NIST Technical Note 1925
 

Simulation of Residential Carbon Monoxide 

Exposure Due to Generator Operation in 

Enclosed Spaces 

Steven J. Emmerich 

Brian Polidoro 

W. Stuart Dols 

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NIST Technical Note 1925 

Simulation of Residential Carbon Monoxide 

Exposure Due to Generator Operation in 

Enclosed Spaces 

Steven J. Emmerich 

Brian Polidoro 

W. Stuart Dols 

Energy and Environment Division 

Engineering Laboratory 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1925 

September 2016 

U.S. Department of Commerce 

Penny Pritzker, Secretary 

National Institute of Standards and Technology 

Willie E. May, Under Secretary of Commerce for Standards and Technology and Director 
Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1925

Natl. Inst. Stand. Technol. Tech. Note 1925, 49 pages (September 2016) 

CODEN: NTNOEF 

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ABSTRACT 

The U.S. Consumer Product Safety Commission (CPSC) and others are concerned about the 

hazard of acute carbon monoxide (CO) exposures from portable gasoline powered generators that 

can result in death or serious adverse health effects in exposed individuals. As of May 15, 2015, 

the CPSC databases contain records of at least 702 deaths (involving 523 incidents) from CO 

poisoning in the U.S. caused by consumer use of a generator in the period of 2004 through 2014 

(Hnatov 2015). There were an additional 49 CO poisoning deaths (involving 39 incidents) 

associated with consumer use of both a generator and at least one other CO-producing consumer 

appliance, for a total of 751 CO poisoning deaths (involving 562 incidents) associated with 

generators for the same 11-year period. The majority of these deaths occurred when consumers 

used a generator in an enclosed or partially enclosed space or outdoors near an open door, window 

or vent. While avoiding the operation of such generators in or near an enclosed space is expected 

to reduce indoor CO exposures significantly, it may not be realistic to expect such usage to be 

eliminated completely. Another means of reducing these exposures would be to decrease the rate 

at which CO is emitted from these devices. A computer simulation study was conducted to 

provide CPSC staff with information to support comparisons of modeled residential CO exposures 

reflecting operation of current designs of portable engine-driven electric generators, inside homes 

or in attached garages. These results were compared to simulated operation of reduced emission 

generators meeting a potential CO emission rate limit performance requirement being considered 

by CPSC staff under portable generator rulemaking activities. These simulations employed the 

multizone airflow and contaminant transport model CONTAM, which was applied to a set of 40 

buildings (consisting of 37 houses and 3 detached garages, considered broadly representative of 

fatal CO poisoning incidents reported in CPSC databases) that are primarily based on a collection 

of models representative of the U.S. housing stock. This report presents sample CO and 

carboxyhemoglobin (COHb) simulation results for three of the houses and one of the garages 

modeled. The results presented demonstrate that generators with the reduced CO emission rates 

result in peak CO concentrations that can be reduced by 40 % to more than 90 % depending on the 

specific case being analyzed. The reduced CO emission rates also result in significant reductions 

in COHb in many cases. Additionally, use of a thermal building model coupled with the airflow 

and IAQ model to properly account for thermal effects was shown to be important as the 

interaction of the generator’s heat generation and the ambient weather conditions can significantly 

impact both air change rates and interzone airflow patterns in the buildings. 

KEYWORDS: carbon monoxide; CONTAM; emergency generators; multizone airflow model; 

simulation 

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TABLE OF CONTENTS 

1. INTRODUCTION 1
 

2. ANALYSIS METHOD 3
 

2.1 Modeling approach 3
 

2.2 Baseline house models 4
 

2.2.1 Description of homes 4
 

2.2.2 Source locations and emission rates 7
 

2.3 Simulation cases and output analysis 8
 

2.4 COHb time profile calculation 8
 

3. RESULTS 9
 

3.1 Sample results for a small manufactured house (MH1mod) 9
 

3.2 Sample results for a mid-sized detached house with basement
 

and integral garage (DH-45mod) 19
 

3.3 Sample results for a large 2-story detached house with garage (DH-12) 26
 

3.4 Sample results for a large garage with workshop (GAR3) 33
 

4. SUMMARY AND DISCUSSION 36
 

5. ACKNOWLEDGEMENTS 37
 

6. REFERENCES 37
 

APPENDICES 

A. House Characteristics 39
 

B. Source Locations and Modifications for Each Building 46
 

C. Analysis of Gen X CO Emission Ratio at Reduced O2 vs Ambient 49
 

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1. INTRODUCTION 

The U.S. Consumer Product Safety Commission (CPSC) and others are concerned about the 

hazard of acute carbon monoxide (CO) exposures from portable gasoline powered generators that 

can result in death or serious adverse health effects in exposed individuals. As of May 15, 2015, 

the CPSC databases contain records of at least 702 deaths (involving 523 incidents) from CO 

poisoning caused by consumer use of a generator in the period of 2004 through 2014 (Hnatov 

2015). There were an additional 49 CO poisoning deaths (involving 39 incidents) associated with 

consumer use of both a generator and at least one other CO-producing consumer appliance, for a 

total of 751 CO poisoning deaths (involving 562 incidents) associated with generators for the 

same 11-year period. The majority of these deaths occurred when consumers used a generator in 

an enclosed or partially enclosed space or outdoors near an open door, window or vent. While 

avoiding the operation of such generators in or near an enclosed space is expected to reduce indoor 

CO exposures significantly, it may not be realistic to expect such usage to be eliminated 

completely. 

Another means of reducing these exposures would be to decrease the rate at which CO is emitted 

from these devices. The magnitude of such reductions needed to reduce exposures to some 

specific level depends on the complex relationship between CO emissions from these generators 

and multiple factors influencing occupant exposure. Technically achievable levels of CO 

emissions reduction have been studied by NIST through an experimental investigation of CO 

emissions from generators in a shed and in a house. These investigations included measurements 

on prototype generators that were modified to reduce their CO emission rates (Emmerich et al. 

2013). That study has provided a set of unique measurements of CO emission rates for both 

unmodified and modified generators. 

The issue of how CO emission rates relate to occupant exposure and health impacts involves the 

interaction between generator operation, house characteristics, weather conditions, occupant 

activity, and health status. National Institute of Standards and Technology (NIST) Technical Note 

1782 (Persily et al. 2013) described a computer simulation study conducted to evaluate indoor CO 

exposures as a function of generator source location and CO emission rate to support life-safety 

based analyses of potential CO emission limits. Those simulations employed the multizone airflow 

and contaminant transport model CONTAM (the most recent available version is described in 

detail by Dols and Polidoro 2015), which was applied to a collection of 83 single-family, detached 

dwellings and 4 manufactured homes that are representative of the U.S. housing stock for these 

housing types. All house heating, ventilating and air-conditioning (HVAC) systems were modeled 

as “off” in the simulations based on not having electric power during an outage. The project 

described in this report extended and modified the methods used in the previous work. This new 

work will support CPSC staff efforts to make, for a range of generator sizes, more accurate 

comparisons between likely CO exposures throughout homes resulting from operation of current 

portable engine-driven electric generators in residences and attached garages, as well as exposures 

from generators with low CO emissions that meet a technical feasibility-based performance 

requirement that CPSC staff is considering under its portable generator rulemaking activity. 

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Specific extensions and modification in this effort relative to the previous CO modeling study 

described in Technical Note 1782 include: 

•	 accounting for temperature distributions within the simulated houses, accounting for 

ambient weather conditions and the heat released by the generator, using a version of the 

CONTAM model with heat transfer modeling capability; 

•	 consideration of generator size-dependent CO emission rates; 

•	 use of constant CO emission rates, independent of the source location O2 level, for
 

modeling generators meeting the potential performance requirements;
 

•	 use of generator size-dependent run times; 

•	 calculation of percent carboxyhemoglobin (COHb) profiles for generic adult occupants in 

individual rooms using more refined, short term inhalation rates (respiratory minute 

volumes (RMV)) characteristic of indoor activities over 24 hours; 

•	 modeling a subset of the 87 homes included in the previous study, including some
 

modifications to the floorplans;
 

•	 modeling 3 additional buildings to represent various sizes and styles of detached garages; 

and 

•	 reporting modeling results of all rooms, including unconditioned spaces such as basements 

and garages. 

A total of over 45 thousand individual 24-hour simulations were conducted. This report presents 

detailed CO and COHb simulation results for three of the houses and one of the detached garages. 

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2. ANALYSIS METHOD 

This simulation study was conducted to evaluate indoor CO exposures as a function of generator 

source location and CO emission rate in order to support cost-benefit analyses of potential CO 

emission limits for generators. These simulations employed the multizone airflow and 

contaminant transport model CONTAM, which was applied to 40 buildings including 37 versions 

of dwellings drawn from a collection that are representative of the U.S. housing stock (Persily et 

al. 2006) and three new garage buildings. These buildings were identified as broadly 

representative of fatal generator-related CO poisoning incidents reported in CPSC databases. A 

total of over 45 thousand individual 24-hour simulations were conducted that cover a range of 

house layouts and sizes, airtightness levels and weather conditions, as well as generator locations, 

CO source strengths and operating schedules. The locations include attached garages, crawlspaces 

and basements, in the houses that have such spaces, and two interior rooms in all of the houses 

considered. This section describes the approach used to perform the simulations, including the 

simulation program, the houses, the simulated generator locations and associated CO emission 

rates, and the manner in which the simulations were performed and the output analyzed. 

2.1 Modeling approach 

Using these homes (described below), indoor CO concentrations were calculated using the 

multizone airflow and contaminant transport model CONTAM (Dols and Polidoro 2015) over a 

range of source (generator) locations, CO emission rates, and weather conditions. As described 

below, these simulations yielded CO concentrations in the rooms of each house as a function of 

time during the 24-hour analysis interval, which included a scheduled period of CO emissions 

from generator operation followed by a period with no CO emissions. These concentrations were 

then used to calculate COHb values for an occupant spending the full 24 hours in each occupiable 

zone. This section describes the manner in which these simulations were conducted and the results 

analyzed. 

