Draft

Advisory Board on Radiation and Worker Health

National Institute for Occupational Safety and Health

SC&A’s Evaluation of ORAUT-RPRT-0097, Revision 00, on 

Breathing Zone to General Area Air Concentration Ratios in 

Small Workrooms

Contract No. 75D30119C04183

Document No. SCA-TR-2023-PR097, Revision 0

Prepared by

Syed F. Naeem, PhD

SC&A, Inc.

2200 Wilson Blvd., Suite 300

Arlington, VA 22201-3324

October 16, 2023 

DISCLAIMER

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

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

Occupational Safety and Health (NIOSH) and the Advisory Board on Radiation and Worker 

Health (ABRWH), including its Working Groups or Subcommittees. Documents produced by 

SC&A, such as memorandum, white paper, draft or working documents are not final NIOSH or 

ABRWH products or positions, unless specifically marked as such. This document prepared by 

SC&A represents its preliminary evaluation on technical issues.

NOTICE: This report has been reviewed to identify and redact any information that is protected 

by the Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.
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SC&A, Inc. technical support for the Advisory Board on Radiation and Worker Health’s 

review of NIOSH dose reconstruction program

Document title SC&A’s Evaluation of ORAUT-RPRT-0097, Revision 00, on Breathing 

Zone to General Area Air Concentration Ratios in Small Workrooms

Document number SCA-TR-2023-PR097

Revision number 0 (Draft)

Supersedes NA

Effective date October 16, 2023 

Task manager Kathy Behling [signature on file]

Project manager Bob Barton, CHP [signature on file]

Document reviewer(s)

Kathy Behling [signature on file]

Rose Gogliotti, MS [signature on file]

Bob Barton, CHP [signature on file]

Record of revisions

Revision number Effective date Description of revision

0 (Draft) 10/16/2023 Initial issue
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Table of Contents

List of Tables................................................................................................................... 4

Abbreviations and Acronyms........................................................................................... 5

1 Introduction and Background............................................................................. 6

2 Overview of ORAUT-RPRT-0097 ...................................................................... 6

2.1 Purpose and scope (RPRT-0097, section 1.0, p. 8)........................................... 6

2.2 Introduction (RPRT-0097, section 2.0, pp. 8–12)............................................... 7

2.3 Methodology (RPRT-0097, section 3.0, pp. 12–15) ........................................... 8

2.4 Statistical analysis and conclusions (RPRT-0097, sections 9.0 and 10.0, 

pp. 54–61)........................................................................................................ 12

2.5 BZ:GA ratio application (RPRT-0097, section 11.0, pp. 61–64)....................... 13

3 SC&A’s Review of ORAUT-RPRT-0097 .......................................................... 15

3.1 Review of NIOSH’s approach to BZ:GA concentration ratios........................... 15

3.2 Review of NIOSH’s statistical methods ............................................................ 15

3.3 Evaluation of guidance for applying the BZ:GA ratio data in RPRT-0097 ........ 16

3.4 Review of documentation in ORAUT-RPRT-0097............................................ 17

4 Summary and Conclusions .............................................................................. 17

5 References ...................................................................................................... 17
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List of Tables

Table 1. BZ:GA ratio distributions evaluated by NIOSH for Gonzales et al. (1974) study 

(scenario 1)......................................................................................................... 10

Table 2. BZ:GA ratio distributions evaluated by NIOSH for Gonzales et al. (1974) study 

(scenario 2)......................................................................................................... 10

Table 3. BZ:GA ratio distributions evaluated by NIOSH for Charuau (1987) study ....... 11

Table 4. BZ:GA ratio distributions evaluated by NIOSH for Scripsick et al. (1979a, 

1979b) study....................................................................................................... 12

Table 5. BZ:GA ratio distributions evaluated by NIOSH for Whicker and Moxley (2001) 

study................................................................................................................... 12

Table 6. Summary of the combined BZ:GA ratio distributions evaluated by NIOSH ..... 13
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Abbreviations and Acronyms

ABRWH Advisory Board on Radiation and Worker Health 

AC/hr Air change per hour 

BZ breathing zone 

CEA Commissariat à l’Énergie Atomique

ft foot 

ft2 square feet

GA general area

GM geometric mean

GSD geometric standard deviation 

kg kilogram 

LANL Los Alamos National Laboratory 

m2

 square meter

m3 cubic meter

MMAD mass median aerodynamic diameter

μCi/cm3 microcurie per cubic centimeter

μm micrometer

NH4OH ammonium hydroxide 

NIOSH National Institute for Occupational Safety and Health

ORAUT Oak Ridge Associated Universities Team

PAS personal air sampler 

ROS regression on order statistics 

s second 

SAS stationary air sampler

SRDB Site Research Database

TC transfer coefficient
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1 Introduction and Background

