Statement of U. S. Consumer Product Safety Commission Staff 

on the 

National Institute of Standards and Technology Report,

“Technical Note 1834: Development of a Test Method to Determine Carbon Monoxide Emission 

Rates from Portable Generators”

August 2014

The report titled, “Technical Note 1834: Development of a Test Method to Determine 

Carbon Monoxide Emission Rates from Portable Generators,” presents a test method developed

by the National Institute of Standards and Technology (NIST) for determining carbon monoxide 

(CO) emission rates from portable generators while operating in an enclosed space. NIST

developed the test method under an interagency agreement1 with the U.S. Consumer Product 

Safety Commission (CPSC, the Commission) in support of CPSC staff’s development of a 

proposed mandatory performance standard to address the CO poisoning hazard associated with 

the use of portable generators. 2,3

The NIST test method is designed to be performed in an enclosed space because the vast 

majority of the 800 consumer CO poisoning fatalities reported in CPSC’s databases that occurred 

from 1999 through 2012 happened when consumers used a generator in an enclosed space. 

Furthermore, as reported in NIST Technical Note 17814, the results from NIST’s testing of

carbureted portable generators show that the generators’ CO emission rates increased by several 

times as the oxygen decreased to around 17 percent compared to when measured near ambient

oxygen. This is important because that test program also showed that the oxygen level in an 

enclosed space in which a carbureted portable generator is operated, as was measured by NIST in 

a scenario that is commonly fatal with the generator operating in a garage attached to a single 

family home, drops to, and even below, 17 percent. CPSC staff is taking into consideration the 

information in NIST Technical Note 1834 in the development of a proposed mandatory 

performance standard as directed by the Commission.

 1 CPSC-I-12-0009. 2 This statement was prepared by CPSC staff, and the attached report was produced by NIST for CPSC staff. This statement and 

the NIST report have not been reviewed or approved by, and do not necessarily represent the views of, the Commission. 3 Portable Generators; Advance Notice of Proposed Rulemaking; Request for Comments and Information, Federal Register, 71 

FR 74472, December 12, 2006. http://www.gpo.gov/fdsys/pkg/FR-2006-12-12/pdf/E6-21131.pdf. 4 S. J. Emmerich, A. K. Persily, and L. Wang, Modeling and Measuring the Effects of Portable Gasoline Powered Generator 

Exhaust on Indoor Carbon Monoxide Level (NIST Technical Note 1781), Feb 2013. Available on-line at 

http://www.cpsc.gov/Global/Research-and-Statistics/Technical-Reports/Home/PortableGenerators/PortableGenerators041213.pdf; produced under interagency agreement CPSC-I-06-0012.
NIST Technical Note 1834

Development of a Test Method to Determine 

Carbon Monoxide Emission Rates from Portable

Generators

Steven J. Emmerich

Andrew K. Persily
NIST Technical Note 1834

Development of a Test Method to Determine 

Carbon Monoxide Emission Rates from Portable 

Generators

Steven J. Emmerich

Andrew K. Persily

Energy and Environment Division

Engineering Laboratory

http://dx.doi.org/10.6028/NIST.TN.1834

June 2014

U.S. Department of Commerce

Penny Pritzker, Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director
ii

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 1834

Natl. Inst. Stand. Technol. Tech. Note 1834, 24 pages (June 2014)

CODEN: NTNOEF
iii

ABSTRACT

The U.S. Consumer Product Safety Commission (CPSC) staff is considering developing a 

performance standard to address the hazard of acute residential carbon monoxide (CO) exposures 

from portable gasoline engine-powered generators that result in death or serious and/or lasting 

adverse health effects in exposed individuals. As of April 23, 2013, the CPSC databases contain 

records of at least 739 deaths (in 552 incidents) from CO poisoning caused by consumer use of a 

generator in the period of 1999 through 2012. There were an additional 61 CO poisoning deaths 

(in 45 incidents) involving consumer use of both a generator and at least one other CO-producing 

consumer appliance, for a total of 800 CO poisoning deaths (in 597 incidents) involving 

generators for the same 14-year period. The vast majority of these deaths occurred when 

consumers used a generator in an enclosed space. A small percentage occurred when the consumer 

used the generator outdoors near an opening, such as an open window, which allowed the exhaust 

to enter the building.

The CPSC is working to reduce the occurrence of future generator-related CO poisoning incidents, 

especially those associated with operating a generator in an enclosed space. To that end, the CPSC 

issued an Advance Notice of Proposed Rulemaking; Request for Comments and Information in 

2006 describing its strategy to reduce generator engine CO emission rates. If the CPSC is to issue 

such a rule, it will need to include a test method for determining CO emission rates from portable 

generators while operating in an enclosed space. This report describes work performed to support 

the development of such a test method as well as the draft test method.

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

simulation; test procedure
iv

TABLE OF CONTENTS

1. INTRODUCTION 1

2. REVIEW OF EXISTING TEST STANDARDS AND LITERATURE 2

2.1 Literature 2

2.2 Existing Standards 3

2.3 Summary 3

3. DRAFT TEST METHOD 4

3.1 Discussion of Test Method 4

4. ESTIMATE OF ENTRY OF CO FROM GENERATOR OPERATED OUTDOORS 5

5. SUMMARY 7

6. ACKNOWLEDGEMENTS 7

7. REFERENCES 7

APPENDICES

A. Literature Review Bibliography 10

B. Draft Test Method 20
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. As 

of April 23, 2013, the CPSC databases contain records of at least 739 deaths (in 552 incidents) 

from CO poisoning caused by consumer use of a generator in the period of 1999 through 2012

(Hnatov 2013). There were an additional 61 CO poisoning deaths (in 45 incidents) involving 

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

total of 800 CO poisoning deaths (in 597 incidents) involving generators for the same 14-year 

period. The vast majority of these deaths occurred when consumers used a generator in an 

enclosed space. A small percentage occurred when the consumer used the generator outdoors near 

an opening, such as an open window, which allowed the exhaust to enter the building. Avoiding 

the operation of such generators in or near homes would reduce indoor CO exposures 

significantly. The CPSC has regulations that require packaging and on-product warning labels for 

portable generators that state, in part, the use of a generator in an enclosed space can ‘kill you in 

minutes’, and never to use a generator inside a home or garage, even if doors and windows are 

open. This mandatory labeling for portable generators was established in 2007. However, 

consumers continue to operate generators in enclosed or partially enclosed spaces and near 

partially open doors and windows, and therefore fatalities continue to occur.