CONTAM is a simulation tool for predicting airflows and contaminant concentrations in 

multizone building airflow systems. When using CONTAM, a building is represented as a series 

of interconnected zones (e.g. rooms), with the airflow paths (e.g., leakage sites, open doors) 

between the zones and the outdoors defined as mathematical relationships between the airflow 

through the path and the pressure difference across it. Outdoor weather conditions are also input 

into CONTAM, as they are key determinants of pressure differences across airflow paths in 

exterior walls. System airflow rates must also be defined to capture their effects on building and 

interzone pressure differences. These inputs are used to define mass balances of air into and out of 

each zone, which are solved simultaneously to determine the interzone pressure relationships and 

resulting airflow rates between each zone, including the outdoors. These airflow rates can be 

calculated over time as weather conditions and system airflow rates change. Once the airflows are 

established, CONTAM can then calculate contaminant concentrations over time in each building 

zone based on contaminant source characteristics and contaminant removal information, such as 

that associated with filtration. CONTAM has been used for several decades, and a range of 

validation studies have demonstrated its ability to reliably predict building air change rates and 

contaminant levels (Emmerich 2001, Emmerich et al. 2004, Poppendieck et al. 2016). Emmerich 

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and Dols (2015) report a validation study that specifically evaluated the model’s capability to 

predict CO concentrations in a test house from portable generator operation in an attached garage. 

2. 2 Baseline house models 

2.2.1 Description of homes 

The house models used in the simulations are based on a collection of dwellings that were 

previously defined by Persily et al. (2006), which includes just over 200 dwellings that together 

represented 80 % of the U.S. housing stock. Those dwellings are grouped into four categories: 

detached (83 homes), attached (53 homes), manufactured (4 homes) and apartments (69). The 

definition of that set of dwellings was based on the following variables using the US Census 

Bureau’s American Housing Survey (AHS) (HUD 1999) and the US Department of Energy’s 

(DOE) Residential Energy Consumption Survey (RECS) (DOE 2005): housing type, number of 

stories, heated floor area, year built, foundation type, presence of a garage, type of heating 

equipment, number of bedrooms, number of bathrooms, and number of other rooms. Appendix A 

summarizes the characteristics of these dwellings and identifies the corresponding CONTAM 

project file name and associated floor plan. In addition to defining the dwellings, multizone 

representations were created in the airflow and contaminant transport model CONTAM to support 

their use in analyzing a range of ventilation and indoor air quality issues. The project files and 

floor plans can be downloaded at the CONTAM website www.bfrl.nist.gov/IAQanalysis under 

Case Studies. However, as discussed below, these files were modified for the purposes of this 

analysis. 

Based on the CPSC analysis of CO poisoning death incidents from 2004 through 2012 (Hnatov 

2015), a subset of the NIST suite of homes collection described above (in some cases with 

modifications) were used for this analysis, and includes 31 detached house (DH) models, 4 

attached house (AH) models, and 2 manufactured house (MH) models. The modifications made to 

the models are described in Appendix B. Additionally, 3 new detached garage (GAR) buildings 

were defined and modeled including 2 single-zone garage/sheds (1 car size and 2 car size) and 1 

larger garage/shed with a separate work space inside. None of the apartment models were 

employed due to the challenge in accounting for airflow between units and the lack of air leakage 

data for the partitions between units. 

Air handling system operation: While the homes in the NIST suite of homes collection include air 

handling systems for heating and cooling, this analysis was based on the assumption that the 

forced-air distribution systems were not operating due to a power outage. This is consistent with 

the CPSC analysis of the CO incident database, which does not include incidents where the 

generator was used to operate the central HVAC system. Similarly, all local exhaust fans (kitchen 

and bath) were also assumed to be off. 

Weather conditions and wind exposure: Each house and generator source combination was 

analyzed for 28 individual days. Each of the 28 simulations employed a different day of weather 

conditions, including outdoor temperature, wind speed and wind direction, that varied each day on 

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an hourly basis. These 28 days of weather (used in the previous study) correspond to two weeks of 

cold weather (due to the observed frequency of events during the winter season), one week of 

warm and one week of mild. The hourly weather data for these three conditions were a subset of 

typical weather files for the following three cities: Detroit MI (cold), Miami FL (warm) and 

Columbus OH (mild). Table 1 presents a summary of the weather conditions for the 28 days in the 

form of daily average, minimum and maximum outdoor temperatures and wind speeds. 

Table 1 Summary of Hourly Weather Data Used in Simulations 

Day Outdoor temperature, °C (°F) Wind speed, m/s (mph) 

Average Minimum Maximum Average Minimum Maximum 

1-Jan 0.7 (33.3) -1.7 (28.9) 5.6 (42.1) 3.2 (7.2) 0.0 (0.0) 5.7 (12.8) 

2-Jan 6.1 (43.1) 0.0 (32.0) 12.2 (54.0) 3.9 (8.8) 2.1 (4.7) 5.7 (12.8) 

3-Jan 2.5 (36.6) 1.1 (34.0) 4.4 (39.9) 3.1 (6.8) 2.1 (4.7) 4.1 (9.2) 

4-Jan 0.9 (33.6) 0.0 (32.0) 1.7 (35.1) 2.9 (6.6) 0.0 (0.0) 4.6 (10.3) 

5-Jan -2.9 (26.8) -5.0 (23.0) 0.0 (32.0) 5.8 (13.1) 4.1 (9.2) 8.2 (18.3) 

6-Jan -3.3 (26.1) -5.0 (23.0) -1.7 (28.9) 5.2 (11.6) 1.5 (3.4) 8.2 (18.3) 

7-Jan -3.8 (25.2) -6.1 (21.0) -2.2 (28.0) 3.2 (7.2) 0.0 (0.0) 5.2 (11.6) 

8-Jan -1.7 (28.9) -3.3 (26.1) 0.0 (32.0) 2.4 (5.3) 0.0 (0.0) 5.2 (11.6) 

9-Jan -0.1 (31.8) -1.7 (28.9) 1.1 (34.0) 3.5 (7.7) 1.5 (3.4) 6.2 (13.9) 

10-Jan 1.8 (35.3) 1.0 (33.8) 2.8 (37.0) 3.5 (7.7) 0.0 (0.0) 6.7 (15.0) 

11-Jan 0.6 (33.0) -0.6 (30.9) 1.1 (34.0) 4.3 (9.5) 0.0 (0.0) 5.7 (12.8) 

12-Jan 4.9 (40.7) 0.6 (33.1) 13.3 (55.9) 3.9 (8.7) 0.0 (0.0) 8.8 (19.7) 

13-Jan 9.2 (48.5) 0.6 (33.1) 14.4 (57.9) 6.4 (14.3) 2.6 (5.8) 10.3 (23.0) 

14-Jan -5.5 (22.2) -9.4 (15.1) 1.1 (34.0) 5.3 (11.9) 2.6 (5.8) 7.2 (16.1) 

3-Apr 6.0 (42.7) 2.8 (37.0) 8.3 (46.9) 6.9 (15.5) 0.0 (0.0) 9.8 (21.9) 

4-Apr 6.3 (43.3) -0.6 (30.9) 13.3 (55.9) 2.1 (4.7) 0.0 (0.0) 5.7 (12.8) 

5-Apr 9.0 (48.1) 1.1 (34.0) 15.6 (60.1) 1.8 (4.0) 0.0 (0.0) 3.6 (8.1) 

6-Apr 11.9 (53.4) 5.0 (41.0) 18.9 (66.0) 3.7 (8.3) 2.1 (4.7) 6.2 (13.9) 

7-Apr 16.2 (61.1) 11.1 (52.0) 22.8 (73.0) 5.4 (12.1) 0.0 (0.0) 12.4 (27.7) 

8-Apr 11.0 (51.8) 7.0 (44.6) 13.9 (57.0) 6.0 (13.5) 0.0 (0.0) 9.8 (21.9) 

9-Apr 8.5 (47.3) 3.9 (39.0) 13.3 (55.9) 5.5 (12.4) 0.0 (0.0) 8.2 (18.3) 

25-Jul 28.5 (83.2) 25.6 (78.1) 33.3 (91.9) 2.5 (5.7) 1.0 (2.2) 5.2 (11.6) 

26-Jul 29.3 (84.8) 25.0 (77.0) 35.0 (95.0) 3.4 (7.6) 1.5 (3.4) 7.2 (16.1) 

27-Jul 29.5 (85.2) 25.0 (77.0) 35.0 (95.0) 2.5 (5.7) 1.5 (3.4) 6.2 (13.9) 

28-Jul 30.0 (86.1) 25.6 (78.1) 35.6 (96.1) 3.0 (6.7) 1.0 (2.2) 5.2 (11.6) 

29-Jul 28.5 (83.3) 25.6 (78.1) 33.9 (93.0) 3.3 (7.3) 1.0 (2.2) 11.3 (25.3) 

30-Jul 29.2 (84.5) 26.1 (79.0) 33.3 (91.9) 3.0 (6.7) 1.0 (2.2) 6.2 (13.9) 

31-Jul 29.0 (84.1) 27.8 (82.0) 31.7 (89.1) 4.3 (9.6) 0.0 (0.0) 8.2 (18.3) 

A CONTAM model of a building is associated with a terrain shielding coefficient to account for 

the impacts of surrounding terrain, buildings and vegetation on surface-averaged, wind-induced 

pressures on the exterior façade of the building. CONTAM specifies three categories of terrain for 

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flat exposed areas (e.g., airport), suburban, and dense urban centers, and a user can input 

coefficients to capture a range of terrain options in between the flat and urban extremes. These 

simulations employed the suburban category of terrain shielding, which corresponds to areas with 

obstructions of the size and spacing of single-family homes. The houses were oriented such that 

the predominant wind direction for the simulated weather conditions was directed toward the 

garage door for houses with garages or toward the front of the house for houses without garages. 

Indoor air temperatures: In Persily et al. (2013), the indoor temperature was held constant at 23 °C 

(73.4 °F) in all interior zones during all of the simulations with the following exceptions. For cases 

with constant generator operation for 18 hours, the air temperature in zones containing the 

generators was assumed to increase linearly over two hours from 23 °C (73.4 °F) to 40 °C 

(104 °F). After the generator stopped operating, the temperature was assumed to decrease linearly 

over six hours back to 23 °C (73.4 °F). The air temperature in zones adjacent to the zone 

containing the generator was assumed to increase on the same schedule but only to 30 °C (54 °F). 