In June 2022, the Advisory Board on Radiation and Worker Health tasked SC&A with a 

technical review of ORAUT-RPRT-0097, “Breathing Zone to General Area Air Concentration 

Ratios in Small Workrooms,” revision 00, issued March 29, 2021 (ORAUT, 2021; 

“RPRT-0097”). In RPRT-0097, the National Institute for Occupational Safety and Health 

(NIOSH) evaluates the relationship between the general area (GA) and breathing zone (BZ) air 

concentrations for small workrooms for the purpose of determining inhalation intakes of workers 

when their respective bioassay data are not available. The air sample data are evaluated in terms 

of BZ air concentrations and room air concentrations measured from GA air samplers. The 

minimum workroom area evaluated in this report is 190 square feet (ft2), and the maximum 

workroom area evaluated is 1,130 ft2. BZ to GA (BZ:GA) ratio distributions are presented for 

these workroom areas to determine if adjustments to the GA air concentrations are needed to 

make them equivalent to the BZ air concentrations. NIOSH emphasizes that the workroom’s 

height is usually less of a factor influencing the aerosol concentration (because of gravitational 

settling) than its other dimensions. Hence, room sizes are evaluated in terms of area for 

determining the applicability of the BZ:GA ratio information in this report to a specific room. 

Additionally, elevated releases are considered to be above the typical BZ elevations and can 

include releases originating at a lower elevation that are propelled above the typical BZ 

elevations (e.g., jet releases, over-pressurization releases, aerosol plumes lofted by heat source, 

etc.).

Two worker location scenarios are presented to make distribution of BZ:GA ratios. NIOSH 

summarized BZ:GA ratios for these scenarios by fitting BZ:GA ratio distribution datasets with 

lognormal models using regression on order statistics (ROS), generating a geometric mean (GM) 

and geometric standard deviation (GSD) for each model. 

This report presents SC&A’s evaluation of the technical approach, statistical methods, and 

documentation used by NIOSH in RPRT-0097 as follows. Section 2 outlines the methods used 

by NIOSH to evaluate BZ:GA concentration ratios, and section 3 presents a critical evaluation of 

the approach, statistical methods, and documentation used by NIOSH. 

2 Overview of ORAUT-RPRT-0097

This section briefly describes RPRT-0097 to develop an understanding of statistical methods 

used by NIOSH to evaluate BZ:GA concentration ratios for various workroom areas. 

2.1 Purpose and scope (RPRT-0097, section 1.0, p. 8)

The report states that its purpose is to evaluate the relationship between the GA and BZ air 

concentrations in the form of BZ:GA ratios for small radiological workrooms or test rooms. A 

“workroom” refers to a real workspace having a single distinguishable air space. A “test room” 

refers to a mockup of a real or hypothetical workspace having a single distinguishable air space. 

BZ air concentrations represent air breathed by workers, and GA air concentrations represent air 

in a workspace or a test room. BZ:GA ratios are used to determine if adjustments to the GA air 

concentrations are needed to make them equivalent to BZ air concentrations in a workspace. BZ 

air concentrations are used to determine inhalation intakes of workers when their bioassay data 
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are not available. The report presents a statistical evaluation of the potential ratios of the BZ air 

concentrations and the GA air concentrations. The use of BZ:GA air concentration ratio 

information should be justified on a case-by-case basis.

2.2 Introduction (RPRT-0097, section 2.0, pp. 8–12)

In an ideal situation, the air concentration measured at any location within a room would be the 

same as having the BZ:GA ratio equal to 1. This means that the concentration of respirable 

airborne radioactive material would be homogenous throughout the airspace in a workroom 

when there is complete air mixing. However, complete air mixing rarely occurs, resulting in 

nonhomogeneous air concentrations measured at various locations within the room. Hence, the 

central tendency (median) of BZ:GA ratios distribution can shift away from 1 because of 

incomplete air mixing at various locations within the room. Incomplete air mixing can also 

increase the spread of the distribution denoted by GSD. The GA air concentration should be 

adjusted to account for the increased uncertainty in the BZ air concentration when the median of 

the BZ:GA ratio distribution becomes significantly greater than 1 or the GSD becomes large. 

NIOSH defines the term “significant” as “practically significant” as opposed to “statistically 

significant” (ORAUT, 2021, p. 8). Hence, the term “significant” in this report means that the 

difference is large enough to influence how a parameter is used or treated in practice.

As noted in section 2.1, the use of the BZ:GA air concentration ratio information should be 

justified on a case-by-case basis due to the large number of potential parameters and scenarios 

influencing BZ and GA air concentrations within a workroom. Hence, BZ:GA ratio information 

should be justified for a user-specific application. 

