MEMORANDUM

SUBJECT: Exposure Descriptors for CEB Reports - Final

FROM: Ward Penberthy, Chief

Chemical Engineering Branch (7406)

TO: CEB Staff and Management

We have revised the exposure descriptor tables to incorporate consensus and discussion

from the three CEB exposure descriptors meetings, meetings with EPA’s Office of Research and

Development (ORD), discussions with the Exposure Assessment Branch (EAB), and comments

from within OPPT. The revised guidance includes boilerplate language to be incorporated into

all CEB assessments. Attached is a document entitled “Guidance for Characterizing

Assessments of Occupational Exposure and Environmental Release ” dated January 1997. This

guidance will help to ensure that all CEB assessments of potential for occupational exposure and

environmental release are consistent with the Agency exposure assessment guidance and the risk

characterization policy. The guidance contains a checklist for evaluating CEB assessments with

respect to exposure descriptors and exposure characterization, the revised tables which

characterize CEB “base” methodologies and generic scenarios, and boilerplate language for CEB

reports. 

The attached tables will be updated as additional information is gathered and as methods

and tools are evaluated and updated. This has been a long and arduous process, and I thank all

of you for your assistance with this task. If you have any questions, please contact me at 260-

1664.

cc: Mary Ellen Weber

Larry Longanecker

Tom Murray

Nhan Nguyen

Cathy Fehrenbacher

Pat Kennedy

Lynn Delpire

Bob Boethling
Guidance for Characterizing Assessments of

Occupational Exposure and Environmental Release

A Supplement to the CEB Engineering Manual

U.S. Environmental Protection Agency

Office of Pollution Prevention and Toxics

Chemical Engineering Branch

401 M Street, S.W. (7406)

Washington, DC 20460

January 1997
Table of Contents

Section Page #

I. Introduction 1

A. Background 1

1. EPA Guidelines for Exposure Assessment 2

2. EPA Risk Characterization Policy 3

B. Organization of this Document 4

II. Evaluating CEB Assessments for Appropriate Use of Exposure

Descriptors - A Checklist 5

III. Standard Language for Use in CEB Assessments 6

A. Standard Language for IRERs 6

1. Assessment of Environmental Release 7

2. Assessment of Inhalation Exposure 7

3. Assessment of Dermal Exposure 8

B. Standard Language for SRERs and RM1 Reports 9

1. Assessment of Environmental Release 9

2. Estimated Number of Workers Using NOES 10

3. Assessment of Inhalation Exposure 10

4. Assessment of Dermal Exposure 12

C. Standard Language for RM2 and Use/Exposure Reports 13

1. Assessment of Environmental Release 13

2. Estimated Number of Workers Using NOES 14

3. Assessment of Inhalation Exposure 15

a) OSHA PEL for Particulates (PNOR) 15

b) Other OSHA Permissible Exposure Limits 16

c) Mass Balance Ventilation Model 17

d) OCIS Compliance Monitoring Data 19

4. Assessment of Dermal Exposure 20

IV. Listing of CEB Methods 24

Table 1. Listing of Base Methods 24

Table 2. Listing of CEB Generic Scenarios 27

Table 3. Listing of CEB Generic Scenarios Based on Monitoring Data 33

V. References 38

VI. Appendices 39

Appendix A. NOES Error Tables 40

Appendix B. Assumptions Regarding Breathing Rate and Duration of Exposure 41
Appendix C. Suggestions for Presenting Monitoring Data in Reports 42

Appendix D. Definitions of Exposure Descriptors 43

Appendix E. Potential Areas of Uncertainty Associated with an 

Assessment of Occupational Exposure 45
1

 

1 U.S. Environmental Protection Agency. Guidelines for Exposure Assessment. Office of Health and Environm

EPA/600/Z-92/001. 1992. 

 

2 Carol M. Browner. Policy for Risk Characterization at the U.S. Environmental Protection Agency. U.S. Envir

Agency. March, 1995.

I. Introduction

This guidance document was prepared to assist the Chemical Engineering Branch (CEB)

in developing assessments of occupational exposure and environmental release in accordance

with the Agency Guidelines for Exposure Assessment1

 and the recent Risk Characterization

Policy2. It is intended to be used to supplement the Preparation of Engineering Assessments

Volume I: CEB Engineering Manual, and is an in-house working document which is subject to

change as new information and methods are developed.

A. Background

The CEB is responsible for providing assessments of the potential for occupational

exposure and environmental release resulting from manufacture, processing, and use of

chemicals and biological agents in support of Agency assessments of the potential for human and

ecological risk. The Branch is also responsible for evaluating and providing recommendations

for prevention and risk management options. Assessments developed by CEB are based on

Agency guidance and policy, and methods and policies developed by the Branch and EPA’s

Office of Pollution Prevention and Toxics (OPPT). Many of CEB’s methods and policies for

assessing occupational exposure and environmental release are provided in the Preparation of

Engineering Assessments Volume I: CEB Engineering Manual. 

Adequately defining the population which is the subject of the occupational exposure

assessment is crucial to the appropriate interpretation and use of the results of the assessment. 

Many CEB exposure assessment methods were developed for screening level assessments where

data is unavailable, and are based on generic information and data which is applicable to an

industry sector or overall population. Exposure data and information for the specific

subpopulation(s) of interest is often not available. For example, in the absence of data, CEB

often assumes that worker inhalation exposures to particulates are at or below the Occupational

Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) for Particulates

Not Otherwise Regulated (PNOR). Based on our evaluation of the OSHA compliance data for

particulates, this is a valid assumption for screening level assessments, and the exposure is

appropriately characterized as a high end estimate. While this assumption may be quite

appropriate for a screening level assessment, additional evaluation of the available data for the

specific subpopulation of interest would be a likely next step when preparing a more detailed

assessment of occupational exposure. 

For example, if the identified subpopulation of interest is those workers who package

powder detergents, then an evaluation of the OSHA compliance data for that specific Standard

Industrial Code (SIC), and for that activity would provide a more accurate assessment of
2

 

3 Memorandum from Breeda Reilly, Chemical Engineering Branch, to Pat Kennedy, Exposure Assessment Bra

18, 1994.

exposure. The additional effort required to develop this occupational exposure assessment may

not be justified for a screening level assessment, but is appropriate for more detailed assessments

of exposure. 

Because predictions of environmental release are not “exposure” or “dose” estimates, no

exposure descriptors are presented with release estimates. However, environmental release

estimates are used to develop estimates of general population and environmental exposure, and

appropriate characterization of releases is critical to selection of the appropriate exposure

descriptor for the resulting exposure or dose. Currently, CEB provides only the conditions and

assumptions under which our estimates are made, the point estimate value of the release, and a

statement that the estimate cannot be characterized as to where it falls on the distribution.3 

Where possible, additional information is provided to assist in selecting an exposure descriptor

for general population exposure assessments which are derived in part from CEB’s assessment of

potential for environmental release. As methodologies and data sources are improved, CEB will

attempt to incorporate information and approaches which would help us to better characterize the

estimate in terms of where it falls on the distribution. 

 

1. EPA Guidelines for Exposure Assessment

The Agency Guidelines for Exposure Assessment established standard terminology for

characterizing exposures using exposure descriptors. As a result of the guidelines, CEB

carefully evaluated all available methodologies and developed recommendations for appropriate

exposure descriptors. Those descriptors are presented here. Exposure descriptors for individual

risk should include both central tendency and high end estimates where possible. However,

bounding estimates and “what-if” estimates are common in screening level assessments due to

the lack of available data and time constraints.

It is important to understand and distinguish between variability and uncertainty. 

Variability arises from true differences or heterogeneity in characteristics (e.g., differences in

contaminant levels in the environment) and may vary with space and time across the population. 

The central tendency and high end exposure descriptors for individual risk are intended to

capture only the variability in exposure, lifestyles, worker practices, and other factors that lead to

a distribution of risk across a population. Differences between central tendency and high end

estimates reflect the variability in the population of individuals that are subjects of the

assessment, not the uncertainty inherent in the assessment. If sufficient information about the

variability in the exposure variable is available, complex methodologies (e.g., Monte Carlo

analysis or parametric statistical analyses) may be used to evaluate the overall variability of the

exposure distribution. However, this level of detail is rarely available for CEB assessments of

occupational exposure or release.
3

Uncertainty is the lack of knowledge about the correct value for a specific exposure

measure or estimate. There are several approaches for treating data with limitations imposed by

uncertainties. These procedures range from relatively simple methods (e.g., qualitatively

characterizing uncertainties, presenting ranges), to methods which are quite complex (e.g., use of

Monte Carlo analysis.) The selection of the appropriate uncertainty analysis method depends on

the type of assessment being developed, the available data and knowledge regarding uncertainty

and variability, and the available resources. It is generally inappropriate to combine distributions

reflecting both uncertainty and variability for purposes of determining an overall population

distribution. The majority of CEB assessments of occupational exposure and release are driven

by uncertainty due to lack of data, rather than variability, and hence, many CEB assessments are

characterized as either bounding or “what-if” estimates. Where enough information exists to

define the distribution of exposure, an assessment should present an estimate of both central

tendency and high end exposure where possible. A characterization of uncertainty (either

qualitative or quantitative) should accompany all CEB numerical estimates of exposure and

release. 

The Agency guidelines also defined "exposure" and "potential dose". Measurements of

exposure are defined as contact with the outer boundary of the organism integrated over time,

based on the concentration of the contaminant in the medium in contact. In terms of

occupational exposure, the analogy is an airborne concentration (inhalation) or for dermal, a

surface concentration, integrated over the duration of exposure. By combining the airborne

concentration or the surface concentration with an assumed breathing rate or surface area of skin

contacted, a potential dose rate (PDR) is developed in units of mg/day. A PDR is the amount

ingested, breathed, or bulk material applied to the skin per unit time. Thus, values of mg/day (or

mg/kg/day) for both inhalation and dermal exposure should be characterized in CEB reports as

PDRs. As CEB computerizes the generation of reports, we will add the capability to present our

results in units such as mg/kg/day as a Lifetime Average Daily Dose (LADD), etc. Additional

guidance will be developed for those calculations at that time.

B. EPA Risk Characterization Policy

The recent Agency Policy for Risk Characterization also established requirements for

exposure and other assessments developed in support of risk assessments. The policy requires

these assessments to be transparent, consistent, clear, and reasonable. For exposure assessments,

a discussion of uncertainty should accompany the exposure descriptors used, and assumptions

made should be identified. Technical terms should be defined, and jargon should be avoided. 

The scientific and policy bases should be described, and the assessment should be consistent

with Agency policy and guidance. The assessment should be based on the best available

scientific information and expert judgment, and sources should be documented. The assessment

should be based on common sense, and be forthright in acknowledging uncertainty. Other

reasonable alternatives or conclusions should be presented. The OPPT is currently developing a

statement for implementation of the Agency policy, including specific guidance for screening

level, intermediate level, and comprehensive exposure assessments developed by CEB in support
4

of OPPT risk assessments. 