These indoor air temperature schedules in the source zone and adjacent zones are based on the 

results of a series of experimental studies of generator operation reported by Emmerich et al. 

(2013). The indoor air temperatures of unconditioned spaces (i.e., crawl spaces, unfinished 

basements, garages and attics), were held constant at 23 °C (73.4 °F). This assumption in Persily 

et al. (2013) does not capture temperature variations in such unconditioned spaces caused by the 

outdoor weather. 

For this study, temperature distributions within the simulated buildings were calculated using a 

version of the CONTAM model with heat transfer modeling capability (Emmerich 2006, Wang et 

al. 2012). This model accounts for heat transfer conducted through the building envelopes due to 

ambient weather conditions and for the heat produced by the generator and thus results in more 

realistic spatial and temporal temperature variations in the buildings. The generator heat source 

varied depending on generator size and is reported in Table 2 along with the CO emission rates. 

Door and window positions: Interior doors were assumed to be open 5 cm during the simulations 

and all exterior doors and windows closed with the following exceptions. Stairway doors between 

finished living space levels other than the first floor door were modeled with fully open doorways. 

Kitchen, dining, family and living room doors were modeled as fully open doorways. For cases in 

which the generator was located in an attached garage, the door from the garage to the house was 

assumed be open roughly 5 cm to accommodate an extension cord connecting the generator to 

appliances in the house. 

2.2.2 Source Locations and Emission Rates 

For each building modeled, scenarios included up to three different source locations, a range of 

“constant” CO generation rates, and different durations of maintained source emissions. The 

specific source locations used for each simulated house are listed in Appendix B but in general the 

source locations included: 

• Closed garage (if applicable to the model house) 

• First floor room (kitchen or other most likely such room based on floor plan) 

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•	 An additional location in either the basement (if applicable to the model house, bedroom or 

den furthest away from master bedroom or in smallest bedroom or den if master bedroom 

is on 1st floor) if finished basement) OR crawlspace (if applicable) OR a second room on 

the first floor room if there is no basement (bedroom furthest away from master bedroom 

or other likely space) 

The simulations require CO emission rates (g/h) and input values for source duration and source 

heat release rate. These were supplied by CPSC staff, derived from an analysis of currently 

marketed generators, and generator products/sizes identified in CPSC incident databases (Hnatov 

et al. 2016). Table 2 summarizes values for all of these modeled variables for four size ranges of 

generator products: HH (generators powered by spark-ignited (SI) handheld engines), C1 

(generators powered by SI Class I non-handheld engines), C2 (generators powered by SI Class II 

non-handheld single cylinder engines) and C2 twin (generators powered by SI Class II nonhandheld twin cylinder engines). For each generator size category, the baseline CO emission rate 

represents three times the EPA’s 6-mode weighted ambient CO emission rates of carbureted 

engines used in multiple brands of popular generators (see Appendix C for more information on 

this factor). Table 2 also contains six potential rule-compliant reduced CO emission rates (to 

support the analysis of multiple options for cost-benefit analysis). The run-time represents the 

generators’ advertised run time (determined by the CPSC market analysis to be representative of 

typical generators of that engine class, Hnatov et al. 2016), for one full tank of gasoline, when 

operated at half-load, which nominally represents the weighted load of the 6-mode profile. Two 

schedules were used for each generator size. The first was a full tank operation starting at 12 a.m. 

(called full schedule) and the second was a half tank operation starting at 8 a.m. (called half 

schedule). 

Table 2 Baseline and reduced CO emission rates, run-times and heat rates for the generators 

Generator 

size 

Baseline CO 

emission rate at 

reduced O2 (g/h) 

Reduced CO emission 

rates (g/h) 

Run-time 

(h) 

Heat 

release 

rate (kW) 

Notes 

HH 900 50, 125, 250, 500 8 2 Only used in 

DH8 and 

MH1mod 

C1 1800 50, 125, 250, 500, 1000 9 6 

C2 single 4700 50, 125, 250, 500, 1000, 

2000 

10 13 

C2 twin 9100 50, 125, 250, 500, 1000, 

2000 

9 25 Only used in 

GAR1 and 

GAR3 

Notes: Baseline generators were simulated with a CO rate two-thirds of the table value for the first 

2 hours of operation as the enclosed space starts at ambient oxygen level. Engine classifications 

are U.S. Environmental Protection Agency (EPA) definitions. 

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2.3 Simulation cases and output analysis 

The simulations that were run are depicted in Figure 1, which shows the 40 buildings (37 houses 

and 3 detached garages), 3 source locations, up to 10 source strength levels, 28 days of weather 

and 2 schedule types. Note that not all combinations were simulated as not all buildings have 

garages, basements or crawlspaces and the HH and C2 twin sources were only used in 2 buildings. 

Houses 

- Detached (31) 

- Manufactured (2) 

-Attached (4) 

-Garages (3) 

Weather/schedule 

- 14 days cold 

- 7 days warm 

- 7 days transition 

Full and half 

schedule for each 

day 

Source locations 

Constant (for up to 10 hours)

- closed garage (when applicable)

- basement/crawlspace (when applicable, first

floor bedroom when there is no basement)

- kitchen 

Up to 10 source strength levels for each of

the source scenarios 

Figure 1 Schematic showing simulation cases 

Each simulation corresponds to one house, one source location, one source strength, one schedule 

and one day of weather. The output of each simulation are the CO concentrations versus time in 

each zone of the house. Based on the simulation time step of 1 min, the output consists of 1440 

concentrations values in each zone over each 24-h simulation. As noted earlier, the CO generation 

commenced either at the beginning of each 24-h period for the full schedule or at 8 a.m. for the 

half schedule. After the CO generation stopped, the indoor CO concentrations started decreasing 

back to ambient levels. 

2.4 COHb time profile calculation 

The COHb (%) level reflects the percentage share of the body’s total hemoglobin pool occupied 

by CO. In acute, modeled exposure scenarios, it serves as a useful measure to compare expected 

poisoning severity in a reference individual. COHb levels were calculated for an occupant in each 

occupiable zone of the house and garage over the 24-h simulation period using the CoburnForster-Kane (CFK) non-linear differential equation (Peterson and Stewart 1975, Coburn et al. 

1965) and input values determined in consultation with CPSC, specifically three RMV (respiratory 

minute volume) values of 10 L/min (representing a time-weighted average 24 hour value for males 

and females 16 to 80 years old, for expected residential indoor activity), 12 L/min (representing a 

time-weighted 75th percentile 24 hour value for adult males and females 16 to 80 years old for 

expected residential indoor activity), and 6 L/min (representing a baseline 75th percentile 24 hour 

value for adult males and females 16 to 80 years old for sleeping/sedentary activity levels, 

especially likely in bedrooms) and an initial COHb level of 0.00056 ml/ml. 

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3. RESULTS 

This section presents a sample of the results of the simulations discussed in the previous section 

for four of the modeled buildings. 

3.1 Sample results for a small manufactured house (MH1mod) 

This section presents sample results for the building MH1mod, which was created for this project 

as a smaller version of the manufactured house MH-1 (also included in this study) from the NIST 

suite of homes discussed earlier. Figure 2 shows the floorplan of MH1mod as represented in the 

CONTAM Sketchpad. MH1mod has 82.5 m2 of floor area with 2 bedrooms, 1 bathroom and a 

kitchen. MH1mod was modeled with generators located in the kitchen, bedroom 2 and the 

crawlspace. 

Kitchen 

Bedroom 2 

Hall 

Bedroom 1 

Bathroom 

Figure 2 Floor plan of house MH1mod as represented in CONTAM 

Figure 3 shows individual zone CO concentration results for the source located in bedroom 1 of 

house MH1mod on January 1st. Note that Figure 3 (and each of the following results plots) shows 

the results zone by zone for a single day along the x-axis. The concentration of CO in bedroom 1 

reached a peak of over 8,000 μL/L (μL/L are equivalent to the commonly used unit for CO 

concentration of parts per million by volume or ppmv) for the HH baseline source and peak 

concentrations ranged from around 1700 μL/L to 3000 μL/L in the other zones. Peak 

concentrations for the reduced rates of 50 g/h to 500 g/h were lower than the HH baseline source 

peaks by 40 % to more than 90 %. 

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Figure 4 shows individual zone COHb levels calculated with an RMV = 10 L/min for the same 

cases as Figure 3 (source in bedroom 1 on January 1st). Note that the calculation of COHb was cut 

off at 95 % for all cases because the calculated COHb levels are not meaningful at these high 

levels. Therefore, in some of the COHb figures the COHb is shown to artificially level off at 95 %. 

For reference, COHb levels of 70 % or greater are associated with death in less than 3 min, levels 

of 50 % are associated with headache, dizziness and nausea in 5 min to 10 min and death within 

30 min, levels of 30 % with dizziness, nausea and convulsions within 45 min and becoming 

insensible within 2 h, and levels of 20 % with a slight headache in 2 h to 3 h and a loss of 

judgment (Goldstein 2008). In the absence of rescue, COHb levels that reach 60 % or more, 

typically end in acute lethal outcome (personal communication from S. Inkster of U.S. CPSC). 

The COHb quickly exceeded 40 % in all zones for both the HH and 500 g/h sources, but remained 

below 40 % in all zones for the 50 g/h source. 

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Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

Figure 3 Individual zone transient CO results for the HH source in Bedroom 1 of MH1mod on 

January 1st 

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Figure 4 Individual zone transient COHb (RMV = 10 L/min) results for the HH source in 

Bedroom 1 of MH1mod on January 1st. Note that the calculation of COHb was cut off at 95 % for 

all cases. 

