Draft Risk Evaluation for Carbon Tetrachloride Supplemental File: Occupational Exposure Assessment CASRN 56-23-5 January 2020


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v>EPA

United States	Office of Chemical Safety and

Environmental Protection Agency	Pollution Prevention

Draft Risk Evaluation for Carbon Tetrachloride

Supplemental File:

Occupational Exposure Assessment

CASRN: 56-23-5

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January 2020

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TABLE OF CONTENTS/

ABBREVIATIONS	7

EXECUTIVE SUMMARY	9

1	INTRODUCTION	11

1.1	Overview	11

1.2	Scope	11

1.3	General Approach and Methodology for Occupational Exposures	17

1.3.1	Process Description and Worker Activities	17

1.3.2	Number of Workers and Occupational Non-Users	17

1.3.3	Inhalation Exposure Assessment Approach and Methodology	17

1.3.3.1	General Approach	18

1.3.3.2	Approach for thi s Ri sk Evaluati on	19

1.3.4	Dermal Exposure Assessment Approach and Methodology	19

1.3.5	Environmental Release Assessment Approach and Methodology	20

2	ENGINEERING ASSESSMENT	21

2.1	Domestic Manufacturing	21

2.1.1	Process Description	21

2.1.2	Exposure Assessment	21

2.1.2.1	Worker Activities	21

2.1.2.2	Number of Potentially Exposed Workers	22

2.1.2.3	Occupational Exposure Results	23

2.2	Import and Repackaging	24

2.2.1	Process Description	25

2.2.2	Exposure Assessment	25

2.2.2.1	Worker Activities	26

2.2.2.2	Number of Potentially Exposed Workers	26

2.2.2.3	Occupational Exposure Assessment Methodology	27

2.2.2.4	Occupational Exposure Results	27

2.3	Processing as a Reactant or Intermediate	27

2.3.1	Process Description	27

2.3.2	Exposure Assessment	28

2.3.2.1	Worker Activities	28

2.3.2.2	Number of Potentially Exposed Workers	28

2.3.2.3	Occupational Exposure Assessment Methodology	30

2.3.2.3.1	Inhalation Exposure Assessment Results Using Monitoring Data	30

2.3.2.3.2	Inhalation Exposure Assessment Results Using Surrogate Data	31

2.4	Incorporation into Formulation, Mixture, or Reaction Product	31

2.5	Specialty Uses - Aerospace Industry	32

2.6	Specialty Uses - Department of Defense Data	32

2.6.1	Data Overview	33

2.6.2	OBOD Clean-Up Process Description	34

2.6.3	Exposure Assessment	34

2.7	Reactive Ion Etching	35

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2.7.1	Process Description	35

2.7.2	Exposure Assessment	35

2.7.2.1	Worker Activities	35

2.7.2.2	Number of Potentially Exposed Workers	36

2.8	Industrial Processing Agent/Aid	36

2.8.1	Process Description	36

2.8.2	Exposure Assessment	38

2.8.2.1	Worker Activities	38

2.8.2.2	Number of Potentially Exposed Workers	38

2.8.2.3	Occupational Exposure Assessment Methodology	39

2.8.2.4	Occupational Exposure Results	39

2.9	Additive	39

2.9.1 Process Description	39

2.9.1 Exposure Assessment	40

2.9.1.1	Worker Activities	40

2.9.1.2	Number of Potentially Exposed Workers	40

2.9.1.3	Occupational Exposure Assessment Methodology	41

2.9.1.4	Occupational Exposure Results	41

2.10	Laboratory Chemicals	41

2.10.1	Process Description	41

2.10.2	Exposure Assessment	41

2.10.2.1	Worker Activities	41

2.10.2.2	Number of Potentially Exposed Workers	42

2.11	Disposal/Recycling	43

2.11.1	Process Description	43

2.11.2	Exposure Assessment	47

2.11.2.1	Worker Activities	47

2.11.2.2	Number of Potentially Exposed Workers	48

2.11.2.3	Occupational Exposure Assessment Methodology	49

2.11.2.4	Occupational Exposure Results	49

2.12	Dermal Exposure Assessment	49

2.13	Summary of Occupational Exposure Assessment	51

3 DISCUSSION OF UNCERTAINTIES AND LIMITATIONS	53

3.1	Variability	53

3.2	Uncertainties and Limitations	53

3.2.1	Number of Workers	53

3.2.2	Analysis of Exposure Monitoring Data	53

3.2.3	Modeling Dermal Exposures	54

REFERENCES	55

APPENDICES	60

Appendix A Approach for Estimating Number of Workers and Occupational Non-Users	60

Appendix B Equations for Calculating Chronic (Non-Cancer and Cancer) Inhalation Exposures
65

B.l Exposure Duration (ED)	66

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B.2 Exposure Frequency (EF)	66

B.3 Working Years (WY)	67

B.4	Lifetime Years (LT)	69

Appendix C Sample Calculations for Calculating Acute and Chronic (Non-Cancer and Cancer)
Inhalation Exposures	70

C.	1 Example High-End ADC and LADC	70

C.2	Example Central Tendency ADC and LADC	70

Appendix D Tank Truck and Railcar Loading and Unloading Release and Inhalation Exposure
Model Methodology	72

D.l	Displacement of Saturated Air Inside Tank Trucks and Railcars	72

D.2 Emissions of Saturated Air that Remain in Transfer Hoses/Loading Arm	73

D.3 Emission from Leaks	75

D.4	Exposure Estimates	78

Appendix E Dermal Exposure Assessment Approach and Parameters	81

E.	1 Incorporating the Effects of Evaporation	81

E.l.l Modification of EPA Models	81

E.2 Calculation of fabs	81

E.2.1 Small Doses (Case 1: Mo < Msat)	82

E.2.2 Large Doses (Case 2: Mo > Msat)	83

E.3 Comparison of fabs to FRabs in the Consumer Exposure Model (CEM)	84

E.4 Comparison of fabsto Experimental Values for 1-BP	86

E.5 Potential for Occlusion	86

E.6 Incorporating Glove Protection	87

E.7 Proposed Dermal Dose Equation	88

E.8 Equations for Calculating Acute and Chronic (Non-Cancer and Cancer) Dermal Doses	89

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LIST OF TABLES

Table 1-1. Crosswalk of Subcategories of Use Listed in the Problem Formulation Document to

Conditions of Use Assessed in the Risk Evaluation 13

Table 2-1. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During

Manufacturing 23

Table 2-2. Summary of Worker Inhalation Exposure Monitoring Data for Manufacture of Carbon

Tetrachloride 24

Table 2-3. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During Import

and Repackaging 26

Table 2-4. Summary of Exposure Modeling Results for Import and Repackaging 27

Table 2-5. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During

Processing as a Reactant 29

Table 2-6. Summary of Inhalation Exposure Monitoring Data for Use as a Reactant for Carbon

Tetrachloride 30

Table 2-7. Summary of Surrogate Data Results for Processing as a Reactant 31

Table 2-8. DOD Inhalation Monitoring Results 33

Table 2-9. Summary of Worker Inhalation Exposure Monitoring Data for Specialty Use of Carbon

Tetrachloride 35

Table 2-10. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During Use as a

RIE 36

Table 2-11. List of Uses of Carbon Tetrachloride as Process Agents in MP Side Agreement, Decision

X/14: Process Agents 37

Table 2-12. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During Use as a

Processing Agent/Aid 39

Table 2-13. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride when used as

an Additive 40

Table 2-14. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During Use as a

Laboratory Chemical 42

Table 2-15. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During Waste

Handling 48

Table 2-16. Glove Protection Factors for Different Dermal Protection Strategies 50

Table 2-17. Estimated Dermal Retained Dose (mg/day) for Workers in All Conditions of Use 51

Table 2-18. Summary of Occupational Exposure Assessment for Workers 52

LIST OF FIGURES

Figure 2-1. General Process Flow Diagram for Import and Repackaging 25

Figure 2-2. General Laboratory Use Process Flow Diagram 41

Figure 2-3. Typical Waste Disposal Process 44

Figure 2-4. Typical Industrial Incineration Process 45

Figure 2-5. General Process Flow Diagram for Solvent Recovery Processes 47

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LIST OF APPENDIX TABLES

Table_Apx A-l. SOCs with Worker and ONU Designations for All Conditions of Use Except Dry Cleaning

Table_Apx A-2. SOCs with Worker and ONU Designations for Dry Cleaning Facilities 62

Table_Apx A-3. Estimated Number of Potentially Exposed Workers and ONUs under NAICS 812320 ... 63

Table_Apx B-l. Parameter Values for Calculating Inhalation Exposure Estimates 66

Table_Apx B-2. Overview of Average Worker Tenure from U.S. Census SIPP (Age Group 50+) 68

Table_Apx B-3. Median Years of Tenure with Current Employer by Age Group 69

Table_Apx D-l. Example Dimension and Volume of Loading Arm/Transfer System 73

Table_Apx D-2. Default Values for Calculating Emission Rate of Carbon Tetrachloride from

Transfer/Loading Arm 75

Table_Apx D-3. Parameters for Calculating Emission Rate of Carbon Tetrachloride from Equipment

Leaks 76

Table_Apx D-4. Default Values for Fa and N 77

Table_Apx D-5. Parameters for Calculating Exposure Concentration Using the EPA Mass Balance Model

Table_Apx D-6. Calculated Emission Rates and Resulting Exposures from the Tank Truck and Railcar

Loading and Unloading Release and Inhalation Exposure Model for Carbon Tetrachloride

Table_Apx E-l. Estimated Fraction Evaporated and Absorbed (fabs) using Equation_Apx E-8 83

Table_Apx E-2. Exposure Control Efficiencies and Protection Factors for Different Dermal Protection

Strategies from ECETOC TRA v3 88

Table_Apx E-3. Carbon Tetrachloride Parameter Values Used to Calculate Acute or Chronic Exposure

Estimates 90

Table_Apx E-4. Overview of Average Worker Tenure from U.S. Census SIPP (Age Group 50+) 93

Table_Apx E-5. Median Years of Tenure with Current Employer by Age Group 93

LIST OF APPENDIX FIGURES

Figure_Apx D-l. Illustration of Transfer Lines Used During Tank Truck Unloading and Associated

Equipment Assumed by EPA 78

Figure_Apx E-l. Estimated Fraction Absorbed for 1-BP (CEM Equation) 85

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ABBREVIATIONS

AC

Acute Concentration

ACGM

American Conference of Government Industrial Hygienists

ADC

Average Daily Concentration

AIA

Aerospace Industries Association

AIHA

American Industrial Hygiene Association

AM

Arithmetic Mean

ATSDR

Agency for Toxic Substances and Disease Registries

BLS

Bureau of Labor Statistics

CAA

Clean Air Act

CBI

Confidential Business Information

ecu

Carbon Tetrachloride

CDR

Chemical Data Reporting

CFC

C hlorofluorocarb on

cm2

Square Centimeter(s)

cm3

Cubic Centimeter(s)

CPS

Current Population Survey

CPSC

Consumer Product Safety Commission

cs2

Carbon Disulfide

CSM

Chlorosulphonated polyolefin

CT

Central Tendency

CWA

Clean Water Act

DOD

Department of Defense

EDC

Ethylene dichloride

EPA

Environmental Protection Agency

ESD

Emission scenario documents

g

gram(s)

GM

Geometric mean

GS

Generic scenario

HCFC

Hy drochl orofluorocarb on

HC1

Hydrochloric Acid

HE

High-end

HFC

Hy drofluorocarb on

HFO

Hydrofluoroolefin

HHE

Health Hazard Evaluation

HSIA

Halogenated Solvents Industry Alliance

HVLP

High Volume, Low Pressure

IBC

Intermediate Bulk Containers

kg

Kilogram(s)

L

Liter(s)

LA DC

Lifetime Average Daily Concentration

lb

Pound

LOD

Limit of Detection

3

m

Cubic Meter(s)

mg

Milligram(s)

MP

Montreal Protocol

MEMA

Motor and Equipment Manufacturer Association

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MW

Molecular Weight

MWC

Municipal Waste Combustor

NAICS

North American Industry Classification System

NC13

Nitrogen Trichloride

ND

Non-Detected

NIOSH

National Institute for Occupational Safety and Health

NPDES

National Pollutant Discharge Elimination System

OARS

Occupational Alliance for Risk Science

OAQPS

Office of Air Quality Planning and Standards

ODS

Ozone Depleting Substance

OECD

Organisation for Economic Co-operation and Development

OEL

Occupational Exposure Limit

OES

Occupational Employment Statistics

ONU

Occupational Non-Users

OPPT

Office of Pollution Prevention and Toxics

OSHA

Occupational Safety and Health Administration

PCE

Perchloroethylene

PEL

Permissible Exposure Limit

PF

Protection Factor

POTW

Publicly Owned Treatment Works

PPE

Personal Protective Equipment

ppm

part(s) per million

QC

Quality Control

RCRA

Resource Conservation and Recovery Act

RDF

Refuse-Derived Fuel

REL

Recommended Exposure Limit

RFI

Reporting Forms and Instructions

RIE

Reactive Ion Etching

s

second(s)

SDWA

Safe Drinking Water Act

SIPP

Survey of Income and Program Participation

SOC

Standard Occupational Classification

SUSB

Statistics of US Businesses

T

Temperature

TCLP

Toxicity Characteristic Leaching Procedure

TLV

Threshold Limit Value

TRI

Toxic Release Inventory

TSCA

Toxic Substances Control Act

TSDF

Treatment, Storage and Disposal Facilities

TWA

Time-weighted Average

UNEP

United Nations Environment Programme

U.S.

United States

WEEL

Workplace Environmental Exposure Limit

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EXECUTIVE SUMMARY

The Toxic Substances Control Act, TSCA § 6(b)(4) requires the United States Environmental Protection
Agency (U.S. EPA) to establish a risk evaluation process. In performing risk evaluations for existing
chemicals, EPA is directed to "determine whether a chemical substance presents an unreasonable risk of
injury to health or the environment, without consideration of costs or other non-risk factors, including an
unreasonable risk to a potentially exposed or susceptible subpopulation identified as relevant to the risk
evaluation by the Administrator under the conditions of use." In December of 2016, EPA published a list
of 10 chemical substances that are the subject of the Agency's initial chemical risk evaluations (81 FR
91927), as required by TSCA § 6(b)(2)(A). Carbon tetrachloride (CCU) was one of these chemicals.

CCU is a colorless liquid with a sweet, aromatic and ethereal odor resembling chloroform and is subject
to federal and state regulations and reporting requirements. In 1970, the Consumer Product Safety
Commission (CPSC) banned the use of CC14 in consumer products (excluding unavoidable residues not
exceeding 10 ppm atmospheric concentration). Effective January 1, 1987, CCU became a Toxics
Release Inventory (TRI)-reportable substance and in the same year was listed as an ozone depleting
substance (ODS) under the Montreal Protocol (MP). The MP and Title VI of the Clean Air Act (CAA)
Amendments of 1990 led to a phase-out of CCU production in the United States for most non-feedstock
domestic uses by 1996. Currently, carbon tetrachloride is used as a feedstock in the production of
hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs). The
use of carbon tetrachloride for non-feedstock uses (i.e., process agent, additive) is regulated in
accordance with the MP.

Focus of this Risk Evaluation

During scoping and problem formulation, EPA considered all known TSCA uses for CCU. CCU has
been manufactured and imported in the U.S. in large volumes with the most recently available data from
the 2016 Chemical Data Reporting (CDR) indicating approximately 143 million pounds were either
manufactured or imported in the U.S. in 2015. Domestic production and importation of CCU is currently
prohibited under regulations implementing the MP and CAA Title VI, except when transformed (used
and entirely consumed, except for trace quantities, in the manufacture of other chemicals for commercial
purposes), destroyed (including destruction after use as a catalyst or stabilizer), or used for essential
laboratory and analytical uses(
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approaches to estimate dermal exposures. EPA used release data from literature sources where available
and used modeling approaches where release data were not available.

Uncertainties of this Risk Evaluation

There are a number of uncertainties associated with the monitoring and modeling approaches used to
assess CCU exposures and releases. For example, the sites used to collect exposure monitoring data were
not selected randomly, and the data reported therein may not be representative of all exposure scenarios.
Further, of necessity, modeling approaches employed knowledge-based assumptions that may not apply
to all use scenarios. Because site-specific differences in use practices and engineering controls exist, but
are largely unknown, this represents another source of variability that EPA could not quantify in the
assessment.

Human Populations Considered in this Risk Evaluation

EPA assessed risks for chronic exposure scenarios in workers (those directly handling CCU) and
occupational non-users (workers not directly involved with the use of CCU) for CCU in the uses outlined
under Focus of this Risk Evaluation. EPA assumed that workers and occupational non-users would be
individuals of both sexes (age 16 years and older, including pregnant workers) based upon occupational
work permits, although exposures to younger workers in occupational settings cannot be ruled out.

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1 INTRODUCTION

1.1 Overview

The Toxic Substances Control Act, TSCA § 6(b)(4), requires the United States Environmental
Protection Agency (U.S. EPA) to establish a risk evaluation process. In performing risk evaluations for
existing chemicals, EPA is directed to "determine whether a chemical substance presents an
unreasonable risk of injury to health or the environment, without consideration of costs or other non-risk
factors, including an unreasonable risk to a potentially exposed or susceptible subpopulation identified
as relevant to the risk evaluation by the Administrator under the conditions of use." In December of
2016, EPA published a list of 10 chemical substances that are the subject of the Agency's initial
chemical risk evaluations (81 FR 91927), as required by TSCA § 6(b)(2)(A). Carbon tetrachloride
(CCU) was one of these chemicals.

1.2 Scope

Workplace exposures and releases have been assessed for the following industrial and commercial uses
of CCU:

1. Manufacturing;

2. Import and Repackaging;

3. Reactant/Intermediate;

4. Incorporation into Formulation;

5. Specialty Uses - Aerospace Industry;

6. Reactive Ion Etching;

7. Inert Solvent, Processing agent/aid;

8. Additive; and

9. Disposal/Waste Handling.

For work place exposures, EPA considered exposures to both workers who directly handle CCU and
occupational non-users (ONUs) who do not directly handle CCU but may be exposed to vapors or
mists that enter their breathing zone while working in locations in close proximity to where CCU is
being used. Although EPA considered both ONU and worker exposures, no data was found to
estimate ONU exposures for any of the conditions of use.

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The assessed conditions of use were described in Table 2-3 of the Problem Formulation of the Risk
Evaluation for Carbon Tetrachloride (Methane, Tetrachloro-) (Problem Formulation Document)
(U.S. EPA. 2018c); however, due to similarities in both processes and exposures/releases several of
the subcategories of use in Table 2-3 were grouped and assessed together during the risk evaluation
process. A crosswalk of the conditions of use in Table 2-3 to the conditions of use assessed in this
report is provided in Table 1-1.

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Table 1-1. Crosswalk of Subcategories of Use Listed in the Problem Formulation Document to Conditions of Use Assessed in the Risk
Evaluation

Life Cycle Stage

Category 1

Subcategory 2b

Assessed Condition of Use

Manufacture

Domestic manufacture

Domestic Manufacturing
(Section 2.1)

Import

Import and Repackaging
(Section 2.2)

Processing

Processing as a reactant/
intermediate

Hydrochlorofluorocarbons
(HCFCs), Hydrofluorocarbon
(HFCs) and Hydrofluorooleftn
(HFOs)

Processing as a Reactant or
Intermediate (Section 2.3)

Perchloroethylene (PCE)

Reactive ion etching (i.e.,
semiconductor manufacturing)

Reactive Ion Etching (Section
2.7)

Incorporation into
Formulation, Mixture or
Reaction products

Petrochemicals-derived
manufacturing; Agricultural
products manufacturing; Other
basic organic and inorganic
chemical manufacturing.

Incorporation into Formulation,
Mixture, or Reaction Product
(Section 2.4)

Processing - repackaging

Laboratory Chemicals

Import and Repackaging
(Section 2.2)3

Recycling

Disposal/Recycling (Section
2.11)

1 These categories of conditions of use appear in the Life Cycle Diagram, reflect CDR codes and broadly represent conditions of use of carbon tetrachloride in industrial
and/or commercial settings.

2 These subcategories reflect more specific uses of carbon tetrachloride.

3 Repackaging is assessed, but not specifically for the use of laboratory chemicals

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Life Cycle Stage

Category 1

Subcategory 2b

Assessed Condition of Use

Distribution in commerce

Distribution

Distribution in commerce

Activities related to distribution
(e.g., loading, unloading) are
considered throughout the life
cycle, rather than using a single
distribution scenario

Industrial/commercial use

Petrochemicals-derived
products manufacturing

Processing aid

Industrial Processing Agent/Aid
(Section 2.8)

Additive

Additive (Section 2.9)

Agricultural products
manufacturing

Processing aid

Industrial Processing Agent/Aid
(Section 2.8)

Other Basic Organic and
Inorganic Chemical
Manufacturing

Manufacturing of chlorinated
compounds used in solvents for
cleaning and degreasing

Processing as a Reactant or
Intermediate (Section 2.3)

Other Basic Organic and
Inorganic Chemical
Manufacturing

Manufacturing of chlorinated
compounds used in adhesives
and sealants

Processing as a Reactant or
Intermediate (Section 2.3)

Other Basic Organic and
Inorganic Chemical
Manufacturing

Manufacturing of chlorinated
compounds used in paints and
coatings

Processing as a Reactant or
Intermediate (Section 2.3)

Other Basic Organic and
Inorganic Chemical
Manufacturing

Manufacturing of inorganic
chlorinated compounds (i.e.,
elimination of nitrogen
trichloride in the production of
chlorine and caustic)

Processing as a Reactant or
Intermediate (Section 2.3)

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Life Cycle Stage

Category 1

Subcategory 2b

Assessed Condition of Use

Other Basic Organic and
Inorganic Chemical
Manufacturing

Manufacturing of chlorinated
compounds used in asphalt

Processing as a Reactant or
Intermediate (Section 2.3)

Other Basic Organic and
Inorganic Chemical
Manufacturing

Manufacturing of
Pharmaceuticals

Industrial Processing Agent/Aid
(Section 2.8)

Other uses

Processing aid (i.e., metal
recovery).