B. Organization of this Document

The remainder of this document contains five sections. Section II provides a general

checklist for evaluating CEB exposure assessments with respect to exposure descriptors and

exposure characterization. Section III presents standard language to be incorporated into CEB

reports, organized by the level of complexity of the assessment (e.g., screening level,

intermediate level, or detailed assessments). This language will also be distributed electronically

to facilitate incorporation into CEB reports. As CEB computerizes report generation, this

language will be incorporated into the computerized report format. Use of this standard

language in CEB reports should help to ensure that the exposure assessment is appropriately

characterized within the risk assessment, and that the risk characterization appropriately

communicates this information for development of risk management options and decisions. 

Section IV includes Tables A and B which list the CEB “base” methodologies and

generic scenarios. A "base" method has wide applicability and can be used in the absence of

monitoring data to assess exposure, depending on the physical/chemical state of the substance

and the exposure scenario. Table A contains a listing of CEB "base" methods and tools used to

estimate occupational potential dose rates, the applicable exposure descriptor, and current status

of the method. Table B contains a list of CEB generic scenarios for occupational exposure and

environmental release, the basis for the assessment, and the applicable exposure descriptors. It

should be noted that the current compilation of generic scenarios does not include exposure

descriptors or a characterization of exposure. Table B should be used by CEB to supplement the

generic scenarios when developing an assessment of exposure and environmental release. 

Finally, Table C contains the key information, assumptions, uncertainty and a description of the

population for those generic scenarios where monitoring data is available. A copy of Tables B

and C will be included in the Branch library copy of the CEB Compilation of Generic Scenarios,

1994. 

Section V presents a list of relevant references, and Section VI contains a series of

appendices with additional information that may be helpful in preparing the assessment. 

Appendix A contains the error tables provided by the National Institute for Occupational Safety

and Health (NIOSH) for characterizing the population of workers potentially exposed to the

substance using the National Occupational Exposure Survey (NOES) data. In preparing an

assessment of potential dose rate, CEB makes assumptions regarding breathing rate and duration

of exposure that may affect the variability of predicted exposures received by the population of

interest. Appendix B describes common assumptions made by CEB regarding breathing rate. 

Appendix C provides some specific suggestions for reporting monitoring data in CEB

assessments. Appendix D provides definitions of the exposure estimators and descriptors based

on the EPA Guidelines for Exposure Assessment. Appendix E presents information that may be

helpful in describing the uncertainty associated with assessments of occupational exposure.
5

II. Evaluating CEB Assessments for Appropriate Use of Exposure Descriptors and

Characterization of Exposure and Release - A Checklist

9 Numbers are clearly identified as estimates if applicable.

9 “Potential dose rate” (PDR) is used to describe estimates presented in units of

mg/day or mg/kg/day.

9 Exposure descriptors (i.e., high end, arithmetic mean, geometric mean, etc.) are

included and are appropriately used.

9 The underlying assumptions used in developing the assessment of exposure are

presented in the assessment. This is especially critical where a “what-if” or

bounding estimate is presented.

9 Standard language describing the methodology used and defining the exposure

descriptor has been included in the report

9 Where standard language is unavailable, or needs to be supplemented, the

assessment presents the methods used, assumptions made, and includes a

discussion of uncertainty and bias.

9 A discussion of uncertainty (and if appropriate, an uncertainty analysis)

accompanies the numerical estimated PDR.

9 Tables are used when there is enough information to warrant one.

9 Tables are appropriately titled (e.g., make sure the table clearly distinguishes

estimates from monitoring data), and footnotes highlight important sources of

data and assumptions made.
6

III. Standard Language for Use in CEB Reports.

This section presents standard language to incorporate into CEB reports to assist in

meeting the Agency Guidelines for Exposure Assessment and Risk Characterization Policy. 

The standard language includes the most commonly-used methods in developing assessments of

occupational exposure and environmental release. This language should be modified where

appropriate based on the specifics of the assessment. If an assessment is prepared based on a

generic scenario for which standard language has not yet been developed, additional information

from Tables B and C may need to be added to the CEB report. This standard language guidance

will also be distributed in electronic format to facilitate incorporation into reports. As new

information is developed and methods are updated, this language will be modified.

A. Standard Language to be Incorporated into All Screening Level Reports as an

Appendix:

Screening level assessments are currently exemplified by CEB’s Initial Review

Engineering Report (IRER) prepared for the new chemicals program. CEB standard

methodologies and procedures for assessing occupational exposure and environmental release

are presented in Preparation of Engineering Assessment, Volume I: CEB Engineering Manual. 

Screening level assessments rely on the use of readily available information and data and are

generally conservative (protective) in nature. However, screening level estimates are often quite

uncertain and may over- or under-estimate exposures by one or more orders of magnitude. 

Where applicable, exposure descriptors such as central tendency and high end

accompany the numerical estimated Potential Dose Rates (PDRs). A PDR is the amount

ingested, breathed, or bulk material applied to the skin per unit time. Definitions of applicable

terms used in characterizing exposures are:

High-end exposure (dose) estimate - A plausible estimate of individual exposure or dose

for those persons at the upper end of an exposure or dose distribution, conceptually above the

90th percentile, but not higher than the individual in the population who has the highest exposure

or dose.

Arithmetic mean - the sum of all the measurements in a data set divided by the number of

measurements in the data set. The arithmetic mean is one of the measures of central tendency

for a distribution.

Median - value in the measurement data set such that half of the measured values are

greater and half are less. The median is one of the measures of central tendency for a

distribution.

Bounding estimate - an exposure or dose which is higher than any exposure or dose
7

expected to occur in the actual population. The estimate is outside (higher than) the distribution

of actual exposures. If the bounding estimated value does not pose an unacceptable risk, then the

exposure group can be eliminated from further analysis.

“What-if” scenario - an estimate based on a set of hypothetical conditions or under a set

of conditions for which actual exposure or release parameter data are incomplete or nonexistent. 

The calculated exposure, dose, or release quantity is not intended to provide information about

how likely the combination of exposure or release parameter values might be in the actual

population or about how many, if any, persons might actually be subjected to the calculated

exposure or release.

Many CEB assessments are based on what-if scenarios due to a lack of exposure data, 

or due to limited exposure data which is anecdotal or of poor quality. For these assessments,

CEB characterizes the assessment as what-if based on the hypothesis that the exposure of the

subpopulation of interest is similar to the exposure of the population for which exposure data

exists. 

1. Assessment of Environmental Release:

Generic Release Assessments: the release estimate is a “what-if scenario”. Due to a lack

of data, CEB provides only the conditions and assumptions under which our estimates are made,

the point estimate value of the release, and a statement that the estimate cannot be characterized

as to where it falls on the distribution. 

Releases from Degreasing Operations: the release estimate is expected to represent a

best estimate of the industry average emissions for the equipment category. The estimate is

based on an average mass flux rate, a standard-sized degreaser for the category, and a standard

duty cycle. 

2. Assessment of Inhalation Exposure:

General Assumptions: 

Potential Dose Rate (PDR) estimates are generally for the entire population of workers

potentially exposed, and may not be representative of the specific operations assessed in this

report. The breathing rate of 1.25 m3/hr for 8 hr/day is a default value used to predict inhalation

exposure, unless otherwise stated. OSHA PELs do not apply to all industries, and OSHA

generally inspects only facilities with greater than 10 employees. 

Specific Assessments:
8

Particulate Exposures: OSHA PEL for Particulates Not Otherwise Regulated (PNOR). 

PDRs are high end estimates assuming compliance with the OSHA PEL of 15 mg/m3

 as an 8-

hour TWA using primarily engineering controls. 

Assessments Based on Compliance with OSHA PELs (other than the OSHA PNOR). 

PDRs are generally “what-if” scenarios assuming compliance with the applicable OSHA PEL,

using primarily engineering controls.

Vapor Exposures: Mass balance model predictions of vapor exposure are bounding PDR

estimates and "what-if" scenarios, depending on the default values used. Many simplifying

assumptions are made when using the model, such as steady state conditions, no use of controls

or protective equipment, as described in Preparation of Engineering Assessment, Volume I: 

CEB Engineering Manual. Estimates, overall are likely to be protective, based on a limited

evaluation.

Mist Exposure During Spray Application: Spray coating scenarios are high end PDR

estimates assuming compliance with the OSHA PEL for Particulates Not Otherwise Regulated of

15 mg/m3

 as an 8-hour TWA, and "what-if" scenarios based on very limited data from 1981. 

Weighing of Textile Dyes: Textile dye weighing scenario is used for dye weighing

operations and very similar weighing operations where small quantities are weighed with precise

scoop/shake/pour techniques. A mean and high end PDR estimate are presented based on data

collected during the Textile Dye Weighing Monitoring Survey. 

Oil Mist Exposure: OSHA PEL for oil mist; high end PDR as a time-weighted average,

assuming compliance with the OSHA PEL of 5 mg/m3

 as an 8-hour TWA using engineering

controls. 

Printing Operations (ink mist): a "what-if" estimate is presented based on very limited

data collected in 1976 and 1978.

Tire Manufacture: PDR as a “what-if” estimate for total particulates while emptying

bags into bins, based on a 1984 study of 20 plants and detailed surveys at 7 sites. 

3. Assessment of Dermal Exposure:

Dermal PDRs are bounding estimates for workers not wearing equipment or using

controls, based on limited data and engineering judgment. Estimates are often based on limited

information and data and include many simplifying assumptions.
9

B. Standard Language to be Incorporated into All Intermediate Level Reports

Intermediate level assessments are currently exemplified by CEB reports prepared for the

new chemicals Standard Review Engineering Report (SRER), the existing chemicals Risk

Management 1 (RM1) report, and testing program reports. CEB standard methodologies and

procedures for assessing occupational exposure and environmental release are presented in

Preparation of Engineering Assessment, Volume I: CEB Engineering Manual. Screening level

assessments rely on the use of readily available information and data and are generally

conservative (protective) in nature. However, screening level estimates are often quite uncertain

and may over- or under-estimate exposures by one or more orders of magnitude. 

Where applicable, exposure descriptors such as central tendency and high end

accompany the numerical estimated Potential Dose Rates (PDRs). A PDR is the amount

ingested, breathed, or bulk material applied to the skin per unit time. Definitions of applicable

terms used in characterizing exposures are:

High-end exposure (dose) estimate - A plausible estimate of individual exposure or dose

for those persons at the upper end of an exposure or dose distribution, conceptually above the

90th percentile, but not higher than the individual in the population who has the highest exposure

or dose.

Arithmetic mean - the sum of all the measurements in a data set divided by the number of

measurements in the data set. The arithmetic mean is one of the measures of central tendency

for a distribution.

Median - value in the measurement data set such that half of the measured values are

greater and half are less. The median is one of the measures of central tendency for a

distribution.

Bounding estimate - an exposure or dose which is higher than any exposure or dose

expected to occur in the actual population. The estimate is outside (higher than) the distribution

of actual exposures. If the bounding estimated value does not pose an unacceptable risk, then the

exposure group can be eliminated from further analysis.

“What-if” scenario - an estimate based on a set of hypothetical conditions or under a set

of conditions for which actual exposure or release parameter data are incomplete or nonexistent. 

The calculated exposure, dose, or release quantity is not intended to provide information about

how likely the combination of exposure or release parameter values might be in the actual

population or about how many, if any, persons might actually be subjected to the calculated

exposure or release.