Figure 5 shows individual zone CO concentration results for the source located in bedroom 1 of 

house MH1mod on July 25th. Due to the lower infiltration rate caused by the smaller indoor to 

outdoor temperature difference during the warmer weather, the concentration of CO in bedroom 1 

reaches a much higher peak of over 16,000 μL/L for the HH baseline source (900 g/h), with peak 

concentrations ranging from around 7000 μL/L to 10,000 μL/L in the other zones. Reductions in 

peak concentrations for the reduced emission rates of 50 g/h to 500 g/h compared to the baseline 

HH source were similar to the January 1st reductions of 40 % to over 90 %. 

Figure 6 shows zone COHb values calculated with an RMV = 10 L/min for the same cases as 

Figure 5 (source in bedroom 1 on July 25th). The COHb quickly exceeded 40 % in all zones for 

most of the source strengths. The COHb remained below or peaked at around 40 % in the nonsource zones for the 50 g/h source. 

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HH 50 g/h 125 g/h 250 g/h 500 g/h 

Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

Figure 5 Individual zone transient CO results for the HH source in Bedroom 1 of MH1mod on 

July 25th 

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Figure 6 Individual zone transient COHb (with RMV = 10 L/min) results for the HH source in 

Bedroom 1 of MH1mod on July 25th 

Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

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Figures 7 and 8 show individual zone CO concentration and COHb results, respectively, for the 

C1 source (1800 g/h, generators powered by SI class I non-handheld engines) and reduced rate 

sources located in bedroom 1 of house MH1mod on January 1st. Since the C1 source is twice as 

strong as the HH source, the CO concentrations for the baseline case reach much higher 

concentrations in Figure 7 compared to Figure 3. However, the increase is less than a full 

doubling, which is likely due primarily to air change rate differences since the C1 source has a 

higher heat release rate and thus results in higher zone temperatures. The higher zone temperatures 

mean the indoor-outdoor temperature difference that drives infiltration is larger. The higher air 

change rate with the C1 source also results in somewhat lower CO concentrations for the reduced 

rate sources in Figure 7 compared to Figure 3. Reductions in peak concentrations for the reduced 

emission rates of 50 g/h to 1000 g/h compared to the baseline C1 source peaks ranged from 40 % 

to over 90 %. The COHb results shown in Figure 8 were generally similar to those of Figure 4 

with somewhat higher results for the larger C1 baseline case compared to the HH baseline as the 

COHb quickly exceeded 40 % in all zones for most of the source strengths. The COHb remained 

below 40 % in all zones for the 50 g/h source and in the non-source zones for the 125 g/h source. 

Figures 9 and 10 show individual zone CO concentration and COHb results, respectively, for the 

C1 source (1800 g/h) and reduced rate sources located in bedroom 1 of house MH1mod on July 

25th. As with the January 1st results the stronger C1 source resulted in higher, but less than double, 

CO concentrations for the baseline case in Figure 9 compared to Figure 5. Reductions in peak 

concentrations for the reduced rates of 50 g/h to 1000 g/h compared to the baseline C1 source 

peaks again ranged from around 40 % to over 90 %. The COHb results shown in Figure 10 were 

generally similar to those of Figure 6 with somewhat higher results for the larger C1 baseline case 

compared to the HH baseline as the COHb quickly exceeded 40 % in all zones for most of the 

source strengths. The COHb remained below 40 % in non-source zones for the 50 g/h source only. 

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C1 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 

Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

Figure 7 Individual zone transient CO results for the C1 source in Bedroom 1 of MH1mod on 

January 1st 

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Figure 8 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

Bedroom 1 of MH1mod on January 1st 

Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

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Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

Figure 9 Individual zone transient CO results for the C1 source in Bedroom 1 of MH1mod on July 

25th COHb (%) 

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 Bedroom 1
 Bathroom Kitchen Hallway 

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Figure 10 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

Bedroom 1 of MH1mod on July 25th 

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The previous results in Figures through 9 were all for cases with the generator in the bedroom 1 

zone. Figures 11 and 12 show individual zone CO concentration and COHb results, respectively, 

for the C1 source and reduced sources for the generator located in the kitchen of house MH1mod 

on January 1st. As discussed in Section 2.2.1, kitchens, including the kitchen zone of MH1mod, 

were connected to adjacent zones with fully open doorways rather than slightly ajar doors. As seen 

in Figure 11, this results in lower CO concentrations in the source zone (kitchen of Figure 11 

compared to bedroom 1 of Figure 7) but higher CO concentrations in the non-source zones. 

However, reductions in peak concentrations for the reduced rates of 50 g/h to 1000 g/h compared 

to the baseline C1 source still ranged from around 40 % to over 90 %. The COHb results shown in 

Figure 12 were generally similar to those of Figure 8, with the COHb quickly exceeding 40 % in 

all zones for most of the source strengths but remaining near or below 40 % in all zones for the 

50 g/h source and in the non-source zones for the 125 g/h source. 

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Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

Figure 11 Individual zone transient CO results for the C1 source in Kitchen of MH1mod on 

January 1st 

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Figure 12 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

Kitchen of MH1mod on January 1st 

Figures 13 and 14 show individual zone CO concentration and COHb results, respectively, for the 

C1 source and reduced rate sources located in the kitchen of house MH1mod on July 25th. As with 

the bedroom 1 source location, the warmer temperatures (and lower air change rates) on July 25th 

result in higher CO concentrations and COHb compared to the January 1st results shown in Figures 

11 and 12. 

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14000 

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Bedroom 2 Bedroom 1 Bathroom Kitchen Hallway 

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Figure 13 Individual zone transient CO results for the C1 source in Kitchen of MH1mod on July 

25th COHb (%) 

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Figure 14 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

Kitchen of MH1mod on July 25th 

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3.2 Sample results for a mid-sized detached house with basement and integral garage (DH45mod) 

This section presents example results for building DH-45mod, which was created for this project 

based on the detached house DH-45 (also included in this study) from the NIST suite of homes. 

As described in Appendix B, two modifications were made to the DH-45 model. Part of the 

unfinished basement was converted to an integral garage and the air leakage was modified based 

on year built and floor area to represent the newest category of construction (1990 and newer) in 

the suite of homes analysis. Figure 15 shows the floorplan of DH-45mod as represented in the 

CONTAM Sketchpad. DH-45mod has 180 m2 of floor area with a kitchen, dining room, living 

room, two bathrooms and one bedroom on the first floor and three bedrooms, a bathroom and a 

den on the second floor. DH-45mod was modeled with generators located in the kitchen, the 

unfinished basement and the garage. 

Bedroom 2 

Stair 

Bedroom 3 Bedroom 4 

Bathroom 2 

Den 

Hall 

Unfinished 

basement 

Garage Stair 

Half-bath 

Bathroom 1 

Bedroom 1 

Kitchen 

Dining Living 

Figure 15 Floor plan of house DH-45mod as represented in CONTAM 

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Figures 16 and 17 show individual zone CO concentration and COHb results, respectively, for the 

C1 source and reduced rate sources located in the garage of house DH-45mod on January 1st. The 

peak CO concentrations resulting from the C1 baseline source reached around 17,000 μL/L in the 

source zone, over 14,000 μL/L in the adjacent unfinished basement zone and from around 

8,000 μL/L to 10,000 μL/L in the remaining non-source zones. Reductions in peak concentrations 

for the reduced rates of 50 g/h to 1000 g/h, compared to the baseline C1 source peaks, were similar 

to those seen for the MH1mod cases and ranged from over 40 % to well over 90 %. As with many 

of the MH1mod cases, the COHb shown in Figure 17 exceeded 40 % in all zones for most of the 

source strengths, but remained below 40 % in all non-source zones for just the 50 g/h source. 

However, COHb generally increased more gradually in the 1st and 2nd floor zones since the source 

was in the garage on the basement level. 

Figures 18 and 19 show individual zone CO concentration and COHb results, respectively, for the 

C1 source and reduced rate sources located in the garage of house DH45-mod on July 25th. As 

with the MH1mod cases, the warmer temperatures on July 25th result in significantly higher CO 

concentrations in the source zone than on January 1st (results in Figure 16). However, the results 

for the 1st and 2nd floor zones are much different on July 25th, as the 1st floor concentrations are 

somewhat lower and the 2nd floor concentrations are significantly lower compared to January 1st . 

The warmer outdoor air reduces the flow of air from the basement up to the 1st and 2nd floors due 

to a smaller indoor to outdoor temperature difference. However, the reductions in peak 

concentrations for the reduced sources are still in a range of over 40 % to over 90 % compared to 

the baseline C1 source. As seen in Figure 19, the COHb results were also quite different on July 

25th compared to January 1st, with somewhat lower values for the 1st floor zones and significantly 

lower values for the 2nd floor zones, including a few zones that stayed below 40 % for all source 

strengths. 

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Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

Figure 16 Individual zone transient CO results for the C1 source in Garage of DH-45mod on 

January 1st 

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Figure 17 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

Garage of DH-45mod on January 1st 

Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

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Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

Figure 18 Individual zone transient CO results for the C1 source in Garage of DH-45mod on July 

25th 

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Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

Figure 19 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

garage of DH-45mod on July 25th 

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Figures 20 and 21 show individual zone CO concentration and COHb results, respectively, for the 

C1 source (baseline 1800 g/h) and reduced rate sources located in the kitchen of house DH-45mod 

on January 1st. The peak CO concentrations resulting from the C1 baseline source reached around 

11,000 μL/L in the source zone and around 10,000 μL/L in most of the 1st and 2nd floor non-source 

zones. Concentrations were near zero in the basement zones due to cold outdoor temperatures 

resulting in stack effect primarily causing flow upwards within the house. Reductions in peak 

concentrations for the reduced rates of 50 g/h to 1000 g/h, compared to the baseline C1 source 

peaks, were similar to those seen for other cases and ranged from over 40 % to well over 90 %. 

The COHb shown in Figure 21 exceeded 40 % in nearly all zones for most of the source strengths 

but remained below 40 % in all non-source zones for just the 50 g/h source. However, COHb 

stayed well below 10 % on the basement level. 

