attempt to clarify any remaining issues and concerns. 

SC&A reviewed the following six exposure pathways [SC&A 2021a]: 

1. Subsurface Inside

2. Subsurface Outside

3. Roof and Overhead 

4. Welding 

5. HVAC Maintenance

6. Remaining (nonmaintenance) 

SC&A's review summarized each exposure pathway and the data supporting the intake model 

and included any concerns the M&C WG and petitioners expressed. Then SC&A replicated the

annual committed effective dose calculations to demonstrate they understood NIOSH’s 

assumptions used from the pathway. 

For most pathways, SC&A calculated a similar but lower dose and presented conclusions that 

include the following [SC&A 2021a]: 

• “SC&A reviewed the NIOSH revised modeling in the matrix and agreed with the 

penetrating dose modeled. SC&A modeled beta doses and had a modestly different 

interpretation of beta dosimetry results. SC&A calculated a similar but lower dose 

of 9.7 mrem/month. The difference is modest; therefore, SC&A believes this 

concern is not worth pursuing further" [PDF p. 8]. 

• "SC&A believes there is no evidence that suggests that equal weights of thorium 

should be expected when uranium is present; however, there is not sufficient 

information to establish that it could not be that high. It is reasonable to conclude 

that it is unlikely that thorium weights would be greater than uranium weights. 

Therefore, given the uncertainties associated with the thorium-to-uranium ratios 
Response Paper NIOSH Response to SC&A’s Metals and Controls Corp. 

Exposure Pathway Evaluation and Dust Loading Commentary

January 12, 2022

Page 3 of 7 

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

present on site and the fact that we cannot rule out a 1:1 mass ratio of uranium to 

thorium, the NIOSH approach is claimant favorable" [PDF p. 13].

• "SC&A believes the impacts of the conservativeness of the assumptions applied to 

the model are greater than the impacts of the uncertainties associated with material 

dilution and extraction. Taken in combination, SC&A believes that the methods

and assumptions used by NIOSH to reconstruct internal doses to M&C workers 

involved in subsurface maintenance and repurposing activity in Building 10 during 

the residual period are scientifically sound and claimant favorable" [PDF p. 15]. 

• “SC&A agrees with the WG members’ concern that the data from the waste and associated 

contamination in the burial grounds are representative of only a subset of the work performed 

during operations. The wastes do not capture the entirety of the operations period. However, 

SC&A does not believe this represents a DR infeasibility. Although the data do not represent 

all of the operations period, they do represent the remaining source term onsite throughout 

the residual period” [PDF p. 18].

NIOSH RESPONSES TO SC&A EXPOSURE PATHWAY FINDINGS AND 

OBSERVATIONS

This section presents the SC&A exposure pathway findings and observations that require 

clarification or a NIOSH response.

SC&A Finding 1: Building 10 subsurface external exposures not bounded

SC&A finds that NIOSH's proposed external dose rate assumptions are inconsistent 

with the contamination levels assumed for the subsurface of Building 10. SC&A's 

independent calculations suggest dose rates from the modeled pathway are expected to 

be substantially greater. NIOSH's 2017 SEC ER proposed using the 95th percentile 

dosimetry values (with adjustments for missed dose) of 200 mrem/year (16.7 

mrem/month). SC&A believes it is more appropriate to assign elevated subsurface 

exposures inside Building 10 using the 95th percentile of the dosimetry with occupancy 

adjustments [SC&A 2021a, PDF p. 16].

NIOSH Response to SC&A Finding 1

Although SC&A recommends using the 95th percentile film-badge data for the indoor subsurface 

model, they do not recommend it for outdoor subsurface exposures because of their comparison 

to a value calculated using Federal Guidance Report (FGR) No. 12. NIOSH believes using the 

actual soil contamination data workers were exposed to (as calculated by SC&A) is appropriate 

for modeling subsurface exposures. NIOSH can use the dose coefficients for exposure to soil 

contaminated to an infinite depth tabulated in FGR 12 and the same soil contamination values 

used in our subsurface internal exposure model to assign doses. If NIOSH changes the model, we 

will also use this method to model outdoor subsurface exposures to remain consistent. 
Response Paper NIOSH Response to SC&A’s Metals and Controls Corp. 

Exposure Pathway Evaluation and Dust Loading Commentary

January 12, 2022

Page 4 of 7 

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

SC&A Observation 1: Indoor and outdoor subsurface scenarios

SC&A reviewed the claimant interviews and does not believe that there is sufficient 

evidence to limit any individual's subsurface exposures to a single subsurface scenario. 

