DISCLAIMER: This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A, for use in discussions with the National Institute for Occupational Safety and 

Health (NIOSH) and the Advisory Board on Radiation and Worker Health (ABRWH), including its Working Groups 

or Subcommittees. Documents produced by SC&A, such as memorandum, white paper, draft or working documents 

are not final NIOSH or ABRWH products or positions, unless specifically marked as such. This document prepared 

by SC&A represents its preliminary evaluation on technical issues.

NOTICE: This document 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. 

MEMORANDUM

TO: Blockson Chemical Company Work Group 

FROM: SC&A, Inc.

DATE: May 22, 2018 

SUBJECT: Final SC&A Position on the Application of Overtime Hours at Blockson 

Introduction

As part its review of Special Exposure Cohort (SEC)-00225 for the Blockson Chemical 

Company (SC&A 2016a, 2016b), SC&A raised concerns about the National Institute for 

Occupational Safety and Health’s (NIOSH’s) assumption of 2,000 work hours per year in 

formulating external dose assignments during the residual period. This issue was discussed 

during the Blockson Work Group teleconference on June 28, 2016 (ABRWH 2016). During that 

discussion, NIOSH raised a number of questions/concerns as follows: 

1. Is the evidence of overtime work related to the residual period, operational period, or 

potentially both? (See ABRWH 2016, page 31.) 

2. As a follow-on to item 1, would the issue of overtime affect other dose reconstruction 

(DR) techniques currently utilized in the site profile? (See ABRWH 2016, page 33.) 

3. Was the reported overtime of a “casual” or “consistent” nature? (See ABRWH 2016, 

page 32.) 

Following that discussion, NIOSH and the Work Group agreed that the issue of overtime work 

needed to be more thoroughly vetted before coming to a conclusion (see ABRWH 2016, pages 

33–35). NIOSH provided a response memo to the Work Group and SC&A on March 9, 2018, 

that discussed the issue of potential overtime work, among other issues related to Blockson 

(NIOSH 2018). In that response, NIOSH did not reevaluate the evidence of overtime work, but 

rather modeled a new dose rate distribution by fitting the background-corrected survey data to a 

lognormal distribution.1

1 The original dose rate distribution was a “modeled” (rather than “fitted”) distribution that assumed the median 

parameter was the background of the instrument measurements (0.03 milliroentgen per hour [mR/hr]) and the 95th

percentile parameter was the maximum observed hot spot (0.2 mR/hr).

Using this newly calculated “fitted” distribution in conjunction with 

2,500 hours per year, NIOSH concluded that their original external dose estimates were more 

claimant favorable. Therefore, NIOSH does not intend to update the dose reconstruction 

methodology to include overtime work. 

 
Memo – Evaluation of Overtime at Blockson 2 SC&A – May 22, 2018 

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Privacy Act 5 USC §552a and has been cleared for distribution. 

This memorandum provides SC&A’s final technical position on the treatment of overtime hours 

at Blockson. As part of SC&A’s response to NIOSH’s current position, SC&A also provides 

analysis and discussion of the three questions/concerns that were posited during the 2016 work 

group meeting, as well as observations that arose during SC&A’s further investigation of the 

issue. Following the discussion in the next section is a summary of SC&A’s final 

recommendation to NIOSH and the Work Group concerning overtime at Blockson. 

Discussion of Overtime Issue

NIOSH’s main contention in its recent response (NIOSH 2018) to the issue of overtime is that

claimant-favorable assumptions had been applied in other aspects of the external dose 

assignment (namely, the dose rate distribution) that indirectly account for the potentially longer 

exposure times associated with overtime. To illustrate this point, NIOSH calculated a new dose 

rate distribution by fitting the limited available survey data to a lognormal distribution after 

correcting for natural background. This newly formulated dose rate distribution, when combined 

with an assumption of 500 additional overtime hours per year (or 2,500 hours per year total), 

resulted in a lower annual external dose than the original method, which assumed 2,000 hours 

per year. 