Figures 22 and 23 show individual zone CO concentration and COHb results, respectively, for the 

C1 source and reduced rate sources located in the kitchen of house DH-45mod on July 25th. As 

with the garage source in Figure 18, the warm ambient temperatures on July 25th result in 

significant variations in CO concentrations, depending primarily on the floor of the house. The 

peak CO concentrations resulting from the C1 baseline source reached over 25,000 μL/L in the 

source zone and most other 1st floor zones (well-connected due to fully open doorways), between 

15,000 μL/L and 20,000 μL/L in the 2nd floor zones, and at or below 5,000 μL/L in the basement 

zones. Once again, the reductions in peak concentrations for the reduced sources are in a range of 

over 40 % to over 90 % compared to the baseline C1 source. As seen in Figure 23, the COHb 

results were also quite different on July 25th compared to January 1st, with somewhat lower values 

and slower increases for the 2nd floor zones and significantly lower values and much slower 

increases for the basement zones. 

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Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

Figure 20 Individual zone transient CO results for the C1 source in Kitchen of DH-45mod on 

January 1st 

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Figure 21 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

Kitchen of DH-45mod on January 1st 

Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

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Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

Figure 22 Individual zone transient CO results for the C1 source in Kitchen of DH-45mod on July 

25th 

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Bedroom 2 Bedroom 4 Kitchen Living Basement Garage 

Figure 23 Individual zone transient COHb (with RMV = 10 L/min) results for the C1 source in 

Kitchen of DH-45mod on July 25th 

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3.3 Sample results for a large 2-story detached house with garage (DH-12) 

This section presents simulation results for detached house DH-12 from the NIST suite of homes. 

Figure 24 shows the floorplan of DH-12 as represented in the CONTAM Sketchpad. DH-12 has 

276 m2 of floor area with a bedroom, den, family room and bathroom in the basement, a kitchen, 

dining room, living room, bathroom and attached garage on the first floor and three bedrooms and 

a bathroom on the second floor. DH-12 was modeled with generators located in the kitchen, 

bedroom 4 in the basement and the garage. 

Bedroom 4 

Stair 

Bathroom 2 

Family 

Den 

Garage 

Kitchen Dining 

Stair 

Living 

Half-bath 

Bedroom 1 

Stair 

Bedroom 3 

Bedroom 2 

Bathroom 1 

Figure 24 Floor plan of house DH-12 as represented in CONTAM 

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As with the DH-45mod results in Figures 16 through 23, the results for DH-12 shown in Figures 

25 through 32 show significant variation by level of the house depending on the source location 

and weather. Figures 25 and 26 show individual zone CO concentration and COHb results, 

respectively, for the C2 single source (baseline 4700 g/h) and reduced rate sources located in the 

garage of house DH-12 on January 1st. The peak CO concentrations resulting from the C2 single 

baseline source reached around 20,000 μL/L in the source zone, around 3,000 μL/L to 6,000 μL/L 

in the non-source zones on the 1st and 2nd floors, and remained below 400 μL/L in the basement 

zones. Reductions in peak concentrations for the reduced rates of 50 g/h to 2000 g/h, compared to 

the baseline C2 single source peaks, were similar to those seen for the previous cases and ranged 

from over 50 % to well over 90 %. Unlike previous cases, the COHb shown in Figure 26 remained 

below 40 % in many non-source zones for reduced source strengths up to 500 g/h and below 40 % 

in the basement zones for all source strengths. 

Figures 27 and 28 show individual zone CO concentration and COHb results, respectively, for the 

C2 single source and reduced rate sources located in the garage of house DH-12 on July 25th. For 

this case, the peak CO concentration reached around 23,000 μL/L in the garage but stayed below 

2,000 μL/L in the other 1st floor zones, with little CO transport to the basement and none to the 2nd 

floor zones for this case. The reductions in peak concentrations for the reduced sources are still in 

a range of over 50 % to well over 90 % compared to the baseline C2 single source. As seen in 

Figure 28, the COHb remained below 40 % for all sources strengths up to 1000 g/h in all 1st floor 

non-source zones and below 20 % for all source strengths in the basement and 2nd floor zones. 

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Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

Figure 25 Individual zone transient CO results for the C2 single source in Garage of DH12 on 

January 1st 

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Figure 26 Individual zone transient COHb (with RMV = 10 L/min) results for the C2 single source 

in Garage of DH12 on January 1st 

Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

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0 

5000 

10000 

15000 

20000 

25000 

0 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 

Concentration (μL/L) 

Time (h of day) 

C2 single 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h 

Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

Figure 27 Individual zone transient CO results for the C2 single source in Garage of DH12 on July 

25th 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

0 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 

COHb (%) 

Time (h of day) 

C2 single 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h 

Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

Figure 28 Individual zone transient COHb (with RMV = 10 L/min) results for the C2 single source 

in Garage of DH12 on July 25th 

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Figures 29 and 30 show individual zone CO concentration and COHb results, respectively, for the 

C2 single baseline source and reduced rate sources located in bedroom 4 in the basement of house 

DH-12 on January 1st. Due to the relative lack of outdoor air infiltration into the basement, the 

peak CO concentrations resulting from the C2 single source reached 50,000 μL/L in the source 

zone, over 30,000 μL/L in the adjacent family room, and 15,000 μL/L to 20, 000 μL/L in most of 

the other zones (not including the garage). Reductions in peak concentrations for the reduced rates 

of 50 g/h to 2000 g/h compared to the baseline C2 single source peaks once again ranged from 

over 50 % to well over 90 %. The COHb shown in Figure 30 remained below 40 % in the nonsource zones for only the 50 g/h source, but reached or exceeded 40 % in all house zones (not 

including the garage) for all other source strengths. 

Figures 31 and 32 show individual zone CO concentration and COHb results, respectively, for the 

C2 single source and reduced rate sources located in bedroom 4 in the basement of house DH-12 

on July 25th. For this case, the peak CO concentration for the C2 single source reached almost 

100,000 μL/L in the garage, over 68,000 μL/L in the other basement zones and nearly 

40,000 μL/L in the 1st floor zones. CO concentrations were much lower in the 2nd floor zones but 

still in the range of 1,000 μL/L to 5,000 μL/L. The reductions in peak concentrations for the 

reduced sources again range from over 50 % to well over 90 % compared to the baseline C2 single 

source. As seen in Figure 32, the COHb exceeded 40 % for all sources strengths in the basement 

zones, remained below 40 % for just the 50 g/h source in the 1st floor zones, and remained near or 

below 40 % for all sources up to 500 g/h in all 2nd floor zones. 

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0 

10000 

20000 

30000 

40000 

50000 

60000 

0 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 

Concentration (μL/L) 

Time (h of day) 

C2 single 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h 

Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

Figure 29 Individual zone transient CO results for the C2 single source in Bedroom 4 of DH12 on 

January 1st 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

0 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 

COHb (%) 

Time (h of day) 

C2 single 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h 

Figure 30 Individual zone transient COHb (with RMV = 10 L/min) results for the C2 single source 

in Bedroom 4 of DH12 on January 1st 

Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

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0 

20000 

40000 

60000 

80000 

100000 

120000 

0 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 

Concentration (μL/L) 

Time (h of day) 

C2 single 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h 

Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

Figure 31 Individual zone transient CO results for the C2 single source in Bedroom 4 of DH12 on 

July 25th 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

0 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 

COHb (%) 

Time (h of day) 

C2 single 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h 

Figure 32 Individual zone transient COHb (with RMV = 10 L/min) results for the C2 single source 

in Bedroom 4 of DH12 on July 25th 

Bedroom 1 Garage Kitchen Living Bedroom 4 Den 

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3.4 Sample results for large garage with workshop (GAR3) 

This section presents sample results for the building GAR3, which was created for this project as a 

large two zone garage with 60.4 m2 of floor area including a separate workshop zone. 

Workshop Garage 

Figure 33 Floor plan of house GAR3 as represented in CONTAM 

Figures 34 and 35 show individual zone CO concentration and COHb results, respectively, for the 

C2 twin baseline source (9100 g/h) and reduced rate sources located in the garage zone of GAR3 

on January 1st. The peak CO concentrations resulting from the C2 twin source reached almost 

35,000 μL/L in the garage and over 12,000 μL/L in the workshop. Reductions in peak 

concentrations for the reduced rates of 50 g/h to 2000 g/h, compared to the baseline C2 twin 

source, ranged from nearly 80 % to well over 90 %. The COHb shown in Figure 35 remained at or 

below 40 % in both zones for the 50 g/h and 125 g/h sources, but reached or exceeded 40 % in 

both zones for all source strengths over 500 g/h. However, Figure 35 also shows that the COHb 

increases more slowly in both zones as the source strength drops. 

Figures 36 and 37 show individual zone CO concentration and COHb results, respectively, for the 

C2 twin source and reduced rate sources located in the garage zone of GAR3 on July 25th. The 

results for this case are quite similar to the January 1st results, with somewhat higher CO 

concentrations and COHb due to the lower air change rate during the warmer weather. 

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40000 

Workshop Garage 

35000
 

30000
 

25000
 

20000
 

15000
 

10000
 

5000
 

0
 

Time (h of day)
 

C2 twin 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h
 

Figure 34 Individual zone transient CO results for the C2 twin source in the Garage zone of GAR3 

on January 1st 

0 4 8 12 16 20 24 4 8 12 16 20 24
 

Concentration (μL/L) 

100
 

90
 

80
 

70
 

60
 

Figure 35 Individual zone transient COHb (with RMV = 10 L/min) results for the C2 twin source 

in the Garage zone of GAR3 on January 1st 

Workshop Garage 

0 4 8 12 16 20 24 4 8 12 16 20 24
 

COHb (%) 50
 

40
 

30
 

20
 

10
 

0 

Time (h of day) 

C2 twin 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h 

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45000 

Workshop Garage 

40000
 

35000
 

30000
 

25000
 

20000
 

15000
 

10000
 

5000
 

0
 

Time (h of day)
 

C2 twin 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h
 

Figure 36 Individual zone transient CO results for the C2 twin source in the Garage zone of GAR3 

on July 25th 

0 4 8 12 16 20 24 4 8 12 16 20 24
 

Concentration (μL/L) 

100
 

Figure 37 Individual zone transient COHb (with RMV = 10 L/min) results for the C2 twin source 

in the Garage zone of GAR3 on July 25th 

90
 

80
 

70
 

60
 

50
 

40
 

30
 

20
 

10
 

0
 

Time (h of day)
 

C2 twin 50 g/h 125 g/h 250 g/h 500 g/h 1000 g/h 2000 g/h
 

Workshop Garage 

0 4 8 12 16 20 24 4 8 12 16 20 24
 

COHb (%) 

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4. SUMMARY AND DISCUSSION 

This simulation study was conducted to evaluate indoor CO exposures as a function of generator 

source location and CO emission rate in order to support cost-benefit analyses of potential CO 

emission limits for generators. These simulations employed the multizone airflow and 

contaminant transport model CONTAM, which was applied to 40 residential buildings including 

37 versions of dwellings drawn from a collection that are representative of the U.S. housing stock 

and 3 new detached garage buildings. A total of over 45 thousand individual 24-hour simulations 

were conducted that covered a range of house layouts and sizes, airtightness levels, weather 

conditions, generator locations, CO source strengths and operating schedules. The simulated 

generator locations include attached garages, crawlspaces and basements, in the houses that have 

such spaces, and two interior rooms in all of the houses considered. COHb levels were then 

calculated from the CO concentration results for an occupant in each occupiable zone of the 

buildings over the 24-h simulation period using 3 RMV values. This report presents sample 

simulation results of predicted CO concentration and COHb levels in individual zones for three of 

the modeled houses and one of the garages. 