NIOSH presented the relationship between the GA and BZ air concentrations by identifying 

parameters affecting the level of mixing of an aerosol and parameters only affecting the BZ:GA 

ratio. These parameters are discussed next.

2.2.1 Parameters affecting the level of mixing of an aerosol

There are a large number of parameters that affect the level of mixing of an aerosol within a 

workroom. Less aerosol mixing tends to lead to larger air concentration gradients, and more 

aerosol mixing tends to lead to smaller air concentration gradients. Air concentration gradients 

have a significant and direct effect on BZ:GA ratios and the GA air concentrations in a 

workroom. The analysis should consider the parameters affecting the level of mixing of an 

aerosol when looking to apply BZ:GA ratios to GA air concentrations to make them equivalent 

to BZ air concentrations for the workroom where the GA air samples are collected. 

NIOSH emphasized the following four parameters that tend to have the most effect on the level 

of mixing: (1) room size (in terms of room area), (2) aerosol particle distribution (only respirable 

size particles with aerodynamic diameters < 20 micrometers (μm) because the presence of larger 

nonrespirable particles could result in an unreasonable overestimate of the worker’s intake), 

(3) room ventilation rate, and (4) room complexity. 

2.2.2 Parameters affecting the BZ:GA ratio

According to NIOSH, two dominant parameters affecting the BZ:GA ratio distribution are 

(1) sampler and release locations, and (2) low-number concentrations of dominant aerosol 
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particles in a workroom. For the first parameter, the radioactive aerosol release point location, 

worker location (BZ location), and GA air sampler location can have significant effects on the 

BZ:GA ratio distribution. For the second parameter, low-in-number radioactive particles have a 

relatively high specific activity and radiotoxicity, adversely impacting the collection of 

meaningful and reproducible air samples. Personal air samplers (PASs) are used as a statistical 

sampling device in an environment having only a few to few tens of particles per cubic meters 

(m3

). However, air sample data from workrooms with dominant particles are unreliable because 

of the stochastic nature of sampling low-number concentrations of airborne radioactive particles. 

For this reason, the Oak Ridge Associated Universities Team (ORAUT) does not recommend 

using air sample data from workrooms known to have dominant aerosol particles for developing 

BZ:GA ratios.

In addition to these two dominant parameters, NIOSH adds that there are many other parameters 

and factors that can affect BZ:GA ratio distribution and are “beyond the scope of this report”

(ORAUT, 2021, pp. 10–11). An example given by NIOSH is the evaluation of the relationship 

between the GA and BZ air concentration by considering additional parameters, such as details 

about collection and analysis of individual samples, when these data are available. Continuing 

with the notion, SC&A suggests that the relationship between the GA and BZ air concentration 

could also be evaluated for GA sampler location with respect to the release point and the worker. 

2.3 Methodology (RPRT-0097, section 3.0, pp. 12–15)

NIOSH evaluated the air sample data from the five air sampling studies for small rooms. The 

minimum room area evaluated in this report is 190 ft2

, and the maximum room area evaluated is 

1,130 ft2. Because only respirable size particles (i.e., < 20 μm) contribute to worker inhalation 

intakes, aerosol size particles up to 10.5 μm were evaluated. The worker location (BZ location) 

in a room is usually limited to the air volume intake that is in close proximity to a worker’s head 

or face.

Two worker location scenarios are evaluated by NIOSH to adjust the site-specific GA air 

concentrations to make them equivalent to BZ air concentrations: 

• Scenario 1. The worker and the aerosol release point are always located at the same X, Y

coordinates in a room. This scenario generally applies to acute exposure and represents 

the worst-case scenario that yield the highest BZ:GA ratios.

• Scenario 2. The worker and the aerosol release point are not necessarily located at the 

same X, Y coordinates in a room. The potential BZ locations have the same probability of 

being located anywhere in the room. This scenario represents most radiological 

processing areas that have multiple workstations and workers moving around in a room. 

BZ:GA ratio distributions resulting from scenario 2 would usually be more appropriate 

for assessing chronic exposure scenarios.

For both scenarios, the Z-axis represent vertical aspects of various configurations in studies 

evaluated by NIOSH. NIOSH evaluated scenarios 1 and 2 in five studies presented next. 
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2.3.1 Gonzales et al. (1974)

This study was conducted by Los Alamos National Laboratory (LANL) in 1974 to evaluate the 

relationship between air sampling data from glove box work areas and inhalation risk to the 

worker. A simulated glovebox leak was used in a mockup plutonium test room to evaluate 

aerosol dispersal patterns in a 20- × 20- × 8-foot (ft) tall space. 