Many CEB assessments are based on what-if scenarios due to a lack of exposure data, 

or due to limited exposure data which is anecdotal or of poor quality. For these assessments,
10

CEB characterizes the assessment as what-if based on the hypothesis that the exposure of the

subpopulation of interest is similar to the exposure of the population for which exposure data

exists. 

1. Assessment of Environmental Release:

Generic Release Assessments: the release estimate is a “what-if scenario”. Due to a lack

of data, CEB provides only the conditions and assumptions under which our estimates are made,

the point estimate value of the release, and a statement that the estimate cannot be characterized

as to where it falls on the distribution. 

Releases from Degreasing Operations: the release estimate is expected to represent a

best estimate of the industry average emissions for the equipment category. The estimate is

based on an average mass flux rate, a standard-sized degreaser for the category, and a standard

duty cycle. 

2. Estimated Number of Workers Using NOES:

The National Occupational Exposure Survey (NOES) database is frequently used to

estimate the number of workers potentially exposed to substances during industrial and

commercial operations. The survey was conducted in 1980 - 1983 and information was

extrapolated to make national estimates of numbers of workers potentially exposed and numbers

of facilities where the substance is present. Because of the age of the data, the survey itself, and

the extrapolation to national averages, there are several uncertainties associated with the data. 

NOES estimates are uncertain, but are believed to be conservative (e.g., over predictive).

3. Assessment of Inhalation Exposure:

General Assumptions:

Potential Dose Rate (PDR) estimates are generally for the entire population of workers

exposed, and may not be representative of the specific operations addressed in this report. A

breathing rate of 1.25 m3/hr for 8 hr/day are default values used for inhalation exposure, unless

otherwise stated. Estimates are often based on limited information and data and include many

simplifying assumptions. Where compliance with an OSHA PEL is assumed, note that OSHA

standards apply only to certain industrial sectors (e.g., General Industry, Shipbuilding, Maritime,

Construction, and Agriculture), and the requirements may vary from sector to sector. OSHA

generally inspects only facilities with greater than 10 employees.

Specific Assessments:

Particulate Exposure: OSHA PEL for Particulates Not Otherwise Regulated. Estimates
11

are high end PDRs as a time-weighted average, assuming compliance with the OSHA PEL of 15

mg/m3

 as an 8-hour TWA using engineering controls. An evaluation of the OSHA

Computerized Information Service (OCIS) database confirms that over all SIC codes for which

compliance monitoring data is available, 95% of the personal samples collected are below the

OSHA PEL.

Assessments Based on Compliance with OSHA PELs (other than the OSHA PNOR). 

PDRs are generally “what-if” scenarios assuming compliance with the applicable OSHA PEL,

using primarily engineering controls. The assumption of compliance with the OSHA standard is

a postulated hypothesis (a "what-if" scenario) and information about the probability that

exposures in the overall industry are below the OSHA standard has not been evaluated at this

time.

Vapor Exposure During Transfer Operations: Mass balance model for transfer operations

as described in Preparation of Engineering Assessment, Volume I: CEB Engineering Manual to

generate prediction inhalation bounding PDR as a bounding estimate using default input values

selected from the upper end of the range of values, and a “what-if” estimate based on default

input values selected from the midrange of values. Assumes no use of controls or protective

equipment. Based on a limited evaluation, overall, estimates are likely to be protective, and

bounding estimates may overestimate exposures by 1 or 2 orders of magnitude.

Vapor Exposure During Open Surface Operations: Mass balance model for open surface

operations as described in Preparation of Engineering Assessment, Volume I: CEB Engineering

Manual to generate prediction inhalation bounding PDR as a bounding estimate using default

input values selected from the upper end of the range of values, and a “what-if” estimate based

on default input values selected from the midrange of values. Assumes no use of controls or

protective equipment. Based on a limited evaluation, overall, estimates are likely to be

protective, and bounding estimates may overestimate exposures by 1 or 2 orders of magnitude.

Mist Exposure During Spray Application: Spray coating scenario; PDR as a high end

estimate of the 8-hour time-weighted average assuming compliance with the OSHA PEL for

Particulates Not Otherwise Regulated using engineering controls. Note this standard does not

apply to all industries, and OSHA generally inspects only facilities with greater than 10

employees. A "what-if" scenario based on limited data collected in 1978 may also be presented.

Weighing of Textile Dyes: Textile dye weighing scenario; for dye weighing operations

and very similar weighing operations using small quantity with precise scoop/shake/pour

technique, mean and high end PDR; for weighing operations where the precision and technique

are unknown, "what-if" scenario; based on data collected during a probability sampling of 24

sites of more than 1000 identified printing and dyeing sites during 1989-1990. There are

sampling and non-sampling errors associated with the study. The sampling and analytical

methodology was found to have an overall error rate of ± 40% based on an evaluation of 20

dyes. An equation to predict total dye airborne concentration was developed based on the data

collected. Mass weighed was found to be the best predictor of airborne concentration with a
12

correlation coefficient (R2) of 0.39. 

Oil Mist Exposure: OSHA PEL for oil mist; high end PDR as a time-weighted average,

assuming compliance with the OSHA PEL of 5 mg/m3 as an 8-hour TWA using engineering

controls. An evaluation of the OSHA Computerized Information Service (OCIS) database

confirms that over all SIC codes for which compliance monitoring data is available, 88% of the

personal samples collected are below the OSHA PEL. 

 

Printing Operations (ink mist): a "what-if" scenario is presented based on very limited

data collected in 1976 and 1978.

Tire Manufacture: PDR as a “what-if” estimate for total particulates while emptying

bags into bins, based on a 1984 study of 20 plants and detailed surveys at 7 sites. 

4. Assessment of Dermal Exposure: 

Dermal PDRs are bounding estimates based on limited data and engineering judgment;

assuming 1 contact per day and that workers wash up at meal times and/or end of the shift, as

described in Preparation of Engineering Assessment, Volume I: CEB Engineering Manual. 

Assumes [routine contact of 2 hands] and no use of protective equipment or other controls to

mitigate exposure. [substitute routine contact, 1 hand, immersion, 1 or 2 hands, incidental

contact, 1 or 2 hands as needed]
13

C. Standard Language and Examples to be Incorporated into All Detailed Reports:

Detailed assessments are currently exemplified by existing chemicals Risk Management

2 (RM2) reports, Toxic Release Inventory (TRI) reports, Design for the Environment (DfE)

reports, and Use and Exposure Profiles. For detailed assessments of occupational exposure,

potential dose rate summary tables should include footnotes with key information and

assumptions. The following descriptions of the method and standard assumptions are quite

lengthy and may appropriately be included in an appendix to the report. The standard language

from Section B above for intermediate level reports can be included in the text of the CEB report

with referral to the appropriate appendix for additional detail. Where applicable, exposure

descriptors such as central tendency and high end accompany the numerical estimated Potential

Dose Rates (PDRs). A PDR is the amount ingested, breathed, or bulk material applied to the

skin per unit time. Definitions of applicable terms used in characterizing exposures are:

High-end exposure (dose) estimate - A plausible estimate of individual exposure or dose

for those persons at the upper end of an exposure or dose distribution, conceptually above the

90th percentile, but not higher than the individual in the population who has the highest exposure

or dose.

Arithmetic mean - the sum of all the measurements in a data set divided by the number of

measurements in the data set. The arithmetic mean is one of the measures of central tendency

for a distribution.

Median - value in the measurement data set such that half of the measured values are

greater and half are less. The median is one of the measures of central tendency for a

distribution.

Bounding estimate - an exposure or dose which is higher than any exposure or dose

expected to occur in the actual population. The estimate is outside (higher than) the distribution

of actual exposures. If the bounding estimated value does not pose an unacceptable risk, then the

exposure group can be eliminated from further analysis.

“What-if” scenario - an estimate based on a set of hypothetical conditions or under a set

of conditions for which actual exposure or release parameter data are incomplete or nonexistent. 

The calculated exposure, dose, or release quantity is not intended to provide information about

how likely the combination of exposure or release parameter values might be in the actual

population or about how many, if any, persons might actually be subjected to the calculated

exposure or release.

Many CEB assessments are based on what-if scenarios due to a lack of exposure data, 

or due to limited exposure data which is anecdotal or of poor quality. For these assessments,

CEB characterizes the assessment as what-if based on the hypothesis that the exposure of the

subpopulation of interest is similar to the exposure of the population for which exposure data

exists. 
14

1. Assessment of Environmental Release:

Generic Release Assessments: the release estimate is a “what-if scenario”. Due to a lack

of data, CEB provides only the conditions and assumptions under which our estimates are made,

the point estimate value of the release, and a statement that the estimate cannot be characterized

as to where it falls on the distribution. 

Releases from Degreasing Operations: the release estimate is expected to represent a

best estimate of the industry average emissions for the equipment category. The estimate is

based on an average mass flux rate, a standard-sized degreaser for the category, and a standard

duty cycle. 

2. Estimated Number of Workers Using NOES

NIOSH began work on the National Occupational Exposure Survey (NOES), a

nationwide data gathering effort, in 1980 in order to develop estimates of occupational exposures

in all industries except agriculture and mining. Data gathering continued into 1983. The study

was built around a field survey of industrial facilities in 98 different geographic locations. 

Information from these facilities was extrapolated to generate national estimates of potentially

exposed workers for more than 10,000 different chemicals. An excerpt of the NOES database

comprising approximately 70,000 individual records covering 20,000 chemicals and 66 different

2-digit Standard Industrial Codes (SIC) is used by CEB in the absence of other data for

estimating the number of workers potentially exposed to the subject chemical. NOES also

includes information on estimated number of facilities using the chemical.

There are several limitations on information in the database, including the age of the data. 

Due to a large number of facilities in the U.S., only a small sample (4,636 establishments with 8

or more workers in the U.S.) was selected and surveyed. NOES estimates are uncertain, but are

generally believed to over predict number of workers.

 

Because the survey was extrapolated to make national estimates of exposure there are 

uncertainties associated with the data. NIOSH has developed a table of standard errors to be

used with NOES estimates. These standard error estimates have been incorporated into CEB

assessments based on NOES data. NOES does not provide estimates of actual exposures, their

duration, their level or whether chemical protective equipment or engineering controls reduced

or prevented them. NOES data is most appropriately used for the development of screeninglevel occupational exposure assessments. It is assumed that each industry processes or uses the

subject chemical and, as a result, has reported occupational exposures to the subject chemical. 

Care must be taken when using NOES data during later stages of the regulatory process.

Guidance and Examples for Presenting NOES Data in CEB Reports:
15

NOTE: since this is not an estimate of exposure, no exposure descriptor is needed. However, we

consider NOES data to be uncertain.

1. In all cases, present estimates to 2 significant digits.

2. If the data point is < 500, present a range from 1 to (x + (2*(std. error)), where x is the data

point. The standard error is the multiplier times x.

Example: data point is 339, multiplier is 0.5. Present the range in CEB reports as “1 - 680"

3. If the data point is between 500 and 8000, present the range incorporating the standard error.

Example: data point is 4,926, multiplier is 0.27. Present the range in CEB reports as “2,300 -

7,600.”

