### CPSC Staff Statement on the

National Institute of Standards and Technology Report,

“ NIST Technical Note 1782 : Residential Carbon Monoxide Exposure due to Indoor Generator

Operation: Effects of Source Location and Emission Rate ” 1



### July 2013

The repor t titled

, “ NIST Technical Note 1782 : Residential Carbon Monoxide Exposure

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

, ” presents the

findings of research conducted by the National Institute of Standards and Technology (N IST)

under an interagency agreement with the U.S. Consumer Product Safety Commission (CPSC)

. 2



### NIST performed this research in support of CPSC’s advance notice of proposed rulemaking

(ANPR) to address the carbon monoxide (CO) poisoning hazard associated wit h portable

generators

. 3



### Under this agreement with CPSC, NIST performed a computer simulation study

, using

the multizone airflow and contaminant transport model CONTAM on a collection of 87

dwellings that are representative of the U.S. housing stoc k

, with a portable generator operating

within the home in locations identified in CPSC’s incident data

. Coupled with a variety of

weather conditions

, NIST conducted almost 100,000 individual

, 24

- hour simulations

. This report

presents the simulation results in te rms of the maximum levels of percent carboxyhemoglobin

that occupants could experience in the occupied portions of the dwellings as a function of CO

emission rate for different indoor source locations.

NIST has already published Technical Note 1782, ava ilable at :

http://www.nist.gov/customcf/get_pdf.cfm?pub_id=912394

.

1 This statement was prepared by the CSPC staff, and the attached report was produced by NIST for CPSC staff . The statement

and report have not been reviewed or approved by, and do not necessarily represent the views of, the Commission.

2 CPSC

- I

- 09

- 0017

.

3 Portable Generators; Advance Notice of Proposed Rulemaking; Request for Comments and Information

, Feder al

Register, 71 FR 74472, December 12, 2006.

# NIST Technical Note 1782

Residential Carbon Monoxide Exposure due

to Indoor Generator Operation: Effects of

Source Location and Emission Rate

Andrew K. Persily

Yanling Wang

Brian Polidoro

Steven J Emmerich

# NIST Technical Note 1782

Residential Carbon Monoxide Exposure due

to Indoor Generator Operation: Effects of

Source Location and Emission Rate

Andrew K. Persily

Yanling Wang

Brian Polidoro

Steven J Emmerich

Energy and Environment Division

Engineering Laboratory

J une 2013

U.S. Department of Commerce

Cameron F. Kerry, Acting Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and DirectorCertain 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 1782

Natl. Inst. Stand. Technol. Tech. Note 1782

, 47 pages ( June 2013 )

CODEN: N TNOEF

### iii ABSTRACT

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

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

generators that can result in death or serious adverse health effects in exposed individuals. CPSC

databases contain records of 755 deaths from CO poisoning associated with consumer use of

generators in the period of 1999 through 2011, with nearly three-quarters of those occurring

between 2005 and 2011 [ 1 ]. The majority of these incidents occur during power outages, or

when a generator is used to provide power to a structure that is not wired for electrical power.

Typically, these deat hs occur when consumers use 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 a home 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 amount of CO emitted from these devices. In

order to support life- safety based analyses of potential CO emission limit s, a computer

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

source location and CO emission rate. These simulations employed the multizone airflow and

contaminant transport model CONTAM, which was applied to a collection of 87 single- family,

detached dwellings that are representative of the U.S. housing stock for that housing type. A total

of almost one hundred thousand individual 24-hour simulations were conducted. This report

presents the simulation results in t erms of the maximum levels of carboxyhemoglobin that would

be experienced by occupants in the occupied portions of the dwellings as a function of CO

emission rate for different indoor source locations.

KEYWORDS : carbon monoxide; CONTAM; emergency generato rs; multizone airflow model;

simulation

### iv TABLE OF CONTENTS

1. INTRODUCTION 1

2. ANALYSIS METHOD 1

2.1 Description of homes 1

2.2 Modeling approach 3

2.2.1 CONTAM model 3

2.2.2 Baseline house models 3

2.2.3 Source locations and emission rates 6

2.2.4 Simulation cases and output analysis 7

3. RESULTS 9

3.1 House airtightness and air change rates 9

3.2 Detailed results for one detached house (DH -10) 11

3.3 Summary results for all houses 14

3.4 Summary results for subsets of houses 20

4. S UMMARY AND DISCUSSION 24

5. ACKNOWLEDGEMENTS 26

6. REFERENCES 26

APPENDICES

A. House Characteristics 28

B. Source Locations for Each House 32

C. Integral Mass Balance Analysis of Burst Sources 35

D. Cumulative Frequency Distributions of MaxCOHb in Tabular Form 38

### 1 1. INTRODUCTION

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

hazard of acute residential carbon monoxide ( CO ) exposures from portable gasoline-powered

generators , which can result in death or serious adverse health effects in exposed individuals.

CPSC databases contain records of 755 deaths from CO poisoning associated with consumer use

of generators in the period of 1999 through 2011, with nearl y three -quarters of those occurring

between 2005 and 2011 [ 1 ]. The majority of these incidents occur during power outages, or when

a generator is used to provide power to a structure that is not wired for electrical power. Typically,

these deaths occur when consumers use a generator in an enclosed or partially enclosed space or

outdoors near a partially open door, window or vent. While avoiding the operation of such

generators in or near a home 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 amount of CO emitted from these devices. The magnitude of

such reductions needed to reduce exposures to some specific level depend s on the complex

relationship between CO emiss ions from these generators and occupant exposure. Technically

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

investigation of CO emission s from generators in a shed and a house. These investigations

included measurements on prototype generators that were modified to reduce their CO emission

rates [ 2 ]. That study 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 involves the interaction between

generator operation, house characteristics, occupant activity, and weather conditions. In order to

support life- safety based analyses of potential CO emission limits for generators, a computer

simulation study was cond ucted to evaluate indoor CO exposures as a function of generator source

location and CO emission rate. These simulations employed the multizone airflow and

contaminant transport model CONTAM [ 3 ], which was applied to a collection of 87 single- family,

detached dwellings that are representative of the U.S. housing stock for that housing type . A total

of almost one hundred thousand individual 24-hour simulations were conducted. This r eport

presents the simulation results in terms of the maximum levels of percent carboxyhemoglobin

(COHb) that would be experienced by occupants in the occupied portions of the dwellings as a

function of CO emission rate for different indoor source lo cation s.

2. ANALYSIS METHOD

This section describes the approach used to perform the simu lations, including the houses that

were considered , the simulated generator locations and CO emission rates, and the manner in

which the simulations were performed and the output analyzed. In designing this study, the goal

was to be reasonably conservative in terms of the assumptions and inputs employed. Decisions

about the assumptions and inputs used in the analysis were made not to result in worst- case conditions (highest CO exposures ), but rather to tend towards higher exposures while still being

realistic and technically sound.

2.1 Description of homes

Th e homes used in the simulations are based on a collection of dwellings that were previously

defined by Persily et al. [ 4 ], which includes just over 200 dwellings that together represent 80 %

of the U.S. housing stock. Those dwellings are grouped into four categories: detached (83 homes ),

### 2 attached (53 homes), manufactured homes (4) and apartments (69). The definition of this set of

dwellings was based on the following variables using the US Census Bureau’s American Housing

S urvey (AHS) [ 5 ] and the US Department of Energy’s (DOE) Residential Energy Consumption

Survey (RECS) [ 6 ] : 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. 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 [ 3 ].

Only the detached and manufacture d home models were used in this analysis, for a total of 87

homes. The attached and apartment models were not employed based on the challenge in

accounting for airflow between units and the l ack of air leakage data for th e partitions between

units. Given the prevalence of s ingle-family dwellings within the U.S. housing stock, these 87

homes represent on the order of 60 % of U.S. dwellings. Appendix A summarizes the

characteristics of the 87 dwellings included in the analysis and identifies the corresponding

CONTAM project fi le name and associated floor plan. 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.

In constructing this collection of dwellings, the year of construction was used to assign the

exterior wall leakage based on data from studies of the airtightness i n single- family homes [ 7-9 ].

Exterior wall leakage is commonly defined in terms of the normalized leakage area, which for

these dwellings is a function of the year built and house floor area as presented in Table 1 [ 4 ]. The

normalized leakage (NL) values from this table are converted to an effective leakage area (ELA)

for use in the house models based on the following equation [ 10 ]:

NL = 1000 ELA

A f 

### � H

2.5 

### � 0

. 3 

### (1)

where , A f 

### is the floor area in m 2 

### and H is the building height in m.

Normalized leakage area (dimensionless)

Year built Floor area less than

148.6 m 2 (1600 ft 2 ) Floor area greater than

148.6 m 2 (1600 ft 2 )

Before 1940 

### 1.29 0.58

1940

- 1969 

### 1.03 0.49

1970

- 1989 

### 0.65 0.36

1990 and newer 

### 0.31 0.24

Table 1 Normalized leakage by construction year and floor area

In developing the house models used in this study, the conditioned floor area of each house was used in conjunction with Table 1 to determin e its ELA value by solving Equations (1) for ELA.

The value of ELA was calculated using the NL from the table, and A f 

### and H for the house. The

floor area used in this calculation did not include garages, attics and unfinished basements.