Industrial Processing Agent/Aid
(Section 2.8)

Specialty uses (i.e., aerospace
industry)

Specialty Uses - Aerospace
Industry (Section 2.5)

Specialty Uses - Department of
Defense Data (Section 2.6)

Laboratory chemicals

Laboratory chemical

Laboratory Chemicals (Section
2.10)

Disposal

Industrial pre-treatment

Disposal/Recycling (Section
2.1l)4

Industrial wastewater treatment

Publicly owned treatment works
(POTW)

Underground injection

Municipal landfill

Hazardous landfill

Other land disposal

Municipal waste incinerator

4 Each of the conditions of use of CCI4 may generate waste streams of the chemical that are collected and transported to third-party sites for disposal, treatment, or
recycling. Industrial sites that treat, dispose, or directly discharge onsite wastes that they themselves generate are assessed in each condition of use assessment. This
section only assesses wastes of CCli that are generated during a condition of use and sent to a third-party site for treatment, disposal, or recycling.

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Life Cycle Stage

Category 1

Subcategory 2b

Assessed Condition of Use

Hazardous waste incinerator

Off-site waste transfer

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1.3 General Approach and Methodology for Occupational Exposures

The occupational exposure assessment of each condition of use comprises the following components:

• Process Description: A description of the condition of use, including the role of the chemical in
the use; process vessels, equipment, and tools used during the condition of use;

• Worker Activities: Descriptions of the worker activities, including an assessment for potential
points of worker exposure and environmental releases.

• Number of Workers and Occupational Non-Users: An estimate of the number of sites,
number of workers and occupational non-users potentially exposed to the chemical for the given
condition of use.

• Inhalation Exposure: Central tendency and high-end estimates of inhalation exposure to
workers and occupational non-users. See Section 1.3.3 for a discussion of EPA's statistical
analysis approach for assessing inhalation exposure.

In addition to the above components for each condition of use, a separate dermal exposure section is
included that provides estimates of the dermal exposures for all the assessed conditions of use.

1.3.1 Process Description and Worker Activities

EPA performed a literature search to find descriptions of processes involved in each condition of use to
identify worker activities that could potentially result in occupational exposures. Where process
descriptions were unclear or not available, EPA referenced relevant emission scenario documents
(ESDs) or generic scenarios (GSs). Process descriptions for each condition of use can be found in the
applicable subsections of Engineering Assessment 2.

1.3.2 Number of Workers and Occupational Non-Users

Where available, EPA used CDR data to provide a basis to estimate the number of workers and ONUs.
EPA supplemented the available CDR data with U.S. economic data using the following method:

1. Identify the North American Industry Classification System (NAICS) codes for the industry
sectors associated with these uses.

2. Estimate total employment by industry/occupation combination using the Bureau of Labor
Statistics' Occupational Employment Statistics (OES) data (U.S. BLS. 2016).

3. Refine the OES estimates where they are not sufficiently granular by using the U.S. Census'
Statistics of US Businesses (SUSB) data on total employment by 6-digit NAICS (U.S. Census
Bureau. 2015).

4. Use market penetration data to estimate the percentage of employees likely to be using CCU
instead of other chemicals. If no market penetration data were available, estimate of the number
of sites using CCU from given NAICS code and multiply by the estimated workers and
ONUs/site provided in BLS data.

5. Where market penetration data are not available, use the estimated workers/ONUs per site in the
6-digit NAICS code and multiply by the number of sites estimated from CDR or TRI.

6. Combine the data generated in Steps 1 through 5 to produce an estimate of the number of
employees using CCU in each industry/occupation combination, and sum these to arrive at a total
estimate of the number of employees with exposure.

1.3.3 Inhalation Exposure Assessment Approach and Methodology

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1.3.3.1 General Approach

EPA provided occupational exposure results representative of central tendency conditions and high-end
conditions. A central tendency is assumed to be representative of occupational exposures and
environmental releases in the center of the distribution for a given condition of use. For risk evaluation,
EPA may use the 50th percentile (median), mean (arithmetic or geometric), mode, or midpoint values of
a distribution as representative of the central tendency scenario. EPA's preference is to provide the 50th
percentile of the distribution. However, if the full distribution is not known, EPA may assume that the
mean, mode, or midpoint of the distribution represents the central tendency depending on the statistics
available for the distribution.

A high-end is assumed to be representative of occupational exposures that occur at probabilities above
the 90th percentile but below the exposure of the individual with the highest exposure (U.S. EPA 1992).
For risk evaluation, EPA provided high-end results at the 95th percentile. If the 95th percentile is not
available, EPA may use a different percentile greater than or equal to the 90th percentile but less than or
equal to the 99.9th percentile, depending on the statistics available for the distribution. If the full
distribution is not known and the preferred statistics are not available, EPA may estimate a maximum or
bounding estimate in lieu of the high-end.

For occupational exposures, EPA may use measured or estimated air concentrations to calculate
exposure concentration metrics required for risk assessment, such as average daily concentration and
lifetime average daily concentration. These calculations require additional parameter inputs, such as
years of exposure, exposure duration and frequency, and lifetime years. EPA may estimate exposure
concentrations from monitoring data, modeling, or occupational exposure limits.

For the final exposure result metrics, each of the input parameters (e.g., air concentrations, working
years, exposure frequency, lifetime years) may be a point estimate (i.e., a single descriptor or statistic,
such as central tendency or high-end) or a full distribution. EPA will consider three general approaches
for estimating the final exposure result metrics:

• Deterministic calculations: EPA will use combinations of point estimates of each parameter to
estimate a central tendency and high-end for each final exposure metric result. EPA will
document the method and rationale for selecting parametric combinations to be representative of
central tendency and high-end.

• Probabilistic (stochastic) calculations: EPA will pursue Monte Carlo simulations using the full
distribution of each parameter to calculate a full distribution of the final exposure metric results
and selecting the 50th and 95th percentiles of this resulting distribution as the central tendency and
high-end, respectively.

• Combination of deterministic and probabilistic calculations: EPA may have full distributions for
some parameters but point estimates of the remaining parameters. For example, EPA may pursue
Monte Carlo modeling to estimate exposure concentrations, but only have point estimates of
working years of exposure, exposure duration and frequency, and lifetime years. In this case,
EPA will document the approach and rationale for combining point estimates with distribution
results for estimating central tendency and high-end results.

EPA follows the following hierarchy in selecting data and approaches for assessing inhalation

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exposures:

1. Monitoring data:

a. Personal and directly applicable

b. Area and directly applicable

c. Personal and potentially applicable or similar

d. Area and potentially applicable or similar

2. Modeling approaches:

a. Surrogate monitoring data

b. Fundamental modeling approaches

c. Statistical regression modeling approaches

3. Occupational exposure limits (OELs):

a. Company-specific OELs (for site-specific exposure assessments, e.g., there is only one
manufacturer who provides to EPA their internal OEL but does not provide monitoring data)

b. OSHA PEL

c. Voluntary limits (ACGIH TLV, NIOSH REL, Occupational Alliance for Risk Science (OARS)
workplace environmental exposure level (WEEL) [formerly by AIHA])

1.3.3.2 Approach for this Risk Evaluation

EPA reviewed workplace inhalation monitoring data collected by government agencies such as OSHA
and NIOSH, monitoring data submitted by industry organizations through public comments, and
monitoring data found in published literature (i.e., personal exposure monitoring data and area
monitoring data). Studies were evaluated using the evaluation strategies laid out in the Application of
Systematic Review in TSCA Risk Evaluations (U.S. EPA. 2018a).

Exposures are calculated from the datasets provided in the sources depending on the size of the dataset.
For datasets with six or more data points, central tendency and high-end exposures were estimated using
the 50th percentile and 95th percentile. For datasets with three to five data points, central tendency
exposure was calculated using the 50th percentile and the maximum was presented as the high-end
exposure estimate. For datasets with two data points, the midpoint was presented as a midpoint value
and the higher of the two values was presented as a higher value. Finally, data sets with only one data
point presented the value as a what-if exposure. For datasets including exposure data that were reported
as below the limit of detection (LOD), EPA estimated the exposure concentrations for these data,
following EPA's Guidelines for Statistical Analysis of Occupational Exposure Data (U.S. EPA. 1994)

which recommends using the ^'=¦ if the geometric standard deviation of the data is less than 3.0 and

if the geometric standard deviation is 3.0 or greater. Specific details related to each condition of use can
be found in Section 2. For each condition of use, these values were used to calculate chronic (non-cancer
and cancer) exposures. Equations and sample calculations for chronic exposures can be found in
Appendix B and Appendix C.

EPA used exposure monitoring data and exposure models to estimate inhalation exposures for all
conditions of use. Specific details related to the use of monitoring data for each condition of use can be
found in Section 2. Descriptions of the development and parameters used in the exposure models used
for this assessment can be found in Appendix A through Appendix E.

1.3.4 Dermal Exposure Assessment Approach and Methodology

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Dermal exposure data was not readily available for the conditions of use in the assessment. Because
CCU is a volatile liquid that readily evaporates from the skin, EPA estimated dermal exposures using the
Dermal Exposure to Volatile Liquids Model. This model determines a dermal potential dose rate based
on an assumed amount of liquid on skin during one contact event per day and the steady-state fractional
absorption for CCU based on a theoretical framework provided by Kasting and Miller (Kasting and
Miller. 2006). The amount of liquid on the skin is adjusted by the weight fraction of CCU in the liquid to
which the worker is exposed. Specific details of the dermal exposure assessment can be found in Section
2.12 and equations and sample calculations for estimate dermal exposures can be found in Appendix E.

1.3.5 Environmental Release Assessment Approach and Methodology

CCU environmental releases are not assessed in this risk evaluation because exposure from
environmental releases are controlled under regulatory programs of other environmental statutes,
administered by EPA, which adequately assess and effectively manage exposures, i.e., the CAA, the
Safe Drinking Water Act (SDWA), the Clean Water Act (CWA) and the Resource Conservation and
Recovery Act (RCRA). Office of Pollution Prevention and Toxics (OPPT) worked closely with the
offices within EPA that administer and implement the regulatory programs under these statutes. In some
cases, EPA has determined that chemicals present in various media pathways (i.e., air, water, land) fall
under the jurisdiction of existing regulatory programs and associated analytical processes carried out
under other EPA-administered statutes and have been assessed and effectively managed under those
programs. EPA believes that the TSCA risk evaluation should generally focus on those exposure
pathways associated with TSCA conditions of use that are not adequately assessed and effectively
managed under the regulatory regimes discussed above because these pathways are likely to represent
the greatest areas of risk concern. Section 2.5.3 of the problem formulation document outlines the
rationale for excluding these exposure pathways from the risk evaluation. Therefore, the engineering
assessment does not evaluate releases of CCU to the environment (U.S. EPA 2018c).

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2 Engineering Assessment

The following sections contain process descriptions and the specific details (worker activities, analysis
for determining number of workers, exposure assessment approach and results) from the assessment for
each condition of use. EPA assessed the conditions of use as stated in the Problem Formulation of the
Risk Evaluation for Carbon Tetrachloride (Methane, Tetrachloro-) published by EPA in May 2018
(U.S. EPA. 2018c).

2.1 Domestic Manufacturing

Domestic production of CCU is currently prohibited under regulations implementing the MP and C AA
Title VI, except when transformed (used and entirely consumed, except for trace quantities, in the
manufacture of other chemicals for commercial purposes), destroyed (including destruction after use as
a catalyst or stabilizer), or used for essential laboratory and analytical uses (40 CFR Part 82, 60 FR
24970, 24971 (May 10, 1995)) (U.S. EPA 2018c). Therefore, once manufactured, the CCU will be
handled again either on-site or by another facility for the identified uses described in detail in the
following sections.

2.1.1 Process Description

CCU was previously produced solely through the chlorination of carbon disulfide (CS2); however, in the
1950s chlorination of hydrocarbons became popular (Hoibrook. 2000). Currently, most CCU is
manufactured using one of three methods: chlorination of hydrocarbons or chlorinated hydrocarbons;
oxychlorination of hydrocarbons; or CS2 chlorination (Holbrook. 2000).

Chlorination of hydrocarbons or chlorinated hydrocarbons - The chlorination of hydrocarbons
involves a simultaneous breakdown of the organics and chlorination of the molecular fragments at
pyrolytic temperatures and is often referred to as chlorinolysis (Holbrook. 2000). A variety of
hydrocarbons and chlorinated hydrocarbon waste streams can be used as feedstocks; however, methane
is the most common (Holbrook. 2000). Perchloroethylene (PCE) is formed as a major byproduct of this
process with small volumes of hexachloroethane, hexachlorobutadiene and hexachlorobenzene also
produced (Holbrook. 2000).

Oxychlorination of hydrocarbons - The oxychlorination of hydrocarbons involves the reaction of
either chlorine or hydrochloric acid (HC1) and oxygen with a hydrocarbon feedstock in the presence of a
catalyst (Marshall and Pottenger. 2016; Holbrook. 2000). This process can be used to convert HC1
produced as a byproduct during the manufacture of chlorinated hydrocarbons into useful products
(Marshall and Pottenger. 2016).

CS2 Chlorination - The chlorination of CS2 involves the continuous reaction of CS2 with chlorine in an
annular reaction (Holbrook. 2000). The CCU produced is distilled to have a CS2 content of 0 to 5 ppm.
This process produces disulfur dichloride as a byproduct that is reduced with hydrogen without a
catalyst or with a ferric chloride catalyst (Holbrook. 2000).

2.1.2 Exposure Assessment

2.1.2.1 Worker Activities

During manufacturing, workers are primarily exposed while connecting and disconnecting hoses and
transfer lines to containers and packaging to be loaded (e.g., railcars, tank trucks, totes, drums, bottles)
and intermediate storage vessels (e.g., storage tanks, pressure vessels). Workers near loading racks and

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container filling stations are potentially exposed to fugitive emissions from equipment leaks and
displaced vapor as containers are filled. These activities are potential sources of worker exposure
through dermal contact with liquid and inhalation of vapors.

ONUs include employees that work at the site where CCU is manufactured, but they do not directly
handle the chemical and are therefore could have lower inhalation exposures and may not have dermal
exposures. ONUs for manufacturing include supervisors, managers, and tradesmen that may be in the
same area as exposure sources but do not perform tasks that result in the same level of exposures as
workers.

2.1.2.2 Number of Potentially Exposed Workers

EPA estimated the number of workers and occupational non-users potentially exposed to CCU at
manufacturing sites using 2016 CDR data, 2017 TRI data, Bureau of Labor Statistics' OES data (BLS
Data) and the U.S. Census' SUSB (SUSB Data). The method for estimating number of workers from the
Bureau of Labor Statistics' OES data and U.S. Census' SUSB data is detailed in Appendix A. These
estimates were derived using industry- and occupation-specific employment data from the BLS and U.S.
Census. Based on activity information reported in the 2016 CDR and 2016 TRI, EPA identified seven
sites that domestically manufacture CCU.

EPA identified the NAICS code 325199, All Other Basic Organic Chemical Manufacturing, and
325180, Other Basic Inorganic Chemical Manufacturing, as the codes would include manufacturing sites
(U.S. EPA. 2017c). Based on data from the BLS for NAICS code 325199 and related standard
occupational classification (SOC) codes, there are an average of 39 workers and 18 ONUs per site, or a
total of 57 potentially exposed workers and ONUs for sites under this NAICS code (U.S. BLS. 2016).
Data from the BLS for NAICS code 325180 and related SOC codes identifies an average of 25 workers
and 12 ONUs per site, or a total of 37 potentially exposed workers and ONUs for sites under this NAICS
code (U.S. BLS. 2016; U.S. Census Bureau. 2015).

To determine the total number of workers and ONUs, EPA used the average worker and ONUs
estimates from the BLS analysis based on each site's reported NAICS codes in TRKU.S. BLS. 2016).
For sites not reporting in TRI, EPA used the worker estimates for NAICS code 325199 as EPA
considered most sites manufacturing CCU to be organic chemical manufacturers. This resulted in five
sites being classified under 325199 and 2 sites under 325180. There is a total of 243 workers and 115
ONUs (see Table 2-1).

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Table 2-1. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During
Manufacturing

Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

High-End

193

284

Total Exposed Workers and ONUs

243

115

358

a For the sites using values from the BLS analysis, the total number of workers and occupational non-users are calculated
using the number of workers and occupational non-users per site estimated from BLS and multiplying by the number of sites.
The number of workers and occupational non-users per site presented in the table rounds the values estimated from the BLS
analysis to the nearest integer.

After review of 2017 TRI data, EPA discovered that multiple facilities that reported as a manufacturer in
CDR submitted additional uses as a reactant or as a processing agent/aid (U.S. EPA 2017c; 2016). To
properly analyze worker exposure without overestimation, the exposure from these submissions is
accounted for in the manufacturing section because the data indicates that once CCU is manufactured it
is transferred through piping to another location at the same site into the appropriate process for use. The
manufacturers could use piping systems that enclose the chemical and limit exposure to fugitive
emissions from minor leaks. The manufacturer would also sell the CCU as a product to be used
elsewhere, and the exposures from those uses are captured and assessed in the sections below.

2.1.2.3 Occupational Exposure Results

EPA assessed inhalation exposures during manufacturing using identified monitoring data. Table 2-2
summarizes 8-hr and 12-hr TWA samples obtained from data submitted by the Halogenated Solvents
Industry Alliance (HSIA) via public comment for two companies (HSIA. 2019). In addition to the data
submitted by HSIA, EPA also identified data from a NIOSH investigation at a magnesium
manufacturing site where CCU is manufactured as a byproduct (Kim et al.. 2005). However, the
manufacture of CCU as a byproduct would not be representative of sites where CCU is manufactured
intentionally; therefore, the data was not considered in this assessment.

HSIA (2019) provided monitoring data for CCU collected by two companies listed as "Company A" and
"Company B". The data were collected between 2005 and 2018 with full-shift data collected over 8 to
12 hours during which workers engaged in a variety of activities including collecting catch samples;
performing filter changes; line and equipment opening; loading and unloading; process sampling; and
transferring of hazardous wastes (HSIA 2019). EPA assessed two exposure scenarios: 1) 8-hr TWA; 2)
12-hr TWA.

The discrete samples from companies A and B specified the sampling time for each data point (HSIA
2019). EPA assessed an exposure duration of 8 hours (480 minutes) per day for averaging data points
that specified sampling time between 390 minutes (6.5 hours) and 540 minutes (9 hours). If the sample
time for a data point was less than 8 hours, EPA calculated the 8-hr TWA exposure assuming exposure
to be zero outside the sampling time. EPA assessed an exposure duration of 12 hours (720 minutes) per
day for averaging data points that specified sampling time between 540 minutes (9 hours) and 720

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minutes (12 hours). Similar to 8-hr TWAs, where sample times were less than 12-hrs, EPA calculated
the 12-hr TWA exposure assuming exposure to be zero outside the sampling time.

It should be noted that approximately 83% of the 8-hr TWA exposure data and 72% of the 12-hr TWA
exposure data were below the LOD. Analysis showed that the geometric standard deviation for 8-hr

TWA was less than 3.0, therefore, EPA assessed non-detectable data as per the Guidelines for

Statistical Analysis of Occupational Exposure Data (U.S. EPA. 1994). For the 12-hr TWA data, the
geometric standard deviation was greater than 3.0, therefore, EPA assessed the non-detectable data as

(U.S. EPA 1994). Because over 50% of 8-hr and 12-hr TWA exposure data are below the LOD,

calculating statistics from this data does present the potential to introduce biases into the results.
Estimation of exposure values for results below the LOD may over- or under-estimate actual exposure
thus skewing the calculated statistics higher or lower, respectively. The overall directional bias of the
exposure assessment, accounting for both the overestimate and underestimate, is not known.

Table 2-2. Summary of Worker Inhalation Exposure Monitoring Data for Manufacture of Carbon

Tetrachloride

Central

Confidence Rating

Number of

Tendency

High-End

of Associated Air

Exposure Calculation

Samples

(mg/m3)

Concentration Data

8-hr TWA Results for Company A and B

Full-Shift TWA

0.76

4.0

Acute Concentration (AC)

0.76

4.0

Average Daily Concentration
(ADC)

127

0.76

4.0

High

Lifetime Average Daily
Concentration (LADC)

0.07

0.47

12-hr TWA Results for Company A and B

Full-Shift TWA

0.50

4.8

246

0.50

4.8

High

ADC

0.50

4.8

LADC

0.069

0.83

ADC = Average Daily Concentration and LADC = Lifetime Average Daily Concentration. Equations and parameters for
calculation of the ADC, and LADC are described in Appendix B.

2.2 Import and Repackaging

Domestic production and importation of carbon tetrachloride is currently prohibited under regulations
implementing the Montreal Protocol (MP) and CAA Title VI, except when transformed (used and
entirely consumed, except for trace quantities, in the manufacture of other chemicals for commercial
purposes), destroyed (including destruction after use as a catalyst or stabilizer), or used for essential
laboratory and analytical uses. (40 CFRPart 82, 60 FR 24970, 24971 (May 10, 1995)) Therefore, once

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imported or manufactured, carbon tetrachloride will be handled again either on-site or by another facility
for the identified uses described in detail in the following sections.

The import and repackaging scenario covers only those sites that purchase carbon tetrachloride from
domestic and/or foreign suppliers and repackage the carbon tetrachloride from bulk containers into
smaller containers for resale. It does not include sites that import carbon tetrachloride and either: (1)
store the chemical in a warehouse and resell directly without repackaging; (2) act as the importer of
record for carbon tetrachloride but carbon tetrachloride is never present at the site5; or (3) import the
chemical and process or use the chemical directly at the site. In case #1, there is little or negligible
opportunity for exposures or releases as the containers are never opened. In case #2, the potential for
exposure and release is at the site receiving carbon tetrachloride, not the "import" site and
exposures/releases at the site receiving carbon tetrachloride are assessed in the relevant scenario based
on the condition of use for carbon tetrachloride at the site. Similarly, for case #3, the potential for
exposure and release at these sites are evaluated in the relevant scenario depending on the condition of
use for carbon tetrachloride at the site.