4. If the data point is > 8,000, present the data point and the standard error.

Example: data point is 53,608, multiplier is 0.15. Present the range in CEB reports as 54,000

(8,000), with a footnote that denotes 8,000 as the standard error, or with 8,000 placed in a

separate column labeled as the standard error. According to NIOSH, values <8,000 are not

reliable and only ranges should be presented.

5. Multipliers for NOES can be found in the Standard Error Tables found in Appendix A. 

3. Assessment of Inhalation Exposure

a) OSHA Permissible Exposure Limit for Particulates Not Otherwise

Regulated (PNOR)

In the absence of monitoring data, compliance with the OSHA Permissible Exposure

Limit (PEL) for Particulates Not Otherwise Regulated as described in the OSHA Air

Contaminants Standard is assumed when estimating potential occupational exposures to dusts or

particulate materials. Chemicals for which PELs have been promulgated are listed in the OSHA

Air Contaminants Standards and are applicable to the General Industry, Shipyards, Marine

Terminals, Longshoring, Construction and Agriculture only (29 CFR 1910, 1915, 1918, 1926,

and 1928). The OSHA standard specifies that exposures to particulates that are not regulated by

some other standard shall not exceed 15 mg/m3

 as an eight hour time weighted average (TWA). 

The assumptions that workers breathe at a rate of 1.25 m3

/hr for an 8 hour day are

frequently used to estimate potential inhalation exposure for a full work day. For particulates

this would give an estimated PDR of 150 mg/day. The assumption of compliance with this

standard to estimate potential exposures usually results in a high end estimate of inhalation
16

potential dose rate for the industry overall. The potential inhalation dose estimates do not take

into account respiratory protection or engineering controls that may be used to mitigate

inhalation exposures.

Note that a TWA is based on exposure averaged over an 8 hour period and is calculated

to allow for excursions above the exposure level provided they are compensated by equivalent

excursions below the exposure level during the workday. The estimated exposure is the total

amount of substance to which a worker can be exposed per 8 hour day whether the exposures are

for short duration at high concentrations or long duration at low concentrations. There is no

need to compensate the value for periods of time the worker is involved in activities that do not

result in exposure.

OSHA generally only inspects workplaces with greater than 10 employees for

compliance. Hence, this approach to estimating potential exposures to particulates is applicable

only to populations of workers that are employed in workplaces that are in compliance with the

OSHA Standard. A review of the OSHA compliance monitoring data for total dust revealed that

about 95% of the approximately 200 measurements of total dust in a wide range of Standard

Industrial Classification codes were below the OSHA standard. While this demonstrates

compliance overall for those facilities where measurements were taken, it is not known whether

the specific individual facilities or companies identified in this report are in compliance with the

OSHA standard.

b) Other OSHA Permissible Exposure Limits (PEL)

Workplace inhalation exposures to air contaminants are regulated by OSHA Permissible

Exposure Limits (PELs). Chemicals for which PELs have been promulgated are listed in the

OSHA Air Contaminants Standards and are applicable to the General Industry, Shipyards,

Marine Terminals, Longshoring, Construction and Agriculture only (29 CFR 1910, 1915, 1917,

1918, 1926, and 1928). Some OSHA requirements may vary between industrial sectors. 

Employers may comply with OSHA PELs with the use of engineering controls (e.g., local

exhaust ventilation), but personal protective equipment (e.g., a respirator) is also allowed under

certain circumstances.

In the absence of monitoring data, OPPT's Chemical Engineering Branch may assume

compliance with the OSHA PELs to estimate potential occupational inhalation exposure, where

appropriate . For detailed assessments, CEB will often obtain, review, and evaluate OSHA

compliance data, and may prepare an assessment based on this data. OSHA generally only 

inspects workplaces with greater than 10 employees. 

PELs are usually expressed in terms of time weighted average (TWA) concentrations that

must not be exceeded any 8 hour work shift of any 40 hour workweek. A TWA is based on

exposure averaged over an 8 hour period and is calculated to allow for excursions above the

exposure level provided they are compensated by equivalent excursions below the exposure level
17

during the workday. The estimated exposure is the total amount of substance to which a worker

can be exposed per 8 hour day whether the exposures are for short duration at high

concentrations or long duration at low concentrations. There is no need to compensate the value

for periods of time the worker is involved in activities that do not result in exposure.

OSHA maintains a database of exposure monitoring measurements which has been

gathered at selected industrial sites in order to determine compliance with PELs. This database

is the OSHA Computerized Information System (OCIS) and may give helpful insight into the

level of compliance with a specific PEL. It may also provide more accurate exposure data for a

given industrial sector and a better indication of whether exposures are in fact below the PEL.

Guidance and Examples for Presenting OSHA PELs in CEB Reports:

1. If OSHA compliance data has been evaluated as described in section d below (OCIS

Compliance Monitoring Data): Based on a review of OSHA compliance data, about __% of

approximately __ measurements were below the OSHA standard. Therefore, assuming

compliance with the OSHA standard would result in an estimated [high end] inhalation potential

dose rate for the overall industry, although the applicability to the specific facilities identified in

this report is unknown. 

2. If OSHA compliance data has not been evaluated: The assumption of compliance with the

OSHA standard is a postulated hypothesis (a "what-if" scenario) and information about the

probability that exposures in the overall industry are below the OSHA standard has not been

evaluated at this time.

c) Mass Balance Ventilation Model

When exposure monitoring data or other approaches to assessing occupational exposures

can not be used, OPPT's Chemical Engineering Branch often uses a mass-balance or "box"

model to predict airborne concentrations of a specific chemical. This model is most applicable

to vapor and gaseous emissions because vapors follow currents freely and are not greatly

influenced by gravity. The steady state model used by CEB is described in Preparation of

Engineering Assessment, Volume I: CEB Engineering Manual and is based on the mass balance

of a substance in an enclosed space. The simplest form of the mass balance model is used to

estimate airborne concentrations, based on the following assumptions:

! there is perfect and instantaneous mixing of the contaminant with incoming

general dilution air;

! the airborne concentration of the contaminant in the exfiltration air is the same as

in the room;

! only one source within the work area emits the contaminant;

! extinction of the chemical (adsorption, absorption, or chemical transformation)
18

 

4

 U.S. Environmental Protection Agency. 1991. Preparation of Engineering Assessments. Volume I: CEB En

Draft. Washington, D.C.: Office of Toxic Substances, U.S. Environmental Protection Agency. pp 4-25 - 4-

 

5 A. A. Hummel, K. O. Braun, and M. C. Fehrenbacher. Evaporation of a Liquid in a Flowing Airstream. A

Assoc. J. Vol. 57, pp 519-525. June, 1996.

resulting from deposition on walls and equipment, condensation of hot vapors,

and photodegradation of chemicals is negligible;

! the incoming air is contaminant-free;

! the concentration of contaminant at initial time (t=0) is negligible;

! the generation and ventilation rates are constant over time;

! room air and ventilation air mix ideally;

! the concentration approaches steady state; and

! the mass transfer resistance on the gas side is limiting.

Predictive equations for generation rate have been developed for transfer operations (e.g.,

drumming, tank car loading, tank truck loading), and evaporation from open surfaces (e.g.,

sampling)4. The generation rate for transfer operations is based on displacement of vapor

equivalent to the volume of the container for each container filled. The generation rate for open

surface operations is based on evaporation of a liquid from an open container in a flowing air

stream. The assumption of steady state conditions is an important factor, as many occupational

exposure scenarios are of short duration such that steady state conditions would not be reached. 

However, the simplicity of the steady state model lends itself to screening level estimates where

data is lacking.

In addition to the assumptions listed above, the following apply to use of the mass

balance model for open surface operations5:

! surface temperature of the liquid and the evaporation rate are constant;

! heat of evaporation is provided by the surroundings;

! diffusion at the edge of the pool and in the direction of the air stream are

negligible;

! air velocity is constant and flowing only in one direction;

! there is no mixing in the area above the pool of liquid;

! no local exhaust or physical barriers are present at the edges of the pool;

! substance has a low to moderate vapor pressure (< approximately 35 torr); and

! heat transfer is neglected.

A number of default input values have been selected for use in the mass balance model in

the absence of data. For transfer operations, default input values for ventilation flow rate,

volume of container, saturation factor, fill rate, and mixing factor are selected from either

midrange or conservative values, depending on the type of assessment desired (e.g., “what-if” or

bounding assessment. ) For open surface operations, default input values for surface area of the

pool of liquid, ventilation flow rate, mixing factor, and length of the pool are selected from

midrange or conservative values. Values for saturation factor and mixing factors are derived
19

 

6 M. C. Fehrenbacher and A. A. Hummel. Evaluation of the Mass Balance Model Used by the Environment

for Estimating Inhalation Exposure to New Chemical Substances. Am. Ind. Hyg. Assoc. J.. Vol. 57, pp 5

1996. 

from limited data presented in standard reference materials, and other default input values are

based on professional judgment or knowledge of common industrial operations. Thus, model

estimates are fairly uncertain. The estimated vapor pressure may also be uncertain, especially

for mixtures and new chemicals. The incorporation of a mixing factor term is a very simplistic

means of addressing non-uniform mixing in a room, which is actually quite complex. However,

it is commonly used in estimating occupational inhalation exposure.

A sensitivity analysis of the mass balance model and uncertainty analysis of model

parameters confirmed that values selected for ventilation flow rate and vapor generation rate

have a significant impact on calculated airborne concentrations and must be carefully selected. 

Input values for vapor pressure must also be selected with care6. A rigorous evaluation of model

estimates when compared with monitoring data for selected industrial operations demonstrated

that “what-if” model predictions were within one order of magnitude of the monitoring data but

may over- or under-estimate exposures when mid-range default input values are selected. 

Estimates based on selection of upper bound default input values resulted in estimates which

were one or two orders of magnitude higher than the monitoring data. 

Guidance and Example for Presenting Modeling Estimates in CEB Reports:

Table XX. Estimated Inhalation Exposure for Dimethylchickenwire

Worker Activity Estimated Number

of Workers

Potentially

Exposed1

Estimated

Airborne

Concentration,

(mg/m3

)

Potential

Inhalation Dose

Rate, (mg/day)

Personal

Protective

Equipment1

Sampling 48 <<0.012,3, 0.073,4 0.012,5 , 0.784,5 Cartridge respirator,

Tyvek suit

Product Loading

(Drumming)

48 0.022,6 - 2.24,6 0.242,5, 224,5 Cartridge respirator,

Tyvek suit

Product Loading

(other transfers)

143 0.012,7 - 0.064,7 0.152,5, 0.624,5 Cartridge respirator,

Tyvek suit

1

 Based on information reported by industry.

2 “what-if” hypothetical estimate based on midrange default input values

3

 Estimated using mass balance model per Preparation of Engineering Assessments, Volume I: CEB Engineering

Manual, sampling operation using default input values.

4 Bounding estimate based on protective default input values.

5

 Assumes breathing rate of 1.25 m3/hour for an 8-hour workday.

6

 Estimated using mass balance model per Preparation of Engineering Assessments, Volume I: CEB Engineering

Manual, drumming operation using default input values.