Plutonium releases from the glovebox into the test room were simulated using a nonradioactive 

submicron tracer aerosol having mass median aerodynamic diameter (MMAD) aerosol particles 

ranging from 0.640 to 0.86 μm with GSDs ranging from 1.48 to 1.49. Test schemes were 

simulated for 6, 9, and 12 room air changes per hour (AC/hr) and 0°, 90°, and 180° airflow 

directions relative to the aerosol leak flow direction. A light-scattering photometer was used to 

measure room aerosol concentrations at several locations to determine the aerosol dispersal 

patterns from a given test scheme.

NIOSH evaluated this study using nine iso-concentration graphs from Gonzales et al. (1974) for 

the 1- and 2-ft-above aerosol leak-level elevations (4.75 and 5.75 ft above the floor). These 

elevations are selected because the radiological worker locations (BZ location) in most 

radiological processing areas are normally located above the glovebox leak levels. The 

evaluation for iso-concentration graphs was done using the Measurement Log feature in Adobe 

Photoshop CC 20.00 Release, in which iso-concentration graphs were divided into five potential 

air concentration regions for the following four assumed scenarios derived from two scenarios 

presented in section 2.3.

• Scenario 1A. The worker (BZ location) and the aerosol release point were always located 

at the same X, Y coordinates in a test room. Additionally, potential GA air samplers were

randomly located anywhere in the room.

• Scenario 1B. The worker (BZ location) and the aerosol release point were always located 

at the same X, Y coordinates in a test room. Additionally, GA air samplers were randomly 

located anywhere in the room with the exception of the middle of the room. The 

exclusion area for the potential GA sampler locations was defined as a 4- × 6-ft area in 

the middle of the room.

• Scenario 2A. The worker (BZ location) and the aerosol release point were not 

necessarily located at the same X, Y coordinates in a test room. Additionally, potential 

GA air samplers were randomly located anywhere in the room.

• Scenario 2B. The worker (BZ location) and the aerosol release point were not necessarily 

located at the same X, Y coordinates in a test room. Additionally, GA air samplers were

randomly located anywhere in the room with the exception of the middle of the room. 

The exclusion area for the potential GA sampler locations was defined as a 4- × 6-ft area 

in the middle of the room.

The probabilities for each potential BZ:GA ratio combination were evaluated using the area 

fractions for the five air concentration regions for every potential BZ location and GA air 

sampler location combination. A collective scenario 1 (by combining scenarios 1A and 1B) 

BZ:GA ratio distribution dataset for each airflow direction (0°, 90°, and 180°) was fitted with 
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lognormal models using ROS to generate a GM and GSD for each airflow direction. Similarly, a 

collective scenario 2 (by combining scenarios 2A and 2B) BZ:GA ratio distribution dataset for 

each airflow direction (0°, 90°, and 180°) was fitted with lognormal models using ROS to 

generate a GM and GSD for each airflow direction. Tables 1 and 2 show BZ:GA ratio GMs and 

GSDs evaluated by NIOSH for scenarios 1 and 2. 

Table 1. BZ:GA ratio distributions evaluated by NIOSH for Gonzales et al. (1974) study 

(scenario 1)

Airflow direction BZ:GA ratio GM BZ:GA ratio GSD

0° 1.35 3.37

90° 1.59 4.13

180° 0.852 2.00

Source: ORAUT (2021), table 4-4.

Table 2. BZ:GA ratio distributions evaluated by NIOSH for Gonzales et al. (1974) study 

(scenario 2)

Airflow direction BZ:GA ratio GM BZ:GA ratio GSD

0° 1.06 3.86

90° 1.04 6.80

180° 1.08 2.28

Source: ORAUT (2021), table 4-5.

2.3.2 Charuau (1987) 

This French study was conducted by the Commissariat à l’Énergie Atomique (CEA) in 1987. 

NIOSH analyzed these contamination transfer study data for a plutonium laboratory to determine 

BZ:GA ratio GMs and BZ:GA ratio GSDs for two different particle size aerosols, one with a 

MMAD of 2.3 μm and the other with a MMAD of 10.5 μm. Plutonium releases were simulated 

in a 49- × 23- × 15-ft tall laboratory with multiple gloveboxes and workstations. Nonradioactive 

tracer gas and tracer aerosol (helium gas and a fluorescent aerosol) were used to simulate 

plutonium releases. The average ventilation rate in the CEA study was 10 AC/hr. A gas and 

aerosol source release point and 10 sampling locations were located at an elevation of 4.9 ft 

above the floor. The units of air concentrations at sampling locations were reported in terms of 

transfer coefficient TC (seconds per cubic meter (s/m3

)), defined as the ratio of the locally 

measured concentration of gas (m3

/m3) or aerosols (kilograms (kg)/m3) to the emission flux from 

the source of gas (m3/s) or aerosols (kg/s).