2.2.1_ Process Description

In general, commodity chemicals are imported into the United States in bulk via water, air, land, and
intermodal shipments (Tomer and Kane. 2015). These shipments take the form of oceangoing chemical
tankers, railcars, tank trucks, and intermodal tank containers. Chemicals shipped in bulk containers may
be repackaged into smaller containers for resale, such as drums or bottles. Domestically manufactured
commodity chemicals may be shipped within the United States in liquid cargo barges, railcars, tank
trucks, tank containers, intermediate bulk containers (IBCs)/totes, and drums. Both imported and
domestically manufactured commodity chemicals may be repackaged by wholesalers for resale; for
example, repackaging bulk packaging into drums or bottles.

The exact shipping and packaging methods specific to CCU are not known. For this risk evaluation, EPA
assesses the repackaging of CCU from bulk packaging to drums and bottles at wholesale repackaging
sites (see Figure 2-1).

Figure 2-1. General Process Flow Diagram for Import and Repackaging

The import and repackage scenario is meant to include sites that receive CCU from either a domestic or
foreign (importer) supplier that then repackage CCU prior to selling it to downstream users. Sites that
import and use CCU directly at the import site (e.g. import for use as an intermediate, processing aid,
etc. at the site) are included in the assessment for the appropriate use scenario.

2.2.2 Exposure Assessment

5 In CDR, the reporting site is the importer of record which may be a corporate site or other entity that facilitates the import
of the chemical but never actually receives the chemical. Rather, the chemical is shipped directly to the site processing or
using the chemical.

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2.2.2.1 Worker Activities

Based on EPA's knowledge of the chemical industry, worker activities at import and repackaging sites
are potentially exposed while connecting and disconnecting hoses and transfer lines to containers and
packaging to be unloaded (e.g., railcars, tank trucks, totes), intermediate storage vessels (e.g., storage
tanks, pressure vessels), analyzing quality control (QC) samples, and final packaging containers (e.g.,
drums, bottles). Workers near loading racks and container filling stations are potentially exposed to
fugitive emissions from equipment leaks and displaced vapor as containers are filled. These activities
are potential sources of worker exposure through dermal contact with liquid and inhalation of vapors.

ONUs include employees that work at the site where CCU is repackaged, but they do not directly handle
the chemical and are therefore would have lower inhalation exposures and may not have dermal
exposures. ONUs for repackaging include supervisors, managers, and tradesmen that may be in the
repackaging area but do not perform tasks that result in the same level of exposures as repackaging
workers.

2.2.2.2 Number of Potentially Exposed Workers

EPA reviewed 2016 CDR data, 2017 TRI data, BLS Data and SUSB Data to determine the number of
potentially exposed workers for importing and repacking of CCU. The method for estimating number of
workers from the Bureau of Labor Statistics' OES data and U.S. Census' SUSB data is detailed in
Appendix A. As described in Section 2.1.2.2, one site was determined to be an importing site. None of
the CDR submissions reported a repackaging activity in the industrial processing and use section.

In the 2017 TRI data, one submission reported an import activity and one submission reported a
repackaging activity. The site reporting import in the 2017 TRI also reported use of CCU as a processing
aid. This site is included in the assessment of use of CCU as a processing aid (see Section 2.8). The TRI
entry marked for repackaging has primary NAICS code 562211, Hazardous Waste Treatment and
Disposal, and is most likely a waste disposal facility. Therefore, this site is included in the waste
handling/recycling assessment (see Section 2.9) and not included in the import and repackaging
assessment.

Based on the information reported in the 2016 CDR and 2017 TRI, EPA assesses one possible
import/repackaging site for CCU (U.S. EPA 2017c; 2016). EPA identified the NAICS code 424690,
Other Chemical and Allied Products Merchant Wholesalers, as the code would include sites importing
and repackaging CCU. EPA assesses the number of potentially exposed workers based on data from the
BLS for NAICS code 424690 and related SOC codes. There is a total of one potentially exposed
workers and one ONU for sites under this NAICS code (see Table 2-3)(U.S. BLS. 2016; U.S. Census
Bureau. 2015).

Table 2-3. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During

Import and

Repackaging

Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

Total Exposed Workers and ONUs

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a For the sites using values from the BLS analysis, the total number of workers and occupational non-users are calculated
using the number of workers and occupational non-users per site estimated from BLS and multiplying by the number of sites.
The number of workers and occupational non-users per site presented in the table round the values estimated from the BLS
analysis to the nearest integer.

2.2.2.3 Occupational Exposure Assessment Methodology

2.2.2.4 Occupational Exposure Results

EPA did not identify any inhalation exposure monitoring data related to the repackaging of CCU.
Therefore, EPA assessed inhalation exposures during repackaging using the Tank Truck and Railcar
Loading and Unloading Release and Inhalation Exposure Model, conservatively assuming CCU is
present at 100 percent concentration when imported or repackaged. The model estimates the potential
concentration of CCU in air when it is unloaded or loaded at an industrial facility. The model accounts
for the displacement of saturated air containing the chemical of interest as the container/truck is filled
with liquid, emissions of saturated air containing the chemical of interest that remains in the loading
arm, transfer hose and related equipment, and emissions from equipment leaks from processing units
such as pumps, seals, and valves.

EPA calculated 8-hr TWA exposures to workers during loading activities. The 8-hr TWA exposure is
the weighted average exposure during an entire 8-hr shift, assuming zero exposures during the
remainder of the shift. Table 2-4 presents a summary of the exposure modeling results. The model
estimates the central tendency exposure of 0.057 mg/m3 8-hr TWA and a high-end exposure of 0.30
mg/m3 8-hr TWA.

Table 2-4. Summary of Exposure Modeling Results for Import and Repackaging

Exposure
Calculation

Central
Tendency
(mg/m3)

High-
End

(mg/m3)

Confidence Rating
of Associated Air
Concentration
Data

Full-Shift TWA

0.057

0.30

N/A - Modeled
Data

0.057

0.30

ADC

0.057

0.30

LA DC

0.0052

0.035

2.3 Processing as a Reactant or Intermediate

2,3.J^ Process Description

Processing as a reactant or intermediate is the use of CCU as a feedstock in the production of another
chemical product via a chemical reaction in which CCU is consumed. In the past, CCU was mainly used
as feedstock for the manufacture of chlorofluorocarbons (CFCs) (Marshall and Pottenger. 2016).
However, due to the discovery that CFCs contribute to stratospheric ozone depletion, the use of CFCs
was phased-out by the year 2000 to comply with the Montreal Protocol (Holbrook. 2000). One of the
primary CFC replacements was the HFCs. Most HFCs, do not require CCU for their manufacture.
However, CCU is used as a feedstock to produce HFC-245fa and HFC-365mfc. The production of

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hydrofluorocarbons HFC-245fa and HFC-365mfc accounted for 71% and 23%, respectively, of total
CCU consumption in 2016 (MacRoy. 2017).

Currently, CCU is used as a reactant to manufacture a variety of products in addition to HFCs, including
HCFCs, HFOs, hydrochloric acid, vinyl chloride, ethylene dichloride (EDC), Perchloroethylene (PCE),
chloroform, hafnium tetrachloride, thiophosgene, and methylene chloride (Krock. 2017; U.S. EPA.
2017b; Marshall and Pottenger. 2016; Weil et al.. 2006; Holbrook. 2004. 2003). In the catoxid®
catalytic oxidation process, CCU is also reacted in order to manufacture anhydrous HC1 (Krock. 2017).
The specifics of the reaction process (e.g., use and types of catalysts, reaction temperature) vary
depending on the product being produced; however, a typical reaction process involves unloading CCU
from containers and feeding into the reaction vessel(s), where CCU either fully or partially reacts with
other raw materials to form the final product. Following the reaction, the product may be purified to
remove unreacted CCU or other materials if needed.

CCU is used in the manufacturing of other chlorinated compounds/solvents that may be subsequently
added to commercially available products (i.e., solvents for cleaning/degreasing, adhesives/sealants, and
paints/coatings). However, given the high volatility of CCU and the extent of reaction and efficacy of the
separation/purification process for purifying final products, there could be insignificant or unmeasurable
concentrations of CCU in the manufactured chlorinated substances in the commercially available
products.

2.3.2 Exposure Assessment

2.3.2.1 Worker Activities

Similar to when manufacturing carbon tetrachloride, workers are potentially exposed while connecting
and disconnecting hoses and transfer lines to containers and packaging to be unloaded (e.g., railcars,
tank trucks, totes) and adding raw materials into intermediate storage vessels (e.g., storage tanks,
pressure vessels) when processing carbon tetrachloride as a reactant. Workers near loading racks and
container filling stations are potentially exposed to fugitive emissions from equipment leaks and
displaced vapor as containers are filled. These activities are potential sources of worker exposure
through dermal contact with liquid and inhalation of vapors.

ONUs include employees that work at the site where CCU is reacted, but they do not directly handle the
chemical and are therefore would have lower inhalation exposures and may not have dermal exposures.
ONUs for processing as a reactant include supervisors, managers, and tradesmen that may be in the
same area as exposure sources but do not perform tasks that result in the same level of exposures as
workers.

2.3.2.2 Number of Potentially Exposed Workers

EPA estimated the number of workers and occupational non-users potentially exposed to CCU at sites
processing CCU as a reactant using 2016 CDR data, 2017 TRI data, BLS Data and SUSB Data. The
method for estimating number of workers from the Bureau of Labor Statistics' OES data and U.S.
Census' SUSB data is detailed in Appendix A. These estimates were derived using industry- and
occupation-specific employment data from the BLS and U.S. Census. From the 2016 CDR data, seven
submitters reported eight records of processing CCU as a reactant with each record reporting fewer than
10 sites that process CCU as a reactant. However, five of the eight CDR records are also reported
manufacture locations of CCU. EPA assesses these five records among the manufacturing section
(Section 2.1.2.2). EPA assesses the remaining three reports from CDR in this section. Upon review of

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2017 TRI, EPA found eight sites reported using CCU as a reactant (U.S. EPA 2017c). and five of these
sites are reported manufacturers of CCU in CDR. This falls within the rangereported for number of sites
from the 2016 CDR. EPA assessed three of the listed TRI submissions that use CCU as a reactant.
Between CDR and TRI, EPA assessed a range of six to thirty sites.

EPA determined the number of workers using the related SOC codes from BLS analysis that are
associated with the primary NAICS codes listed in TRI. Two of the three submissions in TRI identified
the primary NAICS code to be 325199, All Other Basic Organic Chemical Manufacturing, while one
was listed as 325120, Industrial Gas Manufacturing (U.S. EPA 2017c). For NAICS code 325199, there
are an average of 39 workers and 18 ONUs per site, or a total of 57 potentially exposed workers and
ONUs. For NAICS code 325120, there are an average of 14 workers and 7 ONUs per site, or a total of
21 potentially exposed workers and ONUs (U.S. BLS. 2016). Similarly, two of the three submissions in
CDR identified the primary NAICS code to be 325199 and one was listed as 325120 (U.S. EPA. 2016).

To determine the high-end total number of workers and ONUs, EPA used the high-end of ranges
reported for number of sites in the three 2016 CDR reports. Then, EPA assessed using the corresponding
number of workers from BLS analysis that are associated with the primary NAICS codes for those
entries. (U.S. EPA. 2016; U.S. BLS. 2016). For the other three TRI submissions, EPA used the average
worker and ONUs estimates from the BLS analysis based on their NAICS codes (U.S. BLS. 2016). This
resulted in an estimated 911 workers and 429 ONUs (see Table 2-5).

To determine the low-end total number of workers and ONUs, EPA used the low-end of ranges reported
for number of sites in the three CDR reports. Then, EPA assessed using the corresponding number of
workers from BLS analysis that are associated with the primary NAICS codes for those entries. (U.S.
EPA. 2016; U.S. BLS. 2016). For the remaining three TRI sites, EPA used the average worker and
ONUs estimates from the BLS analysis and TRI reported NAICS codes (U.S. EPA. 2017c; U.S. BLS.
2016). This resulted in an estimated 182 workers and 86 ONUs (see Table 2-5).

Table 2-5. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During
Processing as a Reactant

Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

High-End

18a

695

327

1,022

114

125

184

Total Exposed Workers and ONUs

911

429

1,340

Low-End

154

227

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Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

Total Exposed Workers and ONUs

182

268

a For the sites using values from the BLS analysis, the total number of workers and occupational non-users are calculated
using the number of workers and occupational non-users per site estimated from BLS and multiplying by the number of sites.
The number of workers and occupational non-users per site presented in the table round the values estimated from the BLS
analysis to the nearest integer.

2.3.2.3 Occupational Exposure Assessment Methodology

EPA identified one source for inhalation exposure monitoring data related to the use of CCU as a
reactant; however, the discrete sample values were not available. EPA supplemented the identified
monitoring data using surrogate data from HSIA manufacturing CCU. as there are similarities in
processes and potential exposure points between manufacturing and processing CCU as a reactant. The
following subsections detail the results of EPA's occupational exposure assessment for use of CCU as a
reactant based on inhalation exposure monitoring data and surrogate data.

2.3.2.3.1 Inhalation Exposure Assessment Results Using Monitoring Data

Table 2-6 summarizes full-shift TWA sample data obtained from aNIOSH Health Hazard Evaluation
(HHE) report (Gilles and Lybarger. 1978). Data were collected from Allied Chemical in 1978 for full-
shift exposures to CCU (Gilles and Lybarger. 1978). During operation, there were two to three operators
present each shift, 10 to 14 employees were involved in packaging operations, four employees were
engaged in tank farm operations, and there were six to eight individuals in the laboratory who collected
and analyzed samples (Gilles and Lybarger. 1978).

Table 2-6. Summary of Inhalation Exposure Monitoring Data for Use as a Reactant for Carbon

Tetrachloride

Study or
Company

Full-shift TWA
(mg/m3)

Number of Full-
shift Samples

Short-
Term
TWA
(mg/m3)

Number of Short-term Samples

Allied
Chemical

Max: 6.92
Min: 3.15
Mean: Not
provided

Not provided

Short-term samples not collected

GM = Geometric Mean; AM = Arithmetic Mean; ND = Non-detected

Exposure calculations were not performed because there is no data (i.e., mean or median) for estimating
a central tendency exposure level. Additionally, the number of samples is not provided, which does not
indicate how representative the results are of central tendency and high end exposures. The age of the
data (40 years) also indicates that the results from Allied Chemical may be from operations, equipment,
and worker activities that could be outdated. Therefore, surrogate monitoring data from manufacturing
activities will be utilized to assess exposure.

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2.3.2.3.2 Inhalation Exposure Assessment Results Using Surrogate Data

The exposure sources, exposure routes, and exposure levels when using CCU as a reactant could be
similar to those when manufacturing CCU. See Section 2.1.2.3 for the details of the assessment of
worker exposure from chemical manufacturing activities.

Upon examining the two data sources, the surrogate data provided by HSIA estimates a central tendency
exposure of 0.76 mg/m3 8-hr TWA and a high-end exposure of 4.0 mg/m3 8-hr TWA. The high-end
surrogate data exposure levels are less than the maximum value in the identified monitoring data from
Allied Chemical. This may be because the number of samples taken and the process activities are
unknown. It is unclear how representative the Allied Chemical data are of typical central tendency and
high end exposures. However, the central tendency surrogate exposure level, 0.76 mg/m3, is less than the
minimum value provided by monitoring data, 3.15 mg/m3. There were limited details provided to
describe the process information, specific worker activities when interacting with CCU, and engineering
controls included when analyzing the monitoring data for use of CCU as a reactant. This made it difficult
to identify specific causes of differing results. It is known that the data is from 1978, so the worker
activities and operations may be somewhat out of date with what is included in the modelling scenario.
Best practices evolve over time when more information is available, so it's possible the typical exposure
results from the model are more representative of today's processes.

as a Reactant

Central

Confidence Rating

Number of

Tendency

High-End

of Associated Air

Exposure Calculation

Samples

(mg/m3)

Concentration Data

8-hr TWA Results for Company A, B, and C

Full-Shift TWA

0.76

4.0

127

0.76

4.0

High

ADC

0.76

4.0

LA DC

0.069

0.47

12-hr TWA Results for Company A, B, and C

Full-Shift TWA

0.50

4.8

234

0.50

4.8

High

ADC

0.50

4.8

LADC

0.069

0.83

2.4 Incorporation into Formulation, Mixture, or Reaction Product

After manufacture, CCU may be supplied directly to end-users, or may be incorporated into various
products and formulations at varying concentrations for further distribution. Incorporation into a
formulation, mixture, or reaction product refers to the process of mixing or blending several raw
materials to obtain a single product or preparation. There are current regulatory actions that prohibit the
direct use of CCU as reactant or additive in the formulation of commercially available products for
industrial/commercial/consumer uses (including aerosol and non-aerosol adhesives/sealants,

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paints/coatings, and cleaning/degreasing solvent products), besides as a laboratory chemical. The use of
CCU (and mixtures containing it) in household products has also been banned by the CPSC since 1970,
with the exception of "unavoidable manufacturing residues of carbon tetrachloride in other chemicals
that under reasonably foreseen conditions of use do not result in an atmospheric concentration of carbon
tetrachloride greater than 10 parts per million." (16 CFR 1500.17(a)(2)). Based on the current
regulations and the information provided by industry, EPA has determined that these conditions of use
do not warrant evaluation.

The categories and subcategories originally listed in the problem formulation document for
incorporation into formulation could be either the use of carbon tetrachloride as a reactant to
manufacturing a chlorinated compound that is subsequently formulated into a product or as a processing
aid/agent used to aid in the manufacture of formulated products (agricultural chemicals, petrochemicals-
derived products, and any other basic organic and inorganic chemical manufacturing). The former case
is evaluated in the reactant section and the latter in the processing aid section. In both cases, carbon
tetrachloride is not meant to make it into the final product (although may be present as impurities as
mentioned above).

2.5 Specialty Uses - Aerospace Industry

EPA has conducted public outreach and literature searches to collect and review information about CCU
conditions of use. As a result of that analysis, EPA has determined uses of CCU that were previously
thought to be a condition of use are actually no longer used in current practices. Consequently, EPA will
not consider or evaluate these activities and conditions of use or associated exposures in the risk
evaluation for CCU. Specialty uses of CCU, specifically adhesives and cleaning operations, were
identified in the aerospace industry by the Aerospace Industries Association (AIA) (Riegle. 2017).
However, upon reaching out to AIA for specific use details, AIA replied with the following statement:

"After additional investigation, usage identified by AIA companies were based upon products
that have been discontinued. There appear to be products that contain trace amounts of carbon
tetrachloride (<1%) that might be a reaction by-product, contaminant or imperfect distillation of
perchloroethylene. Therefore, carbon tetrachloride is no longer an AIA concern. " ((AIA). 2019)

Based on all present information, EPA will not evaluate the use of CCU in cleaning operations (vapor
degreasing, etc.) or use as an adhesive in the risk evaluation as there are no data supporting its use or its
presence as an intended component of product formulations used in the aerospace industry.

Additionally, there are current regulatory actions (MP and Title VI of the CAA) that prohibit the direct
use of CCU in the formulation of commercially available products for industrial, commercial, and
consumer uses (including aerosol and non-aerosol adhesives/sealants, paints/coatings, and
cleaning/degreasing solvent products), except as a laboratory chemical (Section 2.2.2.1 of thq Problem
Formulation of the Risk Evaluation for Carbon Tetrachloride (Methane, Tetrachloro-) (U.S. EPA.
2018c).

2.6 Specialty Uses - Department of Defense Data

EPA reached out to the Department of Defense (DOD) for monitoring data for the first 10 chemical
substances that are the subject of the Agency's initial chemical risk evaluations. The DoD provided
monitoring data from its Defense Occupational and Environmental Health Readiness System - Industrial
Hygiene (DOEHRS-IH), which collects occupational and environmental health risk data from each
service branch. The DOD provided inhalation monitoring data for three branches of the military: the

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Army, Air Force, and Navy ((DOEFtRS-IH), 2018). These data are not distinguished among the three
branches.

The following subsections provide an overview of the DOD data. EPA only used the OBOD (definition
of abbreviation not provided in data) clean-up data in this assessment as these were the only data EPA
could use to assess 8-hr TWA exposures. The sampling results for the remaining six processes were
measured over a period less than 50 percent of the duration of the process (or an 8-hr shift if the process
duration was not specified). Since only a fraction of the process time (or an 8-hr shift) was sampled for
these remaining processes, EPA could not use them to estimate 8-hr TWA exposure.

2,6A_ Data Overview

The data provided by DOD includes 105 data points for carbon tetrachloride from samples taken during
seven processes:

1. OBOD Clean-Up

2. Detonation Chamber

3. Mobile Detonation Test Facility

4. Plastics/Modeling (Thermoforming)

5. Solvent Extraction of Explosive Samples

6. Glue Sound Dampening Material to Torpedo Body

7. Spray Painting - High Volume, Low Pressure (HVLP) Spray Gun

The provided personal breathing zone samples for all of the DOD activities are summarized in Table
2-8. All sample results are indicated as less than a value, which is considered to be the limit of detection
(LOD). The DOD data stated that all workers monitored worked an 8-hr shift. For some processes, the
DOD data do not provide the process duration.

}le 2-8. DOD Inhalation Monitoring Results

Min.

Max.

Worker

Process

Sample

Number

Sample

Activity

Duration

Result

Duration

Sample

Process

Description

Frequency

(min)

(mg/m3)

Samples

(min)

Date

OBOD Clean-Up

Cleaning and
sampling
residual
metal and ash

2-3 Times
per Week

1-2 hours

< 1.261

< 1.26

140

Jan. 27,
2015

Detonation

Destruction

Special

>10

<2.9

<30

14-140

2011

Chamber

of munition
and storage
of resulting
liquid waste

Occasions

hours

Mobile Detonation

Destruction

Special

>10

<3.8

< 17

24-116

June 15,

Test Facility

of munition
and storage
of resulting
liquid waste

Occasions

hours

2011

Plastics/

None

2-3 Times

<31.46

104

Dec. 4,

Modeling
(Thermoforming)

provided

per Month

2015

Solvent Extraction

Sampling of

Weekly

6-8 hours

<5.52

Sept. 22,

of Explosive
Samples

energetics
with solvent

1993

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Glue Sound
Dampening
Material to
Torpedo Body

None
provided

Special
Occasions

<0.217

221

June 22,
2011

Spray Painting -
High Volume, Low
Pressure (HVLP)
Spray Gun

None
provided

Weekly

<3.2

June 5,
2016

1 All three samples provided were listed as < 0.2 ppm (1.26 mg/m3).

2 This was the exact information provided and no explanation was given for this value.

2.6.2 OBOD Clean-Up Process Description

During the OBOD clean-up process, employees clean up residual metal and ash. Small metal pieces and
ash are drummed and stored. Once drum(s) are full, personnel perform sampling to determine disposal
requirements. Larger pieces of metal can be sold for recycling once deemed inert. Clean-up is performed
in steel toe boots, coveralls, and respiratory protection (powered air-purifying respirator [PAPR] with
tight-fitting facepiece and organic vapor and HEPA cartridge). A self-contained breathing apparatus
(SCBA) is available for emergencies and as needed for clean-up ((DOEHRS-IH). 2018).