7

 Estimated using mass balance model per Preparation of Engineering Assessments, Volume I: CEB Engineering

Manual, tank car loading operation using default input values, wind speed = 9 mph.
20

d) OCIS Compliance Monitoring Data

OSHA maintains a database of exposure monitoring measurements analyzed by the

OSHA Salt Lake City Laboratory which has been gathered by OSHA compliance inspectors at

selected industrial sites in order to determine compliance with PELs. This database is the OSHA

Computerized Information System (OCIS). Information available within the database includes

over 520,000 individual sampling results from 1981 to the present. Results can be searched by

company name, SIC code, CAS number or sampling type (area vs. personal). This database is

only one of several OSHA databases, and includes data collected by Federal OSHA inspectors

only. 

1. If you only have an OCIS Lab Sample Results printout: These results do not identify

the activity of the worker sampled, and it is unclear if the results represent time-weighted

average results or short-term samples. In addition, the analytical method used to quantify the

measurement is not reported, but one could assume that the method used is that reported in other

OSHA documents. Because of these uncertainties, only a range of measurement results is

reported, and it is not known if the sampling results are representative of the specific industries

and worker activities that are described in this report. Potential dose rates for inhalation

exposure based on OCIS data are generally “what-if” estimates. It should be noted that some of

the results included in the [ appendix or table] may reflect area or bulk samples, and often

analytical or field blanks are reported. In addition, not every sample has been coded to

distinguish between field blanks, bulk samples, personal samples, etc. 

2. If you have additional information on the analytical methods used, the SIC and worker

activity, you should summarize this information in the assessment, and characterize the exposure

data appropriately. Where possible, data from the appropriate SIC should be used in assessing

occupational exposure for detailed assessments. 

Guidance and Examples for Presenting OCIS data in CEB Reports:

1. If you only have an OCIS Lab Sample Results printout: When reporting OCIS data,

include the data print-out in an appendix or table, including the PELCODEs to aid in interpreting

the results. Because we can only interpret the data that has been coded with a PELCODE, only

make statements about that data. At best, you can only report a range of values for appropriate

measurements. This data would be considered “Type 3" (anecdotal) data as reported in the

Guidelines for Statistical Analysis of Occupational Exposure Data.

In addition to the above standard language, within the text of the report, include

information similar to the following:

There were 245 OCIS monitoring records for dimethylchickenwire. Out of the 245

measurements, 176 were either blank samples, bulk samples, or were not coded and are assumed
21

 

7

 Versar, 1984. Exposure Assessment for Retention of Chemical Liquids on Hands. Office of Toxic Substanc

Contract 68-01-6271.

 

8 Popendorf, W.J. and Leffingwell, J.T., 1982. Regulating OP Pesticide Residues for Farmworker Protection. 

Vol. 82, pp 156-157.

to be not representative of personal exposure. Without additional information, only 69 samples

ranging from 0.99 to 25 ppm can be evaluated for predicting inhalation exposures during

industrial operations. None of the coded samples were above the OSHA PEL. 

2. If you have additional information on SIC code and worker activity, you may be able

to group the data into groups individuals with similar exposures, and may be able to provide

some statistical descriptors (mean, confidence limits, etc.) Consult the Guidelines for Statistical

Analysis of Occupational Exposure Data for additional detail. This data would be considered

“Type 2" data as reported in the guidelines.

4. Assessment of Dermal Exposure

The OPPT Chemical Engineering Branch's Dermal Exposure Method is frequently used

to develop bounding estimates of the potential amount of a chemical remaining on a worker's

hand(s) (usually expressed in terms of mg/day) and available for absorption, after the worker

completes various common industrial activities leading to occupational exposure. The method

links assumptions based on limited experimental data contained in a study7

 which measured

amounts of different materials remaining on the skin after completion of several tasks

representing various degrees of exposure with estimates of skin surface area in contact with the

contaminant8. The method does not consider volatilization, humidity, skin conditions, and

clothing practices, or the presence or absence of warning properties such as visual changes to the

skin or irritation. However, dermal exposure is assumed to be negligible when mitigated by the

corrosivity of the substance, high temperature or other conditions which would preclude dermal

contact. Absorption through the skin is considered separately and is evaluated by another group

within OPPT. The method also assumes that a single contact with the chemical results in the

total quantity of substance deposited on the skin for a full work day and that no dermal

protection, such as gloves, is used by the worker to limit exposure. Therefore, the method

generates estimates of potential dermal dose rate only for the sub-population of workers that

does not use dermal protection. Gloves and other chemical protective clothing and equipment

are commonly used in industrial operations, but quantification of the level of protection provided

by gloves during actual use is not performed due to a lack of data.

There are many uncertainties associated with an assessment of dermal exposure, and

characterization of the potential for dermal exposure and absorption through the skin is very

complex. In addition, the performance of chemical protective clothing and equipment in

industrial operations adds another layer of uncertainty and complexity to the assessment. An

assessment of dermal exposure encompasses developing an understanding of the exposure

scenario (including the duration, frequency, and amount of contaminant deposited on the skin),
22

 

9 U.S. Environmental Protection Agency, Risk Reduction Engineering Laboratory. Methods to Assess the Perm

Through Protective Clothing Polymers. User Manual. Supplement to Manual for the Preparation of Enginee

Arthur D. Little, Inc. Contract No. 68-C9-0037, September 1990.

coupled with an assessment of the skin surface area contacted, and consideration for any

mitigation of exposure based on the physical/chemical properties of the chemical, handling

procedures, environmental conditions, or the use of protective equipment or clothing. 

Absorption through the skin is currently evaluated separately. The amount of contaminant

contacting the skin can vary by several orders of magnitude, depending on the individual worker

activities and work practices. Due to a lack of data and information to provide a more definitive

characterization of the exposure scenario for most industrial operations, CEB must rely on

default assumptions which are believed to be reasonable for the entire population of workers

potentially exposed via dermal contact in industrial operations in general. As additional data and

information becomes available, CEB’s methodology will be updated to reflect the new

information.

With respect to the performance of chemical protective clothing during actual use, CEB

generally relies on the default assumption that gloves or other control measures are not used due

to a lack of data and information with which to adequately quantify the protection provided

during use. There are many factors which impact the protection provided by chemical protective

clothing, including availability, cost, worker compliance, impact on job performance, chemical

and physical properties of the substance and the protective clothing, and use, decontamination,

maintenance, storage, and disposal practices applicable to the industrial operation9

. The physical

and chemical performance of the chemical protective clothing are a function of the permeation,

penetration, and degradation characteristics of the protective clothing/chemical combination and

contribute to the overall effectiveness of the barrier. Permeation is the process by which a

chemical moves through the protective clothing material on a molecular level. Penetration is the

movement of a chemical through holes (e.g., seams, porous materials, imperfections, etc.) on a

nonmolecular level by mechanisms such as wicking, wetting, pressure gradients, or bulk flow. 

Degradation is any undesirable change (e.g., swelling, shrinkage, loss of puncture or tear

resistance, increase in stiffness, etc.) in a physical property or appearance of the clothing

material due to contact with the substance of interest. There are standard test methods for

measuring these physical and chemical characteristics, but these are only a few of the factors

which impact the protection provided by protective clothing during use. Very little is known

about the performance characteristics of complex mixtures which are common in industrial

operations. The environmental and worker-related aspects of the issue of the performance of

chemical protective clothing during actual use are not well understood. A few studies have

identified several environmental and operation-specific factors that may adversely impact the

performance of chemical protective clothing during actual use. The elevated temperature of the

skin, and stress and flexing of the glove during use have been found to reduce the performance
23

 

10 E. T. Zellers, R. Sulewski. Modeling the Temperature Dependence of N-Methylpyrrolidone Permeation Throu

Natural-Rubber Gloves. Am. Ind. Hyg. Assoc. J. (54): 465-478. September, 1993.

 

11 E. C. Gunderson, B. A. Kingsley, C. L. Witham, and D. C. Bomberger. A Practical Study in Laboratory and W

Testing. Appl. Ind. Hyg. 4(12): 324-329. December, 1989.

 

12 U.S. Environmental Protection Agency, Office of Toxic Substances. Assessment of Airborne Exposure and D

Acrylamide During Chemical Grouting Operations. EPA 560/5-87-009, July, 1987.

 

13 K. Cummins, D. Morton, D. Lee, E. Cook and R. Curtis. Exposure to Acrylamide in Chemical Sewer Grouting 

Occup. Environ. Hyg. 7(6): 385-391. June, 1992.

of gloves during actual use in industrial applications10, 11. Finally, wearing gloves may impede

the performance of the specific task or activity and thus, gloves may be inappropriately used or

not used at all12, 13. Where glove permeation data is available, it is generally evaluated by CEB

with a focus on identifying procedures and workplace practices which will help to ensure that the

protective clothing will be appropriately selected, maintained, and used.

Guidance and Example for Presenting Dermal Estimates in CEB Reports:

Table XX. Estimated Dermal Potential Dose Rate (PDR) for Dimethylchickenwire

Worker Activity Number of

Workers

Quantity Retained on

the Skin per Unit

Surface Area**,

(mg/cm2)

Skin Area

Exposed**

(cm2)

Dermal PDR*,

(mg/day)

Processing and

Loading

130 1 - 3 1300 1300 - 3900

* Bounding estimate, assuming routine, 2-hand dermal contact, no dermal protection, such as gloves, are used by the

worker to limit exposure. A bounding estimate is an exposure or dose which is higher than any exposure or dose

expected to occur in the actual population. The estimate is clearly outside (higher than) the distribution of actual

exposures. 

** Based on the Preparation of Engineering Assessments Volume I: CEB Engineering Manual.
24

IV. Listing of CEB Methodologies

This section presents a series of tables which list the methods used by CEB, the type of estimate or exposure descriptor

resulting from use of the method, and the current status of the method. In addition, notations regarding the use and limitations of the

method are included. Because the generic scenarios largely rely on default assumptions for predicting environmental release and

potential for dermal exposure, this information is not included in the table. It is important to note that while many of these methods

are final, all methods are subject to change as new information and data are obtained. A discussion of uncertainty associated with the

monitoring data has been incorporated into Table C. Uncertainty is an important consideration in developing any assessment of

occupational exposure and release. The standard language presented in section III of this document identifies some of the uncertainty

associated with the base methods. This information is applicable to the methods and generic scenarios presented in Tables A and B

below. In addition, Appendix D presents information that may be helpful in identifying additional uncertainties associated with CEB

assessments.

Table 1. Listing of Base Methods 

CEB Base Method Exposure Descriptor or Type of Estimate Current Status of the Method Notes

Dermal Exposure

Assessment 

Bounding estimate for workers wearing no

dermal protection.

Final. This method is currently under

evaluation and will be modified in the future.

Report values to 2 significant digits.

Mass Balance Ventilation

Model

"What-if" if scenario using mid-range default

values; 

Bounding estimate when using default values

selected from the upper end of the range.

Final. This method has been evaluated by

comparison with available monitoring data. The

method is currently under revision to

incorporate new approaches for predicting timedependent exposures and consideration for

incomplete mixing. 

Report values to 2 significant digits

(e.g. <0.1, <<0.1).

OSHA PEL for Particulates

Not Otherwise Regulated

(PNOR)

High end estimate, based on OSHA Compliance

Information System (OCIS) database for all

reported SIC codes combined.

