Review of ORAUT-RPRT-0097 for Breathing 

Zone to General Area Air Concentration 

Ratios in Small Workrooms

Syed F. Naeem, SC&A, Inc.

Advisory Board on Radiation and Worker Health, 

Subcommittee for Procedure Reviews

November 16, 2023
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ORAUT-RPRT-0097 purpose

 NIOSH evaluated the relationship between breathing zone (BZ) 

to general area (GA) air concentration ratios for the purpose of 

determining inhalation intakes of workers when their respective 

bioassay data are not available

 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 radiological workspace
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RPRT-0097 overview

 BZ air concentrations represented air breathed by workers and GA 

air concentrations represented air in a radiological workspace

 Respirable airborne radioactive material

– In an ideal situation, the air concentration measured at any location within a 

room would be the same as having the BZ:GA ratio = 1

– Complete air mixing rarely occurs, resulting in nonhomogeneous air 

concentrations measured at various locations within the room resulting in the 

BZ:GA ratios distribution shifting away from 1

 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
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RPRT-0097 parameters with the scope of this 

report that affect BZ:GA

Parameters affecting the level of 

mixing of an aerosol

 Room size (in terms of room area)

 Aerosol particle distribution 

 Room ventilation ratio

 Room complexity

Parameters affecting the BZ:GA 

ratio distribution

 Sampler location and radioactive 

aerosol release point locations

 Low-number concentrations of 

dominant aerosol particles in a 

workroom. NIOSH does not 

recommend using this parameter 

for developing BZ:GA ratios
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RPRT-0097 methodology

 Air sample data were evaluated from 5 air sampling studies for 

workrooms areas ranged from 190 ft2 to 1,130 ft2

 Aerosol size particles up to 10.5 μm were evaluated because only 

respirable size particles <20 μm contribute to worker inhalation 

intakes

 Two worker location scenarios were assumed to determine the 

distribution of BZ:GA ratios

 BZ:GA ratios for these scenarios were determined 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
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NIOSH’s RPRT-0097 worker location scenarios

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.
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RPRT-0097 statistical analysis

 NIOSH performed Monte Carlo simulations to combine 

datasets from each study to create a single dataset for BZ 

location scenarios 1 and 2

 The scenario 1 dataset was further subdivided into open and 

obstructed workspaces in the middle of the room to understand 

their impact on BZ:GA ratios
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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
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RPRT-0097 BZ:GA ratio application

 If the use of the BZ:GA ratio distribution can be justified, 

NIOSH provides guidance to select the most appropriate ratio 

from the evaluated BZ:GA ratio distributions table 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
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RPRT-0097 conclusions about scenario 1

 Scenario 1 – open workspaces: BZ:GA ratios did not indicate a 

significant difference between the BZ:GA ratios when the room is 

generally open in the middle.

 Scenario 1 – obstructed workspaces: BZ:GA ratios can be 

significantly higher when the room has a lot of obstructions in the 

middle.

 Scenario 1 – open and obstructed workspaces: BZ:GA ratios 

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.
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RPRT-0097 conclusions about scenario 2

Scenario 2 – open and obstructed workspaces:

 BZ:GA ratios 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.
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RPRT-0097 conclusions about ventilation rates

Individual and combined BZ:GA ratio distributions for scenarios 1 

and 2 indicate that ventilation rates for six different air change 

(AC) rates per hour (6, 9, 10, 12, 15, and 90 AC/hr) have no 

significant effect on the BZ:GA ratio distribution.
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SC&A’s review of RPRT-0097

 SC&A found the approach used 

in RPRT-0097 to develop a 

sampling plan to be reasonable 

and technically correct. 

 SC&A agreed with the two 

worker location scenarios to 

adjust the site-specific GA air 

concentrations to make them 

equivalent to BZ air 

concentrations.

 SC&A found the statistical 

methods used in the sampling 

plan to be acceptable. SC&A 

additionally provided 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.
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SC&A’s review of RPRT-0097 approach to 

BZ:GA concentration ratios

 SC&A is satisfied that the NIOSH’s selection of 5 studies is 

adequate and representative of the population of available data

 SC&A did not identify any issues with the general approach 

used by NIOSH in RPRT-0097 to determine BZ:GA 

concentration ratios in small workrooms 
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SC&A’s review of RPRT-0097 statistical 

methods

 SC&A evaluated statistical methods that generated BZ:GA 

ratios for radiological exposure scenarios. BZ:GA ratios are 

generated by fitting BZ:GA ratio distributions for each of the 

evaluated exposure scenario datasets with lognormal models 

using ROS.

 SC&A concluded that statistical methods for developing the 

BZ:GA ratio distributions to generate GM and GSD values are 

appropriate.
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SC&A’s observation 1

Observation 1: Needs guidance for when data are insufficient to 

select a scenario

 If sufficient data are not available to the dose reconstructor, 

NIOSH should instruct the user to select the most claimantfavorable values

 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
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SC&A’s observation 2

Observation 2: Needs guidance to document professional 

judgements

 NIOSH specified that it is the responsibility of the dose 

reconstructor to justify their decisions

 The guidance in RPRT-0097 should explicitly state that these 

professional decisions be included in the dose reconstruction 

documentation
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Summary of SC&A’s review of RPRT-0097

 SC&A found the technical approach, statistical analysis, 

application, and documentation used to develop RPRT-0097 to 

be valid

 SC&A identified 2 observations about the application of 

RPRT-0097:

– Observation 1: 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

– Observation 2: The guidance in RPRT-0097 should explicitly state that these 

professional decisions be included in the dose reconstruction documentation
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Questions?