### 3 2.2 Modeling approach

Using this set of homes, indoor CO concentration s were calculated using the multizone airflow

and contaminant transport model CONTAM [ 3 ] 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 analysis interval. In

order to compare the results for different cases, the concentrations from each simulation were then

used to calculate COHb values for an occupant spending the full 24 hours in each room. T he

maximum COHb (maxCOHb) value among the occupied rooms of the house was used as a metric

of CO exposure for that house, source and weather scenario. This section describes the manner in

which these simulations were conducted and the results were analyzed.

2.2.1 CONTAM model

As noted previously, the indoor CO concentration s were calculated using the multizone airflow

and contaminant transport model CONTAM [ 3 ] . CONTAM is a simulation tool for pred icting

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 and doorways ) 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 p aths 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 simultaneous ly to

determine the interzone pressures relationships and resulting airflow rates between each zone,

including the outdoor s. These airflow rates can be calculated over time as weather conditions and

system airflow rates change. Once the airflows are establis hed, 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, an d a range of validation studies have demonstrated

its ability to reliably predict building air change rates and contaminant levels [ 11

, 12 ].

2.2.2 Baseline house models

The models used in this analysis were based on the 83 detached and 4 manufactured homes

described above

. In general, these models were used as previously defined. However, a number of

decisions on their configuration were required as well as some limited modifications

.

Air handling system operation : While many of the 87 homes in this 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. The limited electrical output of these generators reduces

the likel ihood that whole-house space conditioning systems will be operating . Also

, forced

- air

system operation will increase ventilation rates [ 10 ], thereby reducing CO concentrations.

Therefore , having the system off is con sistent with the goal of the analysis being reasonably

conservative. In addition, all local exhaust fans (k itchen and bath) were assumed to be off.

Wind exposure : A CONTAM model of a building must be associated with a coefficient to account

for the impacts of surrounding terrain, buildings and vegetation on wind-induced pressures on the

exterior façade of the building. CONTAM describes three categories of terrain including flat

,

### 4 exposed areas (e.g., airport), suburban and dense urban centers . A user can input coefficients to

describe terrain options in between the flat and urban extremes . These simulations employ ed 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 dir ected into the garage door. This orientation

was used so as to increase the transport of CO from the garage of the house, consistent with the

goal of being reasonably conservative.

Weather conditions : Each house and generator source combination was analyzed for 28 individual

days

, with each CO release event occurring at the beginning of each 24-h analysis period. Each of

the 28 simulation s employed a different day of weather conditions, including outdoor temperature,

wind speed and wind direction, that varied on an hourly basis. The 28 days of weather correspond

to two weeks of cold weather, one week of warm and one week of mild. The hourly weather data

were based on weather files for the following three cities: Detroit MI (cold)

, Miami FL (warm)

and Columbus OH (mild). The file s were o btained from the EnergyPlus Energy Simulation

Software website: http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data.c fm

. Table

2 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. Summary values are also

included for the cold

, mild and warm days separately.

Indoor air temperatures : 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. The air temperature in

zones containing the generators was assumed to increase linearly over two ho urs 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 (86 °F). These indoor air temperature changes are based on the results of a series of

experimental studies of generat or operation conducted at NIST [ 2 ] . These temperature schedules

were applied to the constant source cases (described below) . In the burst source simulations (also

described below), the generator was assumed to release all of the associated CO over a very short

period of time and no change in the interior temperatures was simulated. The indoor air

temperatures of unconditioned spaces, i.e., crawl spaces, unfinished basements, garages and attics,

were held constant 23 °C (73.4 °F). This assumption does not capture temperature variations in

su ch unconditioned spaces based on weather and interaction with the outdoors. However, the use

of a constant temperature greatly simplifies the analysis and generally serves to reduce the driving

forces of building air change, consistent with the reasonably conservative simulation approach

.

Door and window positions : All interior doors were assumed to be open during the simulations

and all exterior doors and windows closed with the following exceptions. When the generator was

located in an unfinished basement, the door between the basement and the upstairs was closed.

Finished basements had an open stairway between the basement and the first floor, and all interior

doors on both levels were open. For cases in which the generator was located in the attached

garage, the door from the garage to the house was assumed be open roughly 5 cm (2 in. ) to

accommodate an extension cord running from to the generator. When the generator was in the

garage with the garage door open, the open garage door was modeled as an opening 4.6 m (15 ft.)

wide and 0.6 m (2 ft. ) high.

### 5 Day Outdoor temperature

, °C (°F) Wind speed, m/s (mph)

Average Minimum Maximum Average Minimum Maximum

Cold

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)

Mild

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)

Warm

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)

Average values for weather periods

Cold days 0.7 (33.2)

- 2.1 (28.2) 3.8 (38.9) 4.0 (9.0) 1.2 (2.6) 6.6 (14.7)

Mild days 9.8 (49.7) 4.3 (39.8) 15.2 (59.3) 4.5 (10.1) 0.3 (0.7) 8.0 (17.8)

Warm days 29.1 (84.5) 25.8 (78.5) 34.0 (93.1) 3.1 (7.0) 1.0 (2.2) 7.1 (15.8)



### Table 2 Summary of Hourly Weather Data Used in Simulations

### 6 2.2.3 Source locations and emission rates

The range of potential CO generation scenarios for indoor operation of generators i n actual homes

i s very large . G iven the goals of being reasonably conservative and avoiding excessive

complexity, the simulated source scenarios covered only a well

- defin ed range. Two types of

sources were considered: a constant CO generation rate lasting 18 hours; and, a short “burst” of

CO intended to represent a generator with some form of CO emission control technology (e.g. a

shut off device) for which a constant generation rate is not a reasonable assumption. The constant

generation rate for the first type of source and the mass released by the seco nd used in the

simulations covered a range of values based on measurements and analyses conducted by CPSC

and NIST. The source scenarios that were analyzed include the following:

Constant generation rate for 18 hours with the source in the following locations:

Closed garage (if applicable to the model house)

Open garage (if applicable to the model house)

Basement (if applicable to the model house)

Interior room (on first floor)

Short term burst source with the source in the following locations:

Closed garage (if applicable to the model house)

Basement (if applicable to the model house)

Interior room ( on first floor)

The interior room for each house was selected from those rooms defined by the exis ting floor

plans of the model homes employed, with the goal of select ing a room on the first floor where a

generator could be expected to be located

. The interior rooms are identified by their CONTAM

“zone name” in Appendix B, which lists the zone names of the constant and burst sources in each

of the simulated houses. In some cases these locations are identified as bathrooms, however this

selection is based on the zones in the existing CONTAM models and is not intended to suggest the

bathroom as a likely generator location. The interior rooms were selected based on their locations

on the first floor and not on their designation in the existing models.

The simulated CO emission rates for the constant (in units of g/h) and the burst (units of total mg

released) sources are contained in Table 3 and Table 4 respectively , along with an explanation of

each value. The short term burst source values are based on an integral mass balance analysis of

generator tests conducted at NIST, which is described in Appendix C of this document. For all of

the simulations the outdoor CO concentration was assumed to equal zero, since the indoor

concentrations of i nterest are well above typical ambient levels.

### 7 1000 g/h Approximate maximum for an unmodified nominal 5.5 kW generator running at

close to amb ient oxygen levels based on NIST measurements [ 13 ]. ( Note that this

value does not constitute a n absolute upper limit on emissions. )

750 g/h Intermediate value of unmodified generator to support assessment of impact

. 500 g/h T ypical value for an unmodified generator running at essentially ambient oxygen

levels based on NIST measurements [ 13 ]

. 400 g/h Two times CPSC “reduced severity” estimate

200 g/h CPSC e stimate of emission rate neede d to reduce severity of CO exposure in the

home [ 14 ]

100 g/h 50 % of CPSC “reduced severity” estimate

50 g/h 25 % of CPSC “reduced severity” estimate

20 g/h 10 % of CPSC “reduced severity” estimate



### Table 3 CO emission rates for the constant source

1000 g Two times the highest “constant source” generation rate running for 30 min

500 g Highest “ constant source” generation rate (1000 g/h) running for 30 min

200 g Based on h ighest value from NIST burst analysis (see Appendix C)

100 g One

- half of highest value

50 g Based on m id

- range value from NIST burst analysis

25 g One

- half of mid

- range value

15 g Based on l owest value from NIST burst analysis

5 g One third of lowest value from NIST analysis



### Table 4 CO emission rates for the burst source

2.2.4 Simulation cases and output analysis

The simulations that were run are depicted in Figure 1 , which shows the 87 houses times 7 source

scenarios with 8 source strengths each and 28 days of weather for each house/source

location/source strength combination. Given that some houses do not have garages and/or

basements, the total number of cases sim ulated is 96096.

Figure 1 Schematic showing simulation cases

Each simulation corresponds to one house, one source location and source strength, and one day of

weather. The output of each simulation is the CO concentration versus time in each zone of the

house. Based on the simulation time step of 5 min , the output consists of 288 concentrations

values in each zone for each 24

- h simulation. As not ed earlier, the CO generation commenced at Houses

- Detached (83)

- Manufactured (4) Weather

- 14 days cold

- 7 days warm

- 7 days mild Source scenarios

Constant (mg/h for 18 h)

- closed garage (when applicable)

- open garage (when applicable)

- basement (when applicable)

- interior room

Short burst (mg)

- closed garage (when applicable)

- basement (when applicable)

- interior room

8 values for each of the 7 source scenarios

### 8 the beginning of each 24-h period. In the case of the constant source, the CO generation stopped

18 hours later, after which the indoor CO concentrations started decreasing back to ambient levels.

