National Institute for Occupational Safety and Health

NIOSH’s Response to SC&A’s Supplemental 

Review of M&C Work Group Issues

LaVon Rutherford, CHP

NIOSH, Health Science Administrator

Advisory Board on Radiation and Worker Health

Metals and Controls Work Group Meeting

May 12, 2023
Overview

 Introduction

 NIOSH Responses

– SC&A Line of Inquiry 1

– SC&A Line of Inquiry 2

– SC&A Line of Inquiry 3

 NIOSH Conclusion

5/12/2023 2
Introduction 
Introduction (1 of 2)

 On August 22, 2022, NIOSH received SC&A’s 

Supplemental Review of M&C Work Group Issues

 NIOSH’s response paper was sent to the work group 

on February 1, 2023

 The response paper addresses comments, 

observations, and findings from that review

5/12/2023 4
Introduction (2 of 2)

 SC&A’s supplemental review posited three lines of 

inquiry based on current work group concerns, and 

NIOSH organized the response paper accordingly

 In each SC&A Line of Inquiry section, NIOSH responds 

to SC&A findings, observations, and other SC&A 

comments where clarification is necessary

5/12/2023 5
NIOSH Response to SC&A Comments, Findings, 

and Observations – SC&A Line of Inquiry 1

Conditions and Work Activities Associated with the Metals 

and Controls Corp. (M&C) Residual Period
M&C Work Activities – Key Issue

 SC&A indicated the key issue before the Work Group is 

how M&C compares to other AWE sites in terms of 

“unusual work activities with high dose potential for 

which NIOSH was unable to evaluate the source term”

5/12/2023 7
Intrusive Nature of Maintenance Work (1 of 2)

 SC&A Comment –

– The active and intrusive nature of the described 

maintenance work at M&C during the residual period 

clearly exceeded the residual period conditions and 

activities at other AWEs, as described in their 

corresponding evaluation reports and site profiles, 

and what would be assumed under OTIB-0070 for 

application of its resuspension and volumetric soil 

values. 

5/12/2023 8
Intrusive Nature of Maintenance Work (2 of 2)

 SC&A Comment –

– It falls within the continuum of post-operational 

intrusive activities ranging from Norton and Vitro 

(very active, D&D-like activities) to that of Linde 

(renovation activities), with M&C being closer to the 

latter, but without the radiological protection 

controls, protective equipment, and personnel 

monitoring that were typical of formal D&D 

programs.

5/12/2023 9
NIOSH Response (1 of 3) 

 Work intrusiveness is primarily addressed by applying 

standard industrial hygiene or nuclear industry 

resuspension factors to a source term

 Norton Co. and Vitro Manufacturing were not added to 

the Special Exposure Cohort (SEC) because of the 

intrusiveness of their activities

 They were added because the lack of useful source-term 

information prevented NIOSH from calculating a 

plausible dose estimate

5/12/2023 10
NIOSH Response (2 of 3)

 This is NOT the case at M&C because NIOSH does have 

relevant source-term information for M&C

 NIOSH suggests SC&A’s Table 1 of their supplemental 

report should be evaluated further 

 NIOSH will develop a table that lists the known activities 

that occurred during the residual period at the AWE sites

 NIOSH previously stated that residual-period tasks at 

other sites also included contaminated soil excavation, 

welding, and torch-cutting in contaminated areas.

5/12/2023 11
NIOSH Response (3 of 3)

 NIOSH Response cont.

– For example, in NIOSH’s brief review of activities 

associated with Bliss and Laughlin, NIOSH identified

• The trench was cleaned, scabbled, jackhammered, and sand-blasted 

• Ceiling trusses and perpendicular members were 

decontaminated

• The concrete pad over trenches and pits removed 

and trench remediated (max 1420 pCi/g)

5/12/2023 12
SC&A comment – Blocked Drains (1 of 3)

 SC&A provided a statement they obtained from an 

interview of a former M&C maintenance worker “who 

spoke of cleaning out blocked drain lines from Building 

10 on a regular basis”

5/12/2023 13
SC&A Comment – Blocked Drains (2 of 3)

 SC&A also pointed to the interview of a Health 

Physicist who worked during the D&D period 

indicating the difference between D&D work and 

maintenance work

– Remediation workers are not handling the material 

in the pipe (sealed entity)

– Maintenance job is to clean the pipe out

5/12/2023 14
SC&A Comment – Blocked Drains (3 of 3)

 SC&A Comment Cleaning out Blocked Drains (cont.)