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 depends on the complex relationship between CO emissions from these generators and 

occupant exposure. Technically achievable levels of CO emissions reduction have been studied by 

the National Institute of Standards and Technology (NIST) through an experimental investigation

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

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

(Emmerich 2013 et al.). 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 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 conducted to evaluate indoor CO exposures as a function of generator source 

location and CO emission rate (Persily et al. 2013). That simulation study employed the multizone 

airflow and contaminant transport model CONTAM (Walton and Dols 2005), which was applied 

to a collection of 87 dwellings that are representative of the U.S. housing stock. A total of almost 

one-hundred 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 and 

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

have such spaces, and an interior room in all of the houses considered. The results of the 

simulations were summarized as frequency distributions of maximum carboxyhemoglobin levels 

in the occupied zones of the simulated homes.
2

The CPSC is working to reduce the occurrence of future generator-related CO poisoning incidents, 

especially those associated with operating a generator in an enclosed space. To that end, the CPSC 

issued an Advance Notice of Proposed Rulemaking; Request for Comments and Information in 

2006 describing its strategy to reduce generator engine CO emission rates. If the CPSC is to issue 

such a rule, it will need to include a test method for determining CO emission rates from portable 

generators operating in an enclosed space. Such a test method needs to consider the fact that when 

portable generators are operated in an enclosed space with inadequate combustion air supply, the 

combustion process can be affected, resulting in increased CO generation. This report describes 

work performed to support the development of such a test method, as well as other information 

needed to support the development of a Notice of Proposed Rulemaking. The report is organized 

around three main tasks of this effort: 

• a literature review of technical publications and standards to identify material that would 

be useful in developing a test method for measuring CO emissions from portable 

generators,

• the development of a draft test method to perform generator emission rate tests in a 

chamber at reduced oxygen level,

• and an estimate of the fraction of CO that is emitted by a generator outdoors and may enter 

a house.

The draft test method itself is included in Appendix B of this report.

2. LITERATURE REVIEW

As an initial step in this effort, a literature review of technical publications and standards was 

performed to identify material that would be useful in developing a test method for measuring CO 

emissions from portable generators. This review was conducted with the support of NIST 

Research Library staff, as well as through the authors’ familiarity with the subject matter. This 

section discusses information that was identified which is relevant to the determination of CO 

emission rates from portable generators operating in an enclosed space. This review was used to 

identify relevant test procedures, equipment specifications, and test conditions (such as test 

enclosure volume, air temperature, pressure, and relative humidity) that will likely be needed by 

the CPSC in the development of a proposed rule. The documents identified in the literature are 

listed in Appendix A of this report.

2.1 Literature

Other than recent work conducted by NIST for CPSC (Emmerich et al. 2013 and Persily et al. 

2013), no other research efforts were identified that were directly relevant to the development of 

test methods for CO emissions from portable generators. However, three studies of interest are 

discussed here. The first is a study of emissions from kerosene space heaters (Carteret et al. 2012). 

Of note is the chamber volume used, 8 m3

, and the air change rates employed, about 3 h-1 to 25 h-1. 

As discussed later in this report, the question of chamber volume and air change are important to 

the development of a test method for portable generators. Priest et al. (2000) reported on a study of 

emissions from lawnmowers in an 8 m3 shed. While this paper does not discuss the control or 
3

measurement of air change rates, the authors report measured CO emission rates in g/h. The third 

study involved emissions tests of a number of combustion devices (a kerosene lamp, an oil lamp, a 

kerosene space heater, a portable gas range, and four unscented candles) in a room, including CO 

emissions (Fan, C.-W. and J. Zhang 2001). The protocol used in that study and the results obtained 

are of interest though not directly relevant to testing portable generators.

Several other studies were identified in the literature review that were far less relevant to the 

current effort for a number of reasons. For example, some reported CO concentrations but not 

emission rates, did not report air change rates, measured emissions on a dynamometer but not in a 

chamber, or focused on combustion devices other than generators or small engines. Others were 

extremely outdated or focused on unrelated issues such as concentration measurement methods 

and effects of fuel blends.

2.2 Existing standards

The review also examined existing standards relevant to the determination of CO emissions from 

portable generators. Four such standards were identified. The U.S. Environmental Protection 

Agency (EPA) has test procedures for measuring emissions from engines (40 CFR part 1065), 

which are focused on emissions to ambient air. In these procedures, the engines are installed on a 

dynamometer with combustion air supplied at ambient oxygen levels. Therefore the test results do 

not apply to indoor operation with reduced oxygen. Also, engine operation and emissions are 

different when the engine is installed in a generator and a load is imposed. The State of California 

also has an engine emissions test method for lawn and garden equipment engines (CA 1995), but 

these tests are also conducted on a dynamometer at ambient oxygen.