The results presented demonstrate that the reduced CO emission rates considered in this study 

result in peak CO concentrations that are reduced by 40 % to more than 90 % depending on the 

specific case being analyzed. The reduced CO emission rates also resulted in significant reductions 

in COHb in many cases. Additionally, use of a thermal model to more accurately account for 

thermal effects was shown to be important as the interaction of the generator heat source and the 

ambient weather conditions can significantly impact both air change rates and interzone airflow 

patterns in the buildings. 

As observed previously by Persily et al. (2013), these simulation results demonstrate the 

complexity of multizone airflow and contaminant transport in buildings, which in turn supports 

the value in considering a wide range of homes and weather conditions in addressing the objective 

of this study. Variations in house layout, generator size (i.e., source strength and heat release), 

operating schedules, source location, and weather conditions can all have significant, and at times 

complex, impacts on airflow and CO transport. This inherent variability means that considering 

only one or a small number of buildings under a limited range of conditions would not be adequate 

to fully understand the levels of CO exposure in residences. Therefore, the results of individual 

cases, such as the ones presented in this report, should not be over-generalized but taken only as 

representative of the conditions for those cases. 

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5. ACKNOWLEDGEMENTS 

This work was funded by the U.S. Consumer Products Safety Commission under interagency 

agreement No. CPSC-I-15-0024. The authors wish to express their appreciation for the support of 

Janet Buyer, Sandra Inkster, and Matthew Hnatov from CPSC in conducting this effort. 

6. REFERENCES 

ASHRAE, Fundamentals Handbook. 2009. Atlanta, GA: American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc. 

Coburn, R.F., R.E. Forster, and P.B. Kane. 1965. Considerations of the physiological variables 

that determine the blood carboxyhemoglobin concentration in man. Journal of Clinical 

Investigation, 1965. 44 (11): p. 1899-1910. 

CPSC. 2012. Technology Demonstration of a Prototype Low Carbon Monoxide Emission Portable 

Generator; U.S. Consumer Product Safety Commission: Bethesda, MD; p 413. 

DOE. Residential Energy Consumption Survey (RECS). 2005; Available from: 

http://www.eia.doe.gov/emeu/recs/contents.html. 

Dols, W.S. and B.J. Polidoro. 2015. CONTAM 3.2 User Guide and Program Documentation. 

NIST Technical Note 1887. National Institute of Standards and Technology. 

Emmerich, S.J., Gorfain, J.E., and C. Howard-Reed. 2003. Air and Pollutant Transport from 

Attached Garages to Residential Living Spaces-Literature Review and Field Test. International 

Journal of Ventilation, Vol., 2 (3). 

Emmerich, S.J. 2001. Validation of Multizone IAQ Modeling of Residential-Scale Buildings: A 

Review. ASHRAE Transactions. 107 (2): p. 619-628. 

Emmerich, S.J. 2006. Simulated Performance of Natural and Hybrid Ventilation Systems in an 

Office Building. International Journal of HVAC&R Research Vol. 12 (4). 

Emmerich, S.J. and W.S. Dols. 2015. Model Validation Study of Carbon Monoxide Transport due 

to Portable Generator Operation in an Attached Garage. Journal of Building Performance 

Simulation Vol. 9 (4): p. 397-410. 

Emmerich, S., Persily, A.K., and L. Wang. 2013. Modeling and Measuring the Effects of Portable 

Gasoline Powered Generator Exhaust on Indoor Carbon Monoxide Level. NIST Technical Note 

1781. 

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Emmerich, S.J., Howard-Reed, C. and S.J. Nabinger. 2004. Validation of multizone IAQ model 

predictions for tracer gas in a townhouse. Building Service Engineering Research Technology. 

25(4): p. 305-316. 

Goldstein, M. 2008. Carbon Monoxide Poisoning. Journal of Emergency Nursing. 34(6): 

p. 538-542. 

Hnatov, M.V. 2015. Incidents, Deaths, and In-Depth Investigations Associated with Non-Fire 

Carbon Monoxide from Engine-Driven Generators and Other Engine-Driven Tools, 2004-2014. 

U.S. Consumer Product Safety Commission. 

Hnatov, M., S. Inkster, and J. Buyer. 2016 (pending report). Estimates Of Epidemiological 

Benefits Associated With Reduced Carbon Monoxide (CO) Emission Rates Compared To CO 

Emission Rates Of Current Portable Generators. U.S. Consumer Product Safety Commission, 

Bethesda, MD, 

HUD. 1999. American Housing Survey for the United States. U.S. Department of Housing and 

Urban Development, U.S. Department of Commerce. 

Persily, A.K., A. Musser, and D. Leber. 2006. A Collection of Homes to Represent the U.S. 

Housing Stock. NISTIR 7330. National Institute of Standards and Technology. 

Persily, A.K., Y. Wang, B. Polidoro, and S. J. Emmerich. 2013. Residential Carbon Monoxide 

Exposure due to Indoor Generator Operation: Effects of Source Location and Emission Rate. 

NIST Technical Note 1782. 

Peterson, J.E. and R.D. Stewart, Predicting the carboxyhemoglobin levels resulting from carbon 

monoxide exposures. Journal of Applied Physiology, 1975. 39 (4): p. 633-638. 

Poppendieck, D., Khurshid, S., Dols, W.S., Ng, L., Polidoro, B. and S.J. Emmerich. 2016. 

Formaldehyde Concentrations in a Net-Zero Energy House: Real-time Monitoring and Simulation. 

Proceedings of Indoor Air 2016 

Wang, L., Emmerich, S.J., and A.K. Persily. 2010. In-situ Experimental Study of Carbon 

Monoxide Generation by Gasoline-Powered Electric Generator in an Enclosed Space. 60: p. 1443­

1451. 

Wang, L., Dols, W.S. and S.J. Emmerich. 2012. Simultaneous solutions of coupled thermal 

airflow problem for natural ventilation in buildings. HVAC&R Research, 18(1-2), pp.264-274. 

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APPENDIX A: House Characteristics 

This appendix contains three tables that define the dwellings in the NIST Suite of Homes, with one table for each housing type: detached 

(A1), attached (A2) and manufactured home (A3). The dwelling definitions in the table are in terms of the variables discussed in detail in 

the report that defines these homes (Persily et al. 2006). Note that not all of these models were used in this simulation study and that some 

of the models were modified to better fit the houses in the CPSC CO incident database. See Appendix B for the details of which houses 

were used and what modifications were made to the models. 

Table A1. Detached Homes (83 total) 

Key for Table A1: 

# of floors: 1 = one story; 2 = two story 

Floor area: 1 = less than 148.5 m2 (1,599 ft2); 2 = 148.6 m2 to 222.9 m2 (1,600 ft2 to 2,399 ft2); 3 = 223.0 m2 (2,400 ft2) or more 

Year Built: 1 = before 1940; 2 = 1940-69; 3 = 1970-89; 4 = 1990 and newer 

Foundation: 1 = concrete slab; 2 = crawl space; 3 = finished basement, 4 = unfinished basement 

Garage: 1 = none; 2 = attached garage 

Forced Air: 1 = other; 2 = central system present 

House 

Number # of Floors 

House Variable # of Rooms 

Floor 

plan Floor area Year Built Foundation Garage Forced -air Bedrooms 

Full 

baths Half baths Other 

DH-1 1 2 3 1 2 2 3 2 0 3 DH-B(1) 

DH-2 1 1 2 3 2 2 3 1 0 3 DH-A(8) 

DH-3 1 1 2 2 1 1 2 1 0 2 DH-A(1) 

DH-4 1 1 2 2 2 2 3 1 0 3 DH-A(7) 

DH-5 1 1 3 1 2 2 3 2 0 3 DH-A(2) 

DH-6 2 1 1 3 2 2 3 1 0 3 DH-D(3) 

DH-7 1 2 2 3 2 2 3 2 0 4 DH-B(5) 

DH-8 1 1 2 1 2 2 3 2 0 3 DH-A(2) 

DH-9 2 1 2 3 2 2 3 1 0 3 DH-D(3) 

DH-10 2 2 3 3 2 2 4 2 1 4 DH-E(8) 

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House 

Number # of Floors 

House Variable # of Rooms 

Floor 

plan Floor area Year Built Foundation Garage Forced -air Bedrooms 

Full 

baths Half baths Other 

DH-11 1 1 2 2 2 1 3 1 0 3 DH-A(7) 

DH-12 2 3 3 3 2 2 4 2 1 5 DH-F(4) 

DH-13 1 2 2 2 2 2 3 2 0 3 DH-B(1) 

DH-14 2 2 1 3 2 2 3 1 1 4 DH-E(5) 

DH-15 2 3 4 3 2 2 4 3 1 5 DH-F(5) 

DH-16 1 1 2 2 1 2 3 1 0 3 DH-A(7) 

DH-17 2 2 2 3 2 2 3 2 1 4 DH-E(6) 