NIOSH evaluated BZ:GA air concentration ratio distributions using the two BZ location 

scenarios described in section 2.3. A lognormal model was fitted to the dataset using ROS, 

generating a GM and GSD for each scenario. Additionally, NIOSH used lognormal models for 

the 2.3 μm and 10.5 μm that were combined using Monte Carlo simulation to create a single 

lognormal model for each scenario. Table 3 summarizes BZ:GA ratio distributions for 

scenarios 1 and 2. 
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Table 3. BZ:GA ratio distributions evaluated by NIOSH for Charuau (1987) study

Scenario for aerosols BZ:GA ratio GM BZ:GA ratio GSD

Scenario 1 4.92 2.50

Scenario 2 1.00 2.94

Source: ORAUT (2021), table 5-3.

2.3.3 Munyon and Lee (2002) 

This 2002 air sampling study was performed at Argonne National Laboratory-East during the 

decommissioning of a previously active plutonium glovebox facility in a 28- × 12- × 8-ft tall 

enclosure. The workroom portion of the enclosure was 16- × 12- × 8-ft tall with a reported 

90 AC/hr. Stationary air samplers (SASs) were used to measure the work area GA activity 

concentrations, whereas PASs were used to measure BZ activity concentrations of workers. The 

study was unique because BZ data were collected from actual workers. Both PASs and SASs 

were located at approximately 4.5 ft above the floor. The average activity median aerodynamic 

diameter of aerosol particles was 3 μm with a corresponding average GSD of 2.4. 

NIOSH only evaluated BZ:GA air concentration ratio distributions for scenario 2 (variable 

worker location relative to the release point described earlier in section 2.3). A lognormal model 

was fitted to the dataset using ROS, generating a GM of 1.08 and a GSD of 5.40. 

2.3.4 Scripsick et al. (1979a, 1979b) 

The study was conducted at LANL in 1979 to measure the dilution of contaminants between 

worker BZ and GA air concentrations in a typical workroom inside a plutonium-handling 

facility. Aerosol releases were simulated from 20 potential release locations inside a 30- × 21- × 

13-ft tall workroom. Plutonium-related work was performed in gloveboxes. A solution of 

fluorescein in NH4OH was used to generate the test aerosol, which was detectable at an air 

concentration of 0.1 μg/m3. Furthermore, the generated aerosol had a count median aerodynamic 

diameter of 0.35 μm with a GSD of 2.1. The ventilation rate for the workroom was 12 AC/hr. 

Fixed and continuous GA area samplers were used to measure workroom air concentrations. 

Fixed area samplers along the glovebox faces were located at ~6.6 ft above the floor, whereas 

continuous air samplers were located at 3.2 ft above the floor. The BZ location was 1.3 ft above 

the release location, i.e., 5.6 ft above the floor. Workroom floorplan with ventilation system 

components and air sampler locations can be seen in RPRT-0097, figure 7-1. Release locations 

used in the study can be seen in RPRT-0097, figure 7-2. 

NIOSH evaluated BZ:GA air concentration ratio distributions using the two BZ location 

scenarios described earlier in section 2.3. A lognormal model was fitted to the dataset using 

ROS, generating a GM and GSD for each scenario. Additionally, lognormal models for the 

2.3 μm and 10.5 μm were combined using Monte Carlo simulation to create a single lognormal 

model for each scenario. Table 4 summarizes BZ:GA ratio distributions for scenarios 1 and 2. 
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Table 4. BZ:GA ratio distributions evaluated by NIOSH for Scripsick et al. (1979a, 

1979b) study

Scenario for aerosols BZ:GA ratio GM BZ:GA ratio GSD

Scenario 1 30.5 3.31

Scenario 2 1.43 3.64

Source: ORAUT (2021), table 9-1, table 9-4.

2.3.5 Whicker and Moxley (2001) 

The study was conducted by LANL personnel in 2001 at the Savannah River Site C-Lab used as 

a low-level plutonium chemistry workroom. The workroom dimensions were approximately 20- 

× 13- × 10-ft tall with a ventilation rate of approximately 15 AC/hr. The workroom contained 

multiple workstations, hoods, and gloveboxes. Radioactive aerosol releases were simulated with 

a nontoxic oil (dioctyl sebacate) having 0.01 to 2 μm size range from six potential release 

locations R1–R6 in the form of 60-seconds “puff-type” releases. A total of 18 simulated releases 

resulting from three separate releases at each of the six locations were used to measure the 

variability of the aerosol dispersion. Aerosol concentrations at 16 sampling locations were 

measured with 16 laser particle counters. 