It is not clear from this response whether NIOSH’s current position is that the original dose rate 

distribution formulation was inappropriate and should have been calculated using the new 

lognormal fit method provided in NIOSH 2018. If NIOSH feels that the original dose rate 

distribution was technically inappropriate, then it seems logical that the older dose distribution 

should be removed for the scientifically appropriate formulation. SC&A assumes that the 

original method for deriving an external dose distribution was chosen due to the limited number 

of survey data points (63) and the fact that only seven of those survey data points were above 

background for the instrument used in the facility survey. SC&A’s assumption appears to be 

supported, at least in part, by the discussion by NIOSH recorded on pages 20–22 of the transcript 

of the 2016 Work Group meeting, specifically:

So, there’s just this one isolated spot. And you really can’t fit a distribution to 

those values. ...if you discount the two that aren’t really relevant in my opinion to 

external exposure reconstruction there is no distribution. [ABRWH 2016, 

page 21]

If the original “modeled” dose rate distribution is technically appropriate, then SC&A does not 

feel using the inherent claimant favorability in the dose rate to account for the potentially 

unfavorable parameter (exposure time) is an appropriate dose reconstruction approach. SC&A 

believes that while different parameters may have varying levels of claimant favorability, each 

parameter should be treated separately and selected such that it is the most technically 

appropriate and defensible for dose reconstruction. 

Moreover, as noted by NIOSH during the 2016 Work Group meeting and discussed in the 

Introduction of this memo, the issue of exposure time may very well have effects beyond the 

annual external dose assignment during just the residual period (see NIOSH questions/concerns 1 

and 2, above). Specifically, the formulation of internal doses to uranium and thorium compounds 
Memo – Evaluation of Overtime at Blockson 3 SC&A – May 22, 2018 

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Privacy Act 5 USC §552a and has been cleared for distribution. 

during the operational period also assumes a standard work year (2,000 hours). The Blockson 

technical basis document (TBD) (NIOSH 2014) develops intake values from calcining 

operations2 at the site in the following manner:

2 SC&A notes that internal exposures to calcining operations are only used for organs for which Type S intakes are 

bounding to the organ of interest. While the Blockson TBD (NIOSH 2014) still includes the instructions to use the 

intakes derived for the calcining operations, it is not clear if this is still a relevant technique “in practice” during the 

operational period. Such an evaluation is beyond the scope of this memo.

Bounding intakes from uranium and thorium (and associated progeny) were 

calculated based on a breathing rate of 1.2 m3/hr and being exposed to that high 

level of dust for 2000 hours per year. [Emphasis added.] [Section 3.2.1, page 17] 

Additionally, the modeling of external dose from a uranium drum during the operational period 

was described in Section 4.2.2 of NIOSH 2014, specifically:

The air kerma values were converted to annual organ doses by assuming a 

worker’s exposure time was lognormally distributed. The median exposure time 

was determined by assuming all workers were working eight hours per day, one 

day per week at a distance of 1 foot (30 cm) from the drum. This was normalized 

to 400 hours per work year. The 95th percentile exposure time was determined by 

assuming the worker spent 2000 hours per year at a distance of 1 foot from the 

drum. This results in a whole body dose distribution with a median value of 

1.592 rad per year with a geometric standard deviation of 2.7. [Emphasis added.]

[Section 4.2.2, page 28] 

Both of these dose reconstruction approaches are used during the operational period; therefore,

NIOSH’s concerns about which time periods are affected by potential overtime work are of 

particular import. To address this concern, SC&A reexamined the claimant population to include 

all workers and not just those workers with covered employment in the residual period. It should 

be noted that as part of this updated analysis, SC&A made a concerted effort to identify claims in 

which overtime work was indicated but for which only intermittent entry into radiological areas 

was also indicated and/or highly likely. For example, in SC&A’s analysis, a claim would not be 

classified as an “overtime” worker if the EE was identified with an administrative position and 

the EE or survivor stated they only entered radiological areas for 25 hours per week (even if it 

was indicated typical work at Blockson was greater than 40 hours per week). 