The American National Standards Institute (ANSI) standard for portable gas camp heaters (ANSI 

Z21.63-2000) is also of interest. These tests are conducted in a 2.8 m3 chamber with air change 

rates of about 1 h-1

. The test does not yield a CO emission rate however; instead it limits the 

measured CO concentration in the chamber to 114 mg/m3

. ANSI Z21.11.2-2013 applies to gasfired room heaters and covers a range of performance issues including shutdown devices, pilot 

operation and pressure regulation. It does contain a limit on CO in a room with no ventilation, but

not an emission rate limit.

The Portable Generator Manufacturers’ Association (PGMA) has a standard for testing portable 

generators (G200). This standard covers a range of performance issues, including electrical output, 

but does not include CO emission rates. However, the testing that is done as part of this standard is 

conducted with a constant supply of ambient air.

2.3 Summary

While the literature review identified some interesting material in the context of developing a test 

method for measuring CO emissions from portable generators, it did not yield anything of direct 

relevance. The standards reviewed are of interest primarily in terms of format and their approaches 

to quality control. 
4

3. DRAFT TEST METHOD

This section discusses the draft test method to perform generator CO emission rate tests in a 

chamber at reduced oxygen levels. The draft test method is included in Appendix B of this report.

The test method was developed based on the experience gained from past CPSC and NIST testing 

of portable generators (as described in Brown 2006 and 2008 and Emmerich et al. 2013) in indoor 

environments ranging from a 10 m3 chamber to a 90 m3 test house garage. These tests 

demonstrated that the CO emissions from portable generators can increase dramatically as O2

levels decrease from ambient conditions to as low as 17 %. Therefore a critical element of the test 

procedure is the necessity of achieving reduced O2 levels low enough and for a sufficient length of 

time to determine the CO emissions under such conditions. Beyond this critical feature, the draft 

test method provides flexibility in terms of chamber type and size, ventilation rate, and 

measurement equipment within limitations of achieving reasonable measurement accuracy.

3.1 Discussion of Test Method

The draft test method in Appendix B consists of a main body, which describes the required 

equipment and test procedures to be followed to perform generator emission rate tests in a 

chamber at a reduced oxygen level, and an appendix with guidance on selecting the chamber size 

and ventilation rate. It is important to note that carbon monoxide is a poisonous gas and that 

appropriate safety measures need to be taken, but this test procedure does not cover the safety 

measures. 

The main body of the draft test method includes four main sections: Equipment, Experimental Setup Verification, Test Procedure and Calculation Procedures. The equipment section contains 

requirements for the test chamber, chamber ventilation fan and measurement of ventilation rate, 

gas concentration analyzers, air temperature and humidity sensors, electric load bank and power 

measurement, and generator fuel and lubricants. 

The chamber size and ventilation rate are not specified to allow flexibility, but they must be 

chosen so as to achieve the reduced O2 levels specified in Section C of the test procedures. The 

appropriate chamber size and ventilation rate will depend on the generator being tested and the 

load setting for a given test. The test method appendix provides guidance on selecting an initial 

chamber size and ventilation rate based on the O2 consumption rate of the generator at the load 

setting. However, since the O2 consumption may not be known in advance, a methodology is 

included that may be used to estimate that value based only on the load setting. This estimation

methodology is derived from the results of previous testing by NIST and CPSC. If the initial test 

does not yield the required O2 levels in Section C, an O2 consumption rate may be calculated from 

the initial test to determine an appropriate adjustment to the ventilation rate or chamber size.

The experimental set-up verification section addresses verifying proper performance of test 

equipment including calibration, determination of chamber volume, and verification of gas 

concentration uniformity in the test chamber. Mixing in the test chamber is expected to be driven 

by the generator engine heat and exhaust, as such, it is considered sufficient to evaluate it once for 
5

each chamber volume, ventilation rate and generator loading combination. Supplemental mixing 

fans may be used if necessary to meet the uniformity requirements.

The test procedure section includes 9 steps which should be performed for each of two load 

settings for each generator being tested. The required load settings are 100 % and 50 % of the 

generator’s rated continuous output at ambient oxygen and standard temperature and pressure 

conditions. Steps 1 through 5 describe setting up equipment, setting test conditions and warming 

up the generator prior to starting the generator for the emission test itself (Step 6). Step 7 describes 

the requirements for the reduced O2 level to be reached for a test to be considered valid. The O2

level must decrease below 18.5 % but cannot decrease below 17.5 % in less than 30 minutes. If the 

O2 level does not decrease sufficiently or decreases too quickly, the test should be repeated with a 

different ventilation rate or chamber volume. An exception is provided for partial load tests at 

generator load settings below 1 kW. Steps 8 and 9 contain additional requirements for repeating 

tests due to either generator or instrumentation malfunction. If the test endpoint is not reached due 

to generator stalling or dropping the load, the test can be restarted no more than four times. There 

is no limit on test restarts due to instrumentation failure.

The calculation procedures section includes the equation used to calculate the CO emission rate 

for the test. The equation is based on a single zone mass balance equation. A sample calculation is 

included to demonstrate the application of the equation.

4. ESTIMATE OF CO ENTRY FROM OPERATION OF GENERATOR OUTDOORS

This section describes an analysis performed to estimate the potential fraction of CO emitted by a 

generator operated outdoors that may enter a house. An estimate of this fraction may be needed to 

evaluate an acceptable continuous operation CO emission rate for a generator which is designed 

with a shut-off mechanism to prevent indoor operation, but which may still be operated outdoors 

but near enough to a house such that CO entry is of potential concern. Since 2001, 16 portable 

generator related CO poisoning deaths occurred in cases where generators were operated outside 

the home (which does not include deaths that occurred when the generator was outside other 

structures, such as a boat, trailer, or temporary shelter) – usually near an open window or vent 

(Hnatov 2013). Additionally, the U.S. Centers for Disease Control has estimated that up to half of 

non-fatal CO poisoning incidents during the hurricane seasons in 2004 and 2005 involved 

generators operated outdoors but within seven feet of the home (CDC 2006).