COHb levels were calculated for an occupant in each occupied zone of the house over the 24-h

simulation period using the Coburn- Forster

- Kane (CFK) equation [ 15

, 16 ] and input values

provided by CPSC , specifically an RMV ( respiratory minute volume ) of 15 L/min and an initial

COHb level of 0.0024 ml/ml. The maximum COHb (maxCOHb) value among the occupied zones

of each house was used as the output metric for each simulation. The maxCOHb values were considered separately for each source location to generate a frequen cy distribution for each

source/ location combination. Fifty

- six such distributions were generated from the simulatio n results, i.e., seven locations times eight source strengths per location.

In order to assess the impact of house size, airtightness, and weather conditions, subsets of the

detached house results were considered separately. With respect to house size, s eparate frequency

distributions were generated for the 37 detached homes in the s mallest size category , for the 16

homes in the largest size category and for the remaining 30 “ mid

- sized” homes

. These size

categories correspond to conditioned floor areas of 107.4 m 2 

### (1152 ft 2 

### ), 180.4 m 2 

### (1942 ft 2 

### ), and

275.5 m 2 

### (2966 ft 2 

### ), respectively for the small, mid

- sized and large detached homes. Note that all

of the manufactured houses are the same size , i.e., 86.3 m 2 

### (929 ft 2 

### ), and their results were also

considered separately. In order to assess the impact of house airtightness, separate frequency

distributions of maxCOHb were generated for the 20 tightest and 20 leakiest detached houses . The

identification of these tight and leaky homes is based on the air change rate at an indoor-outdoor

pressure difference of 50 Pa (0.2 in. H 2 

### O), which is determined by simulating a building

pressurization (blower door) test using CONTAM. Finally, the impacts of weather were examined

for the detached houses by generating separate fr equency distributions of max COHb for the two

cold weeks of weather, one week of mild weather , and one week of warm weather.

### 9 3. RESULTS

This section presents the results of the simulations. The results are presented in the form of

frequency distributions of the maxCOHb values for specific generator locations and source strengths that show the impact of CO emission rates on potential occupant exposure. However,

before those distributions are presented and discussed, the house airtightness values an d air change

rates are summarized and detailed simulation results are presented for one house as an illustration

of the information produced by these simulations.

3.1 House airtightness and air change rates

The CONTAM simulations calcuate airflow rates of each building zone to and from the outdoors

as well as between the indivdual zones. Those airflows are calculated at each time step and depend

primarily on building leakage values, weather conditions and indoor temperatures. As noted in the

previous section, the indoor temperatures change during generator operation due to the heat

released by the generator. Therefore, the ventilation characteristics of the model houses are fairly

complex and depend on the generator location and time during the emission event. Presenting the

house air change rates for all generator locations, weather conditions and times would involve a

very large amount of data. Instead, the building airtightness values and average air change rates

for a single day are summarized for all th e houses. More detailed air change rates are presented for

one house in the following section

.

Figure 2 Frequency distribution of house airtightness values

Building airtightness values for the houses were obtained by performing simulated blower door

tests on each house using CONTAM. The results of these simulations reflect the envelope leakage

values presented in Table 1 , which are used to de termine the leakage area for a given house based

### 10 on its age and size. CONTAM is then run for each house in a mode that determines the airflow

required to pressurize the house to a given reference pressure difference between the indoors and

outdoors. The airflow is then normalized by the building volume to yield the common airtightness

metric of air changes per hour at 50 Pa. The results of these simulations are presented in Figure 2

, which is a frequency distribution of the building air change rate at an indoor-outdoor pressure

difference of 50 Pa. The values for the 87 houses range from 3.6 h -1 

### to 25.6 h -1 

### , with a mean of

11.4 h -1 

### and a standard deviation of 6.2 h -1



### . Note that these air change rates correspond to an

elevated test pressure under a simulated pressurization test and are therefore much higher than the

air change rates induced by weather and normal building operation.

Figure 3 Freq uency distribution of whole house air change rates for Jan01

While the CO simulations accounted for all interzone airflows between building zones and the

outdoors, building air change rates were not output as part of the analysis. However, whole house

air change rates were calculated separately for each house using Jan01 weather data

, and are

summarized in Figure 3 to illustrate the range of air change rates and their dependence on

generator location . This plot contains frequency distributions of the daily av er age air change rates

with the generator off and with the generator operating in the interior room and in the garage. The

mean air change rate with the generator off is 0.54 h -1 

### , while the mean with the generator in the

interior room is 0.57 h -1 

### . As described earlier, when the generator is operating at a constant

generation rate, as in the second case, the indoor temperatures in that zone and adjacent zones are increased to account for the heat released by the generator. These temperature increases resu lt in

higher air change rates . When the generator is operating in the garage, which only applies to 57 of

the simulated homes, the air change rate increase is larger, particularl y with the garage door open.

### 11 The mean daily average air change rate with the generator operating at a constant rate in a closed

garage is 0.62 h -1 

### , while the mean with the generator in the open garage is 0.82 h -1



### .

3.2 Detailed results for one detached house ( DH -10)

This section presents simulation results for detached house DH- 10 as an example of the detailed

information produced by the CONTAM modeling. This particular house was selected because it

has both a garage and a basement, but it s results are not presented as being representative of the

larger group of homes. Figure 4 shows a floor plan of the house. For this house the CO sources

were located in the garage (closed and open), Bathroom 2 in the basement, and the 1⁄2 Bath on the

first floor ( as the interior room source). As noted earlier, these bathrooms source locations are

based on the zones in the existing CONTAM models and not on their designation as bathrooms.

Figure 4 Floor plan of house DH

- 10

As noted earlier , the house air change rates vary with weather conditions (outdoor

temperature, wind speed and wind direction). In addition, the indoor air temperature change s when the generator is running as a constant source (due to the heat released from the

generator) also impact the air change rates. To illustrate these impacts, Figure 5 contains

frequency distributions for the hourly air change rates in house DH10 for all 28 days of

### 12 weather with no generator running and with the generator running in the garage (closed) and

in the interior room , both in the constant source mode. The hourly air change rate s with the

generator off range from 0.06 h -1 

### to 0.62 h -1 

### , with a mean of 0.25 h -1



### . Due to the increase in

indoor temperature s with the generator running, the air change rates are larger with the

constant sources, as seen in Figure 5

. With the generator in the closed garage , the air change

rate ranges from 0.07 h -1 

### to 0.90 h -1 

### , with a mean of 0.36 h -1



### . With the generator running in

the interior room , the air change rates also increase relative to the generator

- off case, but are

less than for the closed garage case.

Figure 5 Frequency distribution of air change rates in DH10 with generator off and on

### 13 Figure 6 shows the predicted CO concentrations in the kitchen zone for DH -10 with the generator

in the closed gar age and a constant source of 1000 g/h. Each line corresponds to the concentrations

for one of the 28 days of simulated weather

, with each day identified as cold, mild or warm . This

plot highlights the variability in the predicted CO concentrations for the different days, which

supports the use of multiple days of weather to obtain a better characterization of the CO exposure

than could be obtained using a ny particular day. Simulation results for only a single d ay are highly

dependent on the specific weather conditions, particularly wind speed and direction, and could

lead to potential misinterpretations relative to considering a wide range of weather conditions.

Figure 6 DH -10 CO concentrations in kitchen for 1000 g/h source in closed garage

Table 5 presents average predicted values of daily maximum and daily mean CO concentrations in

house DH-10 for a constant source of 1000 g/h, which is a high- end value for an unmodified

g enerator as discussed earlier. Average values of the daily maximum and mean concentrations are

included for all four generator locations. Concentrations for each occupied room are contained in

Table 5 and show the impact of source location. F or example, when the generator is in the garage,

the highest average concentrations are on the first floor. For this generator location , the basement

concentrations are much lower than on othe r levels , regardless of the garage door position. With

the generator in the garage , s ignificant amounts of CO reach the basement only during warm

weather conditions due to the downward stack effect that exists when the indoor temperature is

lower than outdoors. When the generator is in the basement, the highest concentrations are in the

### 14 zones on that level. The CO concentrations in the basement and interior room locations are we ll

above those when the generator in the garage, since in the latter cases much of the CO dissipates

to the outdoors before entering the house. In contrast, w hen the generator is in the basement or the

interior room, all of the CO enters the house. Note that this table only includes the occupied zones

of the building and not the bathroom and stairway zones.

CO CONCENTRATIONS (mg/m 3 )

Closed

Garage Open

Garage Basement Interior Room

Max Mean Max Mean Max Mean Max Mean

Level Zone

Basement Bed3 6 2 104 61 13259 8209 1564 791

Bed4 8 3 11 3 23893 15596 2309 1325

1st floor Kitchen 2555 1448 471 291 7153 3825 5723 2956

Living 2326 1315 465 284 5214 2894 14650 8940

Dining 2421 1371 467 287 9765 5475 5732 2962

2nd floor Bed1 511 246 324 194 5816 3675 6995 4157

Bed2 456 213 308 186 5882 3511 8020 4708



### Table 5 Average of daily maximums and means CO concentrations for 1000 g/h constant

source s in DH

- 10

3.3 Summary results for all houses

This section presents the results of the COHb calculations for all of the houses considered in the

simulation s, which reflect the combined effects of source location, source strength and weather

conditions. As noted earlier, the metric employed in analyzin g the simulation results is the

maximum COHb value (maxCOHb) among the occupied zones for each simulation. Each

max COHb value corresponds to a 24-hour simulation of a specific house (among the 87 houses

considered ) for a specific source location, source strength and day of weather. For reference,

COH b levels of 70 % or greater are associated with death in less than 3 min

, levels of 5 0 % 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 [ 17 ].