2.6.3 Exposure Assessment

As the exposure values are reported to be below the LOD, EPA referenced EPA's Guidelines for
Statistical Analysis of Occupational Exposure Data (1994) to estimate the exposure value as —=¦ if the

geometric standard deviation of the data is less than 3.0 and if the geometric standard deviation is

3.0 or greater (U.S. EPA. 1994). However, the given DOD data reports all three samples for the OBOD
clean-up as below the LOD. Since these values are unknown a geometric standard deviation cannot be
calculated. Therefore, EPA assessed the exposure as a range from 0 to 1.26 mg/m3 using the midpoint
(0.68 mg/m3) to calculate the central tendency 8-hr TWA and the maximum value (1.26 mg/m3) to
calculate the high end 8-hr TWA. Additionally, the DOD data indicates that OBOD clean-up has a
duration of one to two hours. The sampling duration of the January 27, 2015 monitoring was 140
minutes (approximately 2.3 hours). Therefore, this monitoring event could have sampled workers during
the entirety of the process and the sample results would be representative of worker exposures over the
course of the process. EPA also considered exposure from the OBOD clean-up process as the only
source of exposure for these workers, and the workers' exposures are zero for the remainder of an 8-hr
shift. Therefore, EPA averaged the 140-minute midpoint and maximum sample results over eight hours
to calculate the 8-hr TWA exposure.

DOD reported the process frequency for the OBOD cleaning as every 2-3 weeks. EPA incorporated this
data and adjusted the exposure frequency to reflect the limited work exposure time when calculating the
central tendency and high-end ADC and LADC. The central tendency ADC and LADC are calculated
using the midpoint of the process frequency range, 2.5 weeks (125 days/year), and the high-end ADC
and LADC are calculated using maximum of the process frequency range, 3 weeks (150 days/year.
Results are presented in Table 2-9.

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Table 2-9. Summary of Worker Inhalation Exposure Monitoring Data for Specialty Use of Carbon
Tetrachloride

Exposure
Calculation 6

Number of
Samples

Central
Tendency
(mg/m3)

High-End
(mg/m3)

Confidence Rating of

Associated Air
Concentration Data

8-hr TWA Results for OBOD Clean-Up

Full-Shift TWA

0.18

0.37

High

0.18

0.37

ADC

0.092

0.22

LADC

0.0083

0.026

2.7 Reactive Ion Etching

2.7.1 Process Description

Reactive ion etching (RIE) is a microfabrication technique used in miniature electronic component
manufacture. Ion bombardment and a reactive gas, such as CCU, are used to selectively etch wafers
(U.S. EPA. 2017b).

Typically, a clean environment is essential for manufacturing the miniature electronic components
(primarily semiconductors) that require RIE. Flaws in the wafer surface or contamination of the
materials used can result in "opens" or "shorts" in the transistor circuits, causing them to be unusable.
Therefore, current semiconductor fabrication facilities (i.e., 'fabs') are built to Class-1 cleanroom
specifications, which means there is no more than one particle larger than 0.5-micron in one cubic foot
of air. In addition, cleaning operations precede and follow most of the manufacturing process steps. Wet
processing, during which wafers are repeatedly immersed in or sprayed with solutions, is commonly
used to minimize the risk of contamination. In addition, many processes operate within a positive
pressure environment (OECD. 2010).

2.7.2 Exposure Assessment

EPA estimates that worker exposures to CCU during RIE are negligible. Due to the performance
requirements of products typically produced via RIE, CCU could be applied in small amounts in a highly
controlled work area, thus eliminating or significantly reducing the potential for exposures. EPA
anticipates that CCU is used in RIE applications in limited quantities and among limited facilities. This
is consistent with assumptions for similar industry processes provided in the ESD on Chemical Vapor
Deposition in the Semiconductor Industry and ESD on Photoresist Use in Semiconductor Manufacturing
(OECD. 2015; OECD. 2010).

2.7.2.1 Worker Activities

Specific worker activities for RIE were not identified, but EPA utilized the worker activities listed in the
ESD on Photoresist Use in Semiconductor Manufacturing because worker activities will be similar for
RTF, as they are for using photoresists. According to the ESD on Photoresist Use in Semiconductor
Manufacturing, there are two main worker activity groups at a facility that utilizes RIE that include:

6 Equations and parameters for calculation of the ADC and LADC are described in Appendix B.

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equipment operators and equipment maintenance/waste management technicians. Equipment operators'
main role is to change-out the liquid etching containers containing CCU Equipment maintenance/waste
management technicians clean empty containers, clean/maintain equipment, and change-out the excess
solvent collection containers (OECD. 2010).

When workers must enter the cleanroom environment to perform their duties, the worker is required to
wear full-body coveralls (i.e., "space suits"), respirators, face shields, and gloves. Additionally, wafers
are often manipulated robotically within the closed system, or transferred within "micro" enclosures
between process steps to limit worker exposure. However, some sites have separate work areas outside
the wafer processing area (e.g., "chemical kitchens") in which the photoresist and other chemical
containers and supply lines are connected. If workers handle the photoresist bottles and other chemical
containers in a separate area, such as the chemical kitchen, they will likely be wearing solvent-resistant
gloves, aprons, goggles, and respirators with organic vapor cartridges to minimize exposure (OECD.
2010).

2.7.2.2 Number of Potentially Exposed Workers

Based on information in the ESD on Photoresist Use in Semiconductor Manufacturing, EPA identified
the NAICS code 334413, Semiconductor and Related Device Manufacturing, as the NAICS code would
include sites using CCU as a RIE (OECD. 2010). EPA estimated the number of workers and ONUs for
this NAICS code using Bureau of Labor Statistics' OES data (BLS Data) and the U.S. Census' SUSB
(SUSB Data). The method for estimating number of workers from the Bureau of Labor Statistics' OES
data and U.S. Census' SUSB data is detailed in Appendix A. This analysis resulted in an average of 50
workers and 45 ONU per site (U.S. BLS. 2016; U.S. Census Bureau. 2015). EPA does not have data to
estimate the number of sites using CCU as a RIE; therefore, only the per site data are presented (see
Table 2-10).

Table 2-10. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During

Use as a RIE

Exposed Workers per
Site

Exposed Occupational
Non-Users per Site

Total Exposed Per
Site

2.8 Industrial Processing Agent/Aid

This section includes the assessment of the use of CCU as a processing agent/aid for petrochemicals-
derived products manufacturing, agricultural products manufacturing, and metal recovery. EPA
determined these industrial uses are subject to the use of CCU as a process agent listed in the MP side
agreement, Decision X/14: Process Agents.

2,8._1^ Process Description

According to the TRI Reporting Forms and Instructions (RFI) Guidance Document, a processing aid is a
"chemical that is added to a reaction mixture to aid in the manufacture or synthesis of another chemical
substance but is not intended to remain in or become part of the product or product mixture". Examples
of such chemicals include, but are not limited to, process solvents, catalysts, inhibitors, initiators,
reaction terminators, and solution buffers" (U.S. EPA. 2018d). Additionally, processing agents are

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intended to improve the processing characteristics or the operation of process equipment, but not
intended to affect the function of a substance or article created (U.S. EPA. 2016).

The domestic and international use of carbon tetrachloride as a process agent is addressed under the MP
side agreement, Decision X/14: Process Agents (UNEP/Ozone Secretariat. 1998). This decision lists a
limited number of specific manufacturing uses of carbon tetrachloride as a process agent (non-feedstock
use) in which carbon tetrachloride may not be reacted or destroyed in the production process. Approved
uses of carbon tetrachloride as a process agent are listed below in Table 2-8.

Table 2-11. List of Uses of Carbon Tetrachloride as Process Agents in MP Side Agreement,
Decision X/14: Process Agents

Elimination of nitrogen trichloride in the
production of chlorine and caustic

Manufacture of chlorinated paraffin

Recovery of chlorine in tail gas from
production of chlorine

Production of pharmaceuticals - ketotifen,
anticol and disulfiram

Manufacture of chlorinated rubber

Production of tralomethrine (insecticide)

Manufacture of endosulphan (insecticide)

Bromohexine hydrochloride

Manufacture of isobutyl acetophenone
(ibuprofen - analgesic)

Diclofenac sodium

Manufacture of 1-1, Bis (4-chlorophenyl)
2,2,2- trichloroethanol (dicofol insecticide)

Cloxacilin

Manufacture of chlorosulphonated polyolefin
(CSM)

Phenyl glycine

Manufacture of poly-phenylene-terephtal-
amide

Isosorbid mononitrate

Manufacture of styrene butadiene rubber

Omeprazol

EPA has identified uses of carbon tetrachloride as a process agent in the manufacturing of
petrochemical-derived products, agricultural products, inorganic compounds (i.e., chlorine),
pharmaceuticals (i.e., ibuprofen), and chlorinated compounds that are used in the formulation of solvents
for cleaning and degreasing, adhesive and sealants, paints and coatings and asphalt (U.S. EPA. 2017b).
Therefore, carbon tetrachloride could only be present in the listed products as an impurity rather than
serving a specific function.

In 1983, EPA presented a report entitled Preliminary Study of Sources of Carbon Tetrachloride: Final
Report (U.S. EPA. 1983). In this report, carbon tetrachloride was used as a solvent to dissolve solid
reactants during the pharmaceutical manufacturing process, which included ibuprofen (U.S. EPA. 1983).
However, in 2008, the Science History Institute published an article titled, The Greening of Chemistry,
which explains that ibuprofen was once manufactured with the use of many process steps and multiple
solvents, one of which was carbon tetrachloride. It continues to explain, ".. .in the early 1990s ibuprofen
got a makeover. Using catalysts rather than excess reagents to drive the reactions, chemists halved the
number of stages in the ibuprofen manufacturing process and eliminated carbon tetrachloride, a toxic
solvent, from the process." (Hoag. 2016) EPA found no evidence to suggest that the manufacturing of
ibuprofen still utilizes carbon tetrachloride.

A current example of using carbon tetrachloride as a process agent in petrochemicals-derived product
manufacturing is the manufacture of chlorinated rubber resins. The resulting resins are thermoplastic,

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odorless, and non-toxic. Carbon tetrachloride is preferred in this process as it is the only solvent not
attacked by chlorine (U.S. EPA. 2017b).

2.8.2 Exposure Assessment

2.8.2.1 Worker Activities

Based on EPA 's knowledge of the chemical industry, worker activities at facilities where CCU is used
as a processing agent/aid may involve manually adding CCU or connecting/disconnecting transfer lines
used to unload containers into storage or reaction vessels, rinsing/cleaning containers and/or process
equipment, collecting and analyzing QC samples, manually loading spent CCU processing aid, or
connecting/disconnecting transfer lines used to load spent CCU processing aid into containers.

During processing, workers are primarily exposed while connecting and disconnecting hoses and
transfer lines to containers and packaging to be unloaded (e.g., railcars, tank trucks, totes, drums,
bottles) and intermediate storage vessels (e.g., storage tanks, pressure vessels). Workers near unloading
racks and container unloading stations are potentially exposed to fugitive emissions from equipment
leaks and displaced vapor as containers are unloaded. These activities are potential sources of worker
exposure through dermal contact with liquid and inhalation of vapors.

ONUs include employees that work at the site where CCU is used as a processing agent/aid, but they do
not directly handle the chemical and are therefore would have lower inhalation exposures and may not
have dermal exposures. ONUs for processing agent/aid include supervisors, managers, and tradesmen
that may be in the same area as emission sources but do not perform tasks that result in the same level of
exposures as workers.

2.8.2.2 Number of Potentially Exposed Workers

EPA estimated the number of workers and ONUs potentially exposed to CCU at processing agent/aid
sites using 2016 CDR data (where available), 2017 TRI data (where available), BLS Data and SUSB
Data. The method for estimating number of workers from the Bureau of Labor Statistics' OES data and
U.S. Census' SUSB data is detailed in Appendix A. These estimates were derived using industry- and
occupation-specific employment data from the BLS and U.S. Census.

In the 2016 CDR, one submitter reported the use as a processing agent/aid in the pesticide, fertilizer, and
other agricultural chemical manufacturing industry and indicated this use occurs at fewer than 10 sites
(U.S. EPA. 2016). EPA identified six sites in TRI that reported using CCU as a processing agent/aid
(U.S. EPA. 2017c). However, four of the six TRI reported sites also reported manufacture and/or
reactant use of CCU. EPA assesses those four sites among the manufacturing and reactant use sections.
EPA assesses the remaining two sites from TRI that reported using CCU as a processing agent/aid in this
section. This agrees with the number of sites from the 2016 CDR.

EPA determined the number of workers using the related SOC codes from BLS analysis that are
associated with the primary NAICS codes listed in TRI. Primary NAICS codes for TRI submissions
were reported as 325199, All Other Basic Organic Chemical Manufacturing, and 211112, Natural Gas
Liquid Extraction (U.S. EPA. 2017c). For NAICS code 325199, there are an average of 39 workers and
18 ONUs per site, or a total of 57 potentially exposed workers and ONUs. For NAICS code 211112,
there are an average of three workers and six ONUs per site, or a total of nine potentially exposed
workers and ONUs. The CDR submission lists NAICS 325320, Pesticide and Other Agricultural

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Chemical Manufacturing, where there are an average of 25 workers and seven ONUs per site, or a total
of 32 potentially exposed workers and ONUs (U.S. EPA. 2016).

To determine the total number of workers and ONUs, EPA used the average worker and ONUs
estimates from the BLS analysis based on their NAICS codes (U.S. BLS. 2016). This resulted in an
estimated 67 workers and 32 ONUs (see Table 2-12).

Table 2-12. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During
Use as a Processing Agent/Aid

Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

Total Exposed Workers and ONUs

a For the sites using values from the BLS analysis, the total number of workers and occupational non-users are calculated
using the number of workers and occupational non-users per site estimated from BLS and multiplying by the number of sites.
The number of workers and occupational non-users per site presented in the table round the values estimated from the BLS
analysis to the nearest integer.

2.8.2.3 Occupational Exposure Assessment Methodology

EPA did not find any exposure data for use of CCU as a processing agent/aid; therefore, exposures from
incorporation into formulation activities were assessed with the Tank Truck and Railcar Loading and
Unloading Release and Inhalation Exposure Model.

2.8.2.4 Occupational Exposure Results

The exposure sources, routes, and exposure levels are similar to those at an import/repackaging facility.
Inhalation exposure assessment for processing CCU as a processing agent/aid is estimated by the Tank
Truck and Railcar Loading and Unloading Release and Inhalation Exposure Model used in the
import/repackaging scenario. See Section 2.2.2.4 for the assessment of worker exposure from chemical
unloading activities.

2.9 Additive

Process Description

Additives are chemicals combined with a chemical product to enhance the properties of the product.
Additives typically stay mixed within the finished product and remain unreacted.

Use of CCU as an additive typically involves unloading formulation components from transport
containers, either directly into the mixing equipment or into an intermediate storage vessel, mixing of
components in either a batch or continuous system, QC sampling, and final packaging of the product
into containers.

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Current known uses of CCU as an additive include both an additive used in plastic components used in
the automotive industry (Holmes. 2017) and a fuel additive (U.S. EPA. 2017b).

2.9.1 Exposure Assessment

2.9.1.1 Worker Activities

Similar to manufacturing facilities, worker activities use of CCU as an additive may involve manually
adding raw materials or connecting/disconnecting transfer lines used to unload containers into storage or
reaction vessels, rinsing/cleaning containers and/or process equipment, collecting and analyzing QC
samples, and packaging formulated products into containers and tank trucks. The exact activities and
associated level of exposure will differ depending on the degree of automation, presence of engineering
controls, and use of personal protective equipment (PPE) at each facility.

ONUs include employees that work at the site where CCU is used as an additive, but they do not directly
handle the chemical and are therefore would have lower inhalation exposures and may not have dermal
exposures. ONUs for use of CCU as an additive include supervisors, managers, and tradesmen that may
be in the same area as exposure sources but do not perform tasks that result in the same level of
exposures as workers.

2.9.1.2 Number of Potentially Exposed Workers

EPA estimated the number of workers and occupational non-users potentially exposed to CCU at
processing sites using 2016 CDR data (where available), 2017 TRI data (where available), BLS Data
and SUSB Data. The method for estimating number of workers from the Bureau of Labor Statistics'
OES data and U.S. Census' SUSB data is detailed in Appendix A. These estimates were derived using
industry- and occupation-specific employment data from the BLS and U.S. Census.

Upon review of the 2017 TRI data, EPA found that one site reported the use of CCU as a formulation
component (U.S. EPA. 2017c). EPA determined the number of workers using the related SOC codes
from BLS analysis that are associated with the primary NAICS codes listed in TRI (U.S. BLS. 2016).
The primary NAICS code is 325211, Plastics Material and Resin Manufacturing. For NAICS code
325211, there are an average of 27 workers and 12 ONUs per site, or a total of 39 potentially exposed
workers and ONUs (see Table 2-13). This analysis resulted in 27 workers and 12 ONUs potentially
exposed at sites incorporating CCU as an additive.

Table 2-13. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride when

used as an Additive

Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

Total Exposed Workers and ONUs

a For the sites using values from the BLS analysis, the total number of workers and occupational non-users are calculated
using the number of workers and occupational non-users per site estimated from BLS and multiplying by the number of sites.
The number of workers and occupational non-users per site presented in the table round the values estimated from the BLS
analysis to the nearest integer.

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2.9.1.3 Occupational Exposure Assessment Methodology

EPA did not find any exposure data for use of CCU as an additive; therefore, exposures from use of CCU
as an additive were assessed with the Tank Truck and Rail car Loading and Unloading Release and
Inhalation Exposure Model.

2.9.1.4 Occupational Exposure Results

EPA assumes the exposure sources, routes, and exposure levels are similar to those at an
import/repackaging facility. Inhalation exposure assessment for the use of CCU as an additive is
estimated by the Tank Truck and Railcar Loading and Unloading Release and Inhalation Exposure
Model used in the import/repackaging scenario. See Section 2.2.2.4 for the assessment of worker
exposure from chemical unloading activities.

2.10 Laboratory Chemicals

2.10.1 Process Description

Carbon tetrachloride is used in a variety of laboratory applications, which include, but are not limited to,
the following:

• Chemical reagent;

• Extraction solvent and;

• Reference material or solvent in analytical procedures, such as spectroscopic measurements
(U.S. EPA 2017b).

Specific process descriptions for how CCU is used in each of these applications is not known. In general,
CCU is received in small containers and used in small quantities on a lab bench in a fume cupboard or
hood. After use, waste CCU is collected and disposed or recycled. Figure 2-2 this general process.

Figure 2-2. General Laboratory Use Process Flow Diagram

2.10.2 Exposure Assessment

EPA does not have data to assess worker exposures to CCU during laboratory use. Considering the
health and safety plan and good laboratory practices would be in place when using chemicals in a
laboratory setting, CCU would be applied in small amounts under a fume hood as per good laboratory
practice, thus reducing the potential for inhalation exposures.

2.10.2.1 Worker Activities

Specific worker activities for using laboratory uses were not identified, but the workers could be
potentially exposed to CCU in laboratories during multiple activities, including unloading of CCU from
the containers in which they were received, transferring CCU into laboratory equipment (i.e., beakers,

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flasks, other intermediate storage containers), dissolving substances into CCU or otherwise preparing
samples that contain CCU, analyzing these samples, and discarding the samples.

ONUs include employees that work at the sites where CCU is used, but they do not directly handle the
chemical and are therefore would have lower inhalation exposures and may not have dermal exposures.
ONUs for this condition of use include supervisors, managers, and other employees that may be in the
laboratory but do not perform tasks that result in the same level of exposures as those workers that
engage in tasks related to the use of CCU.

2.10.2.2 Number of Potentially Exposed Workers

EPA estimated the number of workers and occupational non-users potentially exposed to CCU at
laboratories using 2016 CDR data (where available), BLS Data and SUSB Data. The method for
estimating number of workers from the Bureau of Labor Statistics' OES data and U.S. Census' SUSB
data is detailed in Appendix A. These estimates were derived using industry- and occupation-specific
employment data from the BLS and U.S. Census. The 2016 CDR Data reports one industrial use of CCU
as a laboratory chemical for fewer than ten sites (U.S. EPA 2016).

EPA identified the NAICS code 541380, Testing Laboratories, as the code would include laboratory
chemical use of CCU. Based on data from the BLS for this NAICS code and related SOC codes, there
are an average of one worker and nine ONUs per site, or a total of ten potentially exposed workers and
ONUs per site. EPA assessed the number of workers and ONUs based on the data from BLS (U.S. BLS.
2016).

To determine the high-end total number of workers and ONUs, EPA used the high-end number of sites
from CDR (nine sites) and the BLS OES data to estimate number of workers and ONUs per site (U.S.
EPA. 2016; U.S. BLS. 2016). This resulted in a total of 87 exposed workers and ONUs (see Table 2-14).

To determine the low-end total number of workers and ONUs, EPA used the low-end number of sites
from CDR (one site) and the BLS OES data to estimate workers and ONUs per site listed for these
industrial use sites(U.S. EPA. 2016; U.S. BLS. 2016). This resulted in a total of ten exposed workers
and ONUs (see Table 2-14).

Table 2-14. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During
Use as a Laboratory Chemical

Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

High-End

Low-End

a For the sites using values from the BLS analysis, the total number of workers and occupational non-users are calculated
using the number of workers and occupational non-users per site estimated from BLS and multiplying by the number of sites.
The number of workers and occupational non-users per site presented in the table round the values estimated from the BLS
analysis to the nearest integer.