Table 1 summarizes the number of claimants who reported working overtime during each period 

of interest. As seen in the table, 157 claims3 are included in this analysis, with the number 

reporting overtime work fluctuating between ~67% (operational period only) and ~83% (both 

operational and residual period). Out of the entire claimant population, approximately 80% 

reported working at least some overtime hours. Conversely, only 16% of the total claimant 

population reported working a standard 40-hour work week. 

 

3 NOCTS shows 158 claims; however, one claim had been pulled by the U.S. Department of Labor (DOL) as not 

meeting eligibility requirements, and no useful information was available for the purposes of this analysis.
Memo – Evaluation of Overtime at Blockson 4 SC&A – May 22, 2018 

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Table 1. Summary of Claims Indicating Overtime by Covered Employment Period

Covered 

Employment 

Period

Total # of 

Claims

# of Claims 

Indicating 

Overtime 

(% of total) 

# of Claims 

Indicating 40 

Hours per Week 

(% of Total)

# of Claims with No 

Identified 

Information Relevant 

to Overtime Work

(% of Total)

Operational Period 

Only (March 

1951–June 1960)

15 10 (66.7%) 3 (20.0%) 2 (13.3%)

Residual Period 

Only

(July 1960–

December 1991) 

21 15 (71.4%) 3 (14.3%) 3 (14.3%)

Both Operational 

and Residual 

Periods

121 100 (82.6%) 19 (15.7%) 2 (1.7%)

All Blockson 

Claims 157 125 (79.6%) 25 (15.9%) 7 (4.5%)

In addition to the number of claimants reporting overtime in each period of interest, NIOSH 

expressed concern whether the reported overtime was of a “casual” or more “consistent” nature. 

To attempt to answer this question, SC&A reviewed available claim documentation to gather any 

available quantitative information on the overtime practices for claimants at Blockson. Not 

surprisingly, the relative detail about the amount of overtime work varied significantly among 

different claims but was often sparse in content. Nonetheless, SC&A quantified what information 

was available to characterize the relative magnitude of overtime work observed in the claimant 

population. 

As expected, nearly half of the Blockson claimants (76 of 157 or ~48%) did not provide any 

quantitative information beyond working “40 hours plus.” However, several of the claims in this 

group did qualitatively describe their typical work practices with statements concerning shift 

work, getting called in at night, and/or working weekends (28 of 157 or ~18%). Slightly greater 

than 19% of the claimant population reported working more than 50 hours per week. A small 

number even reported working greater than 60 and 70 hours per week (four claims and two

claims, respectively). 
Memo – Evaluation of Overtime at Blockson 5 SC&A – May 22, 2018 

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Table 2. Quantitative Assessment of Typical Overtime Hours for Blockson Claimants 

Characterization of Typical Work Hours Number of Claims 

(% of Total)

Unknown Work Hours 7 (4.5%)

40 Hours Only (No indication of overtime) 25 (15.9%)

40+ Hours (No additional information identified) 48 (30.6%)

40+ Hours (No additional quantitative information, but

included indications of shift work, nights, and/or 

weekends identified in file) 

28 (17.8%)

40–49 Hours 19 (12.1%)

50+ Hours 24 (15.3%)

60+ Hours 4 (2.5%)

70+ Hours 2 (1.3%)

During the course of its review, SC&A identified several instances in which claimants 

specifically questioned whether overtime work had been properly accounted for in their 

individual dose reconstruction. These individual instances are most often located in (1) “closeout” phone interviews performed by NIOSH after the dose reconstruction had been performed, 

(2) formal protests of DOL’s final case decision, and (3) informal protests of the final case 

decision. Table 3 summarizes the examples observed by SC&A. 

Table 3. Summary of Examples in which Claimants Questioned whether Overtime Was 

Considered in the Dose Reconstruction

NOCTS ID# * Description/Quotations Source from Claim 

File

(Case A) “He has copies of his paycheck stubs and from these he has 

calculated that [the EE] regularly worked between 20 and 30 

hours of overtime per week. (He will send us copies to be 

included in the file.) Won’t this mean that the doses need to 

be recalculated to take into consideration his actual time 

spent at the plant?” 