NIOSH once again evaluated BZ:GA air concentration ratio distributions using the two BZ 

location scenarios described in section 2.3. A lognormal model was fitted to the dataset using 

ROS, generating a GM and GSD for each scenario. Additionally, lognormal models for 

scenario 2 were combined using Monte Carlo simulation to create a single dataset in order to 

perform a lognormal model fit on the new dataset using ROS. Table 5 summarizes BZ:GA ratio 

distributions for scenarios 1 and 2. 

Table 5. BZ:GA ratio distributions evaluated by NIOSH for Whicker and Moxley (2001)

study

Scenario for aerosols BZ:GA ratio GM BZ:GA ratio GSD

Scenario 1 2.28 3.18

Scenario 2 1.02 4.31

Source: ORAUT (2021), table 8-2.

2.4 Statistical analysis and conclusions (RPRT-0097, sections 9.0 and 10.0, 

pp. 54–61)

Monte Carlo simulations were performed to combine datasets from each study to create a single 

dataset for BZ location scenarios 1 and 2. The scenario 1 dataset was subdivided into open and 

obstructed workspaces in the middle of the room to understand their impact on GZ:GA ratios. A 

lognormal model was then fitted to each dataset using ROS, generating BZ:GA ratio GMs and 

GSDs (RPRT-0097, table 10-1, ratios reproduced here in table 6) from the fitted lognormal 

distribution. In the quantile-quantile plots, the quantiles are from the fitted lognormal 

distribution, and the horizontal lines are the 50th, 84th, and 95th percentiles for the plotted data 

(ORAUT, 2020). 
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Table 6. Summary of the combined BZ:GA ratio distributions evaluated by NIOSH

Scenario for aerosols BZ:GA ratio GM BZ:GA ratio GSD

Scenario 1 – open workspaces 1.39 3.27

Scenario 1 – obstructed workspaces 12.0 4.11

Scenario 1 – open and obstructed workspaces 2.95 5.03

Scenario 2 – open and obstructed workspaces 1.08 4.02

Source: ORAUT (2021), table 10-1.

2.4.1 NIOSH’s conclusions

NIOSH’s evaluation had the following conclusions: 

• Table 6, row 1: BZ:GA ratios for scenario 1 did not indicate a significant difference 

between the BZ:GA ratios when the room is generally open in the middle. 

• Table 6, row 2: BZ:GA ratios for scenario 1 can be significantly higher when the room 

has a lot of obstructions in the middle. 

• Table 6, row 3: BZ:GA ratios for scenario 1 indicated a significant difference between 

the BZ:GA ratios when the room is generally open in the middle rather than when the 

room has significant obstructions in the middle. Therefore, it might be more appropriate 

to use a BZ:GA ratio based only on the data from rooms with obstructions in the middle. 

• Table 6, row 4: BZ:GA ratios for scenario 2 did not indicate a significant difference 

between the BZ:GA ratios when the room is generally open in the middle versus when 

the room has a lot of obstructions in the middle. No special consideration is warranted for 

this scenario.

• Individual and combined BZ:GA ratio distributions for scenarios 1 and 2 indicate that 

ventilation rates for six different air change rates (6, 9, 10, 12, 15, and 90 AC/hr) have no 

significant effect on the BZ:GA ratio distribution.

2.5 BZ:GA ratio application (RPRT-0097, section 11.0, pp. 61–64)

Section 11.0 provides guidance to the dose reconstructor on the appropriate application of the 

BZ:GA ratio data. The use of the BZ:GA ratio information is limited to radiological releases with 

relatively long-lived radionuclides in workrooms. The uses of the BZ:GA ratio information need 

to be justified on a case-by-case basis. The justification should consider five key parameters in 

the application of the generic BZ:GA ratio distributions from table 10-1 of RPRT-0097 to sitespecific GA air sample results as follows: (1) room size, (2) aerosol particle distribution, 

(3) room ventilation rate, (4) room complexity, and (5) the presence of dominant particles. 

To assist the dose reconstructor in determining whether the BZ:GA ratios are appropriate for 

various site-specific applications, NIOSH provides expanded guidance on the five key 

parameters as follows: 

1. Room size: Due to the potentially high variability in the term “small workroom,” NIOSH 

specifies that the ratios should be used for room sizes that are reasonably comparable to 

those evaluated in the studies, which ranged from 17.6 to 105.0 square meters (m2

) (190–
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1,130 ft2). The BZ:GA ratios should not be used for rooms greater that 105.0 m2

(1,130 ft2

). In addition, these ratios should not be used for scenarios with elevated 

releases considered to be above the BZ elevation.

2. Particle size: If particle size distribution is known for the GA air samples, consideration

should be given to adjusting the workroom’s GA air sample results to exclude the

nonrespirable fraction before applying the BZ:GA ratio.