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2.11 Disposal/Recycling

This scenario is meant to include sites like hazardous waste treatment sites (treatment, storage and
disposal facilities, or TSDFs), including incinerators, landfills, other forms of treatment, and solvent or
other material reclamation or recycling. These are sites largely covered under RCRA (e.g., RCRA
permitted TSDFs) but also includes municipal waste combustors and landfills.

2.11.1 Process Description

Each of the conditions of use of CCU may generate waste streams of the chemical that are collected and
transported to third-party sites for disposal, treatment, or recycling. Industrial sites that treat or dispose
onsite wastes that they themselves generate are assessed in each condition of use assessment in Sections
1 through 11. Wastes of CCU that are generated during a condition of use and sent to a third-party site
for treatment, disposal, or recycling may include the following:

• Wastewater: CCU may be contained in wastewater discharged to POTW or other, non-public
treatment works for treatment. Industrial wastewater containing CCU discharged to a POTW
may be subject to EPA or authorized National Pollutant Discharge Elimination System (NPDES)
state pretreatment programs.

• Solid Wastes: Solid wastes are defined under RCRA as any material that is discarded by being:
abandoned; inherently waste-like; a discarded military munition; or recycled in certain ways
(certain instances of the generation and legitimate reclamation of secondary materials are
exempted as solid wastes under RCRA). Solid wastes may subsequently meet RCRA's definition
of hazardous waste by either being listed as a waste at 40 CFR §§ 261.30 to 261.35 or by
meeting waste-like characteristics as defined at 40 CFR §§ 261.20 to 261.24. Solid wastes that
are hazardous wastes are regulated under the more stringent requirements of Subtitle C of
RCRA, whereas non-hazardous solid wastes are regulated under the less stringent requirements
of Subtitle D of RCRA.

o CCU is both a listed and a characteristic hazardous waste. CCU is a non-specific-source
listed hazardous waste under waste number F001 (spent halogenated degreasing solvents)
(40 CFR § 261.31) and a source-specific listed hazardous waste under waste number
K016 (heavy ends or distillation residues from the production of CCU, which may
contain residual CCU) (40 CFR §261.32). Discarded, commercial-grade CCU is a listed
hazardous waste under waste number U211 (40 CFR § 261.33).
o CCU is a toxic contaminant under RCRA with waste number DO 19. A solid waste can be
a hazardous waste due to its toxicity characteristic if its extract following the Toxicity
Characteristic Leaching Procedure (TCLP) (or the liquid waste itself if it contains less
than 0.5% filterable solids) contains at least 0.5 mg/L of CCU (40 CFR § 261.24).

• Wastes Exempted as Solid Wastes under RCRA: Certain conditions of use of CC14 may generate
wastes of CCU that are exempted as solid wastes under 40 CFR § 261.4(a). For example, the
generation and legitimate reclamation of hazardous secondary materials of CCU may be exempt
as a solid waste.

2016 TRI data lists off-site transfers of CCU to land disposal, wastewater treatment, incineration, and
recycling facilities (U.S. EPA 2017c). See Figure 2-3 for a general depiction of the waste disposal
process.

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Recycling

Hazardous Waste
Generation

Hazardous Waste
Transportation

Treatment

Figure 2-3. Typical Waste Disposal Process

Source: (U.S. EPA. 2017a)

Municipal Waste Incineration

Municipal waste combustors (MWCs) that recover energy are generally located at large facilities
comprising an enclosed tipping floor and a deep waste storage pit. Typical large MWCs may range in
capacity from 250 to over 1,000 tons per day. At facilities of this scale, waste materials are not generally
handled directly by workers. Trucks may dump the waste directly into the pit, or waste may be tipped to
the floor and later pushed into the pit by a worker operating a front-end loader. A large grapple from an
overhead crane is used to grab waste from the pit and drop it into a hopper, where hydraulic rams feed
the material continuously into the combustion unit at a controlled rate. The crane operator also uses the
grapple to mix the waste within the pit, in order to provide a fuel consistent in composition and heating
value, and to pick out hazardous or problematic waste.

Facilities burning refuse-derived fuel (RDF) conduct on-site sorting, shredding, and inspection of the
waste prior to incineration to recover recyclables and remove hazardous waste or other unwanted
materials. Sorting is usually an automated process that uses mechanical separation methods, such as
trommel screens, disk screens, and magnetic separators. Once processed, the waste material may be
transferred to a storage pit, or it may be conveyed directly to the hopper for combustion.

Tipping floor operations may generate dust. Air from the enclosed tipping floor, however, is
continuously drawn into the combustion unit via one or more forced air fans to serve as the primary
combustion air and minimize odors. Dust and lint present in the air is typically captured in filters or
other cleaning devices in order to prevent the clogging of steam coils, which are used to heat the
combustion air and help dry higher-moisture inputs (Kitto. 1992).

Hazardous Waste Incineration

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Commercial scale hazardous waste incinerators are generally two-chamber units, a rotary kiln followed
by an afterburner, that accept both solid and liquid waste. Liquid wastes are pumped through pipes and
are fed to the unit through nozzles that atomize the liquid for optimal combustion. Solids may be fed to
the kiln as loose solids gravity fed to a hopper, or in drums or containers using a conveyor ({ETC). 2018;

Heritage. 2018).

Incoming hazardous waste is usually received by truck or rail, and an inspection is required for all waste
received. Receiving areas for liquid waste generally consist of a docking area, pumphouse, and some
kind of storage facilities. For solids, conveyor devices are typically used to transport incoming waste

((ETC). 2018; Heritage. 2018).

Smaller scale units that burn municipal solid waste or hazardous waste (such as infectious and hazardous
waste incinerators at hospitals) may require more direct handling of the materials by facility personnel
Units that are batch-loaded require the waste to be placed on the grate prior to operati on and may
involve manually dumping waste from a container or shoveling waste from a container onto the grate.

In incineration, complete combustion is necessary to prevent phosgene formation and acid scrubbers
must be used to remove any haloacids produced (ATSDR. 2005).

Disposal Disposal

Figure 2-4. Typical Industrial Incineration Process
Municipal Waste Landfill

Municipal solid waste landfills are discrete areas of land or excavated sites that receive household
wastes and other types of non-hazardous wastes (e.g. industrial and commercial solid wastes). Standards
and requirements for municipal waste landfills include location restrictions, composite liner
requirements, leachate collection and removal system, operating practices, groundwater monitoring
requirements, closure-and post-closure care requirements, corrective action provisions, and financial

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assurance. Non-hazardous solid wastes are regulated under RCRA Subtitle D, but states may impose
more stringent requirements.

Municipal solid wastes may be first unloaded at waste transfer stations for temporary storage, prior to
being transported to the landfill or other treatment or disposal facilities.

Hazardous Waste Landfill

Hazardous waste landfills are excavated or engineered sites specifically designed for the final disposal
of non-liquid hazardous wastes. Design standards for these landfills require double liner, double leachate
collection and removal systems, leak detection system, run on, runoff and wind dispersal controls, and
construction quality assurance program (U.S. EPA. 2018b). There are also requirements for closure and
post-closure, such as the addition of a final cover over the landfill and continued monitoring and
maintenance. These standards and requirements prevent potential contamination of groundwater and
nearby surface water resources. Hazardous waste landfills are regulated under Part 264/265, Subpart N.

CCU is listed as a hazardous waste under RCRA and federal regulations prevent land disposal of various
chlorinated solvents that may contain CCU (ATSDR. 2005). CCU may be disposed of by absorption in
vermiculite, dry sand, earth, or other similar material and then buried in a secured sanitary landfill or
incinerated (ATSDR 2005).

Solvent Recovery

Waste solvents are generated when it becomes contaminated with suspended and dissolved solids,
organics, water, or other substances. Waste solvents can be restored to a condition that permits reuse via
solvent reclamation/recycling. The recovery process involves an initial vapor recovery (e.g.,
condensation, adsorption and absorption) or mechanical separation (e.g., decanting, filtering, draining,
setline and centrifuging) step followed by distillation, purification and final packaging. Worker activities
could include unloading of waste solvents and loading of reclaimed solvents. Figure 2-5 illustrates a
typical solvent recovery process flow diagram (U.S. EPA 1980).

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Figure 2-5. General Process Flow Diagram for Solvent Recovery Processes

Source: (U.S. EPA. 1980)

2.11.2 Exposure Assessment

The following sections detail EPA's occupational exposure assessment for waste handling of CO4.

2.11.2.1 Worker Activities

At waste disposal sites, workers are potentially exposed via dermal contact with waste containing CCU
or via inhalation of CCU vapor. Depending on the concentration of CCU in the waste stream, the route
and level of exposure may be similar to that associated with container unloading activities.

Municipal Waste Incineration

At municipal waste incineration facilities, there may be one or more technicians present on the tipping
floor to oversee operations, direct trucks, inspect incoming waste, or perform other tasks as warranted by
individual facility practices. These workers may wear protective gear such as gloves, safety glasses, or
dust masks. Specific worker protocols are largely up to individual companies, although state or local
regulations may require certain worker safety standards be met. Federal operator training requirements
pertain more to the operation of the regulated combustion unit rather than operator health and safety.

Workers are potentially exposed via inhalation to vapors while working on the tipping floor. Potentially-
exposed workers include workers stationed on the tipping floor, including front-end loader and crane
operators, as well as truck drivers. The potential for dermal exposures is minimized by the use of trucks
and cranes to handle the wastes.

Hazardous Waste Incineration

More information is needed to determine the potential for worker exposures during hazardous waste
incineration and any requirements for personal protective equipment. There is likely a greater potential

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for worker exposures for smaller scale incinerators that involve more direct handling of the wastes.

Municipal and Hazardous Waste Landfill

At landfills, typical worker activities may include operating refuse vehicles to weigh and unload the
waste materials, operating bulldozers to spread and compact wastes, and monitoring, inspecting, and
surveying the landfill site (CalRecvcle. 2018). The potential for direct worker handling of the wastes is
unknown.

2.11.2.2 Number of Potentially Exposed Workers

EPA estimated the number of workers and occupational non-users potentially exposed to CCU at waste
handling sites using 2016 CDR data (where available), 2017 TRI data (where available), BLS Data and
SUSB Data. The method for estimating number of workers from the Bureau of Labor Statistics' OES
data and U.S. Census' SUSB data is detailed in Appendix A. These estimates were derived using
industry- and occupation-specific employment data from the BLS and U.S. Census.

The 2016 CDR uses did not show any submissions for waste handling, so EPA reviewed the 2017 TRI
data and found twelve sites reported using CCU during waste handling (U.S. EPA 2017c).

EPA determined the number of workers using the related SOC codes from BLS analysis that are
associated with the primary NAICS codes listed in TRI (U.S. BLS. 2016). Ten submissions in TRI
identified the primary NAICS code to be 562211, Hazardous Waste Treatment and Disposal, while one
was listed as 327310, Cement manufacturing, and the last one was listed as 562213, Solid Waste
Combustors and Incinerators. For NAICS code 562211, there are an average of nine workers and five
ONUs per site, or a total of 14 potentially exposed workers and ONUs. For NAICS code 327310, there
are an average of 22 workers and three ONUs per site, or a total of 25 potentially exposed workers and
ONUs. For NAICS code 562213, there are an average of 13 workers and eight ONUs per site, or a total
of 21 potentially exposed workers and ONUs (U.S. BLS. 2016; U.S. Census Bureau. 2015).

This analysis resulted in 130 workers and 63 ONUs potentially exposed at sites using CCU as a
processing agent/aid (see Table 2-15).

Table 2-15. Estimated Number of Workers Potentially Exposed to Carbon Tetrachloride During

Waste I

andling

Number of
Sites

Exposed
Workers per
Site

Exposed
Occupational
Non-Users per
Site

Total Exposed
Workers

Total Exposed
Occupational
Non-Users

Total Exposed

10a

142

Total Exposed Workers and ONUs

125

188

a For the sites using values from the BLS analysis, the total number of workers and occupational non-users are calculated
using the number of workers and occupational non-users per site estimated from BLS and multiplying by the number of sites.
The number of workers and occupational non-users per site presented in the table round the values estimated from the BLS
analysis to the nearest integer

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2.11.2.3 Occupational Exposure Assessment Methodology

EPA did not find any exposure data for waste handling of CCU. The exposure sources, routes, and
exposure levels are similar to those at an import/repackaging facility, where unloading and handling are
the key worker activities; Therefore, exposures from waste handling activities were assessed with Tank
Truck and Railcar Loading and Unloading Release and Inhalation Exposure Model. The following
subsections detail the results of EPA's occupational exposure assessment for waste handling are based
on modeling.

2.11.2.4 Occupational Exposure Results

See Section 2.2.2.4 for the assessment of worker exposure from chemical unloading activities. EPA
assumes the exposure sources, routes, and exposure levels are similar to those at an import/repackaging
facility. Inhalation exposure assessment for the disposal of CCU is estimated by the Tank Truck and
Railcar Loading and Unloading Release and Inhalation Exposure Model used in the import/repackaging
scenario.

2.12 Dermal Exposure Assessment

Because CCU is a volatile liquid, the dermal absorption of CCU depends on the type and duration of
exposure. Where exposure is not occluded, only a fraction of CCU that comes into contact with the skin
will be absorbed as the chemical readily evaporates from the skin. However, dermal exposure may be
significant in cases of occluded exposure, repeated contacts, or dermal immersion. For example, work
activities with a high degree of splash potential may result in CCU liquids trapped inside the gloves,
inhibiting the evaporation of CCU and increasing the exposure duration.

To assess exposure, EPA used the Dermal Exposure to Volatile Liquids Model (see following equation)
to calculate the dermal retained dose for both non-occluded and occluded scenarios. The equation
modifies the EPA 2-Hand Dermal Exposure to Liquids Model by incorporating a "fraction absorbed
(fabs)" parameter to account for the evaporation of volatile chemicals and a "protection factor (PF)" to
account for glove use (U.S. EPA. 2013a). Default PF values, which vary depending on the type of glove
used and the presence of employee training program, are shown in Table 2-16:

Dexp = S X (9"pX^s) X Yderm X FT Equation 1

Where:

S is the surface area of contact (cm2)

Qu is the quantity remaining on the skin (mg/cm2-event)

Yderm is the weight fraction of the chemical of interest in the liquid (0 < Yderm < 1)

FT is the frequency of events (integer number per day)
fabs is the fraction of applied mass that is absorbed (Default: 0.04 for CCU)

PF is the glove protection factor (Default: see Table 2-16)

The steady state fractional absorption (fabs) for CCU is estimated to be 0.04 based on a theoretical
framework provided by Kasting and Miller (Kasting and Miller. 2006). meaning approximately four
percent of the applied dose is absorbed through the skin following exposure in industrial settings.

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Table 2-16. Glove Protection Factors for Different Dermal Protection Strategies

Dermal Protection Characteristics

Setting

Protection
Factor, PF

a. No gloves used, or any glove / gauntlet without permeation
data and without employee training

Industrial and

Commercial

Uses

b. Gloves with available permeation data indicating that the
material of construction offers good protection for the substance

c. Chemically resistant gloves (i.e., as b above) with "basic"
employee training

d. Chemically resistant gloves in combination with specific
activity training (e.g., procedure for glove removal and disposal)
for tasks where dermal exposure could occur

Industrial Uses
Only

Table 2-17 presents the estimated dermal retained dose for workers in various exposure scenarios,
focusing on what-if scenarios for glove use. The dose estimates assume one exposure event (applied
dose) per work day and that approximately four percent of the applied dose is absorbed through the skin
during industrial settings. The conditions of use for CCU are industrial uses that generally occur in
closed systems where dermal exposure is likely limited to chemical loading/unloading activities (e.g.,
connecting hoses) and taking quality control samples. Across all types of uses, the maximum possible
exposure concentration (Yderm) exists during industrial uses that occur in closed systems. Therefore, all
conditions of use for CCU are assessed at the maximum Yderm, or 1.

In addition to the what-if scenarios for glove use, EPA considered the potential for occluded dermal
exposures; however, based on the worker activities for the condition of use for CCU, EPA determined
occluded exposures to be unlikely. Occluded scenarios could occur where workers handling bulk liquid
CCU during use in open systems (e.g., during solvent changeout in vapor degreasing and dry cleaning.
These scenarios are not probable in closed systems (e.g., during connection/disconnection of hoses used
in loading of bulk containers in manufacturing). For further description of the applicable scenarios
including occlusion, see Appendix E. EPA assesses the following what-if glove use scenarios for all
conditions of use of CCU:

• No gloves used: Operators in these industrial uses, while working around closed-system
equipment, may not wear gloves or may wear gloves for abrasion protection or gripping that are
not chemical resistant.

• Gloves used with a protection factor of 5, 10, and 20: Operators may wear chemical-resistant
gloves when taking quality control samples or when connecting and disconnecting hoses during
loading/unloading activities. EPA assumes gloves may offer a range of protection, depending on
the type of glove and employee training provided.

• Scenarios not assessed: EPA does not assess occlusion as workers in these industries are not
likely to come into contact with bulk liquid CCU that could lead to chemical permeation under
the cuff of the glove or excessive liquid contact time leading to chemical permeation through the
glove.

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As shown in the Table 2-17, the calculated retained dose is low for all non-occluded scenarios as CCU
evaporates quickly after exposure. Dermal exposure to liquid is not likely for occupational non-users, as
they do not directly handle CCU.

Table 2-17. Estimated Dermal Retained Dose (mg/day) for Workers in All Conditions of Use

Condition of Use

Manufacture

Import and
repackaging

Additive

Processing as a
Reactant

Processing
Processing
Agent/Aid

Recycling

Waste disposal

Laboratory
Chemicals

Specialty Uses -
Department of
Defense Data

Reactive Ion
Etching

Incorporation into
Formulation

Specialty Uses -
Aerospace

Non-Occluded Exposure

No Gloves

(PF = 1)

30 (CT)
90 (HE)

Protective
Gloves

(PF = 5)

6 (CT)
18 (HE)

Protective
Gloves

(PF = 10)

3 (CT)
9 (HE)

Protective
Gloves

(Industrial

uses,
PF = 20)

1.5 (CT)
4.5 (HE)

Negligible - Highly controlled work areas with sma
applied

Occluded
Exposure

N/A-
occlusion
unlikely

quantities

Not assessing due to regulatory actions banning use of carbon
tetrachloride in commercially available products and lack of current
use of Carbon tetrachloride in aerospace industry

2.13 Summary of Occupational Exposure Assessment

Table 2-18 presents the occupational exposure assessment summary for the conditions of use described
by the previous sections of this report.

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Table 2-18. Summary of Occupational Exposure Assessment for Workers

Condition of Use

8-Hour or 12-Hour
TWA Exposures

Acute Exposures

Chronic, Non-Cancer
Exposures

Chronic, Cancer
Exposures

TWA
Data
Points

Data Type

Ccci4, 8 or 12-hr TWA

(mg/m3)

ADCccw (mg/m3)

LADCccw (mg/m3)

High-
End

Central
Tendency

High-
End

Central
Tendency

High-End

Central
Tendency

High-End

Central
Tendency

Manufacturing - 8-hr TWA

4.0

0.76

4.0

0.76

4.0

0.76

0.47

0.069

127

Monitoring Data

Manufacturing - 12-hr TWA

4.8

0.50

4.8

0.50

4.8

0.50

0.83

0.069

246

Monitoring Data

Import/Repackaging

0.30

0.057

0.30

0.057

0.30

0.057

0.035

0.0052

N/A

Model

Processing as

Reactant/Intermediate - 8-hr
TWA

4.0

0.76

4.0

0.76

4.0

0.76

0.47

0.069

127

Surrogate
Monitoring Data

Processing as

Reactant/Intermediate - 12-hr
TWA

4.8

0.50

4.8

0.50

4.8

0.50

0.83

0.069

246

Surrogate
Monitoring Data

Incorporation into
Formulation

Not assessing due to regulatory actions banning use of CCU in commercially available products

Specialty Uses - Aerospace

Not assessing due to lack of current use of CCI4

Specialty Uses - Department
of Defense Data

0.37

0.18

0.37

0.18

0.22

0.092

0.026

0.0083

Monitoring Data

Reactive Ion Etching

Negligible - Highly controlled work areas with small quantities applied

Industrial Processing Aid

0.30

0.057

0.30

0.057

0.30

0.057

0.035

0.0052

N/A

Model

Additive

0.30

0.057

0.30

0.057

0.30

0.057

0.035

0.0052

N/A

Model

Laboratory Chemicals

No data - exposure would be low as laboratories typically use small quantities inside a fume hood

Waste Handling

0.30

0.057

0.30

0.057

0.30

0.057

0.035

0.0052

N/A

Model

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3 Discussion of Uncertainties and Limitations

3.1 Variability

EPA addressed variability in models by identifying key model parameters to apply a statistical
distribution that mathematically defines the parameter's variability. EPA defined statistical distributions
for parameters using documented statistical variations where available.

3.2 Uncertainties and Limitations

Uncertainty is "the lack of knowledge about specific variables, parameters, models, or other factors" and
can be described qualitatively or quantitatively (U.S. EPA 2001). The following sections discuss
uncertainties in each of the assessed CCU use scenarios.

3.2.1 Number of Workers

There are a number of uncertainties surrounding the estimated number of workers potentially exposed to
CCU, as outlined below.

First, BLS' OES employment data for each industry/occupation combination are only available at the 3-,
4-, or 5-digit NAICS level, rather than the full 6-digit NAICS level. This lack of granularity could result
in an overestimate of the number of exposed workers if some 6-digit NAICS are included in the less
granular BLS estimates but are not, in reality, likely to use CCU for the assessed applications. EPA
addressed this issue by refining the OES estimates using total employment data from the U.S. Census'
SUSB. However, this approach assumes that the distribution of occupation types (SOC codes) in each 6-
digit NAICS is equal to the distribution of occupation types at the parent 5-digit NAICS level. If the
distribution of workers in occupations with CCU exposure differs from the overall distribution of
workers in each NAICS, then this approach will result in inaccuracy.

Second, EPA's judgments about which industries (represented by NAICS codes) and occupations
(represented by SOC codes) are associated with the uses assessed in this report are based on EPA's
understanding of how CCU is used in each industry. Designations of which industries and occupations
have potential exposures is nevertheless subjective, and some industries/occupations with few exposures
might erroneously be included, or some industries/occupations with exposures might erroneously be
excluded. This would result in inaccuracy but would be unlikely to systematically either overestimate or
underestimate the count of exposed workers.