Figure 7 shows example results with the generator in the interior room for two values of a constant

CO source, 1000 g/h and 100 g/h. In both plots the solid vertical bars correspond to the percent of

values among all of the simulations (all houses and weather conditions) for which the maxCOHb

is in each bin on the horizontal axis. For ex ample, in the upper plot corresponding to 1000 g/h,

there are a small fraction of cases with m axCOHb value between 0 % and 5 %; all the rest have

maxCOHb values above 80 %. The small number of cases with max COHb below 5 % occurs

when essentially all of the CO produced by the generator leaves the house without flowing into the

occupied rooms. In those cases, the maxCOHb corresponds to the assumed initial COHb

concentration used in the CFK calculation, i.e. 0.0024 ml/ml. No maxCOHb bins are presented

above 80 % because distinctions between such high levels are not of interest based on health

effects at such high levels. The solid line in each graph is the cumul ative distribution of the

maxCOHb values, which always reaches 100 % for the highest bin. When the source strength is

reduced to 100 g/h, the percent of cases with lower values of maxCOHb increases significantly,

with the fraction of cases at higher values exhibiting a corresponding decrease.

### 15 Figure 7 MaxCOHb values for all cases with generator in an interior room, constant CO sources of

1000 g/h and 100 g/h

Table 6 and Table 7 show the maxCOHb results as discrete and cumulative frequency

distributions for all values of the constant interior room source. Table 6 presents the percent of

cases in each max COHb bin, which corresponds to the vertical bars in Figure 7

. Table 7 shows the

cumulative frequency distribution, which corresponds to the solid lines in Figure 7

. Note that the

last column in Table 8 is the percentage of cases above 80 % COHb, which is not typically the

way in which cumulative distributions are presented but is more meaningful in this situation

.

### 16 The results of all the simulations are summarized in Figure 8 and Figure 9 , with the former

including cases with the generator in the garage and the latter including cases with the generator in

the interior room and the basement. Each of the plots includes all of the simulated source strengths

for the corresponding source location. The individual plots correspond to different source

locations and type, i.e., constant or burst. These seven plots capture the results of all of the

simulations performed in this study. Each plot shows that as the CO emission rates are reduced,

more of the cases correspond to lower values of maxCOHb. This trend is exhibited by the

cumulative frequency distribution curves shifting towards the upper left have corner of the plot,

which corresponds to more of the cases having low values of maxCOHb. In some cases, for the

lowest source strengths, essentially all of the cases have maxCOHb values below 5 %, in which

case the distribution is a horizontal line at 100 % that is not visible in the plots.

The top two plots in Figure 8 show that the constant source in an open garage has

significantly lower values of maxCOHb than in the closed garage, which is not surprising.

However, running the generator in the open garage still results in significant values of

maxCOHb for the high source strengths. Running a generator under conditions corresponding

to a short term burst source, even in a closed garage, greatly reduces the maxCOHb values.

As seen in Figure 9

, a constant CO source in either a n interior room or basement results in

high values of maxCOHb, even for the lower CO source strengths. The maxCOHb values for

these two source locations are lower for the burst source

, but only the lowest source strengths

yield values of maxCOHb that are generally below 20 %

. Appendix D shows the cumulative

frequency distributions for all the cases in the same tabular form used in Table 7

.

### 17 Source

strength

(g/h) maxCOHb (%)

<5 5 to

10 10 to

15 15 to

20 20 to

25 25 to

30 30 to

35 35 to

40 40 to

45 45 to

50 50 to

55 55 to

60 60 to

65 65 to

70 70 to

75 75 to

80 >80

1000 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 97.9

750 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.0 95.9

500 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0. 4 3.7 11.8 82.0

400 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 1 0.0 0.0 0.0 0. 5 3.5 9.0 13.7 71.3

200 1.9 0.1 0.0 0.0 0.0 0.1 0.0 0.0 0.2 1. 2 3.6 8.4 9.7 12.5 13.2 15.5 33.7

100 2.0 0.1 0.1 0.0 0.0 0.3 2. 6 5.6 9.5 9.9 11.3 10.0 11.3 12.1 8.1 10.2 7.0

50 2.0 0.1 0.0 1. 5 7.6 11.7 11.7 12.1 9.9 10. 5 9.4 6.7 7.2 5. 0 2.8 1.4 0.3

20 2.1 3. 9 19.7 19.1 14.2 13.9 8.1 7.0 5.8 3.3 1.4 1.1 0.4 0.0 0.0 0.0 0.0



### Table 6 Frequency distributions of maxCOHb for constant source in interior room

Source

strength

(g/h) maxCOHb (%)

<5 <10 <15 <20 <25 <30 <35 <40 <45 <50 <55 <60 <65 <70 <75 <=80 >80

1000 1.9 1.9 1.9 1.9 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 97.9

750 1.9 1.9 1.9 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.1 4.1 95.9

500 1.9 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.1 2. 5 6.2 18.0 82.0

400 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.1 2. 6 6.0 15.0 28.7 71.3

200 1.9 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.3 3. 5 7.0 15.4 25.2 37.6 50.8 66.3 33.7

100 2.0 2.1 2.1 2.1 2.1 2. 5 5.1 10.7 20.2 30.1 41.3 51.4 62.6 74.7 82.8 93.0 7.0

50 2.0 2.1 2.1 3. 7 11.3 23.0 34.7 46.8 56.7 67.2 76.6 83.3 90.5 95.5 98.3 99.8 0.3

20 2.1 6.0 25.7 44.8 59.0 72.9 81.0 88.1 93.8 97.1 98.5 99.6 100.0 100.0 100.0 100.0 0.0



### Table 7 Cumulative frequency distributions of maxCOHb for constant source in interior room

### 18 Figure 8 Simulation results for all garage source cases in all houses

### 19 Figure 9 Simulation results for all interior room and basement source cases in all houses

### 20 The simulation results constitute a large amount of data as depicted in Figure 8 and Figure 9 . One

way to interpret these data is to consider the percentage of cases that meet a specific criteria for the

target value of maxCOHb . Determination of such criteria is beyond the scope of this project but

for comparison purp oses Table 8 prese nts the maximum source strength for which 80 % of the

cases simulated are below 3 0 % maxCOHb for each of the seven source locations and types

considered. The values of 80 % below 30 % maxCOHb are used only for illustrative purposes and

are not presented as life

- safety based limits to support policy or regulatory decisions

. Note also

that the maxi mum source strengths in the table are estimated by interpolating between the values

used in the simulations. Based on this interpolation, the individual values are estimated to have a n uncertainty of approximately 10 %. As noted in the table, none of the simulated source strengths

in two of the source locations (Basement/constant and Interior room/constant) resulted in 80 % of

th e cases being below 30 % max CO Hb . In tho se cases

, the maximum source strength is noted as

“< 20 g/h,” noting that 20 g/h was lowest v alue simulated

.

Source location /type Maximum sou r ce strength

Closed garage/constant 13 9 g/h

Open garage/constant 6 46 g/h

Closed garage/burst 443 g

Basement/constant < 2 0 g/h *

Basement/burst 123 g

Interior room/constant < 20 g/h*

Interior room/burst 83 g

* No simulated source strengths result in 80 % of cases having maxCOHb < 30 %

.



### Table 8 Maximum source strength corresponding to 80 % of the simulated cases with

maxCOHb < 30 % (source strength s based on interpolation between simulated values)

3.4 Summary results for subsets of houses

As noted earlier , the simulation results were analy zed separately to examine the impact of house

size, airti ghtness and weather. Separate frequency distributions we re generated for the 37 detached

homes in the smallest size category , for the 16 in the largest size category and for the remaining 30

“ mid

- sized” homes , as well as for the four manufactured homes. Separate frequency distributions

were also generated for the 20 tightest and 20 leakiest houses, based on their airtightness values

from simulated blower door test results in units of air changes per hour at 50 Pa

. Finally, the

impacts of weather were examined by generating separate frequency distributions of max COHb

for the two cold weeks of weather, one week of mild weather and one week of warm weather. In

interpreting these results it is important to bear in mind the complexity of airflow and contaminant

transport in multizone buildings and the fact that these homes differ in more than size and

airtightness. Other differences that impact airflow and CO transport include the locations of the

garages, the floor plans of the occupied zones in relation to the basement and garage, and other

house- specific characteri stics. As a result, the differences discussed below are sometimes hard to

explain based solely on the size, tightness and weather. Also, the conversion of indoor CO

concentrations to %COHb is a nonlinear calculation, which makes the variations in the maxim um source strengths for the different cases even more complex.