– “D&D is a controlled environment where the 

workers were very aware of what [they] were 

doing,” whereas the latter was “uncontrolled, 

unconfined, aggressive as hell, using mechanical 

processes that cause aggravation and clouds of 

dust”

– Moreover, maintenance worker “environments 

were rarely cleaned because they are not part of 

the normal process areas” 

5/12/2023 15
NIOSH Response – Blocked Drains (1 of 2)

 The worker indicated they “cut the line with a snap 

cutter, replace the line,” that is not the same as 

“cleaning out blocked drain lines,”

 In fact, it resembles the decontamination and 

decommissioning (D&D) work the health physicist 

describes (i.e., removal as “a sealed entity”). 

 Additionally, M&C placed cones around work areas

 An outside contractor was primarily used to saw-cut 

the concrete floor

5/12/2023 16
NIOSH Response – Blocked Drains (2 of 2)

 Water was applied during cutting as a dust 

suppressant

 After the concrete was broken, two or three M&C 

workers would use shovels to access the clogged pipe 

and remove it. 

 As noted by SC&A in their 2022 paper where they 

quoted a M&C maintenance worker, “it was 

incumbent on us to clean up after we finished the job”

5/12/2023 17
NIOSH Response – D&D vs. Maintenance

As noted earlier SC&A quoted a health physicist who 

worked during the D&D that the maintenance 

activities were significantly different from a control 

perspective than D&D

However, in our response paper we provide quotes 

and portions from maintenance workers interviews 

who worked during the period in question that 

would lead to a different conclusion

5/12/2023 18
Quotes from worker interview (1 of 3)

 Concerning Texas Instruments (TI) Safety 

– “As far as I’m concerned, they (TI) were top-notch

in their security and all of that kind of stuff. They 

really cared about their people.”

– “I was lucky to be there. I loved the job. They were 

so safety conscious. If they said something was 

safe, I believed them.”

– “Texas Instruments had a great safety program. If 

you did not follow the safety procedures, you 

would be terminated quickly.” 

5/12/2023 19
Quotes from worker interview (2 of 3)

 Concerning Surveying prior to equipment removal

– “I know that was done when there were some 

major mills that went into Building 10. Because of 

the foundations that were associated with the 

mills, they had to saw-cut the concrete floor to get 

into the soils below. They did some readings then 

to see if there was still any residual 

contamination.” 

5/12/2023 20
Quotes from worker interview (3 of 3)

 Concerning Surveying prior to equipment removal

– “So, what they wanted to make sure of was that 

there wasn’t anything residual at the floor line 

before they started to cut the floor.” 

5/12/2023 21
Conclusion – SC&A Line of Inquiry 1 (1 of 2)

 NIOSH concludes the conditions and work activities 

associated with the M&C residual period are not 

unusual 

 Still, all sites have differences, so NIOSH starts with 

approved standard modeling procedures and applies 

scientifically sound and conservative modifications 

(e.g., 10-3 resuspension) to tailor these procedures to 

each site 

5/12/2023 22
Conclusion – SC&A Line of Inquiry 1 (2 of 2)

 Furthermore, NIOSH has demonstrated that M&C 

exposure potentials are not higher than those 

addressed by ORAUT-OTIB-0070 and ORAUT-TBD6000. 

5/12/2023 23
NIOSH Response to SC&A Comments, Findings, 

and Observations – SC&A Line of Inquiry 2

Exposure Pathway Bounding Methods for M&C Compared 

to Other AWE Sites
M&C Dose Reconstruction Methods Compared to other AWE 

Residual Periods

 SC&A stated that the threshold questions are whether 

the bounding approach for nonroutine exposure 

pathways applied to M&C are consistent with past 

practice and precedent for AWE residual periods, and 

whether dose reconstruction methods prescribed for 

these pathways can be considered plausible and 

sufficiently accurate. 