3. Ventilation rate: The studies showed that room air change rates (AC/hr) did not have a

significant effect on the BZ:GA ratio distribution. Therefore, NIOSH recommends that

these ratios can be used in all rooms except for the most extreme air change rates.

4. Room complexity: The largest effect on BZ:GA ratio distributions resulted from the

complexity of the room and ventilation flow patterns, but this effect was primarily limited

to scenario 1 when there are obstructions in the middle of the room. When evaluating

exposures similar to scenario 2, the BZ:GA ratio data are likely applicable to all small

workrooms.

5. Dominant particles: Air sample data from workrooms with dominant particles are very

unreliable, and using these data should be avoided when possible. If using these data is

unavoidable, intake distributions should be calculated instead of point estimate.

If the use of the BZ:GA ratio distribution can be justified, NIOSH provides guidance to the dose 

reconstructor to select the most appropriate ratio distribution from table 10-1 of RPRT-0097 

based on whether the exposure scenario is best represented by scenario 1 or scenario 2. The GA 

air sample result for a workroom is then multiplied by the appropriate BZ:GA ratio distribution 

to make the measured air concentrations equivalent to BZ air concentrations in a radiological 

workroom. 

To illustrate how to use the various BZ:GA ratio distributions to convert GA air concentrations 

into equivalent BZ air concentrations for determining inhalation intakes of workers when their 

respective bioassay data are not available, NIOSH provides three examples in section 11.0. The 

following examples use a BZ:GA ratio distribution with a GM of 1.08 and GSD of 4.02 from 

table 10-1 of RPRT-0097 evaluated for the scenario 2 model (refer to section 2.3 of this report).

2.5.1 GA air concentration (lognormal distribution)

Equations 1 and 2 (equations 11-1 and 11-2 in RPRT-0097) are used to calculate the equivalent 

GMBZ and GSDBZ when the GA air concentration has a lognormal distribution with a GMGA and 

GSDGA. The BZ:GA ratio distribution is also used to make the applicable BZ:GA ratio 

distribution equivalent to the probability distribution for the BZ air concentration. 

(1)

(2)

In these equations, GMBZ represents the GM of the BZ air concentration distribution, GSDBZ

represents the GSD of the BZ air concentration distribution, GMBZ:GA represents the GM of the 
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applicable BZ:GA ratio distribution, GSDBZ:GA represents the GSD of the applicable BZ:GA 

ratio distribution, GMGA represents the GM of the GA air concentration distribution, and GSDGA

represents the GSD of the GA air concentration distribution. 

For example, if GMGA = 10 μCi/cm3 and GSDGA = 4.0, then using GMBZ:GA and GSDBZ:GA values 

presented in the last paragraph in section 2.5 of this report, the GMBZ = 11 μCi/cm3 and 

GSDBZ = 7.1. 

2.5.2 GA air concentration (constant) 

Equations 3 and 4 (equations 11-5 and 11-6 in RPRT-0097) are used to calculate the equivalent 

GMBZ and GSDBZ when the GA air concentration is a constant, denoted by CGA. Additionally, the 

BZ:GA ratio distribution is used to make the applicable BZ:GA ratio distribution equivalent to 

the probability distribution for the BZ air concentration.

GGGGBBBB = CCGGGG × GGGGBBBB (3) :GGGG

GGGGGGBBBB = GGGGGGBBBB (4) :GGGG

For example, if CGA = 10 μCi/cm3, then using GMBZ:GA and GSDBZ:GA values in the last 

paragraph in section 2.5 of this report, the GMBZ = 11 μCi/cm3

 and GSDBZ = 4.02. 

2.5.3 GA air concentration (not constant)

The BZ:GA ratio distribution is multiplied to the GA air concentration distribution using Monte 

Carlo techniques when the GA air concentration distribution is not constant. That is, the GA air 

concentration has a distribution other than a lognormal distribution (e.g., a normal distribution 

with an arithmetic mean and standard deviation). 

3 SC&A’s Review of ORAUT-RPRT-0097

The following is a summary of SC&A’s confirmation of the approach, statistical analysis, 

application, and documentation used by NIOSH to develop RPRT-0097. 

3.1 Review of NIOSH’s approach to BZ:GA concentration ratios

The studies evaluated by NIOSH are limited to a minimum workroom area of 190 ft2 and a 

maximum workroom area of 1,130 ft2. Additionally, NIOSH stated that as the workroom size 

increases beyond the maximum workroom area evaluated, there is a point where it will no longer 

be appropriate to use the BZ:GA ratio information presented in this report. 

SC&A is satisfied that NIOSH’s selection of studies is adequate and representative of the 

population of available data. Additionally, SC&A did not identify any issues with the general 

approach used in RPRT-0097 to determine BZ:GA concentration ratios in small workrooms. 