Table 9 presents the maximum source strengths for the different size homes, as well as for the four

manufactured homes, with these source strengths again corresponding to 80 % of the simulated

### 21 cases having a maxCOHb value less than 30 %. As in Table 8 , the source strengths in Table 9 are based on interpolating between the actual simulated source strengths and have an estimated

uncertainty of about 10 %. Considering the closed garage constant source first , the largest homes

have a smaller value of the maximum source strength than the smallest homes. This difference

could be explained in part by the greater air leakage through the house- garage interface (wall) in

the largest homes, leading to more CO entering the house from the garage. While not shown, the

average air change ra tes, in units of m 3 

### /h, for the smallest and largest home s are similar, so this

difference in the maximum source strength for these two home sizes can’t be attributed to the

house air change rate. The mid

- sized homes have lower air change rates on average t han the other

sizes, which is consistent with the lower maximum source strengths . In the case of the open garage

with the constant source, presumably more CO enters the occupied portions of the largest homes

but they have higher air change rates than the smallest homes with garage door open, consistent

with the somewhat higher maximum source strength. The mid

- sized homes have a lower air

change rate on average, which is consistent with its lower maximum source strength. However, the

differences in the maximum source strength for the open garage/constant source location are

within the estimated uncertainty of 10 %. For the burst source in the closed garage, the volume of

the house is more rele vant than the air change rate , but it does not fully explain the differences

seen in the table. The larger leakage area between the house and garage in the largest homes, and

the associated higher rate of CO entry, is consistent with the lower maximum source strength in

the largest homes. Compared with the largest homes, the mid

- sized homes have a smaller volume

and a lower air change rate, bot h of which are consistent with the lower maximum source strength.

However, the mid

- sized homes have a smaller house-garage interface, leading to less CO entry,

which presumably counteracts the effects of volume and air change. The high maximum in the

smallest homes is consistent with a lower rate of CO transport from the garage to the house in the

smaller homes

.

Maxi mum source strength

Source location /type All homes Smallest

homes Largest

homes Mid

- sized

homes Manufactured

homes

Closed garage/constant 13 9 g/h 29 7 g/h 184 g/h 92 g/h

Open garage/constant 646 g/h 65 6 g/h 677 g/h 626 g/h

Closed garage/burst 443 g > 1000 g** 373 g 372 g

Basement/constant < 20 g/h* < 20 g/h* 25 g/h < 20 g/h*

Basement/burst 123 g 50 g 310 g 2 48 g

Interior room/constant < 20 g/h* < 20 g/h* < 20 g/h * 20 g/h < 20 g/h*

Interior room/burst 83 g 49 g 176 g 1 30 g 190 g

* No simulated source strengths result in 80 % of cases having maxCOHb < 30 %; value in table is

the lowest source strength simulated.

** All simulated source strengths result in 80 % of cases having maxCOHb < 30 %; value in table is

the highest source str ength simulated.



### Table 9 Maximum source strength for maxCOHb < 30 % f or 80 % as a function of house size

( source strengths based on interpolation )

In the case of the basement and interior room sources, all of the CO released enters the house and

therefore the impact of the building volume and air change rate is expected to be more

straightforward . For both constant source locations, the lowest source strengths simulated almost

### 22 all result i n less than 80 % of the cases being below 30 % max COHb. The only exception is in the

largest homes but the differences are not significant, given the high levels of % COHb calculated

for all the source values. The maximum source strengths for the burst sour ces in the basement and

interior room correspond to the house sizes, with the smallest homes having the lowest maximum

source strengths and the trend continuing with the mid

- and largest size homes. The manufactured

homes only have the interior room sources, but the maximum value for the burst source is higher

than the detached homes despite the smaller volume of the manufactured homes. The reason for

this difference could be related to all the manufactured homes being one story tall, which means

that air flowing vertically out of the interior room leaves the occupied spaces. Some of the other

homes are two -story, in which upward airflow does not leave the house.

Table 10 presents the maximum source strengths corresponding to 80 % of the cases having a

maxCOHb value less than 3 0 % for the twenty tigh test and twenty leakiest homes. For all three

garage source l ocations, the leakiest homes have higher maximum sources strengths, which is

consistent with their higher air change rates. Similarly, the tightest homes have the lowest

maximum source strengths. As noted in the discussion of house size, none of the constant source

strengths in the basement or interior room result in 80 % of the cases having a maxCOHb below

30 %. For the burst sources located in the basement and the interior room, the maximum source

strength is higher for the tightest homes. This can be exp lained by the tightest homes having larger

volumes than the leakiest homes , since the initial dilution by volume is more important than the

dilution over time associated with air change

.

Maximum source strength

Source location /type All homes Tightest

homes Leakiest

homes

Closed garage/constant 139 g/h 76 g/h 820 g/h

Open garage/constant 646 g/h 618 g/h 731 g/h

Closed garage/burst 443 g 255 g > 1000 g**

Basement/constant < 20 g/h* < 20 g/h* < 20 g/h*

Basement/burst 123 g 229 g 5 7 g

Interior room/constant < 20 g/h* < 20 g/h* < 20 g/h*

Interior room/burst 83 g 143 g 4 9 g

* No simulated source strengths result in 80 % of cases having maxCOHb < 30 %; value

in table is the lowest source strength simulated.

** All simulated source strengths result in 80 % of cases having maxCOHb < 30 %;

value in table is the highest source strength simulated.



### Table 10 Maximum source strength for maxCOHb < 30 % for 80 % as a function of detached

home tightness levels ( source strengths based on interpolation )

### 23 Table 11 presents the maximum source strengths for the different weather conditions: cold, mild

and warm . The highest air change rates exist under cold weather, with the lowest rates under warm

weather. Based on that consideration alone, one would expect the highest maximum source

strengths under cold, mild and then warm weather in that order. This is the tr end seen for the

interior room/burst source, where all of the CO released enters the house directly. This trend in air

change rates explains the higher maximum source strength for all the other source locations under

cold weather versus mild. This trend can also explain the higher maximum source strength for the

closed garage/constant source location under cold weather versus mild. Also, during cold weather,

more CO presumably flows directly from the garage to the outdoors, so that less is available to

en ter the house, which may also contribute to the lower maximum source strength under mild

weather. The high value s for the two closed garage cases under warm weather is associated with

lower rates of CO entry from the garage into the house under these weath er conditions. The low

warm weather value for the open garage, constant source may be due to wind effects playing a

stronger role with the garage door open, forcing more CO into the house. For the constant sources

in the basement and interior rooms, none but the very lowest source strengths result in 80 % of the

maxCOHb values being less than 30 %. The basement burst source has a higher maximum source

strengths under warm weather because, w ith the burst source in the basement, none of the CO

enters the rest of the house during warm weat her due to the downward direction of the stack effect.

Maximum source strength

Source location All

simulations Cold

weather Mild

weather Warm

weather

Closed garage/constant 13 9 g/h 13 3 g/h 126 g/h 173 g/h

Open garage/constant 646 g/h 790 g/h 578 g/h 518 g/h

Closed garage/burst 443 g 439 g 368 g > 1000 g**

Basement/constant < 20 g/h* 26 g/h < 20 g/h* < 20 g/h*

Basement/burst 149 g 122 g 108 g 1 97 g

Interior room/constant < 20 g/h* 24 g/h < 20 g/h* < 20 g/h*

Interior room/burst 82 g 95 g 89 g 47 g

* No simulated source strengths result in 80 % of cases having maxCOHb < 30 %; value in

table is the lowest source strength simulated.

** All simulated source strengths result in 80 % of cases having maxCOHb < 30 %; value in

table is the highest source strength simulated.



### Table 11 Maximum source strength corresponding to maxCOHb < 30 % for 80 % for the

different weather conditions (source strengths based on interpolation)

### 24 4. SUMMARY A ND 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 life

- safety based analyses of potential CO

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

contaminant transport model CONTAM, which was applied to 87 single- family, detached

dwellings that are representative of the U.S. housing stock for that housing type . A total of almost

one-hundred thousand individual 24-hour simulations were conducted that cover a range of house

layouts and sizes, air tightness levels and weather conditions, as well as generator locations and

CO source strengths. The locations include attached garages and basements, in the houses that

have such spaces, and a first floor interior room in all of the houses considered. This report

present s the simulation results in terms of the maximum levels of percent COHb for the occupied

portions of the dwellings as a function of CO emission rate for each indoor source location.

It is important to note that the simulation results presented in this rep ort 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, source location, outdoor temperature and wind speed and

direction 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 may not be adequate to fully understand the levels of CO exposure in

residences as a function of generator location and CO emission rate. While the analysis of the

subsets of cases based on house size, tightness and weather conditions provide interesting insights,

the difficulty in interpreting some of the results highlights the complexity of the problem.

The results of the simulations are summarized as frequency distributions of these max COHb levels

in the occupied zones of the simulat ed homes. Frequency distributions are presented for all the

simulations, as well as for subsets of the simulations based on different size houses, air tightness

levels and weather conditions. To support interpret ation of these data, each frequency distribution

is characterized by the maximum source strength for which 80 % of the cases are below 30 %

maxCOHb. These two values are used only for illustrative purposes and are not presented as life

safety based limits to support policy or regulatory decisions. Figure 10 is the frequency

distribution of the maxCOHb values for all of the constant source cases, i.e. a generator operating

for 18 hours. Considering all the constant source results, the maximum source strength

corresponding to 80 % of the cases having a value of maxCOHb below 30 % is 27 g/h. This value

is on the low end of those simulated, which indicates that operating a generator for 18 hours as

simulated in this st udy is likely to result in high CO exposures whether the generator is in the

house or the garage. Note that the CO emission rates measured in unmodified generators in a

separate NIST study tended to be above this value [ 2 ].