Wang and Emmerich (2010) and Wang et al. (2013) presented a study of the entry of CO from a 

generator exhaust into a one-story house and two-story house, respectively, by numerical 

simulation. A matrix of simulation scenarios was use to consider multiple factors contributing to 

the CO entry, e.g., generator location, exhaust temperature, exhaust speed, exhaust direction, 

window opening size, wind, temperature, house dimensions, and generator distance from the 

house. The transient indoor CO profiles were modeled using the CONTAM indoor air quality 

model (Walton and Dols 2005) integrated with computational fluid dynamics (CFD) models, 
6

CFD0 (Wang 2007) and FDS (McGrattan et al. 2010). These CFD models were used to predict 

outdoor CO dispersion near the house. 

While those studies predicted CO concentrations indoors resulting from outdoor operation of a 

generator for a wide variety of scenarios, they did not directly examine the question of the fraction 

of the CO emitted outdoors that entered the houses. The approach used here is to examine the 

worst case from the previous modeled scenarios (i.e., the case that resulted in the highest indoor 

CO concentration of the cases simulated but not the worst case that is possible in actual usage),

and then to perform CONTAM simulations to determine an indoor CO source that results in 

approximately equal indoor CO concentrations. 

As seen in Figure 1 below (Figure 8 of Wang et al. 2010), the highest peak indoor CO 

concentration occurred for Case 1, which corresponds to the generator being located 1.8 m upwind 

from a two-story house, exhaust pointing toward the house, and a wind speed of 1 m/s. All cases 

considered indoor and outdoor temperatures constant at 20.9 °C, a single window with a 0.31 m2

opening and the generator operating for 8 hours with a CO generation rate of 1000 g/h. Case 1 

resulted in a peak CO concentration in the kitchen (the room with the open window) of about 9200 

mg/m3 after 8 hours. A CONTAM simulation with a generator operating in the kitchen with a 

constant CO emission rate of 350 g/h (under otherwise similar ambient conditions) resulted in a 

peak CO concentration of about 9100 mg/m3 after 8 hours, thus indicating that approximately 35 % 

of the CO emitted by the outdoor generator entered the house for this case. 
7

Figure 1. Maximum indoor CO in the house when the generator operated upwind of the house for 

8 hours under zero indoor and outdoor temperature difference (Figure 8 of Wang et al. 2010). 

Notes: Numbers below bars are case numbers. Case 1 concentration reached 9200 mg/m3.

5. SUMMARY

The CPSC is working to reduce the occurrence of future generator-related CO poisoning incidents, 

especially those associated with operating a generator in an enclosed space. To that end, the CPSC 

issued an Advance Notice of Proposed Rulemaking; Request for Comments and Information in 

2006 describing its strategy to reduce generator engine CO emission rates. If the CPSC is to issue 

such a rule, it will need to include a test method for determining CO emission rates from portable 

generators operating in an enclosed space. This report described work intended to support the 

development of such a test method as well as other information needed to support the development 

of a Notice of Proposed Rulemaking.

6. ACKNOWLEDGEMENTS

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

agreement No. CPSC-I-13-0012. The authors wish to express their appreciation for the support of 

Janet Buyer, Susan Bathalon, and Matt Brookman in conducting this effort. Stacy Bruss of the 

NIST Library assisted in conducting the literature search.

7. REFERENCES

ANSI. 2000. Z21.63-2000 Portable Type Gas Camp Heaters. ANSI.

0

200

400

600

800

1000

1200

1400

1 2 3 4 5 6 7 8 9 10 11 12 25 26 27 28 29 30 31 32 33 34 35 36

1 m/s 5 m/s 10 m/s

1.8 m (6 f) 

4.6 m (15 f)

9.1 m (30 f)

10.7 m (35 f)

Generator Distance

Max House CO (mg/m3) 

1 m/s 5 m/s 10 m/s

Exhaust Pointing Towards House Exhaust Pointing Away From House

> 1400

Wind speed:
8

ANSI. 2013. Z21.11.2-2013 Gas-fired room heaters, volume II, unvented room heaters. ANSI.

Brown C J. 2006. Engine-drive Tools, Phase 1 Test Report for Portable Electric Generators; U.S. 

Consumer Product Safety Commission: Bethesda, MD.

Brown CJ. 2008. Engine-Driven Tools, Phase 2 Test Report: Portable Generator Equipped with a 

Safety Shutoff Device, U.S. Consumer Product Safety Commission.

CA. 1995. California Exhaust Emission Standards and Test Procedures for 1995 and Later Utility 

and Lawn and Garden Equipment Engines. State of California Air Resources Board.

Carteret, M., Pauwels, JF and B Hanoune. 2012. "Emission factors of gaseous pollutants from 

recent kerosene space heaters and fuels available in France in 2010." Indoor Air 22(4): 299-308.

CDC. 2006. Carbon monoxide poisonings after two major hurricanes - Alabama and Texas, 

August - October 2005. Morbidity and Mortality Weekly Report (MMWR), United States Centers 

for Disease Control and Prevention: 4.

Emmerich, SJ, Persily, AK and L Wang. 2013. Modeling and Measuring the Effects of Portable 

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

1781.

EPA. 2012. 40 CFR Part 1065 Engine Testing Procedures. U.S. EPA.

Fan, C-W and J Zhang. 2001. "Characterization of emissions from portable household combustion 

devices: particle size distributions, emission rates and factors, and potential exposures." 

Atmospheric Environment 35(7): 1281-1290.

Hnatov, M. 2013. Incidents, Deaths, and In-Depth Investigations Associated with Non-Fire 

Carbon Monoxide from Engine-Driven Generators and Other Engine-Driven Tools, 1999-2012, 

U.S. Consumer Product Safety Commission, Bethesda, MD, August 2013.