3.2.2 Analysis of Exposure Monitoring Data

This report uses existing worker exposure monitoring data to assess exposure to CCU during all
conditions of use. Some data sources may be inherently biased. For example, bias may be present if
exposure monitoring was conducted to address concerns regarding adverse human health effects
reported following exposures during use.

Some scenarios have limited exposure monitoring data in literature, if any. Where there are few data
points available, it is unlikely the results will be representative of worker exposure across the industry.

In cases where there was no exposure monitoring data, EPA may have used monitoring data from
similar conditions of use as surrogate. While these conditions of use have similar worker activities
contributing to exposures, it is unknown that the results will be fully representative of worker exposure
across different conditions of use.

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Where sufficient data were available, the 95th and 50th percentile exposure concentrations were
calculated using available data. The 95th percentile exposure concentration is intended to represent a
high-end exposure level, while the 50th percentile exposure concentration represents typical exposure
level. The underlying distribution of the data, and the representativeness of the available data, are not
known. Where discrete data was not available, EPA used reported statistics (i.e., median, mean, 90th
percentile, etc.). Since EPA could not verify these values, there is an added level of uncertainty.

EPA calculated ADC and LADC values assuming a high-end exposure duration of 250 days per year
over 40 years and a typical exposure duration of 250 days per year over 31 years. This assumes the
workers and occupational non-users are regularly exposed during their entire working lifetime, which
likely results in an overestimate. Individuals may change jobs during the course of their career such that
they are no longer exposed to CCU, and that actual ADC and LADC values become lower than the
estimates presented.

3.2.3 Modeling Dermal Exposures

To assess dermal exposure, EPA used a modified equation from the EPA 2-Hand Dermal Exposure to
Liquids Model to calculate the dermal absorbed dose for both non-occluded and occluded scenarios. The
Dermal Exposure to Volatile Liquids Model is used to estimate dermal exposure to carbon tetrachloride
in occupational settings. The model assumes a fixed fractional absorption of the applied dose; however,
fractional absorption may be dependent on skin loading conditions. The model also assumes a single
exposure event per day based on existing framework of the EPA 2-Hand Dermal Exposure to Liquids
Model and does not address variability in exposure duration and frequency. The model also incorporates
a "protection factor (PF)" to account for glove use. PF values will vary depending on the type of glove
used and the presence of employee training program. More details on the dermal methodology are
discussed in Appendix E.

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APPENDICES

Appendix A Approach for Estimating Number of Workers and

Occupational Non-Users

This appendix summarizes the methods that EPA used to estimate the number of workers who are
potentially exposed to CCU in each of its conditions of use. The method consists of the following steps:

1. Identify the North American Industry Classification System (NAICS) codes for the industry
sectors associated with each condition of use.

2. Estimate total employment by industry/occupation combination using the Bureau of Labor
Statistics' Occupational Employment Statistics (OES) data (U.S. BLS. 2016).

3. Refine the OES estimates where they are not sufficiently granular by using the U.S. Census
Bureau (2015) Statistics of U.S. Businesses (SUSB) data on total employment by 6-digit NAICS

4. Estimate the percentage of employees likely to be using CCU instead of other chemicals (i.e., the
market penetration of CCU in the condition of use).

5. Estimate the number of sites and number of potentially exposed employees per site.

6. Estimate the number of potentially exposed employees within the condition of use.

Step 1: Identifying Affected NAICS Codes

As a first step, EPA identified NAICS industry codes associated with each condition of use. EPA
generally identified NAICS industry codes for a condition of use by:

• Querying the U.S. Census Bureau's NAICS Search tool using keywords associated with each condition of
use to identify NAICS codes with descriptions that match the condition of use.

• Referencing EPA Generic Scenarios (GS's) and Organisation for Economic Co-operation and
Development (OECD) Emission Scenario Documents (ESDs) for a condition of use to identify NAICS
codes cited by the GS or ESD.

• Reviewing Chemical Data Reporting (CDR) data for the chemical, identifying the industrial sector codes
reported for downstream industrial uses, and matching those industrial sector codes to NAICS codes
using Table D-2 provided in the CDR reporting instructions.

Each condition of use section in the main body of this report identifies the NAICS codes EPA identified
for the respective condition of use.

Step 2: Estimating Total Employment by Industry and Occupation

U.S. BLS (2016) OES data provide employment data for workers in specific industries and occupations .
The industries are classified by NAICS codes (identified previously), and occupations are classified by
Standard Occupational Classification (SOC) codes.

Among the relevant NAICS codes (identified previously), EPA reviewed the occupation description and
identified those occupations (SOC codes) where workers are potentially exposed to CCU. XX shows the
SOC codes EPA classified as occupations potentially exposed to CC14. These occupations are classified

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into workers (W) and occupational non-users (O). All other SOC codes are assumed to represent
occupations where exposure is unlikely.

TableApx A-l. SOCs with Worker and ONU Designations for All Conditions of Use Except Dry

SOC

Occupation

Designation

11-9020

Construction Managers

17-2000

Engineers

17-3000

Drafters, Engineering Technicians, and Mapping Technicians

19-2031

Chemists

19-4000

Life, Physical, and Social Science Technicians

47-1000

Supervisors of Construction and Extraction Workers

47-2000

Construction Trades Workers

49-1000

Supervisors of Installation, Maintenance, and Repair Workers

49-2000

Electrical and Electronic Equipment Mechanics, Installers, and
Repairers

49-3000

Vehicle and Mobile Equipment Mechanics, Installers, and
Repairers

49-9010

Control and Valve Installers and Repairers

49-9020

Heating, Air Conditioning, and Refrigeration Mechanics and
Installers

49-9040

Industrial Machinery Installation, Repair, and Maintenance
Workers

49-9060

Precision Instrument and Equipment Repairers

49-9070

Maintenance and Repair Workers, General

49-9090

Miscellaneous Installation, Maintenance, and Repair Workers

51-1000

Supervisors of Production Workers

51-2000

Assemblers and Fabricators

51-4020

Forming Machine Setters, Operators, and Tenders, Metal and
Plastic

51-6010

Laundry and Dry-Cleaning Workers

51-6020

Pressers, Textile, Garment, and Related Materials

51-6030

Sewing Machine Operators

51-6040

Shoe and Leather Workers

51-6050

Tailors, Dressmakers, and Sewers

51-6090

Miscellaneous Textile, Apparel, and Furnishings Workers

51-8020

Stationary Engineers and Boiler Operators

51-8090

Miscellaneous Plant and System Operators

51-9000

Other Production Occupations

W = worker designation
O = ONU designation

For dry cleaning facilities, due to the nature of work typically occurs at these facilities and that different
workers would share various activities with higher exposure potential (e.g., unloading the dry cleaning
machine, pressing/finishing a dry cleaned load), additional SOC code worker and ONU assignments for

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this condition of use. Table Apx A 2 summarizes the SOC codes with worker and ONU designations
used for dry cleaning facilities.

Table Apx A-2. SOCs with Worker and ONU Designations for Dry Cleaning Facilities

SOC

Occupation

Designation

41-2000

Retail Sales Workers

49-9040

Industrial Machinery Installation, Repair, and
Maintenance Workers

49-9070

Maintenance and Repair Workers, General

49-9090

Miscellaneous Installation, Maintenance, and Repair
Workers

51-6010

Laundry and Dry-Cleaning Workers

51-6020

Pressers, Textile, Garment, and Related Materials

51-6030

Sewing Machine Operators

51-6040

Shoe and Leather Workers

51-6050

Tailors, Dressmakers, and Sewers

51-6090

Miscellaneous Textile, Apparel, and Furnishings
Workers

W = worker designation
O = ONU designation

After identifying relevant NAICS and SOC codes, EPA used BLS data to determine total employment
by industry and by occupation based on the NAICS and SOC combinations. For example, there are
110,640 employees associated with 4-digit NAICS 8123 (Drycleaning and Laundry Services) and SOC
51-6010 (Laundry and Dry-Cleaning Workers).

Using a combination of NAICS and SOC codes to estimate total employment provides more accurate
estimates for the number of workers than using NAICS codes alone. Using only NAICS codes to
estimate number of workers typically result in an overestimate, because not all workers employed in that
industry sector will be exposed. However, in some cases, BLS only provide employment data at the 4-
digit or 5-digit NAICS level; therefore, further refinement of this approach may be needed (see next
step).

Step 3: Refining Employment Estimates to Account for lack of NAICS Granularity

The third step in EPA's methodology was to further refine the employment estimates by using total
employment data in the U.S. Census Bureau (2015) SUSB. In some cases, BLS OES's occupation-
specific data are only available at the 4-digit or 5-digit NAICS level, whereas the SUSB data are
available at the 6-digit level (but are not occupation-specific). Identifying specific 6-digit NAICS will
ensure that only industries with potential CCU exposure are included. As an example, OES data are
available for the 4-digit NAICS 8123 Drycleaning and Laundry Services, which includes the following
6-digit NAICS:

• NAICS 812310 Coin-Operated Laundries and Drycleaners;

• NAICS 812320 Drycleaning and Laundry Services (except Coin-Operated);

• NAICS 812331 Linen Supply; and

• NAICS 812332 Industrial Launderers.

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In this example, only NAICS 812320 is of interest. The Census data allow EPA to calculate employment
in the specific 6-digit NAICS of interest as a percentage of employment in the BLS 4-digit NAICS.

The 6-digit NAICS 812320 comprises 46 percent of total employment under the 4-digit NAICS 8123.
This percentage can be multiplied by the occupation-specific employment estimates given in the BLS
OES data to further refine our estimates of the number of employees with potential exposure.

Table_Apx A-3 illustrates this granularity adjustment for NAICS 812320.

TableApx A-3. Estimated Number of Potentially Exposed Workers and ONUs under NAICS
812320

NAICS

SOC
CODE

SOC Description

Occupation
Designation

Employment
by SOC at 4-
digit NAICS
level

% of Total
Employment

Estimated
Employment
by SOC at 6-
digit NAICS
level

8123

41-

2000

Retail Sales Workers

44,500

46.0%

20,459

8123

49-
9040

Industrial Machinery
Installation Repair, and
Maintenance Workers

1,790

46.0%

823

8123

49-
9070

Maintenance and Repair
Workers, General

3,260

46.0%

1,499

8123

49-
9090

Miscellaneous Installation
Maintenance, and Repair
Workers

1,080

46.0%

497

8123

51-

6010

Laundry and Dry-Cleaning
Workers

110,640

46.0%

50,867

8123

51-

6020

Pressers, Textile, Garment,
and Related Materials

40,250

46.0%

18,505

8123

51-

6030

Sewing Machine Operators

1,660

46.0%

763

8123

51-

6040

Shoe and Leather Workers

Not Reported for this NAICS Code

8123

51-

6050

Tailors, Dressmakers, and
Sewers

2,890

46.0%

1,329

8123

51-

6090

Miscellaneous Textile,
Apparel, and Furnishings
Workers

46.0%

Total Potentially Exposed Employees

206,070

94,740

Total Workers

72,190

Total Occupational Non-Users

22,551

Note: numbers may not sum exactly due to rounding.

W = worker

O = occupational non-user

Source: (U.S. BLS. 2016: U.S. Census Bureau. 2015)

Step 4: Estimating the Percentage of Workers Using CCU Instead of Other Chemicals

In the final step, EPA accounted for the market share by applying a factor to the number of workers
determined in Step 3. This accounts for the fact that CCU may be only one of multiple chemicals used
for the applications of interest. EPA did not identify market penetration data for any conditions of use.
In the absence of market penetration data for a given condition of use, EPA assumed CCU may be used

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at up to all sites and by up to all workers calculated in this method as a bounding estimate. This assumes
a market penetration of 100%. Market penetration is discussed for each condition of use in the main
body of this report.

Step 5: Estimating the Number of Workers per Site

EPA calculated the number of workers and occupational non-users in each industry/occupation
combination using the formula below (granularity adjustment is only applicable where SOC data are not
available at the 6-digit NAICS level):

Number of Workers or ONUs in NAICS SOC (Step 2) x Granularity Adjustment Percentage (Step 3) =
Number of Workers or ONUs in the Industry Occupation Combination

EPA then estimated the total number of establishments by obtaining the number of establishments
reported in the U.S. Census Bureau (2015) SUSB data at the 6-digit NAICS level.

EPA then summed the number of workers and occupational non-users over all occupations within a
NAICS code and divided these sums by the number of establishments in the NAICS code to calculate
the average number of workers and occupational non-users per site.

Step 6: Estimating the Number of Workers and Sites for a Condition of Use

EPA estimated the number of workers and occupational non-users potentially exposed to CC14 and the
number of sites that use CCU in a given condition of use through the following steps:

6. A. Obtaining the total number of establishments by:

i. Obtaining the number of establishments from SUSB data (U.S. Census Bureau. 2015) the
6-digit NAICS level (Step 5) for each NAICS code in the condition of use and summing
these values; or

ii. Obtaining the number of establishments from the Toxics Release Inventory (TRI),
Discharge Monitoring Report (DMR) data, National Emissions Inventory (NEI), or
literature for the condition of use.

6.B. Estimating the number of establishments that use CCU by taking the total number of

establishments from Step 6. A and multiplying it by the market penetration factor from Step
4.

6.C. Estimating the number of workers and occupational non-users potentially exposed to CCU by
taking the number of establishments calculated in Step 6.B and multiplying it by the average
number of workers and occupational non-users per site from Step 5.

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Appendix B Equations for Calculating Chronic (Non-Cancer and

Cancer) Inhalation Exposures

This report assesses CCU exposures to workers in occupational settings, presented as 8-hr time weighted
average (TWA) as well as 12-hr TWA. The 8-hr or 12-hr TWA exposures are then used to calculate
average daily concentration (ADC) for chronic, non-cancer risks, and lifetime average daily
concentration (LADC) for chronic, cancer risks.

ADC and LADC are used to estimate workplace chronic exposures for non-cancer and cancer risks,
respectively. These exposures are estimated as follows:

EquationApx B-l

C x ED x EF x WY

ADC orLADC =

AT orATC

Where:

ADC = average daily concentration (24-hr TWA) used for chronic non-cancer risk calculations

LADC = lifetime average daily concentration (24-hr TWA) used for chronic cancer risk
calculations

C = contaminant concentration in air (8-hr TWA or 12-hr TWA)

ED = exposure duration (denoted with "8" specifies 8 hr/day and "12" specifies 12 hr/day)

EF = exposure frequency (250 days/yr)

WY = exposed working years per lifetime (50th percentile = 31; 95th percentile = 40)

AT = averaging time, non-cancer risks (WY x 365 days/yr x 24 hr/day)

ATC = averaging time, cancer risks (LT x 365 days/year x 24 hr/day; where LT = 78 years)

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Table Apx B-l. Parameter Values for Calculating Inhalation Exposure Estimates

Parameter Name

Symbol

Value

Unit

Exposure Duration, 8-hr TWA

EDg

hr/day

Exposure Duration, 12-hr TWA

ED12

hr/day

Exposure Frequency

250

days/year

Working Years

31 (50th
percentile)

40 (95th
percentile)

years

Lifetime, cancer

years

Averaging Time, non-cancer

271,560 (CT)a
350,400 (HE)b

Averaging Time, cancer

ATC

683,280

a Calculated using the 50th percentile value for working years (WY)
b Calculated using the 95th percentile value for working years (WY)

B.l Exposure Duration (ED)

EPA uses an exposure duration of 8 hours (480 minutes) per day for 8-hr TWA and 12 hours (720
minutes) per day for 12-hr TWA.

B.2 Exposure Frequency (EF)

EPA uses an exposure frequency of 250 days per year. Exposure frequency (EF) is expressed as the
number of days per year a worker is exposed to the chemical being assessed. In some cases, it may be
reasonable to assume a worker is exposed to the chemical on each working day. In other cases, it may be
more appropriate to estimate a worker's exposure to the chemical occurs during a subset of the worker's
annual working days. The relationship between exposure frequency and annual working days can be
described mathematically as follows:

Equation Apx B-2

EF = fx AWD

Where:

EF = exposure frequency, the number of days per year a worker is exposed to the
chemical (day/yr)

f = fractional number of annual working days during which a worker is exposed to

the chemical (unitless)

AWD = annual working days, the number of days per year a worker works (day/yr)

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U.S. BLS (2015) provides data on the total number of hours worked and total number of employees by
each industry NAICS code. These data are available from the 3- to 6-digit NAICS level (where 3-digit
NAICS are less granular and 6-digit NAICS are the most granular). Dividing the total, annual hours
worked by the number of employees yields the average number of hours worked per employee per year
for each NAICS.

EPA has identified approximately 140 NAICS codes applicable to the multiple conditions of use for the
ten chemicals undergoing risk evaluation. For each NAICS code of interest, EPA looked up the average
hours worked per employee per year at the most granular NAICS level available (i.e., 4-digit, 5-digit, or
6-digit). EPA converted the working hours per employee to working days per year per employee
assuming employees work an average of eight hours per day. The average number of days per year
worked, or AWD, ranges from 169 to 282 days per year, with a 50th percentile value of 250 days per
year. EPA repeated this analysis for all NAICS codes at the 4-digit level. The average AWD for all 4-
digit NAICS codes ranges from 111 to 282 days per year, with a 50th percentile value of 228 days per
year. 250 days per year is approximately the 75th percentile.

In the absence of industry- and CCU-specific data, EPA assumes the parameter/is equal to one for all
conditions of use.

B.3 Working Years (WY)

EPA has developed a triangular distribution for working years. EPA has defined the parameters of the
triangular distribution as follows:

• Minimum value: BLS CPS tenure data with current employer as a low-end estimate of the
number of lifetime working years: 10.4 years;

• Mode value: The 50th percentile tenure data with all employers from Survey of Income and
Program Participation (SIPP) as a mode value for the number of lifetime working years: 36
years; and

• Maximum value: The maximum average tenure data with all employers from SIPP as a high-end
estimate on the number of lifetime working years: 44 years.

This triangular distribution has a 50th percentile value of 31 years and a 95th percentile value of 40 years.
EPA uses these values for central tendency and high-end ADC and LADC calculations, respectively.

The U.S. BLS (2014) provides information on employee tenure with current employer obtained from the
Current Population Survey (CPS). CPS is a monthly sample survey of about 60,000 households that
provides information on the labor force status of the civilian non-institutional population age 16 and
over; CPS data are released every two years. The data are available by demographics and by generic
industry sectors but are not available by NAICS codes.

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Census Bureau. 2019b). EPA analyzed the 2008 SIPP Panel Wave 1, a panel that began in 2008 and
covers the interview months of September 2008 through December 2008 (U.S. Census Bureau. 2019a.
b). For this panel, lifetime tenure data are available by Census Industry Codes, which can be cross-
walked with NAICS codes.

SIPP data include fields for the industry in which each surveyed, employed individual works
(TJBIND1), worker age (TAGE), and years of work experience with all employers over the surveyed
individual's lifetime.7 Census household surveys use different industry codes than the NAICS codes
used in its firm surveys, so these were converted to NAICS using a published crosswalk (U.S. Census
Bureau. 2013). EPA calculated the average tenure for the following age groups: 1) workers age 50 and
older; 2) workers age 60 and older; and 3) workers of all ages employed at time of survey. EPA used
tenure data for age group "50 and older" to determine the high-end lifetime working years, because the
sample size in this age group is often substantially higher than the sample size for age group "60 and
older". For some industries, the number of workers surveyed, or the sample size, was too small to
provide a reliable representation of the worker tenure in that industry. Therefore, EPA excluded data
where the sample size is less than five from our analysis.

TableApx B-2 summarizes the average tenure for workers age 50 and older from SIPP data. Although
the tenure may differ for any given industry sector, there is no significant variability between the 50th
and 95th percentile values of average tenure across manufacturing and non-manufacturing sectors.

Table Apx B-2. Overview of Average Worker Tenure from U.S. Census SIPP (Age Group 50+)

Industry Sectors

Working Years

Average

50th
Percentile

95th
Percentile

Maximum

All industry sectors relevant to
the 10 chemicals undergoing
risk evaluation

35.9

Manufacturing sectors (NAICS
31-33)

35.7

Non-manufacturing sectors
(NAICS 42-81)

36.1

Source: (U.S. Census Bureau. 2019b)

Note: Industries where sample size is less than five are excluded from this analysis.

BLS CPS data provides the median years of tenure that wage and salary workers had been with their
current employer. Table Apx B-3 presents CPS data for all demographics (men and women) by age
group from 2008 to 2012. To estimate the low-end value on number of working years, EPA uses the
most recent CPS data for workers age 55 to 64 years, which indicates a median tenure of 10.4 years with
their current employer. The use of this low-end value represents a scenario where workers are only
exposed to the chemical of interest for a portion of their lifetime working years, as they may change jobs
or move from one industry to another throughout their career.

7 To calculate the number of years of work experience we took the difference between the year first worked (TMAKMNYR)
and the current data year (i.e., 2008). We then subtracted any intervening months when not working (ETIMEOFF).

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Table Apx B-3. Median Years of Tenure wil

h Current Employer by Age Group

Age

January 2008

January 2010

January 2012

January 2014

16 years and over

4.1

4.4

4.6

16 to 17 years

0.7

18 to 19 years

0.8

1.0

0.8

20 to 24 years

1.3

1.5

1.3

25 years and over

5.1

5.2

5.4

5.5

25 to 34 years

2.7

3.1

3.2

3.0

35 to 44 years

4.9

5.1

5.3

5.2

45 to 54 years

7.6

7.8

7.9

55 to 64 years

9.9

10.0

10.3

10.4

65 years and over

10.2

9.9

10.3

Source: (U.S. BLS. 2014)

B.4 Lifetime Years (LT)

EPA assumes a lifetime of 78 years for all worker demographics.

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Appendix C Sample Calculations for Calculating Acute and Chronic
(Non-Cancer and Cancer) Inhalation Exposures

Sample calculations for high-end (HE) and central tendency (CT) chronic exposure concentrations for
one setting, manufacturing (using 8-hr TWA), are demonstrated below. The explanation of the equations
and parameters used is provided in Appendix B.