### 25 Figure 10 Frequency Distribution of % COHb for All Constant Sources

Figure 11 is the frequency distribution of the maxCOHb values for all of the burst source cases.

Considering all of the burst results , the maximum source strength corresponding to 80 % of the

cases hav ing a value of maxCOHb below 30 % is 139 g. This value is on the higher end of the

burst source strengths measured by NIST (as indicated in Table 4 ), i.e., there were many

measurements below this value in the modified generators. Therefore, generators that are modified

to limit CO emissions using an effective shut off or other technology ha ve the potential to

signific ant ly reduce indoor CO exposures relative to continuously operating generators with no

such emissions controls.

Figure 11 Frequency Distribution of %COHb for All Burst Sources

### 26 5 . ACK NOWLEDGEMENTS

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

agreement No. CPSC -I- 09 -0017. The authors wish to express their appreciation for the support of

Janet Buyer, Sandra Inkster, Han Lim and Donald Switzer in conducting thi s effort.

6. REFERENCES

1. Hnatov, M.V. 2012. Incidents, Deaths, and In-Depth Investigations Associated with NonFire Carbon Monoxide from Engine-Driven Generators and Other Engine-Driven Tools,

1999-2011. U.S. Consumer Product Safety C ommission.

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

Portable Gasoline Powered Generator Exhaust on Indoor Carbon Monoxide Level.

Technical Note 1781. National Institute of Standards and Technology.

3. Walton , G.N. and W.S. Dols. 2005. CONTAMW 2.4 User Guide and Program

Documentation. NISTIR 7251. National Institute of Standards and Technology.

4. 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.

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

and Urban Development, U.S. Department of Commerce.

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

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

.

7. Sherman, M. and D. Dickeroff, Air -Tightness of U.S. Dwellings. ASHRAE Transactions,

1998. 104 (2) : p. 1359-1367.

8. Chan, W., P. Price, W. Nazaroff, and A. Gadgil, Distribution of Residential Air Leakage:

Implications for Health Outcome of an Outdoor Toxic Release. Indoor Air, 2005. 15 (11) :

p. 1729-1734.

9. Chan, W., P. Price, M. Sohn, and A. Gadgil. 2003. Analysis of U.S. Residential Air

Leakage Database. LBNL -53367. Lawrence Berkeley National Laboratory.

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

Refrigerating and Air-Conditioning Engineers, Inc.

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

Review. ASHRAE Transactions, 2001. 107 (2) : p. 619-628.

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

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

Technology, 2004. 25(4) : p. 305-316.

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

Monoxide Generation 1 by Gasoline-Powered Electric Generator in an Enclosed Space.

2010. 60 : p. 1443-1451.

### 27 14. Inkster, S.E. 2006. An estimation of how reductions in the carbon monoxide (C0)'emission

rate of portable, gasoline-powered generators could impact the chance of surviving an

acute CO exposure resulting from operation of a portable gasoline- powered generator in a

basement. U.S. Consumer Product Safety Commission.

15. 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.

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

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

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

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

p. 538-542.

### 28 APPENDIX A: House Characteristics

This appendix contains two tables that define the 87 dwellings, with one table for each housing type: detached (A1) and manuf actured

home (A2). The dw elling definitions in the table are in terms of the variables discussed in detail in the report that defines these homes [ 4 ].

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 m 2 

### (1,599 ft 2 

### ); 2 = 148.6 m 2 

### to 222.9 m 2 

### (1,600 ft 2 

### to 2,399 ft 2 

### ); 3 = 223.0 m 2 

### (2,400 ft 2 

### ) 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 Bed

- rooms 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)

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)

### 29 House

Number # of Floors House Variable # of Rooms

Floor plan Floor area Year Built Foundation Garage Forced

- air Bed

- rooms Full baths Half baths Other

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)

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)

### 30 House

Number # of Floors House Variable # of Rooms

Floor plan Floor area Year Built Foundation Garage Forced

- air Bed

- rooms Full baths Half baths Other

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)

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)

### 31 House

Number # of Floors House Variable # of Rooms

Floor plan Floor area Year Built Foundation Garage Forced

- air Bed

- rooms Full baths Half baths Other

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)



### TABLE A2. Manufactured Homes

Key for Table A2:

Floor area: 1 = less than 148.5 m 2 

### (1,599 ft 2 

### ); 2 = 148.6 m 2 

### (1,600 ft 2 

### ) 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 Forced

air # 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)