Note: SC&A was unable to determine if the paystubs had 

subsequently been provided to NIOSH based on the available 

NOCTS files.

Close-out Phone 

Conversation Report, 

Version 01, p. 2

(Case B) “[The claimant] had the following questions: 1. Was overtime 

taken into consideration. [Phone interviewer answer]: Yes, all 

the information given in the CATI was used.” 

Close-out Phone

Conversation Report, 

p. 2
Memo – Evaluation of Overtime at Blockson 6 SC&A – May 22, 2018 

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Privacy Act 5 USC §552a and has been cleared for distribution. 

NOCTS ID# * Description/Quotations Source from Claim 

File

(Case C) “[The claimant] would like to know how many working hours 

per week was the DR based on. The reason he is asking is 

because he knows his father worked a lot of overtime... very 

concerned with the overtime issue and the nature of his 

father's work... His father worked lots of overtime at 

Blockson and he does not see where the overtime was 

accounted for anywhere in the DR... He wondered if it was 

modeled using the average employee (40 hrs/week), because 

his father's employment was many, many more hours than 40 

hrs/week.” 

Close-out Phone 

Conversation Report, 

pp. 6, 10

(Case D) “How can you get a dose estimate when they called him to 

work all hours of the day and night to repair and climb on 

and under all equipment... That [the EE] regularly worked 

more than 40 hours per week at Blockson Chemical during 

the aforementioned time frame... My father was on 24 hour 

call at Blockson Chemical Company.”

DOL ANRSD 

Return, Version 01, 

pp. 37, 38, 162

(Case E) “He continually accepted all the overtime offered to him, 

sometimes working 16–18 hours per day, in order to support 

his family.”

An affidavit from a coworker states the EE 

.

DOL ANRSD 

Return, pp. 42, 99

(Case F) “[The claimant] just wanted also to reiterate that his father 

worked in Building 55, and worked a lot of overtime (50 to 60 

hours) each week.” 

DOL ANRSD 

Return, p. 82

(Case G) “All I can tell you is he probably worked more overtime at 

that plant than anybody. He probably had the world’s record 

for that. Which means an awful amount of time spent in that 

place, breathing that place, working in that place... If they 

sent him to do a job, they could count on him to do it, and he 

did it. And so I am saying that the changes for him to get 

further exposure were greater than a lot of people that would 

put in maybe eight hours a day and go home... Any overtime 

that is involved there inside that building, it had to be with 

people that were assigned there, who have been cleared by 

the FBI. We did all of our work. All the labor work we did 

ourselves because outsiders couldn’t come in there. That was 

one of the reasons why I wanted to get in there because the 

overtime was confined to certain people, and I knew nobody 

else could get it, and I wanted to get all I could get. So I mean 

that is what you go to work for to make as much money as 

you can make.”

DOL ANRSD 

Return, pp. 92, 95, 

100
Memo – Evaluation of Overtime at Blockson 7 SC&A – May 22, 2018 

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NOCTS ID# * Description/Quotations Source from Claim 

File

(Case H) “They would call him out in the middle of the night. His work 

was not a 40-hour job. When they call you out in the middle 

of the night, quite a few times, to come out, 2:00, 3:00 o’clock 

in the morning and then don’t come home until 4:00 o’clock 

that night, the next day.”

DOL ANRSD 

Return, Version 01, 

pp. 75, 84

(Case I) “Some liked to work overtime. That meant more money to 

take home to their family... her husband worked 40 and 50 

hour weeks and some overtime.”

DOL ANRSD 

Return, Version 01, 

pp. 19, 71

(Case J) “She states her father worked 60 hours weekly, rather than 40 

hours... The recommended decision fails to provide any 

information relating to the hours worked by [the EE]. The 

initial dose reconstruction, which was provided to our office, 

was based on a 40 hour work week. [The survivor] testified 

that her father worked an average of 60 hours per week. The 

recommended decision does not account for this variation.”