Final. OSHA Compliance data supports using

this method as a high end estimate for an overall

estimate. Analysis of individual SIC codes has

not been done. 

Report values using appropriate

significant digits.
25

CEB Base Method Exposure Descriptor or Type of Estimate Current Status of the Method Notes

Other OSHA PEL “what-if” scenario if no supporting data (e.g.,

OSHA compliance data) is available. If

supporting data is available, carefully evaluate

the data and determine the appropriate exposure

descriptor.

Final. A review of the OSHA compliance data

may provide additional information on the

appropriate exposure descriptor and the

appropriateness of the assumption that facilities

are in compliance.

Report values using appropriate

significant digits.

OSHA Computerized

Information System (OCIS)

Data

Carefully evaluate the data and determine the

appropriate exposure descriptor.

Final. Report values using appropriate

significant digits. OCIS data is

generally applicable to larger

facilities. There are other OSHA

compliance databases which may be

more applicable to smaller facilities.

NIOSH National

Occupational Exposure

Survey (NOES) Database

NOES estimates are fairly uncertain due to data

limitations, and generally over predict the

population of workers potentially exposed.

Final. NIOSH has no plans to update NOES,

and the information is dated.

Report values to 2 significant digits,

and report the uncertainty range.

Environmental Release:

Media of Release

Media of release is based on submitter-supplied

information, documented source (e.g., industry

profile or TRI data), and/or engineering

judgment. If the media is uncertain, it will be so

noted, and the basis for the estimation is

provided in the assessment.

Final. As part of the development of “generic

scenarios”, CEB continues to gather data on

quantity, frequency, and media of releases of

chemicals from specific industries or uses.

Developed for new chemical

assessments.

Environmental Release:

Release of Liquid Residue

from Unloading and Cleanup Operations for Batch

Operations.

Estimates provided for the entire process, single

vessel, tank car/truck, 40 - 60 gal. drums and

smaller containers, based on data collected

during a laboratory study. Assumes that vessel

is emptied by pumping out the residual material

for process, drums or vessel; gravity draining

for tanktruck/cars.

Final. As part of the development of “generic

scenarios”, CEB continues to gather data on

quantity, frequency, and media of releases of

chemicals from specific industries or uses.

Does not consider lining of

containers, viscosity, type and

amount of solvent, cleaning method,

cleanup frequency, and treatment of

residues prior to discharge.

Environmental Release:

Release From Drum Residue

for Solids

Estimate of 1% by weight of drum based on

engineering judgment.

Final. As part of the development of “generic

scenarios”, CEB continues to gather data on

quantity, frequency, and media of releases of

chemicals from specific industries or uses.
26

CEB Base Method Exposure Descriptor or Type of Estimate Current Status of the Method Notes

Environmental Release:

Baghouse/Cyclone

Efficiency

Estimate of 99% efficiency, based on

engineering judgment.

Final.

Environmental Release:

Carbon Adsorption

Eficiency

Estimate of 50% efficiency, based on

engineering judgment.

Final.
27

Table 2. Listing of CEB Generic Scenarios*‡

Generic Scenario (Current Status) Inhalation Method (Descriptors for PDR) Notes

Adhesives Manufacture (Final, February,

1992)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates), 

Vapor: Mass Balance Ventilation Model

(bounding or "what-if" estimates)

Page A2: Calculation of vapor exposure: Where the scenario says “% PMN

conc.” the equation should read “mole fraction.”

Calculation of particulates exposure: Where the scenario says “% PMN” the

equation should read “% PMN/100"

Bioprocessing (Draft, September, 1991,

currently under revision)

Bioaerosols: “What-if” scenario based on area

monitoring data collected by NIOSH.

Carbonless Copy Paper (Final, June,

1991)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates), 

Vapor: Mass Balance Ventilation Model

(bounding or "what-if" estimates)

CFC substitutes - Manufacture; Foam

Blowing; Electronics Cleaning; Metal

Cleaning (Draft, September, 1991)

Vapor: High end and central tendency

estimates based on monitoring data for CFCs

and CFC substitutes.

CFC substitutes - Sterilant Carrier (Draft,

September, 1991)

Vapor: High end and central tendency

estimates based on

CFC substitutes - Refrigeration Servicing

and Mobile Air Conditioning,

Manufacture and Servicing (Draft,

September, 1991)

Vapor: “what-if” estimate using a mass

balance model with a Monte Carlo selection

technique for calculating distributions of

potential exposures.

Coatings - Conventional;

Emulsion/Formulation of Latex

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates), 

Vapor: Mass Balance Ventilation Model

(bounding or "what-if" estimates)

Page B7: The equation at the bottom of the page is inappropriate. The

scenario provides no guidance for calculating the concentration in air, one of

the parameters of the stated equation, and uses weight percent instead of

mole fraction.

Page B8: The first equation is inappropriate. The next paragraph discusses

inhalation exposure to powders, but information pertaining to OSHA PELs is

misstated.

Coatings - Conventional; Automotive

spray application (Final, Revised

January, 1992; currently under revision)

Particulates: "what-if" scenario using spraycoating data.
28

Generic Scenario (Current Status) Inhalation Method (Descriptors for PDR) Notes

Coatings - Conventional; Furniture Spray

Application (Final, Revised February,

1992; currently under revision)

Particulates: "what-if" scenario if spraycoating data is used.

Coatings - Radiation Curable; EB

Curable - Formulation of Coating (Draft,

1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)

Page B7: The equation at the bottom of the page is inappropriate. The

scenario provides no guidance for calculating the concentration in air, one of

the parameters of the stated equation, and uses weight percent instead of

mole fraction.

Page B8: The first equation is inappropriate. The next paragraph discusses

inhalation exposure to powders, but information pertaining to OSHA PELs is

misstated.

Coatings - Radiation Curable; EB

Curable - Roll Application (Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates), 

Vapor: Mass Balance Ventilation Model

(bounding or “what-if” scenarios)

Page B29: In calculating the inhalation exposures, mole fraction and not

weight percent are to be used. The scenario only presents the worst case

default values and not the more typical values.

Coatings - Radiation Curable; UV

Curable - Formulation of Coating ( Draft,

1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates), 

Vapor: Mass Balance Ventilation Model

(bounding or “what-if” scenarios)

Page B36. The equation at the bottom of the page is inappropriate. The

scenario provides no guidance for calculating the concentration in air, one of

the parameters of the stated equation, and uses weight percent instead of

mole fraction.

Page B37: The first equation is inappropriate. The next paragraph discusses

inhalation exposure to powders, but information pertaining o OSHA PELs is

misstated.

Coatings - Radiation Curable; UV

Curable - Roll Application (Draft, 1994,

updated Sept. 1995)

Mist: Based on limited monitoring data

(“what-if” scenario

Vapor: Mass Balance Ventilation Model

(bounding or “what-if” scenarios)

Page B45: The equations at the bottom of the page are inappropriate. The

scenario provides no guidance for calculating the concentration in air, one of

the parameters of the stated equation, and uses weight percent instead of

mole fraction.

Coatings - Powder Coatings, Dry

Blending (Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)

Coatings - Powder Coatings, Melt

Blending (Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)

Coatings - Powder Coatings; Electrostatic

Application (Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)
29

Generic Scenario (Current Status) Inhalation Method (Descriptors for PDR) Notes

Coatings Powder Coatings - Fluidized

Bed Application (Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)

Coatings - Powder Coatings (Draft, 1992) Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)

Electroplating for Metal Treatment

(Draft, 1994, currently under revision)

Mist: use surrogate data (“what-if” scenario). Page C2: The equation is not a standard equation from the CEB Engineering

Manual. The linear relationship between airborne concentration of mists and

concentration in the solution is not supported, and is questionable as mist

generation is a mechanical process which differs considerably from

evaporation. The scenario does not address whether any surrogate data is

available and how to incorporate the OSHA PEL into the assessment.

Electronics - Wet Cleaning Process in

Integrated Circuit Fabrication (Draft,

1994)

Vapor: mass balance model (bounding and

“what-if” scenario, based on default values

used.)

Electronics - Film Deposition in

Integrated Circuit Fabrication (Draft,

1994)

Gas: use surrogate data (“what-if” scenario.) The scenario does not address whether any surrogate data is available.

Electronics - Printed Circuit Board;

Material Fabrication Process for

Manufacture of (Draft, 1994)

Vapor: use surrogate data (“what-if” scenario.) Page C24: The scenario suggests an inhalation rate of 1.75 rather than the

standard 1.25 used by CEB with no adequate explanation. The scenario

provides no guidance on how to calculate C or whether data is available. In

addition, no explanation of the basis for assuming that C is linear with weight

fraction is provided for these activities.

Electronics - Printed Circuit Card -

Assembly Manufacturing Process Using

Conformal Coating (Draft, 1994)

Vapor: use surrogate data (“what-if” scenario.) Page C31: The equation is presented correctly, but the scenario provides no

guidance on whether surrogate data is available.

Electronics -Semiconductors /

Photolithography (Final, 1994)

Not addressed; releases only.

Electronics - Transformer Manufacturing

(Draft, 1994)

Discussed qualitatively.

Fragrances - Manufacture and Use of

(Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates);

“what-if” scenario based on NIOSH data.

This NIOSH data needs to be evaluated.
30

Generic Scenario (Current Status) Inhalation Method (Descriptors for PDR) Notes

Granular Detergents Manufacture (Final,

March, 1991)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end)

Vapor: Mass Balance Ventilation Model

(bounding and "what-if" scenario, based on

default values used).

Hardwood Plywood manufacturing,

Exposure & Release Scenario (June,

1991)

Not addressed; releases only.

Leather Dyeing Spreadsheet (Final, ND) Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates);

“what-if” scenario if based on monitoring data

 This data needs to be evaluated.

Leather Tanning (Draft) Particulates: OSHA PEL for Chromium

(“what-if” scenario)

Need to evaluate OCIS data for compliance with Chromium standard for this

industry.

Lube Oil Additives (Draft) Vapor: Negligible

Metal Cleaning and Degreasing; SemiAqueous Cleaners for Degreasing (Draft,

1994)

Limited monitoring data from NIOSH studies

of solvent degreasing operations (“what-if”

scenarios)

No explanation is provided to support the assumed linear relationship

between the airborne concentration and vapor pressure. Given that vapor

degreasing is not driven by vapor pressure differences (unlike evaporation), it

is possible that some other parameter may be more important.

Metal Cleaning and Degreasing; Vapor

Degreasing (Final, 1994)

Vapor: Mass balance ventilation model using

emission rates data (bounding and "what-if"

scenario, based on default values used).

Environmental Release: The assessment of environmental release is

expected to represent a best estimate of the industry average emissions for

the equipment category. The estimate is based on an average mass flux rate,

a standard sized degreaser for the category, and a standard duty cycle. 

Paper Dyes - Manufacture and Use of

(Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates.)

Petroleum Extraction; Drilling Muds

(Final, 1991)

Vapors: Generally negligible

Petroleum Extraction; Oil Well

Treatment Chemicals (Final, 1991)

Vapors: Generally negligible
31

Generic Scenario (Current Status) Inhalation Method (Descriptors for PDR) Notes

Petroleum Extraction; Well Casing and

Cementing - Application of Chemicals

(Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimate.)