DH-18 2 1 1 3 1 2 3 1 0 3 DH-D(3) 

DH-19 1 1 3 3 2 2 3 1 0 3 DH-A(8) 

DH-20 2 2 1 3 2 1 4 1 0 4 DH-E(7) 

DH-21 1 1 2 1 1 2 3 1 0 3 DH-A(7) 

DH-22 2 3 3 1 2 2 4 3 1 5 DH-F(1) 

DH-23 2 1 1 3 2 1 3 1 0 3 DH-D(3) 

DH-24 2 2 3 1 2 2 4 2 1 4 DH-E(3) 

DH-25 1 1 2 3 2 1 3 1 0 3 DH-A(8) 

DH-26 1 1 2 1 1 1 2 1 0 2 DH-A(1) 

DH-27 1 1 2 3 1 2 3 1 0 3 DH-A(8) 

DH-28 2 3 4 1 2 2 4 3 1 4 DH-F(2) 

DH-29 1 1 1 2 1 1 2 1 0 3 DH-A(3) 

DH-30 1 2 3 2 2 2 3 2 0 3 DH-B(1) 

DH-31 1 1 3 2 2 2 3 2 0 3 DH-A(2) 

DH-32 1 1 4 1 2 2 3 2 0 2 DH-A(6) 

DH-33 1 3 3 1 2 2 4 2 0 4 DH-C(1) 

DH-34 1 1 3 1 1 2 3 1 0 3 DH-A(7) 

DH-35 1 2 2 1 2 2 3 2 0 3 DH-B(1) 

DH-36 2 2 4 1 2 2 4 2 1 4 DH-E(3) 

DH-37 1 2 3 3 2 2 3 2 1 3 DH-B(4) 

DH-38 1 1 3 2 1 2 3 1 0 3 DH-A(7) 

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House 

Number # of Floors 

House Variable # of Rooms 

Floor 

plan Floor area Year Built Foundation Garage Forced -air Bedrooms 

Full 

baths Half baths Other 

DH-39 1 2 2 2 1 2 3 2 0 3 DH-B(1) 

DH-40 2 2 3 2 2 2 4 2 1 4 DH-E(3) 

DH-41 2 2 1 3 1 2 3 1 0 4 DH-E(1) 

DH-42 1 1 3 2 1 1 3 1 0 2 DH-A(4) 

DH-43 2 2 2 3 2 1 4 2 0 4 DH-E(2) 

DH-44 1 1 1 3 2 2 2 1 0 3 DH-A(9) 

DH-45 2 2 3 4 2 1 4 2 1 4 DH-E(3) 

DH-46 1 1 2 1 2 1 2 1 0 2 DH-A(1) 

DH-47 1 1 3 2 2 1 3 1 0 3 DH-A(7) 

DH-48 1 1 4 2 1 2 3 2 0 3 DH-A(2) 

DH-49 1 1 2 3 1 1 3 1 0 3 DH-A(8) 

DH-50 2 1 1 3 1 1 3 1 0 3 DH-D(3) 

DH-51 2 3 3 2 2 2 4 2 1 4 DH-F(3) 

DH-52 2 3 1 4 2 2 4 2 1 4 DH-F(3) 

DH-53 1 2 3 1 1 2 3 2 0 3 DH-B(1) 

DH-54 1 1 1 2 1 2 2 1 0 3 DH-A(3) 

DH-55 1 1 4 2 2 2 3 2 0 2 DH-A(6) 

DH-56 2 1 2 3 1 2 3 1 0 3 DH-D(3) 

DH-57 1 2 2 2 2 1 3 2 0 4 DH-B(3) 

DH-58 2 2 4 3 2 2 3 2 1 4 DH-E(6) 

DH-59 2 3 2 3 2 1 4 2 1 5 DH-F(4) 

DH-60 1 1 3 4 2 1 3 1 0 3 DH-A(7) 

DH-61 1 1 1 4 1 2 2 1 0 2 DH-A(1) 

DH-62 2 3 1 3 2 1 4 2 1 5 DH-F(4) 

DH-63 2 1 2 4 2 1 3 1 1 3 DH-D(4) 

DH-64 1 2 4 1 2 2 3 2 0 3 DH-B(1) 

DH-65 1 1 1 4 1 1 2 1 0 3 DH-A(3) 

DH-66 1 2 2 1 2 1 3 1 0 3 DH-B(2) 

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House 

Number # of Floors 

House Variable # of Rooms 

Floor 

plan Floor area Year Built Foundation Garage Forced -air Bedrooms 

Full 

baths Half baths Other 

DH-67 1 1 1 2 2 2 3 1 0 3 DH-A(7) 

DH-68 2 1 2 3 1 1 3 1 0 3 DH-D(3) 

DH-69 2 3 3 4 2 1 4 2 1 4 DH-F(3) 

DH-70 1 1 3 1 1 1 2 1 0 2 DH-A(1) 

DH-71 2 1 3 1 2 2 3 2 1 3 DH-D(1) 

DH-72 1 2 1 4 2 2 3 2 0 4 DH-B(3) 

DH-73 2 1 3 4 2 2 3 2 0 4 DH-D(2) 

DH-74 1 3 3 4 2 2 3 2 1 5 DH-C(2) 

DH-75 3 2 3 1 2 2 4 2 1 3 DH-G(1) 

DH-76 1 1 4 4 2 2 3 2 1 3 DH-A(5) 

DH-77 3 2 3 4 2 2 3 2 1 4 DH-G(2) 

DH-78 1 1 3 1 2 1 3 1 0 3 DH-A(7) 

DH-79 1 2 3 2 1 2 3 2 0 3 DH-B(1) 

DH-80 1 2 2 4 1 2 3 2 0 4 DH-B(3) 

DH-81 2 2 1 4 1 1 3 2 0 4 DH-E(4) 

DH-82 1 2 2 4 2 1 3 2 0 3 DH-B(1) 

DH-83 1 1 3 3 1 2 3 1 0 3 DH-A(8) 

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Table A2. Attached Homes (53 total) 

Key for Table A2: 

# of floors: 1 = one story; 2 = two story 

Floor area: 1 = fewer than 148.5 m2 (1,599 ft2); 2 = 148.6 m2 to 222.9 m2 (1,600 ft2 to 2,399 ft2); 3 = 223.0 m2 (2,400 ft2) or more 

Year Built: 1 = before 1940; 2 = 1940-69; 3 = 1970-89; 4 = 1990 and newer 

Foundation: 1 = concrete slab; 2 = crawl space; 3 = finished basement, 4 = unfinished basement 

Garage: 1 = none; 2 = attached garage 

Forced Air: 1 = other; 2 = central system present 

House 

Number 

# of 

Floors 

House Variable # of Rooms 

Floor plan 

Floor 

area 

Year 

Built 

Found 

-ation Garage Forced -air 

Bedrooms Full 

baths 

Half 

baths Other 

AH-1 2 1 1 3 1 2 2 1 0 3 AH-C(11) 

AH-2 2 1 3 1 1 2 2 2 1 3 AH-C(7) 

AH-3 1 1 3 1 1 2 2 1 0 2 AH-A(2) 

AH-4 1 1 3 1 2 2 2 1 0 3 AH-A(3) 

AH-5 2 1 2 3 1 1 3 1 0 3 AH-C(15) 

AH-6 2 1 3 1 2 2 2 2 1 3 AH-C(4) 

AH-7 2 1 3 3 1 2 3 2 1 3 AH-C(16) 

AH-8 1 1 2 1 1 1 2 1 0 2 AH-A(2) 

AH-9 2 1 1 3 2 1 3 2 1 4 AH-C(17) 

AH-10 2 1 1 3 1 1 2 1 0 3 AH-C(11) 

AH-11 2 1 2 3 1 2 3 1 0 3 AH-C(15) 

AH-12 1 1 4 1 2 2 2 1 0 2 AH-A(1) 

AH-13 2 1 2 1 1 2 2 2 1 2 AH-C(6) 

AH-14 1 1 2 1 1 2 2 1 0 2 AH-A(2) 

AH-15 2 2 3 1 2 2 3 1 0 3 AH-D(1) 

AH-16 2 1 1 2 1 1 2 1 0 2 AH-C(2) 

AH-17 1 1 2 2 1 1 1 1 0 2 AH-A(5) 

AH-18 2 1 3 1 1 1 2 1 0 2 AH-C(2) 

AH-19 2 1 2 1 2 2 2 1 0 3 AH-C(3) 

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House 

Number 

# of 

Floors 

House Variable # of Rooms 

Floor plan 

Floor 

area 

Year 

Built 

Found 

-ation Garage Forced -air 

Bedrooms Full 

baths 

Half 

baths Other 

AH-20 2 1 1 4 2 2 3 1 0 3 AH-C(12) 

AH-21 2 2 1 4 2 2 3 1 0 3 AH-D(4) 

AH-22 2 1 3 1 2 1 2 2 1 2 AH-C(1) 

AH-23 2 1 3 4 2 2 3 2 1 3 AH-C(13) 

AH-24 2 2 1 3 1 1 3 1 0 3 AH-D(5) 

AH-25 1 1 2 1 2 1 2 1 0 2 AH-A(1) 

AH-26 2 1 4 1 1 2 3 2 1 2 AH-C(5) 

AH-27 2 2 1 4 2 1 3 1 0 5 AH-D(6) 

AH-28 2 2 3 3 1 2 3 2 1 3 AH-D(7) 

AH-29 2 2 4 1 2 2 2 1 0 3 AH-D(2) 

AH-30 1 1 3 2 2 1 2 1 0 2 AH-A(1) 

AH-31 1 1 2 3 1 2 1 1 0 3 AH-A(7) 

AH-32 1 1 2 4 2 2 2 1 0 3 AH-A(4) 

AH-33 1 1 1 3 1 2 1 1 0 2 AH-A(6) 

AH-34 2 3 3 3 1 2 4 3 2 4 AH-E(1) 

AH-35 2 1 2 1 1 1 2 1 0 2 AH-C(2) 

AH-36 1 1 2 1 2 2 2 1 0 2 AH-A(1) 