### 32 Appendix B Source Locations for Each House

House prj Constant source locations Burst source locations

Garage

(Yes/No) Basement

(Yes/No) Floor plan Closed

garage Open

garage Basement Interior

room Closed

garage Basement Interior

room

DH

- 1 Y N DH

- B(1) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 2 Y Y DH

- A(8) GAR GAR Bath 1 Dining GAR Bath1 Dining

DH

- 3 N N DH

- A(1) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 4 Y N DH

- A(7) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 5 Y N DH

- A(2) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 6 Y Y DH

- D(3) GAR GAR Bed2 Kitchen GAR Bed2 Kitchen

DH

- 7 Y Y DH

- B(5) GAR GAR Den Bath1 GAR Den Bath1

DH

- 8 Y N DH

- A(2) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 9 Y Y DH

- D(3) GAR GAR Bed2 Kitchen GAR Bed2 Kitchen

DH

- 10 Y Y DH

- E(8) GAR GAR Bath2 1/2Bath GAR Bath2 1/2Bath

DH

- 11 Y N DH

- A(7) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 12 Y Y DH

- F(4) GAR GAR Bath2 1/2Bath GAR Bath2 1/2Bath

DH

- 13 Y N DH

- B(1) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 14 Y Y DH

- E(5) GAR GAR Den 1/2Bath GAR Den 1/2Bath

DH

- 15 Y Y DH

- F(5) GAR GAR Bath3 1/2Bath GAR Bath3 1/2Bath

DH

- 16 N N DH

- A(7) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 17 Y Y DH

- E(6) GAR GAR Bath2 1/2Bath GAR Bath2 1/2Bath

DH

- 18 N Y DH

- D(3) n.a. n.a. Bed2 Kitchen n.a. Bed2 Kitchen

DH

- 19 Y Y DH

- A(8) GAR GAR Bath Dining GAR Bath Dining

DH

- 20 Y Y DH

- E(7) GAR GAR Den Dining GAR Den Dining

DH

- 21 N N DH

- A(7) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 22 Y N DH

- F(1) GAR GAR n.a. 1/2Bath GAR n.a. 1/2Bath

DH

- 23 Y Y DH

- D(3) GAR GAR Bed2 Kitchen GAR Bed2 Kitchen

DH

- 24 Y N DH

- E(3) GAR GAR n.a. 1/2Bath GAR n.a. 1/2Bath

DH

- 25 Y Y DH

- A(8) GAR GAR Bath Dining GAR Bath Dining

DH

- 26 N N DH

- A(1) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 27 N Y DH

- A(8) n.a. n.a. Bath Dining n.a. Bath Dining

DH

- 28 Y N DH

- F(2) GAR GAR n.a. 1/2Bath GAR n.a. 1/2Bath

DH

- 29 N N DH

- A(3) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 30 Y N DH

- B(1) GAR GAR n.a. Bath2 GAR n.a. Bath2

### 33 House prj Constant source locations Burst source locations

Garage

(Yes/No) Basement

(Yes/No) Floor plan Closed

garage Open

garage Basement Interior

room Closed

garage Basement Interior

room

DH

- 31 Y N DH

- A(2) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 32 Y N DH

- A(6) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 33 Y N DH

- C(1) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 34 N N DH

- A(7) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 35 Y N DH

- B(1) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 36 Y N DH

- E(3) GAR GAR n.a. 1/2Bath GAR n.a. 1/2Bath

DH

- 37 Y Y DH

- B(4) GAR GAR Bath1 1/2Bath GAR Bath1 1/2Bath

DH

- 38 N N DH

- A(7) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 39 N N DH

- B(1) n.a. n.a. n.a. Bath2 n.a. n.a. Bath2

DH

- 40 Y N DH

- E(3) GAR GAR n.a. 1/2Bath GAR n.a. 1/2Bath

DH

- 41 N Y DH

- E(1) n.a. n.a. Den Dining n.a. Den Dining

DH

- 42 N N DH

- A(4) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 43 Y Y DH

- E(2) GAR GAR Bath2 Dining GAR Bath2 Dining

DH

- 44 Y Y DH

- A(9) GAR GAR Bath Dining GAR Bath Dining

DH

- 45 Y Y DH

- E(3) GAR GAR Basement Bath1 GAR Basement Bath1

DH

- 46 Y N DH

- A(1) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 47 Y N DH

- A(7) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 48 N N DH

- A(2) n.a. n.a

. n.a. Bath2 n.a. n.a. Bath2

DH

- 49 N Y DH

- A(8) n.a. n.a. Bath Dining n.a. Bath Dining

DH

- 50 N Y DH

- D(3) n.a. n.a. Bed2 Kitchen n.a. Bed2 Kitchen

DH

- 51 Y N DH

- F(3) GAR GAR n.a. 1/2Bath GAR n.a. 1/2Bath

DH

- 52 Y Y DH

- F(3) GAR GAR Basement 1/2Bath GAR Basement 1/2Bath

DH

- 53 N N DH

- B(1) n.a. n.a. n.a. Bath2 n.a. n.a. Bath2

DH

- 54 N N DH

- A(3) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 55 Y N DH

- A(6) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 56 N Y DH

- D(3) n.a. n.a. Bed2 Kitchen n.a. Bed2 Kitchen

DH

- 57 Y N DH

- B(3) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 58 Y Y DH

- E(6) GAR GAR Bath2 1/2Bath GAR Bath2 1/2Bath

DH

- 59 Y Y DH

- F(4) GAR GAR Bath2 1/2Bath GAR Bath2 1/2Bath

DH

- 60 Y Y DH

- A(7) GAR GAR Basement Bath1 GAR Basement Bath1

DH

- 61 N Y DH

- A(1) n.a. n.a. Basement Bath1 n.a. Basement Bath1

DH

- 62 Y Y DH

- F(4) GAR GAR Bath2 1/2Bath GAR Bath2 1/2Bath

### 34 House prj Constant source locations Burst source locations

Garage

(Yes/No) Basement

(Yes/No) Floor plan Closed

garage Open

garage Basement Interior

room Closed

garage Basement Interior

room

DH

- 63 Y Y DH

- D(4) GAR GAR Basement 1/2Bath GAR Basement 1/2Bath

DH

- 64 Y N DH

- B(1) GAR GAR n.a. Bath2 GAR n.a. Bath2

DH

- 65 N Y DH

- A(3) n.a. n.a. Basement Bath1 n.a. Basement Bath1

DH

- 66 Y N DH

- B(2) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 67 Y N DH

- A(7) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 68 N Y DH

- D(3) n.a. n.a. Bed2 Kitchen n.a. Bed2 Kitchen

DH

- 69 Y Y DH

- F(3) GAR GAR Basement 1/2Bath GAR Basement 1/2Bath

DH

- 70 N N DH

- A(1) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

DH

- 71 Y N DH

- D(1) GAR GAR n.a. 1/2Bath GAR n.a. 1/2Bath

DH

- 72 Y Y DH

- B(3) GAR GAR Basement Bath2 GAR Basement Bath2

DH

- 73 Y Y DH

- D(2) GAR GAR Basement Bath1 GAR Basement Bath1

DH

- 74 Y Y DH

- C(2) GAR GAR Basement Bath1 GAR Basement Bath1

DH

- 75 Y N DH

- G(1) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 76 Y Y DH

- A(5) GAR GAR Basement 1/2Bath GAR Basement 1/2Bath

DH

- 77 Y Y DH

- G(2) GAR GAR Basement Bath2 GAR Basement Bath2

DH

- 78 Y N DH

- A(7) GAR GAR n.a. Bath1 GAR n.a. Bath1

DH

- 79 N N DH

- B(1) n.a. n.a. n.a. Bath2 n.a. n.a. Bath2

DH

- 80 N Y DH

- B(3) n.a. n.a. Basement Bath2 n.a. Basement Bath2

DH

- 81 N Y DH

- E(4) n.a. n.a. Basement Bath1 n.a. Basement Bath1

DH

- 82 Y Y DH

- B(1) GAR GAR Basement Bath2 GAR Basement Bath2

DH

- 83 N Y DH

- A(8) n.a. n.a. Bath Dining n.a. Bath Dining

MH

- 1 N N MH

- B(1) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

MH

- 2 N N MH

- A(1) n.a. n.a. n.a. Bath2 n.a. n.a. Bath2

MH

- 3 N N MH

- B(1) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

MH

- 4 N N MH

- B(1) n.a. n.a. n.a. Bath1 n.a. n.a. Bath1

### 35 Appendix C Integral Mass Balance Analysis of Burst Sources

The following m ethod was used to estimate the total CO mass released during a test in which the

generator runs for a relatively short period of time (minutes), so- called burst sources. This analysis

approach applies to a generator with a shutoff mechanism or some other technology that results in

a generation rate that can’t be well characterized with a constant source strength. As described

below, it was used to estimate the burst source strengths that were employed in the analysis

described in the body of this report and which are listed in Table 4 . This analysis method was

applied to a series of generator tests conducted in the NIST test house, with the generator in the

garage, as described in reference [ 2 ].

The mass balance of CO in a single- zone (i.e., the NIST test house garage) can be expressed as:

where

V

= zone volume, m 3



### C

= CO concentration in zone, mg/m 3



### C

out 

### = CO concentration in outdoors, mg/m 3



### t = time, min

Q = airflow rate through zone, m 3 

### /min

S = CO generation rate, mg/min

Also, T is the length of time (min) over which CO is emitted by the generator.

Assuming that C

out 

### = 0 and taking the integral of both sides of the equation from t 1 

### to t 2 

### yields:

,

which can be expressed as:

where

= average generation rate over the time interval during which CO is released

C 2 

### = C at time t 2



### C 1 

### = C at time t 1



### is the total mass of CO released over the period of interest and is the quantity that is being

estimated with this analysis approach.

In applying this approach to the garage tests conducted in the NIST test house, Q can be estimated

from the decay in the concentration of CO after the generator stops operating for cases in which V dC

dt = QC

out 

### − QC + S ( t )



### V dC

= − Q

t 1 t 2 

# ∫ Cdt

t 1 t 2 

# ∫

+ Sdt

t 1 t 2 

# ∫

S T

= V ( C

2 

### − C

1 

### ) + Q Cdt

t 1 t 2 

# ∫

S



### S T

### 36 the garage was not exhausted immediately after a test. If the latter conditions (exhaust ventilation)

exist, Q can be estimated from a decay under similar conditions. Since the operation of the

generator may impact the garage ventilation rate, the CO decay rate after the generator stops

generally will not be an exact estimate of the rate during generator operation. However, the

relatively short operating times will decrease the impact of this effect. And given that the purpose

of thi s analysis is to estimate the range of CO release rates, the potential errors associated with the

estimated ventilation rates are not viewed as significant. Also, given that the garage is not strictly a

single- zone, the estimate of Q and the estimation of will have some inherent uncertainty. Again,

given the goal of this analysis is to estimate a range of mass generation values and not a single

precise value, the garage not being a true single zone is not a significant concern.

Table C1 presents the resu lts of the analysis applied to 14 short-duration generator tests performed

by NIST in a separate study [ 2 ]. The table contains the test number corresponding to the

referenced report along with the test date and duration and test load. The test loads in the first five

tests were constant at the listed value. The remaining tests employed a cyclic load profile (shown

in Table C2) that was derived from a test cycle developed by industry to replicate typical in- use

operation of small utility engines when used in all types of engine-driven products (CPSC 2012).



### Note that most of the tests involve less than one hour of generator operation, though a few do last

longer. The generator, referred to as S01 in the referenced report, is an off-the- shelf generator

rated at 5 kW that was modified to lower its CO emissions. These modifications included the

addition of an engine management system and associated sensors and actuators, fuel system

components, an electric start system, and a mu ffler integrated with a small catalyst. Some of the

tests were done without the catalyst and are noted in the table as “noncat muffler.” The last

column is the total mass released as calculated per the procedure described above. As noted in the

body of the report, the minimum measured value is about 15 g and the maximum is about 200 g.

Test # Date Test duration

(min) Generator Test load Total mass

released (g)

AK 5/19/10 84 S01, noncat muffler 5500 W 178

AL 5/19/10 36 S01, noncat muffler 5500 W 18

AM 5/20/10 7 S01, noncat muffler 5500 W 73

AN 5/20/10 13 S01, noncat muffler 2500 W 38

AP 5/21/10 10 S01, noncat muffler 500 W 108

L 3/25/10 28 S01 cat muffler Cyclic 68

M 3/31/10 46 S01 cat muffler Cyclic 49

X 4/30/10 35 S01 cat muffler Cyclic 68

Y 4/30/10 31 S01 cat muffler Cyclic 73

AB 5/7/10 61 S01, noncat muffler Cyclic 190

AC 5/7/10 10 S01, noncat muffler Cyclic 135

AD 5/7/10 6 S01, noncat muffler Cyclic 69

AO 5/20/10 64 S01, noncat muffler Cyclic 49

AQ 5/21/10 34 S01, noncat muffler Cyclic 61



### Table C1 Results of Short- term Source Analysis S

### 37 Load bank setting

(W) Duration

(min)

no load 3

500 4

1500 18

3000 17.5

4500 12

5500 5.5



### Table C2 Cyclic Load Profile Employed in Short- term Generator T e sts

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

Generator; U.S. Consumer Product Safety Commission.