McGrattan K, McDermott R, Hostikka S, and J. Floyd. 2010. Fire Dynamics Simulator (Version 5) 

User's Guide. National Institute of Standards and Technology.

Persily, AK, Wang, Y, Polidoro, B and SJ Emmerich. 2013. Residential Carbon Monoxide 

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

NIST Technical Note 1782.

Priest, MW, Williams, DJ and HA Bridgman. 2000. "Emissions from in-use lawn-mowers in 

Australia." Atmospheric Environment 34(4): 657-664.
9

PGMA. 2013. G200, Standard for Testing and Validating Performance of Portable Generators. 

Portable Generator Manufacturers’ Association.

Walton, GN and WS Dols. 2005. CONTAMW 2.4 User Guide and Program Documentation. 

NISTIR 7251. Gaithersburg, MD, USA, National Institute of Standards and Technology: 286.

Wang, L. 2007. Coupling of multizone and CFD programs for building airflow and contaminant 

transport simulations. Mechanical Engineering. Purdue University. PhD: 271.

Wang, L and SJ Emmerich. 2009. Modeling the effects of outdoor gasoline powered generator use 

on indoor carbon monoxide exposures. NIST Technical Note 1637.

Wang, L, Emmerich, SJ, and R Powell, R. 2010. Modeling the effects of outdoor gasoline powered 

generator use on indoor carbon monoxide exposures – Phase II. NIST Technical Note 1666.

Wang, L and SJ Emmerich. 2010. Modeling the effects of outdoor gasoline powered generator use 

on indoor carbon monoxide exposures. Building Simulation, Vol 3(1).

Wang, L, Emmerich, SJ, and C-C Lin. 2013. Study of the Impact of Operation Distance of 

Outdoor Portable Generators under Different Weather Conditions. Indoor and Built Environment.
10

APPENDIX A: Literature Review Bibliography

This appendix contains a bibliography of the results of the literature search described in Section 2

in the form of the references for the publications considered as well as the abstract of each.

Bresenham, D. and J. Reisel (1999). The Effect of High Ethanol Blends on Emissions from Small 

Utility Engines. Warrendale, PA, SAE International.

Emissions of total hydrocarbons, carbon monoxide, nitrogen oxides, and combined hydrocarbons 

and nitrogen oxides from small utility engines were used to judge the effect of ethanol addition 

(zero to 50 %vol) to a hydrocarbon fuel with factory air- fuel ratio carburetor settings. In this 

study, emissions from two 4-stroke 9.3 kW (12.5 hp) side-valve engines and one 4-stroke 9.3 kW 

(12.5 hp) overhead valve engine were assessed to support conclusions. Emissions differences due 

to the differing valve orientations were addressed as a secondary objective. A series of RBOB plus 

ethanol (EtOH) fuel blends were used in this parametric study. RBOB is the base fuel in which 

oxygenates are blended to produce reformulated gasoline (RFG) for use in Clean Air Act 

Amendments-designated Ozone Non-attainment Areas. RBOB+EtOH fuel blend (an oxygenated 

fuel) emissions were compared to RBOB (a nonoxygenated fuel) emissions to assess the effect of 

ethanol addition on emissions. The RBOB+10%EtOH fuel blend is similar to one of the fuel 

blends currently used in Ozone Non- attainment Areas (a slightly higher oxygen content) while the 

higher ethanol fuel blends in this study provide insight into the behavior of air emission as the 

ethanol concentration is increased beyond current levels of oxygenate addition mandates. The fuel 

blends ranged from RBOB+0%EtOH to RBOB+50%EtOH.The emissions were measured by a 5-

gas analyzer which measures total hydrocarbons, carbon monoxide, nitrogen oxides, oxygen, and 

carbon dioxide. EPA small engine test procedures were followed. The fuel flow method option 

was chosen as is the practice of small engine manufacturers. A method to deduce the air-fuel ratio 

from the fuel characteristics (carbon fraction and hydrogen fraction) and emissions was introduced 

by R. S. Spindt for conventional (nonoxygenated) fuels in 1965. This study uses a modified Spindt 

Method to accommodate highly oxygenated fuels developed in a related study for use with this 

engine and fuel set. The Spindt method technique allows estimation of the actual (operating) airfuel ratio from exhaust constituents. With the actual air-fuel ratio, the data may be assessed in 

terms of the equivalence ratio. By using the equivalence ratio, emissions from engines operating 

on varying oxygenate content fuels may be directly compared since the varying stoichiometric airfuel ratios are stabilized.The primary results indicate that increasing the concentration of ethanol 

in gasoline is effective in reducing regulated carbon monoxide emissions from small engines 

designed to operate on nonoxygenated fuels but ineffective in reducing regulated combined 

hydrocarbon and nitrogen oxide emissions. This result has implications on one small engine 

emissions reduction strategy~blending a specialized "lawn and garden'''' highly oxygenated fuel 

for delivery through alternative distribution outlets.The secondary results indicate evidence that 

the overhead- valve technology engine exhibits lower hydrocarbon and carbon monoxide 

emissions characteristics but has no discernible effect on nitrogen oxides and negligible effect on 

combined hydrocarbon and nitrogen oxides emissions. This result has implications on another 

small engine emissions reduction strategy~the shift from side-valve engines to overhead-valve 

engines in small engine applications.
11

Carteret, M., et al. (2012). "Emission factors of gaseous pollutants from recent kerosene space 

heaters and fuels available in France in 2010." Indoor Air 22(4): 299-308.