AH-37 1 1 2 2 2 1 2 1 0 2 AH-A(1) 

AH-38 1 1 1 4 2 1 2 1 0 3 AH-A(4) 

AH-39 1 1 4 1 1 2 2 1 0 2 AH-A(2) 

AH-40 2 1 1 1 1 1 1 1 0 1 AH-C(8) 

AH-41 2 2 2 3 1 2 3 2 1 4 AH-D(8) 

AH-42 2 1 2 4 2 2 2 1 0 3 AH-C(10) 

AH-43 1 2 3 1 2 2 3 1 0 3 AH-B(1) 

AH-44 1 1 3 2 1 1 1 1 0 2 AH-A(5) 

AH-45 1 1 2 2 1 2 2 1 0 2 AH-A(2) 

AH-46 2 1 2 2 1 2 3 1 0 3 AH-C(9) 

AH-47 1 1 3 4 2 2 3 2 1 3 AH-A(8) 

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House 

Number 

# of 

Floors 

House Variable # of Rooms 

Floor plan 

Floor 

area 

Year 

Built 

Found 

-ation Garage Forced -air 

Bedrooms Full 

baths 

Half 

baths Other 

AH-48 2 1 3 2 1 2 2 2 1 2 AH-C(6) 

AH-49 1 1 1 2 2 1 2 1 0 2 AH-A(1) 

AH-50 2 1 3 2 2 2 2 2 1 3 AH-C(4) 

AH-51 2 1 3 3 1 1 2 1 0 3 AH-C(11) 

AH-52 2 2 3 1 1 2 3 2 1 4 AH-D(3) 

AH-53 1 1 4 2 1 2 2 1 0 2 AH-A(2) 

TABLE A3. Manufactured Homes 

Key for Table A3: 

Floor area: 1 = less than 148.5 m2 (1,599 ft2

); 2 = 148.6 m2 (1,600 ft2) or more 

Year Built: 1 = before 1940; 2 = 1940-69; 3 = 1970-89; 4 = 1990 and newer 

Forced Air: 1 = other; 2 = central system present 

House 

Number 

Floor 

area 

Year 

Built 

Forcedair # of 

Bedrooms 

# of 

Baths 

# of Half 

baths 

# of Other 

rooms Floor plan 

MH-1 1 3 2 2 1 0 2 MH-B(1) 

MH-2 1 4 2 3 2 0 2 MH-A(1) 

MH-3 1 3 1 2 1 0 2 MH-B(1) 

MH-4 1 2 2 2 1 0 2 MH-B(1) 

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Appendix B Source Locations and Model Modifications for Each Building 

Table B1 lists the 40 buildings modeled in this simulation study and shows the locations of the 

generator simulated for each building. Based on CPSC analysis of CO poisoning death incidents 

from 2004 through 2012, a subset of the NIST suite of homes collection described above (in some 

cases with modifications to better represent the houses in the CPSC CO incident database) were 

used for this analysis including 31 detached house (DH) models, 4 attached house (AH) models, 

and 2 manufactured house (MH) models. Any modifications are listed in Table B1 and described 

in more detail below. 

Three new building models were created to represent various forms of garages (GAR) modeled 

including 2 single-zone garage/sheds (1 car size and 2 car size) and 1 larger garage with a separate 

work space inside as described below. 

Table B1. Source Locations and Model Modifications for Each Building 

House 

number 

Source locations 

PRJ file 

modified 

(yes/no)? 

Floor 

plan 

Garage Basement/ 

crawlspace 

Interior room(s) 

DH-1 N DH-B(1) GAR n.a. Kit, Bed3 

DH-2 N DH-A(8) GAR Bed1 Kit 

DH-2 Add INT GAR DH-A(8) GAR Bed2 Kit 

DH-3 N DH-A(1) n.a. CRAWL Kit, Bed1 

DH-5 N DH-A(2) GAR n.a. Kit, Bed3 

DH-7 N DH-B(5) GAR Bed3 Kit 

DH-8 N DH-A(2) GAR n.a. Kit, Bed3 

DH-10 N DH-E(8) GAR Den Kit 

DH-12 N DH-F(4) GAR Bed4 Kit 

DH-19 Add INT GAR DH-A(8) GAR bed2 kit 

DH-21 N DH-A(7) n.a. n.a. Kit, Bed3 

DH-21 Year Built DH-A(7) n.a. n.a. Kit, Bed3 

DH-24 

Year Built 

Delete GAR 

DH-E(3) n.a. n.a. Kit, Bed1 

DH-27 N DH-A(8) n.a. Bed1 Kit 

DH-32 N DH-A(6) GAR n.a. Kit, Bed3 

DH-33 Year built DH-C(1) GAR NA Kit, Bed2 

DH-34 N DH-A(7) n.a. n.a. Kit, Bed3 

DH-41 N DH-E(1) n.a. Hall kit 

DH-44 N DH-A(9) GAR Bed1 kit 

DH-45 N DH-E(3) GAR Basement Kit 

DH-45 Year built 

Add INT GAR 

DH-E(3) GAR Basement Kit, 

DH-52 Year built DH-F(3) GAR Basement Kit 

DH-56 N DH-D(3) n.a. Bed2 Kitchen 

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House 

number 

Source locations 

PRJ file 

modified 

(yes/no)? 

Floor 

plan 

Garage Basement/ 

crawlspace 

Interior room(s) 

DH-60 N DH-A(7) GAR Basement Kit 

DH-60 Year Built 

Add INT GAR 

DH-A(7) GAR Basement Kit 

DH-61 Year built DH-A(1) n.a. Basement Kit 

DH-61 N DH-A(1) n.a. Basement Kit 

DH-63 Year Built 

Delete GAR 

DH-D(4) n.a. Basement Kit 

DH-63 Delete Gar DH-D(4) n.a. Basement Kit 

DH-64 N DH-B(1) GAR n.a. Kit, Bed3 

DH-81 N DH-E(4) n.a. Basement Kit 

MH-1 N MH-B(1) n.a. crawl Kit, Bed1 

MH-1 Size 

Year built 

NA n.a. n.a. Kit, Bed1 

AH-3 N AH-A(2) n.a. n.a. Kit, Bed1 

AH-10 N AHC(11) 

n.a. Den Kit 

AH-34 Add GAR AH-E(1) GAR Bed3 Kit 

AH-21 Add INT 

GAR 

AH-D(4) GAR Basement Kit 

GAR-1 new NA GAR NA NA 

GAR-2 new NA GAR NA NA 

GAR-3 new NA GAR NA NA 

The modifications are described further below:
 

DH-2: Bedroom 1 in the basement was converted to an integral garage.
 

DH-19: Bedroom 1 in the basement was converted to an integral garage.
 

DH-21: Air leakage was modified based on year built and floor area per Table 1 and Equation 1 of
 

Persily et al. (2013) to represent the oldest category of construction (before 1940). 

DH-24: Two modifications were made. The side attached garage was deleted and air leakage was
 

modified based on year built and floor area to represent the oldest category of construction (before 

1940). 

DH33: Air leakage was modified based on year built and floor area to represent the newest 

category of construction (1990 and newer). 

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DH-45: Two modifications were made. Part of the unfinished basement was converted to an 

integral garage and air leakage was modified based on year built and floor area to represent the 

newest category of construction (1990 and newer). 

DH-52: Air leakage was modified based on year built and floor area to represent the newest 

category of construction (1990 and newer). 

DH-60: Two modifications were made. internal garage added and air leakage was modified based 

on year built and floor area to represent the second oldest category of construction (1940 to 1969). 

DH-61: Air leakage was modified based on year built and floor area to represent the second oldest 

category of construction (1940 to 1969). 

DH-63 (mod1): Two modifications were made. The side attached garage was deleted and air 

leakage was modified based on year built and floor area to represent the oldest category of 

construction (before 1940). 

DH-63 (mod2): The side attached garage was deleted. 

MH-1: MH1 was modified to be smaller with 78 m2

 (840 ft2) of floor area with 2 bedrooms, 1 

bathroom and a kitchen. The air leakage was modified based on year built and floor area to 

represent the oldest category of construction (before 1940). 

AH-34: The first floor living room was converted to an integral garage. 

AH-21: The side attached garage was deleted and part of the unfinished basement was converted 

to an integral garage. 

GAR-1 was created as a new model of a detached garage with a single 32.5 m2 (350 ft2) zone and 

envelope air leakage of 4.81 cm2/m2 based on the median garage envelope leakage in Table 2 of 

Emmerich et al. 2003. 

GAR-2 was created as a new model of a detached garage with a single 60.4 m2 (650 ft2) zone and 

envelope air leakage of 4.81 cm2/m2 based on the median garage envelope leakage in Table 2 of 

Emmerich et al. 2003. 

GAR-3 was created as a new model of a detached garage with two zones including a main 60.4 m2 

(650 ft2) garage zone and a separate 32.5 m2 (350 ft2) workroom with envelope air leakage of 4.81 

cm2/m2 based on the median garage envelope leakage in Table 2 of Emmerich et al. 2003. 

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Appendix C Analysis of Unmodified Generator X CO Emission Ratio at Reduced O2 vs
 

Ambient
 

The shed test data for unmodified Generator X from Figure 9 of NIST Technical Note 1781 

(Emmerich et al. 2013) were used to assist in determining an appropriate ratio of the generator CO 

emission rate at reduced O2 to the CO emission rate at ambient conditions. Table C1 shows the 

CO emission rate at ambient from the University of Alabama’s testing of unmodified Generator X 

(Tab C of CPSC 2012) and average CO emission rate for all measured data below 18 % O2 for the 

6 loading modes. The calculated 6-mode weighted ratio for the generator was 3.0. 

Table C1. Unmodified Generator X CO Emission Ratio at Reduced O2 

Mode Weighting CO emission rate at 

ambient (g/h) 

CO emission rate 

below 18 % O2 (g/h) 

Ratio 

1 0.09 1000.6 3652 3.6 

2 0.2 671.16 3395 5.0 

3 0.29 697.54 2487 3.6 

4 0.3 1075.6 2100 1.9 

5 0.07 971.04 1810 1.9 

6 0.05 911.78 1623 1.8 

49