5/12/2023 25
SC&A Comment – Materials Released in Drains (1 of 2)

 SC&A Supplemental Review asks

– Would it not be as likely that the regular release of 

a coagulant to the drain line system during active 

Building 10 operations (through 1981) would have 

led to more frequent and substantial blockages, 

perhaps involving higher concentrations of 

uranium and thorium as a function of the binding 

properties of the coagulant oil and other residues? 

5/12/2023 26
SC&A Comment – Materials Released in Drains (2 of 2)

 Additionally SC&A Supplemental Review states

– The accumulation of various artifacts in the M&C 

drain lines can be attributed to missing grates on 

the drains, which allowed production residues and 

items to go down them, contributing to blockages 

that were apparently aggravated by the presence 

of vegetable-based oils used in production that 

coagulated in the drain line 

5/12/2023 27
NIOSH Response – Materials Released in Drains (1 of 12)

 NIOSH questions the premise to the SC&A review

– TI reported to the NRC that the AWE operations 

(Buildings 3, 4, and 10) were decontaminated and 

decommissioned and that all radioactive materials 

were removed during the period from 1955 to 

1968 

– The largest Building 10 cleanup effort occurred at 

the end of 1958 

5/12/2023 28
NIOSH Response – Materials Released in Drains (2 of 12)

 NIOSH questions the premise to the SC&A review 

(cont.)

– Contaminated noncombustible scrap material and 

machinery were collected in 55-gallon steel drums 

and disposed of through authorized agencies or 

buried on-site in compliance with 10CFR20.304

5/12/2023 29
NIOSH Response – Materials Released in Drains (3 of 12)

 NIOSH questions the premise to the SC&A review 

(cont.)

– TI also reported that all three areas were surveyed after 

each area’s respective D&D efforts 

– TI could not locate the survey documentation from 

1968 for Buildings 3, 4, and 10, so in 1982, TI 

resurveyed the areas used for AWE operations and 

documented that the three areas had remained 

decontaminated since the end of AWE Facility 

operations. 

5/12/2023 30
NIOSH Response – Materials Released in Drains (4 of 12)

 NIOSH questions the premise to the SC&A review 

(cont.)

– In 1983, the NRC was satisfied that the interiors of 

Buildings 3, 4, and 10 were sufficiently 

decontaminated and they released Buildings 3, 4, 

and 10 for unrestricted use

– The NRC withheld license termination pending 

further investigations into the former radioactive 

waste burial site

5/12/2023 31
NIOSH Response – Materials Released in Drains (5 of 12)

 NIOSH questions the premise to the SC&A review 

(cont.)

– After hearing reports from M&C workers of 

additional areas of concern, the NRC hired a 

contractor to investigate 

– After identifying contamination in outside areas, 

the NRC directed another review of the Building 10 

interior using revised release criteria and methods 

that are more comprehensive

5/12/2023 32
NIOSH Response – Materials Released in Drains (6 of 12)

 NIOSH questions the premise to the SC&A review 

(cont.)

– The additional contamination identified using 

updated methods included sections of the 

concrete floor and subsurface previously 

inaccessible to outdated survey techniques, and it 

did not present a significant exposure hazard

5/12/2023 33
NIOSH Response – Materials Released in Drains (7 of 12)

 NIOSH questions the premise to the SC&A review 

(cont.)

– Contributions to drain lines from production work 

specifying the use of radioactive materials during 

the residual period (i.e., HFIR) cannot be 

considered in determining EEOICPA covered 

exposures 

– NIOSH modeled the drain sediments as a dusty, dry 

material in the air for claimant favorability

5/12/2023 34
NIOSH Response – Materials Released in Drains (8 of 12)

 NIOSH questions the premise to the SC&A review 

(cont.)

– Any wet or oily material would trap potential 

contaminants, reducing or preventing 

resuspension of the contaminant and limiting the 

potential for inhalation.

5/12/2023 35
NIOSH Response – Materials Released in Drains (9 of 12)

 Additional information to support the use of the 1996 

data

– The sampling plan was developed specifically to identify 

hot spots for upcoming D&D and Maintenance activities

– The survey found a portion of a uranium rod 5 inches 

long and 2 inches in diameter in one pipeline

– Sludge in pipeline as high as 53,000 pCi/g which is 10% 

of the specific activity of pure natural uranium

5/12/2023 36
NIOSH Response – Materials Released in Drains (10 of 12)

 Additional information to support the use of the 1996 

data (cont.)