Page D9: The equation is not a standard equation from the CEB Engineering

Manual. The linear relationship between airborne concentration of mists and

concentration in the solution is not supported, and is questionable as mist

generation is a mechanical process which differs considerably from

evaporation. The scenario does not address whether any surrogate data is

available and how to incorporate the OSHA PEL into the assessment.

Petroleum Extraction; Enhanced Oil

Recovery Steam Stimulation, Steam

Flooding, and Polymer/Surfactant

Flooding - Application of Chemicals 

(Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)

Petroleum refining processing - crude

separation processes and catalytic

cracking (Final, February, 1991)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated, Nickel and Vanadium

(“what-if” scenarios)

Vapor: Mass Balance Ventilation Model

(bounding and "what-if" scenario with

appropriate default values).

Photographic/Film Paper, Manufacturing

of (Draft, ND)

 Weighing of Powders: Textile Dye

Weighing Monitoring data (“what-if”

scenario).

Printing Inks; Newspaper Printing (Draft) Particulates: based on limited monitoring

data (“what-if” scenario).

Printing Inks; Printing Inks- Manufacture

of (Draft, 1994)

Solvents: Semi-empirical model was

developed based on limited monitoring data

(“what-if” scenario.)

Particulates: Based on limited monitoring

data (“what-if” scenario.)

This model has not been evaluated. Based on data from 1981 for various

solvents.

Synthetic Fiber Manufacture (Draft,

1994)

Solvents: OSHA PELs for solvents (“whatif” scenario).

Assumes solvents are the contaminants of interest. Does not address fiber

exposure.

Textile Finishing/Dyeing; Fabric

Finishing (Draft, 1994, currently under

revision)

Not available.
32

Generic Scenario (Current Status) Inhalation Method (Descriptors for PDR) Notes

Textile Finishing/Dyeing; Textile Dyeing

(Final, 1988, currently under revision)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end)

Dye Weighing: Textile Dye Weighing

Monitoring data (mean and high end).

Textile Finishing/Dyeing; Textile Dyeing

Spreadsheet (Final, ND)

Dye Weighing: Textile Dye Weighing

Monitoring data (mean and high end).

Toner Used in Photocopier, Use of PMN

Component (Draft, 1992)

Not addressed; releases only

Water Cooling Towers Chemicals (Final,

ND)

Not addressed; releases only.

Water Treatment Coagulants -

Application (Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates)

Water Treatment Disinfectants -

Application (Draft, 1994)

Particulates: OSHA PEL for Particulates Not

Otherwise Regulated (high end estimates), 

Vapor: Mass Balance Ventilation Model

(bounding or “what-if” scenarios.)

Gases: Use surrogate data (“what-if” scenario.)

Page C55: The equation is not a standard equation from the CEB Engineering

Manual. The linear relationship between airborne concentration of mists and

concentration in the solution is not supported, and is questionable as mist

generation is a mechanical process which differs considerably from

evaporation. The scenario does not address whether any surrogate data is

available and how to incorporate the OSHA PEL into the assessment.

Wood Preservatives - Application of

Waterborne, Using Pressure Treatment

(Draft, 1994)

Particulates: OSHA PEL for Arsenic, and

other PELs (“what-if” scenarios; need to

evaluate OCIS data)

* The Dermal Exposure Assessment Methodology is used in all generic scenarios for estimating dermal contact. In addition, default assumptions are used in predicting the

potential for environmental release for all generic scenarios unless otherwise indicated.

‡

See Table C for additional detail for Generic Scenarios based on monitoring data.
33

Table 3. CEB Generic Scenarios Based on Monitoring Data 

CEB Generic Scenario

Method and Population

Exposure Descriptor

or Type of Estimate

Common Assumptions and Default Values, Variability,

and Uncertainty

Notes

Coatings -

Conventional;

Automotive Spray

Application.

Entire population of

workers who are

employed in facilities

applying finishes to

automobiles by means of

spray coating.

 “what-if” scenario

based on limited

monitoring data from

1981.

Assumes that the NIOSH 1981 study is applicable as a

“what-if” . Inhalation is expected during touch up for

automated operations. 

Limited NIOSH monitoring data based on a 1981 study, as

an 8-hour TWA of total mist based on geometric mean and

variability is: 

 Automobile refinish: 5 mg/m3 using air dry alkyd; urethane

modified alkyd paint (compressed air in a drive-through side

draft booth, 7 cars/shift, 40 min/car) 

Uncertainty: 

The monitoring data is very limited and is dated. Many

thousands of sites performing spray applications using a

variety of application methods and controls, and work

practices. 

We are currently unable to quantify the uncertainty

associated with these estimates due to a lack of data.

NIOSH has evaluated occupational exposure and

control methods used in automobile refinishing

operations. Information has also been submitted with

a few PMN cases. This method has not yet been

updated to reflect the new information.
34

CEB Generic Scenario

Method and Population

Exposure Descriptor

or Type of Estimate

Common Assumptions and Default Values, Variability,

and Uncertainty

Notes

Coatings -

Conventional;

Furniture Spray

Application.

Entire population of

workers who are

employed in facilities

applying finishes to

furniture by means of

spray coating.

 “what-if” scenario

based on limited

monitoring data from

1981. 

Wood furniture coating: 0.1 to 2.5 mg/m3 using an acrylic

lacquer, oleoresin stain, or nitrocellulose lacquer (airless

application method, some compressed air, by robot w/ open

side draft booth); 

 Metal furniture coating: 0.1 to 23.5 mg/m3 using an alkyd

baking enamel or acrylic emulsion (compressed air w/

manual and reciprocator application methods, side draft

booth w/ integral supply air);

Uncertainty: 

The monitoring data is very limited and is dated. There are

hundreds of facilities performing wood or metal furniture

coating. 

We are currently unable to quantify the uncertainty

associated with these estimates due to a lack of data.

Coatings - Radiation

Curable; UV Curable -

Roll Application

Workers applying UV

Curable Coatings via

Roll Application

 “what-if” scenario Based on limited data provided in a PMN submission, the

estimated inhalation exposure due to misting is 0.04 to 0.26

mg/m3.

Uncertainty:

It is not known whether this data is representative of other

operations. The data is limited and has not been fully

evaluated for uncertainty.
35

CEB Generic Scenario

Method and Population

Exposure Descriptor

or Type of Estimate

Common Assumptions and Default Values, Variability,

and Uncertainty

Notes

Metal Cleaning and

Degreasing; SemiAqueous Cleaners for

Degreasing

Workers performing

degreasing using semiaqueous cleaners. 

“what-if” scenario

based on limited

monitoring data.

Based on limited monitoring data collected by NIOSH

during studies of the degreasing industry in 1989 - 1992. 

The monitoring data was collected during operations using

volatile solvents (TCA and TCE). The personal samples (as

8-hour TWAs) range from 8 ppm TCA to 38 ppm TCE. It is

assumed that the operations using volatile solvents are

similar to those using semi-aqueous solvents, and that

exposures would be similar.

Adjustments are made for molecular weight, mole fraction,

etc.

Uncertainty:

It is unknown if the operations are similar. This data has not

been carefully evaluated for applicability to semi-aqueous

operations, and is uncertain. 

No explanation is provided to support the assumed

linear relationship between the airborne

concentration and vapor pressure. Given that vapor

degreasing is not driven by vapor pressure

differences (unlike evaporation), it is possible that

some other parameter may be more important.

Metal Cleaning and

Degreasing; Vapor

Degreasing

Workers performing

degreasing using vapor

degreasers.

“what-if” scenario

based on mathematical

modeling using

emissions data, using

routine default values.

Bounding estimate

using more

conservative default

values.

Measured emission rate information is used in CEB’s

standard “box” model to estimate airborne concentration. 

Uncertainty:

This methodology uses a standard mathematical model to

predict airborne concentration based on measured emission

rate data, and selection of default parameters for ventilation

rate. Based on a comparison with limited monitoring data,

model estimates for two types of degreasers were within one

order of magnitude of the measured data when more routine

default parameters are selected, and one to two orders of

magnitude higher when more conservative default values are

selected. For conveyorized vapor degreasers, the model is

likely to overestimate worker exposures. 
36

CEB Generic Scenario

Method and Population

Exposure Descriptor

or Type of Estimate

Common Assumptions and Default Values, Variability,

and Uncertainty

Notes

Printing Inks; Printing

Inks- Manufacture of

Workers potentially

exposed during

manufacture and use of

printing inks.

“what-if” scenario

based on limited

monitoring data. 

A semi-empirical model was developed based on limited

monitoring data for solvent exposures collected by NIOSH

during a study of one site in 1980. 

Uncertainty:

This data is fairly old and it is not known how representative

this site is of the entire industry. The model has not been

carefully evaluated and is very uncertain.

Adjustments are made for molecular weight, mole fraction,

etc.

The model and monitoring data needs to be

evaluated.

Synthetic Fiber

Manufacture

Entire population of

workers who are

potentially exposed to

specific solvents during

manufacture of synthetic

fibers.

“what-if” scenario. Assumes that solvents are the main focus of the assessment. 

This generic scenario needs to be evaluated.

Uncertainty: Estimates developed using this generic scenario

is very uncertain and must be carefully evaluated. 

 

We are currently unable to quantify the uncertainty

associated with these estimates due to a lack of data.
37

CEB Generic Scenario

Method and Population

Exposure Descriptor

or Type of Estimate

Common Assumptions and Default Values, Variability,

and Uncertainty

Notes

Textile

Finishing/Dyeing;

Textile Dyeing

Entire population of

workers who weigh

powder dyes in textile

processing plants.

Exposure Descriptor: 

Mean and high end

estimate based on the

TDWMS data:

Assumes the TDWMS is representative of exposures of all

dyes used at the facility (and not individual dyes) for the

subpopulation of interest. 

Default values for inhalation exposure: central tendency: 

0.0314 mg x (% solids) x (no. weighings/day) and maximum

exposure range: 0.170 mg x (% solids) x (no.

weighings/day).

Variability: The geometric mean of the distribution of

active colorant was 0.049 mg/m3

, with a geometric standard

deviation of 2.85. The estimated values followed a

lognormal distribution, which is typical of occupational

exposure data. The geometric standard deviation of 2.85 is

typical of occupational exposure data, demonstrating high

variability.

The study found that dye house operations vary

considerably, although the mechanism for weighing and

mixing powder dyes was consistent at those sites studied. 

There was a universal absence of engineering controls to

control dye dust exposure, and industrial hygiene practices

also varied widely.

Uncertainty: There are sampling and non-sampling errors

associated with the study. A predictive model was

developed based on the data collected. Mass weighed was

found to be the best predictor of airborne concentration with

a correlation coefficient (R2) of 0.39.

Estimates of subpopulations (e.g. worker exposure to a

particular dye) are limited by the scope of the study. 

Note: This method is currently being updated and

revised.
38

V. References

1. U.S. Environmental Protection Agency. 1991. Preparation of Engineering Assessments

Volume I: CEB Engineering Manual. Draft. Washington, D.C.: Office of Toxic Substances, 

U.S. Environmental Protection Agency. 