The interviews indicate that, irrespective of an individual's job title, they may have been 

asked to complete any task on site. SC&A believes that means an individual could have 

participated in both indoor and outdoor subsurface scenarios within a year [SC&A 

2021a, PDF p. 20]. 

NIOSH Response to SC&A Observation 1 

Since NIOSH used worker interviews to determine the two-month per year occupancy rate, we 

decided the most claimant favorable method was to assign the location with the highest exposure 

rate. NIOSH's understanding of this observation is that SC&A recommends increasing the total 

subsurface exposures duration (combined indoor and outdoor) to four months. Although this 

assumption is inconsistent with the interviews indicating two months total, NIOSH is open to 

considering this change. This change would amount to four months of subsurface exposure, and 

NIOSH would assign the remaining eight months as “remaining exposures” per the Technical 

Basis Document (TBD). 

SC&A Finding 2: Welding prep resuspension factor

SC&A raised a concern (finding 2) in its 2019 (SC&A, 2019) and 2020 (SC&A, 2020b) 

reviews of welding and thorium activities that a resuspension factor of 10-3/m may not 

be adequate to represent the dust generated by grinding and wire brushing to prepare a 

surface for welding. The work group members echoed this concern during the 

September 2, 2020, M&C Work Group meeting (M&C WG, 2020). To date, this issue 

has not been resolved. SC&A agrees that this is a "TBD issue" rather than an SEC issue

[SC&A 2021a, PDF pp. 24, 25].

NIOSH Response to SC&A Finding 2

NIOSH believes a 10-3 resuspension factor is representative and bounding of work activities and 

conditions at M&C. Work activities are a distribution of actions in which the majority of 

resuspension factors in Table 3-1 of OTIB-0070 are sizably smaller (in most cases orders of 

magnitude smaller) than the proposed 10-3 resuspension factor. 

Although NIOSH believes using a 10-3 resuspension factor is claimant favorable and bounding, 

we agree it is a TBD issue and not an SEC issue. 

CONCLUSIONS AND RECOMMENDATIONS: EXPOSURE PATHWAYS 

This section presents SC&A’s exposure pathways conclusion and NIOSH’s response. 
Response Paper NIOSH Response to SC&A’s Metals and Controls Corp. 

Exposure Pathway Evaluation and Dust Loading Commentary

January 12, 2022

Page 5 of 7 

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

SC&A Exposure Pathways Conclusion 

With the modifications suggested in the finding and observation, SC&A believes 

internal and external doses from each maintenance exposure pathway can be bounded.

SC&A recommends NIOSH develop guidance for dose reconstructors that allows 

modification to the established occupancy factors if statements in the computer-assisted 

telephone interview or evidence in the energy employee's employment records suggest a 

different breakdown of work may be more appropriate. SC&A also recommends that 

NIOSH include guidance to help dose reconstructors prorate doses for partial years of 

employment. SC&A is unaware of any other AWE sites with many exposure pathways 

where precedent has been set for the treatment of partial years of employment. 

Developing guidance would help ensure partial years of employment are treated 

consistently in all M&C cases. SC&A recommends prorating all occupancy factors 

based on partial years of employment [SC&A 2021a, PDF p. 29].

NIOSH Response to SC&A Exposure Pathways Conclusion 

When NIOSH finalizes our dose reconstruction method, we will include additional guidance on 

occupancy factors and assigning partial-year doses. 

BACKGROUND AND DISCUSSION: DUST LOADING

At the March 18, 2021 meeting, the M&C WG tasked SC&A to evaluate the representativeness 

of NIOSH's dust loading values for M&C indoor and outdoor excavations as presented in 

NIOSH’s January 21, 2021 paper Response to Comments from the Metals and Controls Corp. 

Work Group Meeting Held on September 2, 2020 [NIOSH 2021] and the appropriateness of 

using the data as a generic default value for incorporation into ORAUT-OTIB-0070. 

Note: Although NIOSH will use M&C to inform our modeling of similar Energy Employees 

Occupational Illness Compensation Program Act work, we agree with SC&A that “one 

size will not fit all.” We will address this further during the next ORAUT-OTIB-0070

revision.