– As NIOSH identified in a previous paper (July 2020) the 

sediment data was consistent with other AWE data

• Hot Spots with majority of data orders of magnitude 

lower

– NIOSH assumes all of the sediment was produced from 

AWE operations

• Naval Reactors (80% of the radiological work)

• HFIR

5/12/2023 37
NIOSH Response – Materials Released in Drains (11 of 12)

 Additional information to support the use of the 1996 

data (cont.)

– The 95th percentile sediment concentration 6887 

pCi/g is approximately 1% of the specific activity 

pure natural uranium

• Of the samples taken 16 of the 20 were an 

order of magnitude below this

– NIOSH assumes all of the subsurface soil and 

piping are at this level

5/12/2023 38
NIOSH Response – Materials Released in Drains (12 of 12)

 Additional information to support the use of the 1996 

data (cont.)

– NIOSH assumes all workers are occupationally 

exposed or in close contact with the 95th percentile 

concentration for two months per year

5/12/2023 39
NIOSH – Conclusion Subsurface Inside (1 of 3) 

 NIOSH finds the use of the 95th percentile 

concentration is a bounding dose reconstruction 

approach

 SC&A did not provide any new technical information 

or technical justifications to indicate why they do not 

consider the source term developed by NIOSH to be 

bounding

5/12/2023 40
NIOSH – Conclusion Subsurface Inside (2 of 3)

 NIOSH and SC&A have done extensive work on the 

subsurface model and have previously agreed, as 

shown in the following SC&A 2021 paper: 

– 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. 

5/12/2023 41
NIOSH- Conclusion Subsurface Inside (3 of 3 )

 NIOSH and SC&A have done extensive work on the 

subsurface model and have previously agreed, as 

shown in the following SC&A 2021 paper: 

– (cont.)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

5/12/2023 42
M&C Dose Reconstruction Methods Compared to other AWE 

Residual Periods – Subsurface Outside

 SC&A states in the supplemental review that the 

appropriateness of the bounding assumption for the 

data used for the subsurface model are dependent on 

– How much excavations prior to 1984 diluted, 

spread, and otherwise altered the levels of 

contamination

– Whether the bounding levels are sufficiently 

accurate, sufficiently conservative, and plausible 

given there is no data prior to 1984 

5/12/2023 43
SC&A Comment – Subsurface Outside (1 of 2)

 NIOSH construes the lack of NRC regulatory direction 

to signify that the reported “elevated levels” were 

merely “above background, but less than release 

criteria (30 pCi/g),” and that “information related to 

this task supports NIOSH’s outside subsurface model, 

in that the 95th percentile contamination level NIOSH 

applied (118 pCi/g) is approximately four times higher 

than the contamination level these workers 

experienced” (i.e., 30 pCi/g) (citation omitted),...

5/12/2023 44
SC&A Comment – Subsurface Outside (2 of 2)

 ...but without giving any apparent substantiation 

beyond inferring how NRC staff would have perceived 

the risk and what action they would or would not have 

taken 

5/12/2023 45
NIOSH Response – Subsurface Outside (1 of 3)

 NIOSH’s statement was explicitly about the airline 

installation process

 NIOSH concluded the removal of soil and debris for 

installing the airline was below 30 pci/g based on 

statements in documents reviewed

 In early August 1980, Texas Instruments informed 

Region I that while digging a trench for a pipeline, 

slightly contaminated material from an old burial 

ground was dug up. [NRC 1981–1982, PDF p. 14]

5/12/2023 46
NIOSH Response – Subsurface Outside (2 of 3)

 The safety engineer for Texas Instruments, a trained 

health physicist, surveyed the material, dug up, and 

placed any contaminated material into 55-gallon 

drums. [NRC 1981–1982, PDF p. 14]

 The licensee revised the drawing for the compressed 

airline and marked the location where the radioactive 

low-specific activity waste material dump was 

excavated [NRC 1981–1982, PDF p. 14]

5/12/2023 47
NIOSH Response – Subsurface Outside (3 of 3)

 The airline debris area was investigated but did not 

require remediation because the levels of radioactivity 

detected were below applicable NRC release criteria. 