2. U.S. Environmental Protection Agency. 1992. Guidelines for Exposure Assessment. 

Washington, D.C.: Office of Health and Environmental Assistance, U.S. Environmental

Protection Agency. (EPA Pub. No. EPA/600/Z-92/001.) 

3. Carol M. Browner. 1995. Policy for Risk Characterization at the U.S. Environmental

Protection Agency. Washington, D.C.: Office of the Administrator, U.S. Environmental

Protection Agency.

4. Versar, 1984. Exposure Assessment for Retention of Chemical Liquids on Hands. Office of

Toxic Substances, US EPA. Contract 68-01-6271.

5. Popendorf, W.J. and Leffingwell, J.T., 1982. Regulating OP Pesticide Residues for

Farmworker Protection. Residue Review, Vol. 82, pp 156-157.

6. IT Environmental Programs, Inc. and ICF Kaiser Incorporated. 1994. Guidelines for

Statistical Analysis of Occupational Exposure Data. Washington, D.C. U.S. Environmental

Protection Agency, Office of Pollution Prevention and Toxics. EPA Report No. EPA/744/b94/003. 

7. DRAFT Risk Characterization Statement for OPPT Headquarters, March 14, 1996.
39

VI. Appendices
40

 
41

Appendix B. Assumptions Regarding Breathing Rate

and Duration of Exposure

In addition to the assumptions identified in Tables 1 - 3, CEB makes additional

assumptions regarding breathing rate and duration of exposure that may impact whether the

assessment is truly a central tendency, high end, etc., estimate. CEB generally assumes a

breathing rate of 1.25 m3

/hr for occupational exposure. This is based on information developed

by NIOSH in 1976 and represents a breathing rate associated with a volumetric flowrate slightly

above that measured for light work. However, the volumetric flowrate varies as a function of the

type of work being performed, and ranges from about 0.56 m3/hr to 7.9 m3/hr during maximum

work. CEB is monitoring ongoing research on breathing rates in industrial operations and will

update these assumptions as new information becomes available. 

CEB also makes assumptions regarding the duration of exposure, based largely on

information provided or on professional judgement. Information on duration of exposure is

often provided in premanufacture notifications (PMNs) and is also provided through the

CMA/SOCMA/EPA Voluntary Use and Exposure Project. These and other assumptions should

be fully documented in the report, and the uncertainty characterized, as appropriate.
42

Appendix C. Suggestions for Presenting Monitoring Data

 in CEB Assessments

Present data submitted, including as much detail as is possible. The EPA Exposure

Assessment Guidelines recommend providing sufficient background information to explain what

was done and why, including clear documentation of the source of the data and including

references. Important data elements are number of samples, date of sampling, type of sample

taken, sampling and analytical methods utilized, protective equipment worn by the workers,

worker activity, etc. Monitoring data may be collected for a variety of reasons, and the basis for

sample collection should be identified to enable appropriate interpretation of the data collected. 

The assessor should determine the relevancy of the monitoring data to the population being

evaluated, and the quality of the data. When analyzing occupational exposure data, consult the

Guidelines for Statistical Analysis of Occupational Exposure Data, August, 1994. 

Personal confidential information (employee name, social security number) must be held

in confidence and must not be included in CEB reports.

Guidance and Example for Reporting

Industry-Provided Monitoring Data in CEB Reports:

Table XX. Summary of Monitoring Data Submitted by Industry

for Dimethylchickenwire

Company,

Location, and

Year of

Sampling

Worker

Activity

Number of

Samples

Personal Airborne

Concentration, Range

(mg/m3 )*

Personal Protective

Equipment and

Engineering Controls**

ACME Chemicals

(1990, 1991)

Bagging 3*** 0.18 - 0.28 Local exhaust ventilation,

dust mask (worn for

comfort only)

XYZ Chemistry

(1988, 1989,

1990, 1991, 1993)

Bagging 9 < 0.11 - 0.48 Local exhaust ventilation,

half-face respirator

Chemicals R US

(1979-1992)

Process

Operator

5 0.15 - 0.67**** Full-face respirator

(because of acetic acid),

gloves

 * Analysis conducted by collecting total dust samples, dissolving samples followed by GC analysis. Samples were

collected over approximately 7 hours and are 8-hour time-weighted averages except where otherwise noted.

**Equipment and controls as reported by the Company.

***One sample is not reported due to sample fault.

****Short term samples.
43

Figure 1. Schematic of Exposure Estimators for an Unbounded Simulated Population

Distribution.

Appendix D. Definitions of Exposure Descriptors and Related Terminology

from the EPA Guidelines for Exposure Assessment

The exposure descriptors as defined in the EPA Guidelines for Exposure Assessment are

presented in Figure 1.

The exposure descriptors used by EPA are defined as follows:

High-end exposure (dose) estimate - A plausible estimate of individual exposure or dose

for those persons at the upper end of an exposure or dose distribution, conceptually above the

90th percentile, but not higher than the individual in the population who has the highest exposure

or dose.

In developing estimates of high end exposure or dose, the estimate must be on the

expected distribution, and the combination of values assigned to the exposure or dose factors can

be expected to be found in the actual population. The high end estimate of exposure or dose may

be determined directly from the distribution. If no distribution is available, but data on the

parameters used to calculate dose or exposure are available, the distribution can be simulated

using an exposure model or Monte Carlo simulation.

Central tendency exposure (dose) estimate - May be either the arithmetic mean estimate

or the median estimate, but should be clearly labeled as such. Where both the arithmetic mean

and the median are available, it is helpful to present both. For occupational exposures, the

geometric mean should also be presented, but it should be recognized that the arithmetic mean
44

(or median) is often the preferred value for risk assessment purposes.

Arithmetic mean - the sum of all the measurements in a data set divided by the number of

measurements in the data set.

Median - value in the measurement data set such that half of the measured values are

greater and half are less.

In addition to these exposure descriptors, other exposure estimators (e.g., bounding and

“what-if” scenarios) are also used, particularly for screening level assessments. These terms are

defined as follows:

Bounding estimate - an exposure or dose which is higher than any exposure or dose

expected to occur in the actual population. The estimate is clearly outside (higher than) the

distribution of actual exposures. If the bounding estimated value is not significant, then the

pathway can be eliminated from further refinement.

“What-if” scenario - an estimated exposure or dose based on a set of hypothetical

conditions or under a set of conditions for which actual exposure parameter data are incomplete

or nonexistent. The calculated exposure or dose is not intended to provide information about

how likely the combination of exposure parameter values might be in the actual population or

about how many, if any, persons might actually be subjected to the calculated exposure.

If data on the parameters used to calculate dose or exposure are available A bounding

estimate is determined by selecting one or more exposure parameters at the upper end of the

range, and calculating the results. A “what-if” scenario can be developed by constructing a

hypothetical scenario postulated based on available data and information.
45

Appendix E. Potential Areas of Uncertainty Associated with an 

Assessment of Occupational Exposure

The information in this appendix is presented as an example of potential uncertainties

associated with generating an assessment of occupational exposure. It may be helpful in

identifying areas of uncertainty in a specific exposure assessment, although this will vary

depending on the exposure scenario and data and information available with which to construct

the assessment. The general steps and associated uncertainties in determining the occupational

exposure to a population of workers for a given substance of concern include the following:

A. Characterize the industry and the population exposed. 

1. Steps in performing the assessment: 

a) Determine the number of sites where the substance will be manufactured,

processed and used. 

b) Determine the types of processing operations that will occur at the sites. 

c) Determine the types of worker activities (e.g. sampling, drumming, loading and

unloading of tank cars) that will potentially result in occupational exposure.

d) Determine the population of workers who are potentially exposed to the

substance, based on the identified activities.

2. Potential Uncertainties Associated with the Assessment: 

a) Assume that we know the range of and types of processes used for

manufacturing, processing, and using the substance. 

b) Assume that the process changes made over time will not result in an increase in

exposure.

c) Assume that differences in types of equipment used (e.g., a rotary drum filter vs a

tray dryer) between processes will not affect the exposures.

d) Assume that we have identified all potential uses of the substance and that a new

use will not result in additional exposure. 

e) Assume that the worker activities identified represent the range of activities and

the range of potential exposure. 

f) Assume that we know the number of workers potentially exposed per shift and the

number of shifts per site for all of the identified processes in manufacturing,

processing, and use of the substance.

B. Based on the Identified Activities, Evaluate the Potential for Occupational Exposure.

1. Steps in performing the assessment: 
46

a) Determine the physical and chemical properties (e.g., vapor pressure, molecular

weight, physical state, melting point, etc.) of the substance. 

b) Identify the physical form (e.g., vapor, particulate, mist, gas) of the substance for

each worker activity, for each processing operation, during manufacture,

processing and use. 

c) Determine for which workers and for which activities potential exposure will be

assessed. 

d) Determine the frequency and duration of exposure (hours/day and days/year) for

each worker activity, for each processing operation, during manufacture,

processing and use. 

e) Determine the magnitude of exposure by calculating the airborne concentration to

which workers are potentially exposed.

f) Determine what control measures are actually used during manufacturing,

processing, and use of the substance that will mitigate exposure, and to what

extent.

A. If monitoring data is available: 

1) Determine how the samples were collected, and analyzed. 

2) Evaluate the sampling strategy and determine whether the data is

representative of worker exposures of interest (e.g. personal samples and

samples collected for 8 hours are preferable to area samples for

determining occupational exposure). 

3) Determine what QA/QC procedures were used, and the 

accuracy and sensitivity of the analytical method.

 4) Determine the recovery efficiency for the samples and analytical method,

any biases and uncertainties associated with the samples and/or method. 

5) Based on the information, determine the worker activity from the job title

given. 

6) Determine whether the data are representative of other worker exposures

doing similar activities for similar durations at other sites, or industries.

B. If no data is available: 

1) Determine through the use of a model or assumption of compliance with

an OSHA Permissible Exposure Limit (PEL) what the potential for

exposure is.

2. Uncertainties associated with the assessment: 

a) Assume that the physical and chemical properties of the substance are known or

can be determined through models, etc. 

b) If modeled or predicted, assume we know the uncertainty associated with the
47

estimation technique. 

c) Assume that we can identify the physical form of the substance during processing

and handling will not change it (e.g. the manufacturer will always process the

solid substance in solution and not dry and isolate the solid as a particulate). 

d) Assume that the frequency and duration of exposure will not increase over time

and will not result in additional exposure. 

e) Assume that the magnitude of exposure will not increase over time and will not

result in additional exposure.

f) Assume that we have information on the effectiveness of control methods used.

g) Assume that you have enough information available to evaluate the data (e.g. the

sampling strategy, analytical method, worker activities during sampling, etc. are

known). 

h) Assume that the job titles are related to the actual worker activity, although they

are often assigned by personnel specialists and may not correlate to the actual

worker activity. 

I) Assume that the data is representative of exposure of other workers performing

similar activities.

3. Prepare the Exposure Assessment and Characterization 

Once the underlying assumptions and uncertainties have been identified, the next step is

to prepare the assessment of exposure, including the identified assumptions, uncertainties, etc. 

There are several OPPT standard operating procedures and Agency guidance documents which

include recommendations for preparing the assessment of occupational exposure. These

documents, which have been described in this document, should be consulted for additional

information.