On October 25, 2021, NIOSH received SC&A’s report SC&A Commentary on NIOSH's 

Approach to Quantifying Outdoor and Indoor Airborne Dust Loadings [SC&A 2021b]. This 

report provides SC&A's evaluation of the dust load model developed over many iterations in 

support of SEC-00236. Since SC&A and NIOSH have reached a general agreement regarding 

dust loading values, this response paper will briefly describe NIOSH's understanding of SC&A’s

review and attempt to clarify any remaining issues and concerns. 

SC&A's review of NIOSH's dust load model included a statistical analysis of the supporting 

Mound data in determining the model's validity. Then SC&A independently calculated the 95th

percentile to demonstrate they understood NIOSH's assumptions. Their result was "... modestly 

larger though reasonably similar to ..." [SC&A 2021b, PDF p. 11] the NIOSH value. 
Response Paper NIOSH Response to SC&A’s Metals and Controls Corp. 

Exposure Pathway Evaluation and Dust Loading Commentary

January 12, 2022

Page 6 of 7 

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Additionally, SC&A noted, "... that this dust loading when applied at M&C makes no 

adjustment for background (ambient) levels of dust in the air, which adds an additional degree of 

conservatism to the calculation" [SC&A 2021b, PDF p. 11]. 

CONCLUSIONS AND RECOMMENDATIONS: DUST LOADING

Using the Board's surrogate data criteria, SC&A evaluated the model to determine if there were 

any surrogate data issues and noted the following: “SC&A deems the dust loading results of the 

Mound study to be scientifically plausible. This determination was made by analysis of the data 

obtained from the Mound study, which had a range consistent with values expected from 

excavation activities” [SC&A 2021b, PDF p. 13]. 

SC&A summarized several studies that address dust loadings and believes NIOSH should 

reference them as the basis for the dust loading of 212 μg/m3 in addition to the Mound data. 

SC&A also suggests NIOSH address enrichment/enhancement issues for dust loadings. This 

section presents SC&A’s dust loading conclusion and NIOSH’s response. 

SC&A Dust Loading Conclusion

SC&A concludes that NIOSH's adoption of 212 μg/m3 for estimating respirable outdoor 

dust loading during excavation activities is reasonable but not necessarily bounding. 

While SC&A's survey and interpretation of the data indicate that the suggested value of 

212 μg/m3 may not necessarily be sufficiently conservative for many excavation 

scenarios, a number of mitigating factors are also present at M&C that should be 

considered. First, the soil at M&C was likely moist. Second, the dust loading used for 

dose reconstruction at M&C covered the entire assumed time period of 2 months; i.e., 

the suggested exposure models are not trying to reconstruct short-term exposures, 

where dust loading might peak during active and aggressive excavation, but are making 

use of the dust loading for deriving inhalation exposures over a more protracted period 

of time [SC&A 2021b, PDF pp. 21, 22].

NIOSH Response to SC&A Dust Loading Conclusion

NIOSH intends to review the references provided by SC&A and incorporate them as appropriate. 

In addition, NIOSH will update our M&C models that utilize dust loads (i.e., Subsurface Inside, 

Subsurface Outside) to consider the impact of enhancement factors.
Response Paper NIOSH Response to SC&A’s Metals and Controls Corp. 

Exposure Pathway Evaluation and Dust Loading Commentary

January 12, 2022

Page 7 of 7 

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

REFERENCES

NIOSH [2017]. Special Exposure Cohort petition evaluation report petition SEC-00236 Rev. 0 

Metals and Controls Corp. Cincinnati, OH: U.S. Department of Health and Human Services, 

Centers for Disease Control and Prevention, National Institute for Occupational Safety and 

Health. April 5. [SRDB Ref ID: 176720] 

NIOSH [2021]. NIOSH/ORAU: Response to comments from the Metals and Controls Corp. 

work group meeting held on September 2, 2020. Metals and Controls Corp. Cincinnati, OH: U.S. 

Department of Health and Human Services, Centers for Disease Control and Prevention, NIOSH. 

January 21. [SRDB Ref ID: 184642] 

SC&A [2021a]. SC&A draft: Metals and Controls Corp. exposure pathway evaluation. 

Arlington, VA: SC&A, Inc. SCA-TR-2021-SEC004 Rev. 0 draft, October 25. [SRDB Ref ID: 

190928] 

SC&A [2021b]. SC&A draft: Commentary on NIOSH’s approach to quantifying outdoor and 

indoor airborne dust loadings. Arlington, VA: SC&A, Inc. SCA-TR-2021-SEC005 Rev. 0 draft, 

October 25. [SRDB Ref ID: 190929]