C.l Example High-End ADC and LADC

Calculate ADChe:

CHE x ED x EF xWY
ADChe = —

4.01 x 8-7— x 250^^ x 40 years mn

m3 day year * _n^m9

HE~ Uo years x 363^x24^1) ~ " -3

V 17 year day J

Calculate LADChe:

CHE x ED x EF XWY
LADChe = —

"HE AT

A-1 LADC

4.01 8-^- x 250^22^x40 years mn

L ADC„e = —^w yC"r , \ = 0.47—y

(78 years x 365^x24^)
V 17 year day J

C.2 Example Central Tendency ADC and LADC

Calculate ADCct:

Cct x ED XEF XWY

ADCct = — ^

CT ATadc

0.73 x 8-t— x 250^^x 31 years mn

m3 day year * _n^m9

CT (n, ...... nrrdays „nAhours\ ' m3

„srdays „.hours\

31 years x 365—— x 24-t

V 17 year day J

Calculate LADCct:

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CCT x ED x EF XWY

LADCct = — —

CT ATladc

0.73 ^x 8-^x 250^£x 31 years mn

LADCct = —^ dUy „ year „ \ = 0.07

(78 years x 365^x24^)
V 17 year day J

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Appendix D Tank Truck and Railcar Loading and Unloading

Release and Inhalation Exposure Model Methodology

This appendix presents the modeling approach and model equations used in the Tank Truck and Railcar
Loading and Unloading Release and Inhalation Exposure Model. The model was developed through
review of relevant literature and consideration of existing EPA exposure models. The model approach is
a generic inhalation exposure assessment at industrial facilities that is applicable for any volatile
chemical with the following conditions of use:

• Manufacture (loading of chemicals into containers);

• Processing as a reactant/intermediate (unloading of chemicals);

• Processing into formulation, mixture, or reaction products;

• Import (repackaging); and

• Other similar conditions of use at industrial facilities (e.g., industrial processing aid).

As an example, CCU at a manufacturing facility would involve packaging and loading into a container
before distributing to another industrial processing or use site (e.g., formulation sites, sites using CCU as
an intermediate, and sites using CCU as a processing aid). At the industrial processing or use site, CCU
is then unloaded from the container into a process vessel before being incorporated into a mixture, used
as a chemical intermediate, or otherwise processed/used. For the model, EPA assumes CCU is unloaded
into tank trucks and rail cars and transported and distributed in bulk. EPA also assumes the chemical is
handled as a pure substance (100 percent concentration).

Because CCU is volatile (vapor pressure above 0.01 torr at room temperature), fugitive emissions may
occur when CCU is loaded into or unloaded from a tank truck or railcar. Sources of these emissions
include:

• Displacement of saturated air containing CCU as the container/truck is filled with liquid;

• Emissions of saturated air containing CCU that remains in the loading arm, transfer hose, and
related equipment; and

• Emissions from equipment leaks from processing units such as pumps, seals and valves.

These emissions result in subsequent exposure to workers involved in the transfer activity. The
following subsections address these emission sources.

D.l Displacement of Saturated Air Inside Tank Trucks and Railcars

For screening-level assessments, EPA typically uses the EPA/OAQPS AP-42 Loading Model to
conservatively assess exposure during container unloading activities (U.S. EPA 2013b). The model
estimates release to air from the displacement of air containing chemical vapor as a container/vessel is
filled with liquid (U.S. EPA 2013b). The model assumes the unloading activity displaces an air volume
equal to the size of the container, and that displaced air is either 50 percent or 100 percent saturated with
chemical vapor (U.S. EPA 2013b).

Process units at facilities that manufacture CCU as a primary product; use CCU as a reactant or
manufacture CCU as a product or co-product; or are located at a plant that is a major source of
hazardous air pollutants (HAPs) as defined in section 112(a) of the Clean Air Act are required to install

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and operate a vapor capture system and control device (or vapor balancing system) for
loading/unloading operations (U.S. EPA. 1994). Therefore, the majority of industrial facilities could use
a vapor balance system to minimize fugitive emissions when loading and unloading tank trucks and
railcars. As such, vapor losses from displacement of air is likely mitigated by the use of such systems.
Actual fugitive emissions are likely limited to any saturated vapor that remain in the hose, loading arm,
or related equipment after being disconnected from the truck or railcar. This emission source is
addressed in the next subsection.

D.2 Emissions of Saturated Air that Remain in Transfer Hoses/Loading
Arm

After loading is complete, transfer hoses and/or loading arms are disconnected from tank trucks and
railcars. Saturated air containing the chemical of interest that remains in transfer equipment may be
released to air, presenting a source of fugitive emissions. The quantity of CCU released will depend on
concentration in the vapor and the volume of vapor in the loading arm/hose/piping.

TableApx D-l presents the dimensions for several types of loading systems according to an OPW
Engineered Systems catalog (Systems. 2014). OPW Engineered Systems (2014) specializes in the
engineering, designing, and manufacturing of systems for loading and unloading a wide range of
materials including petroleum products, liquefied gases, asphalt, solvents, and hazardous and corrosive
chemicals . These systems include loading systems, swivel joints, instrumentation, quick and dry-
disconnect systems, and safety breakaways. Based on the design dimensions, the table presents the
calculated total volume of loading arm/system and assumes the volume of vapor containing CCU equals
the volume of the loading arm/system.

Based on comments from HSIA (2013). halogenated solvents, such as CCU, could be delivered in either
tank trailers or tank cars. Therefore, EPA modeled the central tendency scenario as tank truck
loading/unloading. EPA modeled the high-end scenario as railcar loading/unloading since railcars are
larger and more likely to use longer transfer arms (and thus represent a higher exposure potential than
tank trucks). To estimate the high-end transfer arm volume, EPA calculated the 95th percentile of the
OPW Engineered Systems loading arms volumetric data resulting in a high-end value of 17.7 gallons.
For the central tendency tank truck scenario, EPA assumed a 2-inch diameter, 12-ft long transfer hose.
This hose has a volume of 2.0 gallons.

Once the volume is known, the emission rate, Et (g/s), can be calculated as follows:

EquationApx D-l

fxMWx3,786AxVhxXxVP

1 ~ ^-disconnect XTXRX 3, 600 X 760

Default values for Equation Apx D-l can be found in Table Apx D-2.

Table Apx D-l. Example Dimension and Volume of Loading Arm/Transfer System

Length of Loading Arm/Connection (in)

Volume, Vh (gal) b

OPW Engineered Systems Transfer Arm

2-inch

3-inch

4-inch

6-inch

2-
inch

3-
inch

4-
inch

6-
inch

Unsupported Boom-Type Bottom Loader

149.875

158.5

165.25

191.75

2.0

4.9

9.0

23.5

"A" Frame Loader M-32-F

153.75

159.75

164.5

2.1

4.9

8.9

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"A" Frame Hose Loader AFH-32-F

180.75

192.75

197.5

2.5

5.9

10.7

CWH Series Counterweighted Hose Loader

309

16.8

Spring Balanced Hose Loader SRH-32-F

204.75

216.75

221.5

2.8

6.6

12.0

Spring Balanced Hose Loader LRH-32-F

270

277.625

8.3

15.1

Top Loading Single Ann Fixed Reach

201.75

207.75

212.5

2.7

6.4

11.6

Top Loading Scissor Type Arm

197.875

206.5

213.25

2.7

6.3

11.6

Supported Boom Ann B-32-F

327.375

335

341.5

4.5

10.3

18.6

Unsupported Boom Ann GT-32-F

215.875

224.5

231.25

2.9

6.9

12.6

Slide Sleeve Ann A-32F

279

292.5

305.125

3.8

9.0

16.6

Hose without Transfer Arm

Hose (EPA judgment)

120

1.6

—

Source: (Systems. 2014)

a - Total length includes length of piping, connections, and fittings.

b - Calculated based on dimension of the transfer hose/connection Vh = totL (converted from cubic inch to gallons).

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TableApx D-2. Default Values for Calculating Emission Rate of Carbon Tetrachloride from
Transfer/Loading Arm

Parameter

Parameter Description

Default Value

Unit

Emission rate of chemical from
transfer/loading system

Calculated from
model equation

g/s

Saturation factor3

dimensionless

Molecular weight of the chemical

153.82

g/mol

Volume of transfer hose

See Table Apx D-l

gallons

Fill rate3

2 (tank truck)
1 (railcar)

containers/hr

tdisconnect

Time to disconnect hose/couplers (escape of
saturated vapor from disconnected hose or
transfer arm into air)

0.25

Vapor pressure correction factor

dimensionless

Vapor pressure of the pure chemical

115

ton-

Temperature

298

Universal gas constant

82.05

atm-
cm3/gmol-K

a - Saturation factor and fill rate values are based on established EPA release and inhalation exposure assessment
methodologies (U.S. EPA. 2013).

D.3 Emission from Leaks

During loading/unloading activities, emissions may also occur from equipment leaks from valves,
pumps, and seals. Per EPA's Chapter 5: Petroleum Industry of AP-42 (U.S. EPA. 2015) and EPA's
Protocol for Equipment Leak Emission Estimates (U.S. EPA. 19951 the following equation can be used
to estimate emission rate El, calculated as the sum of average emissions from each process unit:

EquationApx D-2

Z 1,000

(FaxWFT0CxN)Xj^

Parameters for calculating equipment leaks using Equation Apx B-l can be found in Table Apx D-3.

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TableApx D-3. Parameters for Calculating Emission Rate of Carbon Tetrachloride from
Equipment Leaks

Parameter

Parameter Description

Default Value

Unit

Emission rate of chemical from equipment leaks

Calculated from
model equation

g/s

Applicable average emission factor for the
equipment type

See Table Apx D-4

kg/hr-source

WFtoc

Average weight fraction of chemical in the stream

dimensionless

Number of pieces of equipment of the applicable
equipment type in the stream

See Table Apx D-4

Source

To estimate emission leaks using this modeling approach, EPA modeled a central tendency loading rack
scenario using tank truck loading/unloading and a high-end loading rack scenario using railcar
loading/unloading as discussed in Appendix D.2. EPA used engineering judgment to estimate the type
and number of equipment associated with the loading rack in the immediate vicinity of the loading
operation. EPA assumes at least one worker will be near the loading rack during the entire duration of
the loading operation.

Table Apx D-4 presents the average emission factor for each equipment type, based on the synthetic
organic chemical manufacturing industry (SOCMI) emission factors as provided by EPA's 1995
Protocol (U.S. EPA 19951 and the likely number of pieces of each equipment used for each chemical
loading/unloading activity, based on EPA's judgment. Note these emission factors are for emission rates
of total organic compound emission and are assumed to be applicable to CCU In addition, these factors
are most valid for estimating emissions from a population of equipment and are not intended to be used
to estimate emissions for an individual piece of equipment over a short period of time.

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Table Apx D-4. Default Values for Fa and N

SOCMI Emission
Factor, Fa (kg/hr-
source) a

Number of

Equipment Type

Service

Equipment, N
(central
tendency)

Equipment, N
(high-end)

Valves

Gas
Light liquid
Heavy liquid

0.00597
0.00403
0.00023

3 (gas)
5 (light liquid)

3 (gas)
10 (light liquid)

Pump seals b

Light liquid
Heavy liquid

0.0199
0.00862

—

Compressor seals

Gas

0.228

—

Pressure relief valves

Gas

0.104

Connectors

All

0.00183

Open-ended lines

All

0.0017

—

Sampling connections

All

0.015

Source: (U.S. EPA. 1995)

a - SOCMI average emission factors for total organic compounds fromEPA's 1995 Protocol (U.S. EPA. 1995). "Light
liquid" is defined as "material in a liquid state in which the sum of the concentration of individual constituents with a vapor
pressure over 0.3 kilopascals (kPa) at 20 °C is greater than or equal to 20 weight percent". "Heavy liquid" is defined as "not
in gas/vapor service or light liquid service." Since CCU has a vapor pressure of 115 mmHg (15.33 kPa) at 25 °C. EPA
modeled CCI4 liquid as a light liquid.

b - The light liquid pump seal factor can be used to estimate the leak rate from agitator seals.

EPA assumed the following equipment are used in loading racks for the loading/unloading of tank
trucks and railcars. FigureApx D-l illustrates an example tank truck and unloading rack equipment.

• Tank Truck Loading/Unloading:

o Liquid Service:

¦ Four valves (modeled as valves in light liquid service)

¦ One safety relief valve (modeled as valve in light liquid service)

¦ One bleed valve or sampling connection

¦ One hose connector
o Vapor Service:

¦ Three valves (modeled as valves in gas service)

¦ One pressure relief valve

¦ One bleed valve (modeled as a sampling connection)

¦ One hose connector

• Railcar Loading/Unloading

o Liquid Service: EPA assumed, for the high-end scenario, two parallel liquid service lines,
each using the same equipment as assumed for tank trucks. Therefore, a total of:

¦ Eight valves (modeled as valves in light liquid service)

¦ Two safety relief valves (modeled as valve in light liquid service)

¦ Two bleed valves or sampling connections

¦ Two transfer arm connectors

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o Vapor Service: EPA assumed a single line in vapor service with the same equipment as
assumed for tank trucks.

¦ Three valves (modeled as valves in gas service)

¦ One pressure relief valve

¦ One bleed valve (modeled as a sampling connection)

¦ One transfer arm connector

Vaporservice line

Liquidservice line

FigureApx D-l. Illustration of Transfer Lines Used During Tank Truck Unloading and

Associated Equipment Assumed by EPA

D.4 Exposure Estimates

The vapor generation rate, G, or the total emission rate over time, can be calculated by aggregating
emissions from all sources:

• During the transfer period, emissions are only due to leaks, with emission rate G = EL.

• After transfer, during the disconnection of the hose(s), emissions are due to both leaks and
escape of saturated vapor from the hose/transfer arm with emission rate G = ET + EL.

The vapor generation rate can then be used with the EPA Mass Balance Inhalation Model to estimate
worker exposure during loading/unloading activities (U.S. EPA 2013b). The EPA Mass Balance
Inhalation Model estimates the exposure concentration using Equation Apx D-3 and the default
parameters found in TableApx D-5 (U.S. EPA 2013b). TableApx D-6 presents exposure estimates for
CCU using this approach. These estimates assume one unloading/loading event per day and CO4 is
loaded/unloaded at 100% concentration. The loading operation occurs in an outdoor area with minimal

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structure, with wind speeds of 9 mph (central tendency) or 5 mph (high-end).

EquationApx D-3

_ ^V

m ~ v

TableApx D-5. Parameters for Calculating Exposure Concentration Using the EPA Mass
Balance Model

Parameter

Parameter Description

Default Value

Unit

Mass concentration of chemical in
air

Calculated from model equation

mg/m3

Volumetric concentration of
chemical in air

Calculated as the lesser of:

170.000XTXG 1,000,000 XXXVP

MWxQxk 760

ppm

Temperature of air

298

Vapor generation rate

El during transfer period
Et+El after transfer/during
disconnection of hose/transfer
arm

g/s

Molecular weight of the chemical

153.82

g/mol

Outdoor ventilation rate

237,600 (central tendency)
26,400 x (60 x (high-end)

ft3/min

Air speed

440

ft/min

Mixing factor

0.5

dimensionless

Vapor pressure correction factor

dimensionless

Vapor pressure of the pure
chemical

115

torr

Molar volume

24.45 @ 25°C, 1 atm

L/mol

EPA calculated 8-hr TWA exposures as shown in Equation Apx D-4. The 8-hr TWA exposure is the
weighted average exposure during an entire 8-hr shift, assuming zero exposures during the remainder of
the shift. EPA assumed one container is loaded/unloaded per shift: one tank truck per shift for the central
tendency scenario and one railcar per shift for the high-end scenario.

Equation Apx D-4

( Cm(leak only) ^ Q^event ~ tdisconnect) \^m(leak and hose) ^ tdisconnect) ) ^ ^cont

8-hr TWA = -

Where:

Cm(ieak only) = Airborne concentration (mass-based) due to leaks during unloading while

hose connected (mg/m3)

Cm(ieak and hose) = Airborne concentration (mass-based) due to leaks and displaced air during
hose disconnection (mg/m3)

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hevent = Exposure duration of each loading/unloading event (hr/event); calculated

as the inverse of the fill rate, r : 0.5 hr/event for tank trucks and 1 hr/event
for railcars

hshift = Exposure duration during the shift (hr/shift); calculated as hevent X Ncont• 0.5

hr/shift for tank trucks and 1 hr/shift for railcars
tdiscomiect = Time duration to disconnect hoses/couplers (during which saturated vapor

escapes from hose into air) (hr/event)

Ncont = Number of containers loaded/unloaded per shift (event/shift); assumed one

tank truck per shift for central tendency scenario and one railcar per shift
for high-end scenario

TableApx D-6. Calculated Emission Rates and Resulting Exposures from the Tank Truck and
Railcar Loading and Unloading Release and Inhalation Exposure Model for Carbon
Tetrachloride

Scenario

El
(g/s)

Et
(g/s)

El +
Et
(g/s)

Cm
(leaks
only)
(mg/m3)

(leaks
and
hose
vapor)
(mg/m3)

8-hr

TWA
(mg/m3)

Central Tendency

0.049

0.008

0.057

0.85

0.99

0.057

High-End

0.059

0.071

0.130

1.85

4.08

0.30

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Appendix E Dermal Exposure Assessment Approach and
Parameters

This method was developed through review of relevant literature and consideration of existing exposure
models, such as EPA models, IH SkinPerm, and the European Centre for Ecotoxicology and Toxicology
of Chemicals Targeted Risk Assessment (ECETOC TRA).

E.l Incorporating the Effects of Evaporation

E.l.l Modification of EPA Models

Current EPA dermal models do not incorporate the evaporation of material from the dermis. The dermal
potential dose rate, Dexp (mg/day), is calculated as (U.S. EPA 2013b):

EquationApx E-l

Dexp — S x Qu x Yderm x FT

Where:

S is the surface area of contact (cm2; defaults: 535 cm2 (central tendency); 1,070 cm2 (high end) =
full area of one hand (central tendency) or two hands (high end), a mean value for men > 21 yr
(U.S. EPA 2011). the highest exposed population)

Qu is the quantity remaining on the skin (mg/cm2-event; defaults: 1.4 mg/cm2-event (central
tendency); 2.1 mg/cm2-event (high end))

Yderm is the weight fraction of the chemical of interest in the liquid (0 < Yderm < 1)

FT is the frequency of events (integer number per day).

Here Qu does not represent the quantity remaining after evaporation, but represents the quantity
remaining after the bulk liquid has fallen from the hand that cannot be removed by wiping the skin (e.g.,
the film that remains on the skin).

One way to account for evaporation of a volatile solvent would be to add a multiplicative factor to the
EPA model to represent the proportion of chemical that remains on the skin after evaporation,/abs (0 <

/abs< 1):

Equation Apx E-2

Dexp — $ X ( Qu X f abs) X Yderm X FT

This approach simply removes the evaporated mass from the calculation of dermal uptake. Evaporation
is not instantaneous, but the EPA model already has a simplified representation of the kinetics of dermal
uptake.

E.2 Calculation of fabs

Kasting (2006) developed a diffusion model to describe the absorption of volatile compounds applied to
the skin. As of part of the model, Kasting (2006) define a ratio of the liquid evaporation to absorption, %.
They derive the following definition of % (which is dimensionless) at steady-state:

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EquationApx E-3

P MW3A

X = 3.4 X 10~3u°7

j/rU.76 c
Aoct

Where:

u is the air velocity (m/s)

Koctis the octanol:water partition coefficient

MW is the molecular weight

Sw is the water solubility (ng/cm3)

Pvp is the vapor pressure (torr)

Chemicals for which % » 1 will largely evaporate from the skin surface, while chemicals for which %
« 1 will be largely absorbed; x = 1 represents a balance between evaporation and absorption.

Equation Apx E-3 is applicable to chemicals having a log octanol/water partition coefficient less than or
equal to three (log Kow < 3)8. The equations that describe the fraction of the initial mass that is absorbed
(or evaporated) are rather complex (Equations 20 and 21 of Kasting (2006)) but can be solved.

E.2.1 Small Doses (Case 1: Mo < Msat)

In the small dose scenario, the initial dose (Mo) is less than that required to saturate the upper layers of
the stratum corneum (Mo < Msat), and the chemical is assumed to evaporate from the skin surface at a
rate proportional to its local concentration.

For this scenario, Frasch (2012) calculated the fraction of applied mass that is absorbed, based on the
infinite limit of time (i.e. infinite amount of time available for absorption after exposure):

Equation Apx E-4

, _ mabs(co) 2+fx

Tabs - "2 + 2/

Where:

mabs is the mass absorbed
Mo is the initial mass applied

/is the relative depth of penetration in the stratum corneum (f= 0.1 can be assumed)
X is as previously defined

Note the simple algebraic solution in Equation Apx E-4 provides a theoretical framework for the total
mass that is systemically absorbed after exposure to a small finite dose (mass/area) of chemical, which
depends on the relative rates of evaporation, permeation, and the initial load. At "infinite time", the
applied dose is either absorbed or evaporated (FH. 2012). The finite dose is a good model for splash-
type exposure in the workplace (Frasch and Bunge. 2015).

8 For simplification, Kasting and Miller (Kasting and Miller. 2006) does not consider the resistance of viable tissue layers
underlying the stratum corneum, and the analysis is applicable to hydrophilic-to-moderately lipophilic chemicals. For small
molecules, this limitation is equivalent to restricting the analysis to compounds where Log Kow < 3.

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The fraction of the applied mass that evaporates is simply the complement of that absorbed:

EquationApx E-5

mevapi00) _ _ 2X~fx
M0 ~ !abs ~ 2 + 2/

Where:

mevap is the mass evaporated

The fraction absorbed can also be represented as a function of dimensionless time t (Dt/h2), as shown in
Equation Apx E-6.

Equation Apx E-6

mabs „ V 1 ,, -A*ts( X2+*t? \ (C»S(1 - f) A„ - COSA,, \

M0 ~2Lk(1 e " Xt+AS+x) A /'*» )

where the eigenvalues An are the positive roots of the equation:

Equation Apx E-7

Xn ¦ cot(2n) + X = 0

Equation Apx E-6 and Equation Apx E-7 must be solved analytically. It should be noted that the
dimensionless time t is not a representation of exposure duration for a work activity; rather, it represents
the amount of time available for absorption after the initial exposure dose is applied. Since most dermal
risk assessments are typically more concerned with the quantity absorbed, rather than the time course of
absorption, the simple algebraic solution is recommended over the analytical solution.