Laboratory measurements of the gaseous emission factors (EF) from two recent kerosene space 

heaters (wick and injector) with five different fuels have been conducted in an 8-m3 environmental 

chamber. The two heaters tested were found to emit mainly CO2, CO, NO, NO2, and some volatile 

organic compounds (VOCs). NO2 is continuously emitted during use, with an EF of 100–450 μg 

per g of consumed fuel. CO is normally emitted mainly during the first minutes of use (up to 3 

mg/g). Formaldehyde and benzene EFs were quantified at 15 and 16 μg/g, respectively, for the 

wick heater. Some other VOCs, such as 1,3-butadiene, were detected with lower EFs. We 

demonstrated the unsuitability of a ‘biofuel’ containing fatty acid methyl esters for use with the 

wick heater, and that the accumulation of soot on the same heater, whatever the fuel, leads to a 

dramatic increase in the CO EF, up to 16 mg/g, which could be responsible for chronic and acute 

CO intoxications. Practical Implications Our results show that in spite of new technologies and 

emission standards for unvented kerosene space heaters, as well as for the fuels, the use of these 

heaters in indoor environments still leads to NOx levels in excess of current health 

recommendations. Whereas injection heaters generate more nitrogen oxides than wick heaters, 

prolonged use of the latter leads to a soot buildup, concomitant with high CO emissions, which 

could be responsible for acute and chronic intoxications. The use of a biofuel in a wick heater is 

also of concern. Maintenance of the heaters and adequate ventilation of the room during use of 

kerosene space heaters are therefore of prime importance to reduce personal exposure.

Christensen, A., et al. (2001). "Measurement of Regulated and Unregulated Exhaust Emissions 

from a Lawn Mower with and without an Oxidizing Catalyst:  A Comparison of Two Different 

Fuels." Environmental Science & Technology 35(11): 2166-2170.

Relatively few emission characterization studies have been made on small engines used in garden 

equipment. The present investigation focuses on exhaust characterization from a lawn mower 

engine fueled with two different fuels in combination with and without an oxidizing catalyst. The 

compounds measured in the exhaust are carbon monoxide, hydrocarbons, nitrogen oxides, 

particulates, polycyclic aromatic hydrocarbons, methane, ethane, ethene, ethanol, and nitrous 

oxide. A significant reduction can be achieved by the use of a catalyst. By selection of the fuel, a 

significant reduction of certain carcinogenic compounds (“probably carcinogenic to humans”

according to the IARC; benzo[a]pyrene and benzo[a]anthracene) may be achieved. The highest 

reduction improvement is achieved through the combination of an environmentally improved fuel, 

i.e., alkylate fuel, and a catalyst system. The data presented show that emissions from lawn mower

engines are still relatively large although there is the potential for further improvements.

Dernotte, J., et al. (2009). "Evaluation of Butanol–Gasoline Blends in a Port Fuel-injection, SparkIgnition Engine." Oil & Gas Science and Technology – Revue de l’Institut Français du Pétrole

65(2): 345-351.

This paper assesses different butanol–gasoline blends used in a port fuel-injection, spark-ignition 
12

engine to quantify the influence of butanol addition on the emission of unburned hydrocarbons, 

carbon monoxide, and nitrogen oxide. Furthermore, in-cylinder pressure was measured to quantify 

combustion stability and to compare the ignition delay and fully developed turbulent combustion 

phases as given by 0 %–10 % and 10 %–90 % Mass Fraction Burned (MFB). The main findings 

are: 1) a 40 % butanol/60 % gasoline blend by volume (B40) minimizes HC emissions; 2) no 

significant change in NOx emissions were observed, with the exception of the 80 % butanol/20 % 

gasoline blend; 3) the addition of butanol improves combustion stability as measured by the COV 

of IMEP; 4) butanol added to gasoline reduces ignition delay (0 %–10 % MFB); and 5) the 

specific fuel consumption of B40 blend is within 10% of that of pure gasoline for stoichiometric 

mixture.

Dutton, S. J., et al. (2001). "Indoor Pollutant Levels from the Use of Unvented Natural Gas 

Fireplaces in Boulder, Colorado." Journal of the Air & Waste Management Association (Air & 

Waste Management Association) 51(12): 1654-1661.

High CO and NO2 concentrations have been documented in homes with unvented combustion 

appliances, such as natural gas fireplaces. In addition, polycyclic aromatic hydrocarbons (PAH) 

are emitted from incomplete natural gas combustion. The acute health risks of CO and NO2

exposure have been well established for the general population and for certain high-risk groups, 

including infants, the elderly, and people with heart disease or asthma. Health effects from PAH 

exposure are less well known, but may include increased risk of cancer. We monitored CO 

emissions during the operation of unvented natural gas fireplaces in two residences in Boulder, 

CO, at various times between 1997 and 2000. During 1999, we expanded our tests to include 

measurements of NO2 and PAH. Results show significant pollutant accumulation indoors when the 

fireplaces were used for extended periods of time. In one case, CO concentrations greater than 100 

ppm accumulated in under 2 hr of operation; a person at rest exposed for 10 hr to this environment 

would get a mild case of CO poisoning with an estimated 10 % carboxyhemoglobin level. 

Appreciable NO2 concentrations were also detected, with a 4-hr time average reaching 0.36 ppm. 

Similar time-average total PAH concentrations reached 35 ng/m3. The results of this study provide 

preliminary insights to potential indoor air quality problems in homes operating unvented natural 

gas fireplaces in Boulder.

Eccleston, B. H. and R. W. Hurn (1972). Exhaust Emissions from Small, Utility, Internal 

Combustion Engines. Warrendale, PA, SAE International.