[Texas Instruments 1996c, PDF p. 33]

5/12/2023 48
SC&A Observation 1 – Subsurface Outside

 The use of blended D&D characterization survey data 

from 1984 and 1992 to support a bounding dose for 

outside subsurface activities may not be necessarily 

bounding for work in nonuniform soil contamination, 

given the presence of hot spots that existed during 

the residual period at M&C

5/12/2023 49
NIOSH Response – Observation 1 (1 of 4)

 By definition, hot spots are limited exposures and not 

a normally expected condition

– Hence, NIOSH uses the 95th percentile and not the 

maximum value

– NIOSH does not model systemic exposures to hot 

spots but rather to expected conditions

5/12/2023 50
NIOSH Response – Observation1 (2 of 4)

 SC&A did not provide any new technical information 

or technical justifications to indicate why the 

proposed approach is not considered bounding

 Furthermore, NIOSH and SC&A have done extensive 

work on this model, and SC&A recommended closing 

this issue with the following

5/12/2023 51
NIOSH Response – Observation 1 (3 of 4)

 In theory, we can assume that a worker might be 

involved in subsurface work in Building 10, two 

months per year, and spend ten months per year 

exposed outdoors to resuspended contaminated 

[sediment]. Given this scenario, the additional dose 

from this pathway of less than a mrem per year can be 

ignored. [SC&A 2020, PDF p. 23]

5/12/2023 52
NIOSH Response – Observation 1 (4 of 4)

 Alternatively, we can assign the subsurface internal 

exposures to uranium in Building 10 to the subsurface 

exposures to outdoor workers. The data indicate that 

such an approach would be extremely claimant 

favorable but would still result in relatively small doses 

[SC&A 2020, PDF p. 23]

5/12/2023 53
NIOSH Response to SC&A Comments, Findings, 

and Observations – SC&A Line of Inquiry 3

Source Term, Survey Data, and Other Information Applied 

by NIOSH 
SC&A Supplemental review – Source Term

 SC&A Supplemental Review states

– A guiding principle NIOSH follows for addressing 

the “uncertainty around the work performed” or 

the “complete understanding of the work 

performed (e.g., one person doing all the 

maintenance work)” is that it is “NOT an issue 

when the bounding doses are very low, and 

specifically, during AWE residual periods such as at 

M&C”

5/12/2023 55
SC&A Supplemental review – Site Characterization

 SC&A comments on using Mound data for dust 

loading

– ...in terms of specific site characteristics for M&C, it 

is not apparent how the Mound project addressed 

considerations related to resuspension or dust 

loading in a confined space, such as the various 

manholes, trenches, pits, and vault spaces at M&C 

in which maintenance workers actively worked

5/12/2023 56
NIOSH Response – Confined Space (1 of 2)

 NIOSH agrees that addressing the potential change in 

resuspension in a confined space needs to be 

addressed

– NOTE: This is not a change in source term

 NIOSH concludes this is a global issue that should be 

addressed in OTIB-0070 along with the 

enhancement/enrichment factors SC&A previously 

identified in their 2021 paper

5/12/2023 57
NIOSH Response – Confined Space (2 of 2)

 As for manholes, NIOSH and other SC&A reviewers 

concluded the manholes would not be a significant 

source of contamination at M&C

 SC&A quote from 2021 work group meeting

– Well, there are certainly materials that 

accumulated. But since they weren’t directly 

handling radiological materials in the manholes, as 

far as we know, we wouldn’t expect there to be a 

high contamination level there. 

5/12/2023 58
SC&A Supplemental review – Finding 2

 SC&A Finding 2 - The application of surrogate data 

from the Mound project to provide a dust-loading 

factor for M&C subsurface activities does not satisfy 

the Board’s surrogate data policy

 Specifically, SC&A’s supplemental review indicates the 

criteria for site and process similarities, has not been 

met

5/12/2023 59
NIOSH Response – Finding 2 (1 of 6)

 SC&A’s 2021 report states

– Considering the totality of information compiled in 

this report, SC&A believes that the use of a dust 

loading of 212 μg/m3 for subsurface work both 

indoors and outdoors at M&C is reasonably 

compatible with data and information summarized 

in this report, including the data reported from 

Mound by the interviewed SME.