### 38 Appendix D Cumulative Frequency D istributions of maxCOHb in T abular Form

This appendix presents the cumulative frequency distributions for all source locations in the

tabular format used in Table 7 . The data for the constant source in the interior room, presented in

those figures and tables, is repeated here for completeness. Note again that the last column in each

table is the percentage of cases above 80 % COHb, which is not typically the way in which

cumulative distributions are presented but is more meaningful in this case. T he tables contained in

this appendix are as follows:

Table D1 Cumulative frequency distributions for constant source in closed garage

Table D2 Cumulative frequency distributions for constant source in open garage

Table D3 Cumulative frequency distributions for burst source in closed garage

Table D4 Cumulative frequency distributions for constant source in basement

Table D 5 Cumulative frequency distributions for burst source in basement

Table D 6 Cumulative frequency distributions for constant source in interior room

Table D 7 Cumulative frequency distributions for burst source in interior room

### 39 Source

strength

(g/h) maxCOHb (%)

<5% <10% <15% <20% <25% <30% <35% <40% <45% <50% <55% <60% <65% <70% <75% <=80% >80%

1000 2.4 5.7 12.7 19.7 28.1 34.2 40.0 47.3 51. 2 54. 1 57. 5 62.3 66. 1 70. 4 77.3 83.8 16.2

750 3.1 10.1 18.1 28.2 35.5 43.3 49. 5 52. 8 56. 1 60. 2 64. 2 67. 5 7 2.4 7 8.3 83.9 89.0 11.0

500 5.2 17.3 30.6 39.1 48. 4 52.9 56. 4 61. 3 64. 8 68.1 72.6 78.0 82.6 86.4 91.2 95.9 4.1

400 8.3 23.8 36.1 47. 5 52.8 56. 7 61. 7 65. 5 69.1 73. 9 7 8.4 82.9 86.3 90.9 95.0 99.3 0.7

200 21. 7 44. 4 54.1 60. 8 66. 2 70. 9 76. 8 80. 8 84.9 87.9 91.9 95.1 98.6 99.4 99.5 99.8 0.3

100 42.4 5 8 .8 68.1 75. 7 81. 6 85.7 90.4 93.4 96.7 99.3 99.4 99.5 99.7 99.8 99.9 100.0 0.0

50 57. 6 72. 8 83.2 88.9 93.6 97.9 99.4 99.4 99.6 99.8 99.8 99.9 100.0 100.0 100.0 100.0 0.0

20 77. 7 91.7 98.7 99.4 99.8 99.8 99.9 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0



### Table D1 Cumulative frequency distributions for constant source in closed garage

Source

strength

(g/h) maxCOHb (%)

<5% <10% <15% <20% <25% <30% <35% <40% <45% <50% <55% <60% <65% <70% <75% <=80% >80%

1000 2.4 2.8 4.0 5.5 8.5 18.2 5 8.0 84.5 94. 3 98. 1 99.8 100.0 100.0 100.0 100.0 100.0 0.0

750 2.7 3.5 5.2 9.0 22.7 68.9 90.7 95.8 99.6 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

500 2.8 5.0 10.4 45.4 86.8 95.5 99.5 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

400 3.1 6.5 24. 7 81. 7 95.3 99.5 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

200 6.0 69. 7 96. 8 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

100 57. 5 99.8 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

50 99.6 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

20 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0



### Table D2 Cumulative frequency distributions for constant source in open garage

### 40 Source

strength

(g ) maxCOHb (%)

<5% <10% <15% <20% <25% <30% <35% <40% <45% <50% <55% <60% <65% <70% <75% <=80% >80%

1000 61.6 64.2 65.9 68.1 69. 9 70.7 72.4 74.3 75.2 76.7 78.9 81.5 83.3 86.7 89.3 93.3 6.7

500 64.0 67. 6 70.2 72.7 75.0 77.0 80.7 83.5 86.0 88.2 90.7 93.2 95.5 97.7 99.9 100.0 0.0

200 68.9 74.6 79.3 85.2 89.2 92.7 94.7 97.1 99.1 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

100 73. 6 83.9 91.4 95.3 98.6 99.9 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

50 82.3 94.5 99.4 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

25 93.7 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

15 99.5 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

5 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0



### Table D3 Cumulative frequency distributions for burst source in closed garage

Source

strength

(g/h) maxCOHb (%)

<5% <10% <15% <20% <25% <30% <35% <40% <45% <50% <55% <60% <65% <70% <75% <=80% >80%

1000 3.7 4.3 5.0 5.6 5.9 6.0 6.0 6.2 6.5 6.6 6.6 6.6 6.8 7.1 7.2 7.7 92.4

750 4.0 4.6 5.5 5. 9 6.0 6.0 6.4 6.6 6.6 6.6 6.7 6.9 7.2 7.3 7.7 9.6 90.4

500 4.3 5.5 6.0 6.0 6.4 6.6 6.6 6.6 6.8 7.0 7.2 7.3 7.6 8.3 10.9 21. 7 78. 3

400 4.5 5.7 6.0 6.3 6.6 6.6 6.6 6.9 7.1 7.2 7.3 7.7 8.4 10.8 18. 6 3 3.1 6 6.8

200 5.7 6.1 6.6 6.6 7.0 7.2 7.4 7.7 8.0 9.4 12.1 1 9.1 29. 9 4 5.4 5 7.0 71. 6 28. 4

100 6.0 6.6 7.1 7.4 7.8 8.5 10.4 15.7 2 5.1 3 5 .1 4 9.3 57. 6 68.0 78. 2 84. 4 91. 8 8. 2

50 6.6 7.3 8.1 10. 0 17. 3 27. 5 4 2.5 53. 6 62. 7 72. 8 79.9 84. 5 89. 8 95.2 98.2 99. 9 0.1

20 7.7 11.8 30. 8 52. 6 64. 4 77. 2 8 3.1 8 9.0 93. 1 96.2 98.5 99.7 100.0 100.0 100.0 100.0 0.0



### Table D4 Cumulative frequency distributions for constant source in basement

### 41 Source

strength

(g ) maxCOHb (%)

<5% <10% <15% <20% <25% <30% <35% <40% <45% <50% <55% <60% <65% <70% <75% <=80% >80%

1000 20.9 21.6 22.0 22.2 22.6 23.2 25.5 27.6 32.7 36.6 39.5 46.3 51.2 56.1 65.6 75.6 24.4

500 21.6 22.1 22.8 25.5 30.4 36.1 39.9 47.4 54.2 60.7 69.5 75.9 79.6 81.5 82.0 82.9 17.1

200 22.5 26.9 39.1 49.9 64.5 73.0 79.3 80.7 81.6 82.0 82.8 83.1 83. 6 8 5.2 88.9 93.2 6.8

100 26.5 45.5 70.4 79.7 81.3 82.1 82.9 84.2 8 7.4 9 1.4 93. 6 94. 4 95. 4 96. 5 99.7 100.0 0.0

50 43.5 78.9 81.7 83. 3 8 6 .2 9 3.2 94. 4 95. 8 96. 3 99.8 100 .0 100.0 100.0 100.0 100.0 100.0 0.0

25 77.5 82.8 91. 7 95.1 96. 2 9 9.1 1001 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

15 81.8 9 3.2 9 6.0 99. 6 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

5 95.2 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0



### Table D5 Cumulative frequency distributions for burst source in basement

Source

strength

(g/h) maxCOHb (%)

<5% <10% <15% <20% <25% <30% <35% <40% <45% <50% <55% <60% <65% <70% <75% <=80% >80%

1000 1.9 1.9 1.9 1.9 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 97.9

750 1.9 1.9 1.9 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.1 4.1 9 5.9

500 1.9 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.1 2. 5 6. 2 1 8.0 82. 0

400 1.9 1.9 1.9 2.0 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.1 2. 6 6.0 15.0 28.7 71. 3

200 1.9 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.3 3. 5 7.0 15. 4 25. 2 37.6 50. 8 66.3 33.7

100 2.0 2. 1 2.1 2.1 2.1 2. 5 5.1 10. 7 20. 2 30.1 41.3 51. 4 62. 6 74.7 82.8 93.0 7.0

50 2.0 2.1 2.1 3. 7 1 1.3 2 3.0 34. 7 46.7 56. 7 67.2 76.6 83. 3 90. 5 95.5 98.3 99.8 0.3

20 2.1 6.0 25. 7 44. 8 59.0 72.9 81.0 8 8.1 93.8 97.1 98.5 99.6 100.0 100.0 100.0 100.0 0.0



### Table D6 Cumulative frequency distributions for constant source in interior room

### 42 Source

strength

(g ) maxCOHb (%)

<5% <10% <15% <20% <25% <30% <35% <40% <45% <50% <55% <60% <65% <70% <75% <=80% >80%

1000 30.3 33.3 34.9 36.6 38.1 39.0 40.5 41.8 43.1 44.8 46.8 49.5 51.9 55.0 59.1 63.6 36.5

500 33.0 36.3 38.6 40.6 42.6 45.1 47.3 50.3 52.8 55.3 58.1 62.1 66.3 70.3 74.8 77.6 22.4

200 37.1 41.9 46.5 51.4 55.6 59.7 64.7 69.6 73.5 76.2 77.7 78.5 79.4 81. 7 84. 4 87. 8 12. 2

100 41.4 50.0 57.7 65.3 72. 7 76.0 77.8 79. 8 82. 8 86. 6 89. 4 91.3 93.1 95. 6 97. 7 99.3 0.7

50 49.3 63.7 74. 6 78.4 82. 6 8 8.1 91. 2 93. 5 95. 7 97.4 98.7 99.2 99.9 100.0 100.0 100.0 0.0

25 61.9 77.5 8 6.3 91.8 95. 5 97. 8 98.9 99.5 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

15 74. 8 8 8.0 94. 9 98. 2 99.2 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0

5 93. 3 99.5 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 0.0



### Table D7 Cumulative frequency distributions for burst source in interior room