This material reports findings of an exploratory experimental study designed to add information 

on the contribution to air pollution of exhaust emissions from small, utility engines, and to 

evaluate the procedures used to test small engines. Gross measurements of hydrocarbon, carbon 

monoxide, and nitric oxide are reported for 29 4-cycle and 7 2-cycle engines; sizes of the engines 

ranged 2-22 hp. Emissions measurements were made on each engine for nine combinations of load 

and air-fuel adjustments; only one speed point~full governed~was covered in the tests. Test 

procedures are described. An overall average of the data indicate that, operated at full-load and 

optimum air-fuel ratio, the four-cycle engines emitted about 8 g HC, 180 g CO, and 5 g NO2 per 

horsepower-hour. Under comparable conditions, the 3-6 hp two-cycle engines emitted an average 

of 140 g HC, 240 g CO, and 2 g NO2 per horsepower-hour.
13

Fan, C.-W. and J. Zhang (2001). "Characterization of emissions from portable household 

combustion devices: particle size distributions, emission rates and factors, and potential 

exposures." Atmospheric Environment 35(7): 1281-1290.

A series of source tests were conducted to characterize emissions of particulate matter (PM), 

carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and total hydrocarbon (THC ) from 

five types of portable combustion devices. Tested combustion devices included a kerosene lamp, 

an oil lamp, a kerosene space heater, a portable gas range, and four unscented candles. All tests 

were conducted either in a well-mixed chamber or a well-mixed room, which enables us to 

determine emission rates and emission factors using a single-compartment mass balance model. 

Particle mass concentrations and number concentrations were measured using a nephelometric 

particle monitor and an eight-channel optical particle counter, respectively. Real-time CO 

concentrations were measured with an electrochemical sensor CO monitor. CO2, CH4, and THC 

were measured using a GC-FID technique. The results indicate that all particles emitted during 

steady burning in each of the tested devices were smaller than 1.0 μm in diameter with the vast

majority in the range between 0.1 and 0.3 μm. The PM mass emission rates and emission factors 

for the tested devices ranged from 5.6±0.1 to 142.3±40.8 mg h−1 and from 0.35±0.06 to 9.04±4.0 

mg g−1

, respectively. The CO emission rates and emission factors ranged from 4.7±3.0 to 

226.7±100 mg h−1 and from 0.25±0.12 to 1.56±0.7 mg g−1, respectively. The CO2 emission rates 

and emission factors ranged from 5500±700 to 210,000±90,000 mg h−1 and from 387±45 to 

1689±640 mg g−1

, respectively. The contributions of CH4 and THC to emission inventories are 

expected to be insignificant due both to the small emission factors and to the relatively small 

quantity of fuel consumed by these portable devices. An exposure scenario analysis indicates that 

every-day use of the kerosene lamp in a village house can generate fine PM exposures easily 

exceeding the US promulgated NAAQS for PM2.5.

Francisco, P. W., et al. (2010). "Measured concentrations of combustion gases from the use of 

unvented gas fireplaces." Indoor Air 20(5): 370-379.

Measurements of combustion product concentrations were taken in 30 homes where unvented gas 

fireplaces were used. Measurements of CO, CO2, NOx, NO2, O2 (depletion), and water vapor were 

taken at 1-min interval. The analyzers were calibrated with certified calibration gases for each 

placement and were in operation for 3–4 days at each home. Measured concentrations were 

compared to published health-based standards and guidelines. The two combustion gases that 

exceeded published values were NO2 and CO. For NO2, the Health Canada guideline of 250 ppb 

(1-h average) was exceeded in about 43 % of the sample and the World Health Organization 

(WHO) guideline of 110 ppb (1-h average) was exceeded in 80 % of the sample. Carbon 

monoxide levels exceeded the U.S. EPA 8-h average standard of 9 ppm in 20 % of the sample. 

Moisture problems were not evident in the test homes. An analysis of the distribution of CO 

showed that the CO is dispersed throughout the home almost immediately upon operation of the 

fireplace and that the concentrations throughout the home away from the immediate vicinity of the 

fireplace are 70–80 % of the level near the fireplace. Decay analysis of the combustion gases 

showed that NO was similarly stable to CO and CO2 in the indoor environment but that both NO2

and water vapor were removed from the air at much greater rates. Practical Implications Previous 
14

studies on unvented gas fireplaces have made assumptions of how they are operated by users. This 

article presents the results of field monitoring of 30 unvented gas fireplaces under normal 

operation, regardless of whether users follow industry recommendations regarding installation, 

usage patterns, and maintenance. The monitoring found that health-based standards and guidelines 

were exceeded for CO in 20 % of homes and for NO2 in most homes. There were no identified 

moisture problems in these homes. Nearly, half of the fireplaces were used at least once for longer 

than 2 h, counter to manufacturers’ intended usage as supplemental heating. This demonstrates 

that given actual usage patterns and compared to current health-based thresholds, these appliances 

can produce indoor air concentrations considered to be unhealthy to at least sensitive or at-risk 

individuals.

Gabele, P. (1997). "Exhaust Emissions from Four-Stroke Lawn Mower Engines." Journal of the 

Air & Waste Management Association 47(9): 945-952.

Emissions were characterized from 10 four-stroke lawn mower engines. The ages of the engines 

ranged from new to 15 years, and each was tested using two gasoline fuels: a 1990 national 

average blend and a reformulated gasoline. Reformulated gasoline usage resulted in lower organic 

and carbon monoxide emissions that contributed to lower reactivity-weighted emission rates. 

Aggregate toxic emissions were also reduced because benzene emissions were lower. On the other 

hand, increases in nitrogen oxide emission rates were observed with the reformulated gasoline. 

Compared to the newer engines, older engines had dramatically higher organic and carbon 

monoxide and lower nitrogen oxide emissions.

Gautam, A. S., et al. (2012). A Comparison of the Emissions from Gasoline vs. Compressed 

Natural Gas for an Electronic Fuel Injected Two Cylinder, Four-Stroke Engine. Warrendale, PA, 

SAE International.