5/12/2023 60
NIOSH Response – Finding 2 (2 of 6)

 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

 Additionally, SC&A believes that NIOSH should refer to 

the numerous dust loading studies cited in section 5 as 

the basis for the dust loading of 212 μg/m3 in addition 

to the Mound data 

5/12/2023 61
NIOSH Response - Finding 2 (3 of 6)

 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

– Soil likely moist 

– Assumed close contact entire two-month time 

period 

5/12/2023 62
NIOSH Response – Finding 2 (4 of 6)

 NIOSH Responded to SC&A’s 2021 paper

– 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 

5/12/2023 63
NIOSH Response – Finding 2 (5 of 6)

 SC&A expressed concern in using the dust loading 

factor generically in OTIB-070 

 However, this cannot be said for the use of the 212 

μg/m3 for use as a generic value for outdoor and 

indoor excavations at some unknown facility or site. 

Hence, its use as a generic dust loading in OTIB-0070 

should be uniquely evaluated at each site of proposed 

use 

5/12/2023 64
NIOSH Response – Finding 2 (6 of 6)

 NIOSH responded to this concern

– Although NIOSH will use M&C to inform our 

modeling of similar Energy Employees 

Occupational Illness Compensation Program Act 

work, we agree with "one size will not fit all.” We 

will address this further during the next ORAUTOTIB-0070 revision 

5/12/2023 65
SC&A Supplemental review – Observation 2

 References to the M&C safety and health manual, NRC 

inspection results, operator training, and other 

programmatic considerations do not necessarily 

substantiate the conservatism of the 95th percentile 

soil contamination value being applied

5/12/2023 66
NIOSH Response – Observation 2 (1 of 2)

 NIOSH was not using the M&C Safety and Health 

manual, NRC inspection results, operator training, and 

other programmatic considerations to justify using the 

95th percentile

 The 95th percentile is consistent with the statistical 

approach used at every site under the EEOICPA

5/12/2023 67
NIOSH Response – Observation 2 (2 of 2)

 The M&C Safety and Health manual, NRC inspection 

results, operator training, and other programmatic 

considerations provide credence that the site was 

mindful of the impact associated with the current and 

historical radiological work. 

5/12/2023 68
NIOSH Conclusions
NIOSH Conclusions (1 of 4)

 SC&A’s conclusion states that “Precedent suggests 

that while less precision or technical accuracy can be 

tolerated if the exposure of a worker cohort is 

relatively low... “

 For comparison purposes

– Linde dose 5479 mrem/yr (CED)

– M&C dose 71 mrem/yr (CED)

5/12/2023 70
NIOSH Conclusions (2 of 4)

 The second part of SC&A’s conclusion

– ...the use of a high exposure or concentration 

values based on these data to bound or represent 

that of other workers in a facility or on a site for 

long time periods would not be appropriate if their 

exposure potential could be higher, conditions were 

different, or if there is lack of information upon 

which to make those judgments. 

 This applies at Linde but does not apply at M&C

5/12/2023 71
NIOSH Conclusions (3 of 4)

 NIOSH has a more complete data set to characterize 

M&C and a better understanding of M&C 

maintenance work than we had with Linde

 NIOSH has performed due diligence since 2017 to 

identify the maintenance tasks with the highest 

exposure potential and has created models that 

bound exposures associated with these tasks.

5/12/2023 72
NIOSH Conclusions (4 of 4)

 With the exception of the potential particulate 

enhancement in confined space, SC&A did not provide 

any new technical information or technical 

justifications to indicate why they do not consider the 

proposed approach to be bounding

 NIOSH continues searching for and welcomes any new 

technical information available to improve our 

bounding models. 

5/12/2023 73
For more information, contact CDC

1-800-CDC-INFO (232-4636)

TTY: 1-888-232-6348 www.cdc.gov

The findings and conclusions in this report are those of the authors and do not necessarily represent the 

official position of the Centers for Disease Control and Prevention.