3.2 Review of NIOSH’s statistical methods

SC&A evaluated the statistical methods employed by NIOSH in RPRT-0097 for evaluating the 

relationship between the GA and BZ air concentrations in the form of BZ:GA ratios to determine 

if adjustments to the GA air concentrations are needed to make them equivalent to BZ air 
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concentrations in a workspace. However, the evaluated BZ:GA ratio distributions are limited to 

small radiological workrooms in which BZ air concentrations represent air breathed by workers 

and GA air concentrations represent air in a radiological workspace. 

BZ air concentrations are calculated using equations presented in section 2.5 of this report and 

used to determine inhalation intakes of workers when their bioassay data are not available.

3.2.1 Parameters affecting the relationship between the GA and BZ air concentrations

SC&A agreed with the methodology employed by NIOSH for establishing the relationship 

between the GA and BZ air concentrations, including the following parameters affecting the 

level of mixing of an aerosol and parameter only affecting the BZ:GA ratio: 

• The parameters that tend to affect the level of mixing the most are (1) room size, 

(2) aerosol particle distribution (only respirable size particles with aerodynamic diameters 

<20 μm), (3) room ventilation rate, and (4) room complexity. 

• The parameter that tends to affect the BZ:GA ratio is the presence of low-number 

concentrations of dominant aerosol particles in air sample data. Both ORAUT and 

NIOSH do not recommend using this parameter for developing BZ:GA ratios. 

3.2.2 Scenarios for acute and chronic radiation exposures

SC&A agrees with the two worker location scenarios summarized in section 2.3 of this report to 

adjust the site-specific GA air concentrations to make them equivalent to BZ air concentrations. 

3.2.3 BZ:GA, GM, and GSD

SC&A reviewed air sample data analyzed by NIOSH from the five air sampling studies for small 

workrooms. BZ:GA ratios for acute and chronic radiological exposure scenarios in table 10-1 of 

RPRT-0097 are the result of fitting BZ:GA ratio distributions datasets with lognormal models 

using ROS. This generates a GM and GSD for each scenario and is accomplished by performing 

Monte Carlo simulations to combine datasets from each study to create a single dataset for BZ 

location scenarios for acute and chronic exposures. 

SC&A found NIOSH’s statistical methods in RPRT-0097 for developing the BZ:GA ratio 

distributions to generate GM and GSD values to be appropriate. 

3.3 Evaluation of guidance for applying the BZ:GA ratio data in RPRT-0097

SC&A recognizes that dose reconstructors will encounter a variety of exposure scenarios that 

will likely require considerable professional judgement to justify and select the appropriate 

BZ:GA ratio distribution. Although SC&A acknowledges that RPRT-0097 provided the user 

with some guidance to assist in making these decisions, SC&A had the following two concerns. 

Observation 1: Needs guidance for when data are insufficient to select a scenario

Based on SC&A’s knowledge of the dose reconstruction process, SC&A questions whether the 

dose reconstructor will have access to the data required to make a reasonable decision about the 

appropriate scenario to use on a case-by-case basis. If sufficient data are not available to the dose 

reconstructor, RPRT-0097 should instruct the user to select the most claimant-favorable values.
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Observation 2: Needs guidance to document professional decision

NIOSH in section 11 of RPRT-007 specified that it is the responsibility of the dose reconstructor 

to justify their decisions. The guidance in RPRT-0097 should explicitly state that this 

professional decision be included in the dose reconstruction documentation. 

3.4 Review of documentation in ORAUT-RPRT-0097

SC&A’s review of RPRT-0097 did not identify any notable documentation or clarification 

issues. The report provides adequate data to understand NIOSH’s approach and methods for 

developing the BZ:GA ratios.

4 Summary and Conclusions

SC&A found the approach used in RPRT-0097 to develop a sampling plan to be reasonable and 

technically correct. 

SC&A found the statistical methods used in the sampling plan to be acceptable. In section 3.2 of 

this review, SC&A provides an expanded discussion of the effects that changes in variable 

parameters could have on the results. 

SC&A did not identify any documentation issues that would affect the readability or application 

of the sampling plan. 

However, SC&A did have two observations about the applicability of RPRT-0097 in the dose 

reconstruction process (refer to section 3.3). 

5 References

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workplace aerosol monitoring: October 28–30, 1985 Napa, California (PNL-SA-14225) 

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Gonzales, M., Ettinger, H. J., Stafford, R. G., & Breckinridge, C. E. (1974). Relationship 

between air sampling data from glove box work areas and inhalation risk to the worker (LA5520-MS)., University of California, Los Alamos Scientific Laboratory. SRDB Ref. ID 172405 

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