DOL ANRSD 

Return, pp. 36, 41

(Case K) “[Survivor] wants to know how many overtime hours have 

been calculated for the doses, because the DRR does not 

specifically say.... I informed [the authorized representative 

and survivor] that per the NIOSH HP, we assumed that the 

EE could have worked more than 2,000 hours per year (2,000 

is a bounding amount of time a person could have stook [sic]

in the spots with the highest dose rate.” 

It is not clear to SC&A whether the response to the claimant’s 

concern was meant to state that the EE could NOT have 

worked more than 2,000 hours.

Close-out Phone 

Conversation Report, 

p. 2

(Case L) “They had a few specific questions regarding the monitoring 

of personnel at Building 55 and the amount of time his father 

worked there relative to the doses assigned (assumed a 50 

hour work week for 52 weeks a year)... I explained that this 

was a claimant favorable dose assessment as indicated in the 

DR Report. I also reviewed the various sections pertaining to 

these questions and provided responses for them based on the 

information contained in the DR Report.” 

Close-out Phone 

Conversation Report, 

p. 1

* Case letters in parentheses are arbitrary designations to enable public discussion of this memo and are not 

otherwise associated with the claim in any way.

Summary Conclusion

As a fundamental dose reconstruction strategy, SC&A does not believe it is appropriate to use 

the claimant favorability of one assumption to account for a separate (and potentially 

unfavorable) assumption. In this case, the contention is that the claimant favorability in the 

original dose rate accounts for the lack of consideration of overtime hours. Moreover, the issue 

of overtime work applies to more than just the issue of external dose during the residual period 

for Blockson; the issue of assumed work duration is also applicable to internal and external 

exposures during the operational period. 
Memo – Evaluation of Overtime at Blockson 8 SC&A – May 22, 2018 

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Privacy Act 5 USC §552a and has been cleared for distribution. 

In response to NIOSH’s questions/concerns expressed during the June 2016 Work Group 

meeting, SC&A performed additional detailed analysis of the Blockson claimant population. 

SC&A believes this analysis demonstrates that indications of overtime were applicable to both 

the operational and residual period. Although SC&A’s evaluation of the individual number of 

typical overtime hours worked was limited by the information provided by the claimants, many 

claims qualitatively described performing shift work, going in at night and working on the 

weekend in addition to stating they worked more than 40 hours per week. Nearly 1/5 of the 

claimant population quantitatively reported working greater than 50 hours. 

Finally, SC&A noted several examples where claimants expressed concern that their dose 

reconstruction was not properly accounting for overtime work. Given that this information 

comes directly from the claimants or their respective survivors, SC&A feels it is important that 

the dose reconstruction process accurately reflect this information. SC&A hopes that the analysis 

and discussion in this memo is helpful to the Work Group and NIOSH in considering whether 

modification of the dose reconstruction process to include overtime work is appropriate. 

References

ABRWH 2016. Transcript: Teleconference Meeting of the Advisory Board on Radiation and 

Worker Health, Blockson Chemical Work Group. June 28, 2016. 

NIOSH 2014. Technical Basis Document for Atomic Energy Operations at Blockson Chemical 

Company, Joliet, Illinois, DCAS-TKBS-0002, Revision 04, National Institute for Occupational 

Safety and Health, Cincinnati, OH. May 19, 2014. 

NIOSH 2018. Memorandum: NIOSH Response on Open TBD Issues, National Institute for 

Occupational Safety and Health, Cincinnati, OH. March 9, 2018. [SRDB Ref. ID 170143] 

SC&A 2016a. Draft Review of Blockson Chemical Company Residual Period SEC-00225, SCATR-2016-SEC003, Revision 1, SC&A, Inc., Vienna, VA. June 3, 2016. [SRDB Ref. ID 161258] 

SC&A 2016b. Memorandum: SC&A Responses to NIOSH Response to SC&A Findings on 

SEC-00225 Blockson Chemical Company Residual Contamination Period, Dated May 23, 2016, 

SC&A, Inc., Vienna, VA. June 15, 2016. [SRDB Ref. ID 161253]