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MEMO 

TO: Subcommittee on Dose Reconstruction 

FROM: Harry Chmelynski, SC&A 

DATE: February 26, 2013 

SUBJECT: Questions/Status of Bridgeport Brass Findings 

 

This memorandum is in response to the questions raised during the most recent Subcommittee on 

Dose Reconstruction meeting held on February 4, 2013, concerning the history and current status 

of Findings 2 and 4 for external exposures at the Bridgeport Brass facilities. Finding 2 deals 

with the issue of building a coworker model by sampling from pooled data, and Finding 4 deals 

with the issue referred to as “leave-one-out” as a means of evaluating the significance of data 

outliers on the development of a coworker model. These findings originally were reported by 

SC&A in our limited review of the Bridgeport Brass exposure matrix (SC&A 2008) provided in 

ORAUT-TKBS-0030, An Exposure Matrix for Bridgeport Brass: Havens Laboratory and 

Adrian Plant, Rev. 0 (ORAUT 2005). As explained in this memorandum, the previous 

considerations of these findings appear now to be moot, as NIOSH has recently issued a revised 

version of ORAUT-TKBS-0030 (ORAUT 2013) based on a new methodology for deriving 

coworker models. However, the new methodology is part of an active review of an overarching 

protocol (see below) for developing coworker models. The implications are that, although 

Finding 2 is now moot, it is still of concern as an overarching issue. However, SC&A 

recommends that Finding 4 be closed, because it is no longer an issue in light of the new 

approach being used to develop coworker models that does not involve pooled data. 

Previous discussions concerning these findings were held during a Subcommittee meeting in 

2009, where NIOSH submitted a response to each finding. In response to these discussions, 

SC&A prepared a white paper titled, SC&A Follow-Up to NIOSH’s Responses to Bridgeport 

Brass Site Profile Review Findings (SC&A 2009). These issues again were raised as the subject 

of discussion during the February 4, 2013, Subcommittee meeting. 

During the February 4, 2013, meeting, the Subcommittee was informed that NIOSH recently 

published Rev. 1 of ORAUT-TKBS-0030 (ORAUT 2013). SC&A has not yet been tasked with 

reviewing this revised document, but was directed by the Subcommittee to review the revised 

exposure matrix to the extent needed to address the two open findings. The revised exposure 

matrix appears to use an approach that is similar to the one proposed in SC&A 2009. In this 

approach, annualized doses are estimated for each worker (as opposed to using pooled data), and 

the distribution of annualized individual worker exposures is used to derive a lognormal 

distribution for the coworker model. This general approach to coworker models known as “one 

person, one statistic (OPOS),” has been adopted by NIOSH in ORAUT-RPRT-0053, Analysis of 

Stratified Coworker Datasets (ORAUT 2011a). This document is currently under review by 

SC&A. One difference between the OPOS approach used in ORAUT 2013 and the approach 

recommended by SC&A in 2009 is the treatment of non-detects. 

The numerical results are shown in Table 4-1 of ORAUT-TKBS-0030, Rev. 1, but only the 

following brief description is provided as to the calculations that were done. 
Memo: Bridgeport Brass Findings 2 SC&A – February 26, 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 estimate doses for periods when dosimetry data are unavailable, the approach 

described in ORAUT-OTIB-0020, Use of Coworker Dosimetry Data for External 

Dose Assignment (ORAUT 2011a) was used. The cycle data was [sic] converted 

to annual for all workers. For totals based on less than 1 year of cycle data, the 

partial year doses were prorated to an annual dose. Cycled data below the 

LOD/2 were treated as missed dose. The 50th and 95th percentiles are in Table 

4-1 below. [Emphasis added.] 

The brief text above suggests that the OPOS approach was used in the revised Bridgeport Brass 

exposure matrix. The reference the text refers to is given as ORAUT-OTIB-0020, Rev. 2 

(ORAUT 2011a). Rev. 2 was actually issued in 2008 (ORAUT 2008) and this publication was 

superseded by ORAUT-OTIB-0020, Use of Coworker Dosimetry Data for External Dose 

Assignment, Rev. 3 (ORAUT 2011b). The previous version of ORAUT-OTIB-0020 (Rev. 2) 

contained an example of a procedure that was once used at K-25. This example was removed in 

Rev. 3. Otherwise, the reports are very similar. 

It should be noted that Rev. 3 is a 4-page document containing no details pertaining to the 

calculations described in the quote above. To correct this deficiency, SC&A requests that 

NIOSH provide spreadsheets and a detailed description of the data analyses conducted for 

ORAUT-TKBS-0030, Rev. 1. An analysis of these materials will begin after SC&A is tasked 

with the review of Rev. 1. 