E.2.2 Large Doses (Case 2: Mo > Msat)

For large doses (Mo > Msat), the chemical saturates the upper layers of the stratum corneum, and any
remaining amount forms a residual layer (or pool) on top of the skin. The pool acts as a reservoir to
replenish the top layers of the membrane as the chemical permeates into the lower layer. In this case,
absorption and evaporation approach steady-state values as the dose is increased, similar to an infinite
dose scenario.

The steady-state fraction absorbed can be approximated by Equation Apx E-8.
Equation Apx E-8

/afcsC00)

/ ' I

Table Apx E-l presents the estimated absorbed fraction calculated using the steady-state approximation
for large doses (Equation Apx E-8 for carbon tetrachloride).

Table Apx E-l. Estimated Fraction Evaporated and Absorbed (fabs) using Equation Apx E-8

Chemical Name

Carbon
Tetrachloride

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CASRN

56-23-5

Molecular Formula

CC14

Molecular Weight (g/mol)

153.82

Pvp (torr)

115

Universal gas constant, R
(L*atm/K*mol)

0.0821

Temperature, T (K)

303

Log Kow

2.83

Koct

676.1

Sw (g/L)

0.793

Sw (|ig/cm3)

793

Industrial Setting

u (m/s)a

0.1674

Evaporative Flux, /

23.58

Fraction Evaporated

0.96

Fraction Absorbed

0.04

Commercial Setting

u (m/s)a

0.0878

Evaporative Flux, /

14.25

Fraction Evaporated

0.93

Fraction Absorbed

0.07

a EPA used air speeds from Baldwin (1998): the 50th percentile of industrial occupational environments of 16.74 cm/s is used
for industrial settings and the 50th percentile of commercial occupational enviromnents of 8.78 cm/s is used for commercial
settings.

E.3 Comparison of fabsto FRabs in the Consumer Exposure Model (CEM)

The Dermal Dose from Product Applied to Skin, Fraction Absorbed Model (P_DER2a) within CEM
Version 2.1.6 also uses a fraction absorbed parameter to estimate dermal dose. In this model, a fraction
absorbed parameter (FRabs) is applied to a potential dose (i.e., amount of chemical retained on the skin)
to estimate the amount of chemical that penetrates the skin. P_DER2a references Frasch (2015) to
estimate the fraction absorbed using a simple algebraic approximation at infinite time following a
transient exposure:

EquationApx E-9

3+*[i —exP(-a^)]

abs 3(1+/)

Where:

X is the ratio of the evaporation rate from the SC surface to the dermal absorption rate through

the SC (unitless, see Equation 90 of CEM)
a is constant (2.906)

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texp is the exposure time (h)

tiag is the lag time for chemical transport through the SC (h, see Equation 89 of CEM)

The Frasch (2015) method is one of transient dermal exposure where the skin is exposed to a chemical
for a finite duration, after which the chemical is removed and no residue remains on the skin. At the end
of the exposure period, the chemical within the skin can still enter the systemic circulation. This
transient exposure model can represent exposure from bathing or showering with contaminated water,
where "dermal absorption proceeds for the duration of exposure, but once the bath or shower has ended,
contaminant residing within the skin may still be absorbed by the body while some may evaporate into
the surrounding air" (Frasch and Bunge. 2015).

For highly volatile chemicals such as 1-BP and methylene chloride, the value of FRabs varies from zero
(for small value of texp) to a maximum of one-third. FigureApx E-l below provides a graphical
representation of fraction absorbed (FRabs) over time for 1-BP. It should be noted that the steady-state
fraction absorbed in this transient exposure scenario is substantially higher than the theoretical fraction
absorbed for a large dose scenario presented in Table Apx E-l.

Exposure time, texp (hr)

Figure Apx E-l. Estimated Fraction Absorbed for 1-BP (CEM Equation)

It is important to note that FRabs refers to the post-exposure absorbed fraction of the amount of chemical
present in the skin membrane at the end of the exposure time; it does not account for the amount of
chemical that has been absorbed into the body from the entire transient exposure. Frasch (2015) presents
equations to estimate the total mass absorbed as a function of exposure time, as an infinite series
summation, when experimental values for the permeability coefficient (Kp) and lag time (tiag) are
available. More detailed review of this solution using measured values Kp is recommended for future
work.

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E.4 Comparison of fabsto Experimental Values for 1-BP

Sections E.2 and E.3 present theoretical frameworks for estimating the fraction of volatile chemical
absorbed in finite dose, infinite dose, and transient exposure scenarios. It is unclear whether these
frameworks have been validated against measured data for the specific chemicals of current EPA
interest. Where available, experimental studies and actual measurements of absorbed dose are preferred
over theoretical calculations.

In a 2011 study, Frasch (2011) tested dermal absorption characteristics of 1-BP. For the finite dose
scenario, Frasch (2011) determined that unoccluded exposure resulted in less than 0.2 percent of applied
1-BP dose penetrated the skin - a value substantially lower than the theoretical ~6 percent absorbed
estimated using EquationApx E-8. While this discrepancy is unexplained, the Frasch (2011) study
recognized the large standard deviation of certain experimental results, and the difficulty of spreading a
small, rapidly evaporating dose of 1-BP evenly over the skin surface. Frasch (2011) also raised the
possibility that 1-BP may dehydrate the stratum corneum, thereby decreasing the skin permeability after
initial exposure

E.5 Potential for Occlusion

Gloves can prevent the evaporation of volatile chemicals from the skin, resulting in occlusion.

Chemicals trapped in the glove may be broadly distributed over the skin (increasing S in Equation Apx
E-l), or if not distributed within the glove, the chemical mass concentration on the skin at the site of
contamination may be maintained for prolonged periods of time (increasing Qu in EquationApx E-l).
Conceptually, occlusion is similar to the "infinite dose" study design used in in vitro and ex vivo dermal
penetration studies, in which the dermis is exposed to a large, continuous reservoir of chemical.

The impact of occlusion on dermal uptake is complex: continuous contact with the chemical may
degrade skin tissues, increasing the rate of uptake, but continuous contact may also saturate the skin,
slowing uptake (Dancik et al.. 2015). These phenomena are dependent upon the chemical, the vehicle
and environmental conditions. It is probably not feasible to incorporate these sources of variability in a
screening-level population model of dermal exposure without chemical-specific studies.

Existing EPA dermal models (Equation Apx E-l) could theoretically be modified to account for the
increased surface area and/or increased chemical mass in the glove. This could be achieved through a
multiplicative variable (such as used in Equation Apx E-2 to account for evaporative loss) or a change
in the default values of S and/or Qu. It may be reasonable to assume that the surface area of hand in
contact with the chemical, S, is the area of the whole hand owing to the distribution of chemical within
the glove. Since Qu reflects the film that remains on the skin (and cannot be wiped off), a larger value
should be used to reflect that the liquid volume is trapped in the glove, rather than falling from the hand.
Alternatively, the product S x Qu (cm2 x mg/cm2-event) could be replaced by a single variable
representing the mass of chemical that deposits inside the glove per event, M (mg/event):

Equation Apx E-10

Dexp — Mx Yderm X FT

Garrod (2001) surveyed contamination by involatile components of non-agricultural pesticide products
inside gloves across different job tasks and found that protective gloves were nearly always
contaminated inside. While the study does not describe the exact mechanism in which the contamination

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occurs (e.g. via the cuff, permeation, or penetration through imperfections in glove materials), it
quantified inner glove exposure as "amount of product per unit time", with a median value of 1.36 mg
product per minute, a 75th percentile value of 4.21 mg/min, and a 95th percentile value of 71.9 mg/min. It
is possible to use these values to calculate the value of M, i.e. mass of chemical that deposits inside the
glove, if the work activity duration is known.

Assuming an activity duration of one hour, the 50th and 95th percentile values translate to 81.6 mg and
4,314 mg of inner glove exposure. While these values may be used as default for M in EquationApx
E-10, EPA notes the significant difference between the 50th and 95th percentile deposition, with the 95th
percentile value being two times more conservative than the defaults for the EPA 2-Hand Dermal
Exposure Model (where the product S x Quis 2,247 mg/event) (U.S. EPA 2013b). Given the significant
variability in inner glove exposure and lack of information on the specific mechanism in which the inner
glove contamination occurs, EPA addresses the occlusion scenario in combination with other glove
contamination and permeation factors through the use of a protection factor, as described in the next
section.

The occlusion scenarios would not be a reasonable occurrence for all conditions of use. Specifically,
occlusion might not occur at sites using chemicals in closed systems where the only potential of dermal
exposure is during the connecting/disconnecting of hoses used for unloading/loading of bulk containers
(e.g., tank trucks or rail cars) or while collecting quality control samples including manufacturing sites,
repackaging sites, sites processing the chemical as a reactant, formulation sites, and other similar
industrial sites. Occlusion might not occur at highly controlled sites, such as electronics and
pharmaceuticals manufacturing sites, where, due to purity requirements, the use of engineering controls
would limit potential dermal exposures. The occlusion would be unlikely at sites (such as aerosol
degreasing) where workers are only handling the aerosol cans containing the chemical and not the actual
bulk liquid chemical.

The occlusion could be a reasonable occurrence at sites where workers may come in contact with bulk
liquid chemical and handle the chemical in open systems. This includes conditions of use such as vapor
degreasing, cold cleaning, and dry cleaning where workers could handle bulk chemical during cleanout
of spent solvent and addition of fresh solvent to equipment. Similarly, occlusion could occur at coating
or adhesive application sites when workers replenish application equipment with liquid coatings or
adhesives.

E.6 Incorporating Glove Protection

Data about the frequency of effective glove use - that is, the proper use of effective gloves - is very
limited in industrial settings. Initial literature review suggests that there is unlikely to be sufficient data
to justify a specific probability distribution for effective glove use for a chemical or industry. Instead,
the impact of effective glove use should be explored by considering different percentages of
effectiveness (e.g., 25% vs. 50% effectiveness).

Gloves only offer barrier protection until the chemical breaks through the glove material. Using a
conceptual model, Cherrie (2004) proposed a glove workplace protection factor - the ratio of estimated
uptake through the hands without gloves to the estimated uptake though the hands while wearing gloves:
this protection factor is driven by flux, and thus varies with time. The ECETOC TRA model represents
the protection factor of gloves as a fixed, assigned protection factor equal to 5, 10, or 20 (Marquart et al..
2017). Where, similar to the APR for respiratory protection, the inverse of the protection factor is the

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fraction of the chemical that penetrates the glove.

The protection afforded by gloves can be incorporated into the EPA model (EquationApx E-l) by
modification of Qu with a protection factor, PF (unitless, PF > 1):

Equation Apx E-ll

Dexp = S x x Yderm x FT

Given the limited state of knowledge about the protection afforded by gloves in the workplace, it is
reasonable to utilize the PF values of the ECETOC TRA model (Marquart et al.. 2017). rather than
attempt to derive new values. TableApx E-2 presents the PF values from ECETOC TRA model
(version 3). In the exposure data used to evaluate the ECETOC TRA model, Marquart (2017) reported
that the observed glove protection factor was 34, compared to PF values of 5 or 10 used in the model .

Table Apx E-2. Exposure Control Efficiencies and Protection Factors for Different Dermal
Protection Strategies from ECETOC TRA v3

Affected User
Group

Indicated

Protection
Factor, PF

Dermal Protection Characteristics

Efficiency
(%)

a. Any glove / gauntlet without permeation data
and without employee training

b. Gloves with available permeation data
indicating that the material of construction offers
good protection for the substance

Both industrial
and professional
users

c. Chemically resistant gloves (i.e., as b above)
with "basic" employee training

d. Chemically resistant gloves in combination with
specific activity training (e.g., procedure for glove
removal and disposal) for tasks where dermal
exposure could occur

Industrial users
only

E.7 Proposed Dermal Dose Equation

Accounting for all parameters above, the proposed, overall equation for estimating dermal exposure is:
Equation Apx E-12

(Qu xfabs)

fl — ^ v y V y I7T

uexp pp * 1 derm ^ 11

EPA presents exposure estimates for the following deterministic dermal exposure scenarios:

• Dermal exposure without the use of protective gloves (Equation Apx E-12, PF = 1)

• Dermal exposure with the use of protective gloves (Equation Apx E-12, PF = 5)

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• Dermal exposure with the use of protective gloves and employee training (EquationApx E-12, PF
= 20 for industrial users and PF = 10 for professional users)

• Dermal exposure with occlusion (Equation Apx E-10)

EPA assumes the following parameter values for Equation Apx E-12 in addition to the parameter values
presented in Table Apx E-3:

• S, the surface area of contact: 535 cm2 (central tendency) and 1,070 cm2 (high end), representing
the total surface area of one and two hands, respectively (note that EPA has no data on actual
surface area of contact for any OES).

• Qu, the quantity remaining on the skin: 1.4 mg/cm2-event (central tendency) and 2.1 mg/cm2-
event (high-end). These are the midpoint value and high end of range default value, respectively,
used in the EPA dermal contact with liquids models (U.S. EPA 2013b).

• Yderm, the weight fraction of the chemical of interest in the liquid: EPA will assess a unique value
of this parameter for each occupational scenario or group of similar occupational scenarios.

• FT, the frequency of events: 1 event per day. Equation_Apx E-12 shows a linear relationship
between FT and Dexp; however, this fails to account for time between contact events. Since the
chemical simultaneously evaporates from and absorbs into the skin, the dermal exposure is a
function of both the number of contact events per day and the time between contact events. EPA
did not identify information on how many contact events may occur and the time between
contact events. Therefore, EPA assumes a single contact event per day for estimating dermal
exposures.

For Equation Apx E-10, EPA assumes the quantity of liquid occluded underneath the glove (M) is equal
to the product of the entire surface area of contact (S = 1,070 cm2) and the assumed quantity of liquid
remaining on the skin (Ou = 2.1 mg/cm2-event), which is equal to 2,247 mg/event. See discussion in
Section E.5.

E.8 Equations for Calculating Acute and Chronic (Non-Cancer and
Cancer) Dermal Doses

Equation E-12 estimates dermal potential dose rates (mg/day) to workers in occupational settings. The
potential dose rates are then used to calculate acute retained doses (ARD), and chronic retained doses
(CRD) for non-cancer and cancer risks.

Acute retained doses are calculated using Equation E-13.

Equation Apx E-13

Where:

ARD

Dexn

'exp

acute retained dose (mg/kg-day)
dermal potential dose rate (mg/kg)
body weight (kg)

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CRD is used to estimate exposures for non-cancer and cancer risks. CRD is calculated as follows:
EquationApx E-14

EquationApx E-15

Equation Apx E-16

Dexv x EF x WY
CRD = P

BW x (AT or ATC)
day

AT = WY X250-

ATC = LTx 250

day
yr

Where:

CRD = Chronic retained dose used for chronic non-cancer or cancer risk calculations

EF = Exposure frequency (day/yr)

WY = Working years per lifetime (yr)

AT = Averaging time (day) for chronic, non-cancer risk

ATc = Averaging time (day) for cancer risk

LT = Lifetime years (yr) for cancer risk

summarizes the default parameter values used to calculate each of the above acute or chronic exposure
estimates. Where multiple values are provided for EF, it indicates that EPA may have used different
values for different conditions of use. The rationales for these differences are described below in this
section.

Table Apx E-3. Carbon Tetrachloride Parameter Values Used to Calculate Acute or Chronic
Exposure Estimates

Parameter Name

Symbol

Value

Unit

Exposure Frequency

250

125 to 150 (DoD analysis only)

days/yr

Working years

31 (50th percentile)
40 (95th percentile)

years

Lifetime Years, cancer

years

Body Weight

80 (average adult worker)
72.4 (female of reproductive age)

Averaging Time, non-
cancer

7,750 (central tendency)3
10,000 (high-end)b

day

Averaging Time, cancer

ATC

19,500

day

a Calculated using the 50th percentile value for working years (WY)
b Calculated using the 95th percentile value for working years (WY)

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Exposure Frequency (EF)

EPA generally uses an exposure frequency of 250 days per year with two notable exceptions: dry
cleaning and DoD uses. EPA assumed dry cleaners may operate between five and six days per week and
50 to 52 weeks per year resulting in a range of 250 to 312 annual working days per year (AWD). Taking
into account fractional days exposed (f) resulted in an exposure frequency (EF) of 258 at the 50th
percentile and 293 at the 95th percentile. For the two DoD uses, information was provided indicating
process frequencies of two to three times per week (oil analysis) and two to three times per month (water
pipe repair). EPA used the maximum frequency for high-end estimates and the midpoint frequency for
central tendency estimates. For the oil analysis use this resulted in 125 days/yr at the central tendency
and 150 days/yr at the high-end. For the water pipe repair, this resulted in 30 days/yr at the central
tendency and 36 days/yr at the high-end.

EF is expressed as the number of days per year a worker is exposed to the chemical being assessed. In
some cases, it may be reasonable to assume a worker is exposed to the chemical on each working day. In
other cases, it may be more appropriate to estimate a worker's exposure to the chemical occurs during a
subset of the worker's annual working days. The relationship between exposure frequency and annual
working days can be described mathematically as follows:

EquationApx E-17

EF = fx AWD

Where:

EF = exposure frequency, the number of days per year a worker is exposed to the chemical
(day/yr)

f = fractional number of annual working days during which a worker is exposed to the
chemical (unitless)

AWD = annual working days, the number of days per year a worker works (day/yr)

U.S. BLS (2016) provides data on the total number of hours worked and total number of employees by
each industry NAICS code. These data are available from the 3- to 6-digit NAICS level (where 3-digit
NAICS are less granular and 6-digit NAICS are the most granular). Dividing the total, annual hours
worked by the number of employees yields the average number of hours worked per employee per year
for each NAICS.

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observation that the weighted average of 200 day/yr worked (from BLS/Census) is 80% of the standard
assumption that a full-time worker works 250 day/yr. The maximum of 1 is appropriate as dry cleaners
may be family owned and operated and some workers may work as much as every operating day.

Working Years (WY)

EPA has developed a triangular distribution for working years. EPA has defined the parameters of the
triangular distribution as follows:

• Minimum value: BLS CPS tenure data with current employer as a low-end estimate of the
number of lifetime working years: 10.4 years;

• Mode value: The 50th percentile tenure data with all employers from SIPP as a mode value for
the number of lifetime working years: 36 years; and

• Maximum value: The maximum average tenure data with all employers from SIPP as a high-end
estimate on the number of lifetime working years: 44 years.

The U.S. Census (2019a) Survey of Income and Program Participation (SIPP) provides information on
lifetime tenure with all employers. SIPP is a household survey that collects data on income, labor force
participation, social program participation and eligibility, and general demographic characteristics
through a continuous series of national panel surveys of between 14,000 and 52,000 households (U.S.
Census Bureau. 2019b). EPA analyzed the 2008 SIPP Panel Wave 1, a panel that began in 2008 and
covers the interview months of September 2008 through December 2008 (U.S. Census Bureau. 2019a.
b). For this panel, lifetime tenure data are available by Census Industry Codes, which can be cross-
walked with NAICS codes.

SIPP data include fields for the industry in which each surveyed, employed individual works
(TJBIND1), worker age (TAGE), and years of work experience with all employers over the surveyed
individual's lifetime.9 Census household surveys use different industry codes than the NAICS codes
used in its firm surveys, so these were converted to NAICS using a published crosswalk (U.S. Census
Bureau. 2013). EPA calculated the average tenure for the following age groups: 1) workers age 50 and
older; 2) workers age 60 and older; and 3) workers of all ages employed at time of survey. EPA used
tenure data for age group "50 and older" to determine the high-end lifetime working years, because the
sample size in this age group is often substantially higher than the sample size for age group "60 and
older". For some industries, the number of workers surveyed, or the sample size, was too small to

9 To calculate the number of years of work experience EPA took the difference between the year first worked (TMAKMNYR)
and the current data year (i.e., 2008). EPA then subtracted any intervening months when not working (ETIMEOFF).

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provide a reliable representation of the worker tenure in that industry. Therefore, EPA excluded data
where the sample size is less than five from our analysis.

TableApx E-4 summarizes the average tenure for workers age 50 and older from SIPP data. Although
the tenure may differ for any given industry sector, there is no significant variability between the 50th
and 95th percentile values of average tenure across manufacturing and non-manufacturing sectors.

Table Apx E-4. Overview of Average Worker Tenure from U.S. Census SIPP (Age Group 50+)

Industry Sectors

Working Years

Average

50th Percentile

95th Percentile

Maximum

All industry sectors relevant to the 10
chemicals undergoing risk evaluation

35.9

Manufacturing sectors (NAICS 31-33)

35.7

Non-manufacturing sectors (NAICS 42-81)

36.1

Source: (U.S. Census Bureau. 2019a)

Note: Industries where sample size is less than five are excluded from this analysis.

BLS CPS data provides the median years of tenure that wage and salary workers had been with their
current employer. Table Apx E-5 presents CPS data for all demographics (men and women) by age
group from 2008 to 2012. To estimate the low-end value on number of working years, EPA uses the
most recent (2014) CPS data for workers age 55 to 64 years, which indicates a median tenure of 10.4
years with their current employer. The use of this low-end value represents a scenario where workers are
only exposed to the chemical of interest for a portion of their lifetime working years, as they may
change jobs or move from one industry to another throughout their career.

Table Apx E-5. Median Years of Tenure with Current Em

ployer by Age Grou

Age

January 2008

January 2010

January 2012

January 2014

16 years and over

4.1

4.4

4.6

16 to 17 years

0.7

18 to 19 years

0.8

1.0

0.8

20 to 24 years

1.3

1.5

1.3

25 years and over

5.1

5.2

5.4

5.5

25 to 34 years

2.7

3.1

3.2

3.0

35 to 44 years

4.9

5.1

5.3

5.2

45 to 54 years

7.6

7.8

7.9

55 to 64 years

9.9

10.0

10.3

10.4

65 years and over

10.2

9.9

10.3

Source: (U.S. BLS. 2014)
Lifetime Years (LT)

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EPA assumes a lifetime of 78 years for all worker demographics.

Body Weight (BW)

EPA assumes a body weight of 80 kg for average adult workers and 72.4 kg for females of reproductive
age.

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