The final results presented in Table 4-1 of OTIB-0020, Rev. 1, for Adrian are compared in 

Table 1 with the original SC&A 2008, the NIOSH 2005 results, and the SC&A 2009 results. 

The new NIOSH lognormal distributions using the OPOS approach are similar to the annualized 

dose distribution found by SC&A in 2009, as indicated by similarity of the estimates for the 

lognormal parameters μ and σ. The ORAUT 2013 95th percentile estimate for Adrian Lab is 

higher than the SC&A 2009 estimate for annualized gamma exposure and exceeds all previous 

estimates. The ORAUT 2013 95th percentile estimate is also higher than the SC&A 2009 

estimate for annualized beta exposure, but does not exceed the SC&A 2008 estimate based on 

the bounding assumption of 100% correlation. 

Table 1. Comparison of Adrian Dose Estimates from ORAUT 2005 and ORAUT 

2013 with SC&A 2005 and 2009

GAMMA 

Lognormal 

Parameter 

NIOSH 2013 

Results 

(OPOS) 

SC&A 2009 

Annualized 

Dose 

NIOSH 2005 

Simulation 

(no correlation) 

SC&A 2008 

Simulation 

(100% correlation) 

Units 

μ (mu) 6.39 5.75 1.45 1.45 

σ (sigma) 0.44 0.43 1.31 1.31 

GSD 1.55 1.53 3.70 3.70 

GM (Median) 596 314 4.27 111 mrem 

95th Percentile 1,221 634 452 955 mrem 
Memo: Bridgeport Brass Findings 3 SC&A – February 26, 2013 

 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.

Table 1. Comparison of Adrian Dose Estimates from ORAUT 2005 and ORAUT 

2013 with SC&A 2005 and 2009

NOTICE:

BETA 

Lognormal 

Parameter 

NIOSH 2013 

Results 

(OPOS) 

SC&A 2009 

Annualized 

Dose 

NIOSH 2005 

Simulation 

(no correlation) 

SC&A 2008 

Simulation 

(100% correlation) 

Units 

μ (mu) 7.31 6.50 3.44 3.44 

σ (sigma) 0.83 0.94 1.34 1.34 

GSD 2.29 2.56 3.83 3.83 

GM (Median) 1,495 666 1,817 811 mrem 

95th 

Percentile 5,832 3,118 3,558 7,386 mrem 

Bold: 95th percentile estimates recommended for Adrian in Table 4-1, ORAUT-TKBS-0030, Rev. 1 (ORAUT 

2013). 

Based on a preliminary examination of the results presented in Table 1, SC&A would conclude 

that the current NIOSH model adequately represents the annualized external dose to the 95th

percentile worker. A final conclusion cannot be reached until a review of the OTIB-0020, 

Rev. 1, calculations for Adrian and Havens is completed. 

REFERENCES: 

ORAUT 2005. An Exposure Matrix for Bridgeport Brass: Havens Laboratory and Adrian 

Plant, ORAUT-TKBS-0030, Rev. 0. Oak Ridge Associated Universities Team, Cincinnati, 

Ohio. September 2005. 

ORAUT 2008. Use of Coworker Dosimetry Data for External Dose Assignment, ORAUTOTIB-0020, Rev. 2. Oak Ridge Associated Universities Team, Cincinnati, Ohio. 2008.

ORAUT 2011a. Analysis of Stratified Coworker Datasets, ORAUT-RPRT-0053, Rev. 0. Oak 

Ridge Associated Universities Team, Cincinnati, Ohio. October 2011. 

ORAUT 2011b. Use of Coworker Dosimetry Data for External Dose Assignment, ORAUTOTIB-0020, Rev. 3. Oak Ridge Associated Universities Team, Cincinnati, Ohio. November 

2011. 

ORAUT 2013. An Exposure Matrix for Bridgeport Brass: Havens Laboratory and Adrian Plant, 

ORAUT-TKBS-0030, Rev. 1. Oak Ridge Associated Universities Team, Cincinnati, Ohio. 

January 2013. 

SC&A 2008. Review of the Bridgeport Brass Technical Basis Document (Havens Laboratory 

and Adrian Plant). Attachment 1 to the 8th Set of Dose Reconstruction Audit Reports, S. Cohen 

& Associates, Vienna, Virginia. May 2008. 

SC&A 2009. SC&A Follow-Up to NIOSH’s Responses to Bridgeport Brass Site Profile Review 

Findings, S. Cohen & Associates, Vienna, Virginia. April 2009.