Natural gas is a viable alternative to gasoline and diesel fuel because it is a clean burning fuel that 

is available from a large domestic reserve through a mature infrastructure. The heavy dependence 

of the small engine sector on oil, much of which is imported from foreign countries and the small 

engine sector's negative impact on the air quality in urban areas are two pervasive problems that 

can be helped by using Compressed Natural Gas (CNG) as a small engine fuel. In addition, CNG 

is typically over 80 % methane, which is produced by the decay of organic material, so while 

natural gas is not renewable its use enables much of the infrastructure required for a methanebased renewable energy system.

Guo, L., et al. (2008). "Emissions from Irish domestic fireplaces and their impact on indoor air 

quality when used as supplementary heating source." Global NEST Journal 10(2): 209-216.

A field study on the impact of fireplace on the indoor air quality was carried out between 2004 and 

2006, where two main contaminants, CO and particulate matters, were investigated in twenty 

seven randomly selected Irish houses. The results show that while the physical environment has 

been improved by increasing the room air and radiant temperature, indoor air quality is 

significantly decreased when fireplace is used as additional heating source to the central heating. 

The operation of fireplace increased transient concentrations of CO and airborne particle to several 

times higher than the normal house average level. Statistical analysis showed significant 
15

difference of the average PM10 concentration between house groups with and without using 

fireplace. However fireplace did not demonstrate a significant influence on average CO level from 

our samples. When comparisons were made between houses with various emission sources, i.e. 

fireplace, smoking and open fire gas cooking, and houses free of the above sources, smoking and 

open fire gas cookers were proved to be other major sources of particles and CO. Particularly 

when they exist at the same time with fireplace, significant elevation of CO and airborne particle 

levels is observed in analysis. Cumulative probability analysis in some houses revealed high 

percentage of time exceeding health guidelines which indicated the potential health risk in these 

houses. Mass balance equation was employed to estimate particle emission rates from fireplace, 

namely 0.66 mg min-1 (PM10) and 0.20 mg min-1 (PM2.5) respectively in terms of mass 

concentration. Emission rates on particle numbers were also estimated despite the relatively 

smaller sample. Gas fuel fireplaces tended to emit fewer particles both in mass and in number 

comparing to fireplaces using solid fuels.

Jetter, J. J., et al. (2002). "Characterization of emissions from burning incense." Science of The 

Total Environment 295(1–3): 51-67.

The primary objective of this study was to improve the characterization of particulate matter 

emissions from burning incense. Emissions of particulate matter were measured for 23 different 

types of incense using a cyclone/filter method. Emission rates for PM2.5 (particulate matter less 

than 2.5 μm in aerodynamic diameter) ranged from 7 to 202 mg/h, and PM2.5 emission factors 

ranged from 5 to 56 mg/g of incense burned. Emission rates were also determined using an 

electrical low pressure impactor (ELPI) and a small electrostatic precipitator (ESP), and emission 

rates were compared to those determined using the cyclone/filter method. Emission rates 

determined by the ELPI method were consistently lower than those determined by the 

cyclone/filter method, and a linear regression correlation was found between emission rates 

determined by the two methods. Emission rates determined by the ESP method were consistently 

higher than those determined by the cyclone/filter method, indicating that the ESP may be a more 

effective method for measuring semivolatile particle emissions. A linear regression correlation 

was also found between emission rates determined by the ESP and cyclone/filter methods. Particle 

size distributions were measured with the ELPI, and distributions were found to be similar for 

most types of incense that were tested. Size distributions by mass typically ranged from 

approximately 0.06 to 2.5 μm in aerodynamic diameter, with peak values between 0.26 and 0.65 

μm. Results indicated that burning incense emits fine particulate matter in large quantities 

compared to other indoor sources. An indoor air quality model showed that indoor concentrations 

of PM2.5 can far exceed the outdoor concentrations specified by the US EPA's National Ambient 

Air Quality Standards (NAAQS), so incense smoke can pose a health risk to people due to 

inhalation exposure of particulate matter. Emissions of carbon monoxide (CO), nitric oxide (NO), 

and sulfur dioxide (SO2) were also measured for seven types of incense. Emission rates of the 

gaseous pollutants were sufficient to cause indoor concentrations, estimated using the indoor air 

quality model, to exceed the outdoor concentrations specified by the NAAQS under certain 

conditions. However, the incense samples that were tested would fill a room with thick smoke 

under these conditions.
16

Leigh-Smith, S. (2004). "Carbon Monoxide Poisoning in Tents—A Review." Wilderness & 

Environmental Medicine 15(3): 157-163.

This review discusses the overlooked problem of carbon monoxide (CO) poisoning within small 

tents. It summarizes previous case reports, reviews the toxicity of CO, and attempts to draw 

conclusions from experimental work. Finally, practical recommendations are developed on 

avoiding CO poisoning within tents. The term carbon monoxide was used in a search of the 

Medline database covering the years 1966 to 2003. The results were combined with the terms 

atmosphere or camps or stoves or climbs or mountains or tents or poisons. The resulting articles 

were reviewed, and those relevant to this problem were obtained. Hard copies were hand searched 

for further relevant articles until no more citations could be found. Three original articles were 

impossible to obtain but have been cited to assist others seeking to find them. Other data and 

articles were obtained from the Ministry of Defence but are unpublished for security reasons.

samples that were tested would fill a room with thick smoke under these conditions.

Leigh-Smith, S., et al. (2004). "Does Pan Diameter Influence Carbon Monoxide Levels During 

Heating of Water to Boiling Point With a Camping Stove?" Wilderness & Environmental 

Medicine 15(3): 171-174.

Objectives To determine whether pan diameter influences carbon monoxide (CO) concentration 

during heating of water to boiling point with a camping stove. The hypothesis was that increasing 

pan diameter increases CO concentration because of greater flame dispersal and a larger flame. 

Method This was a randomized, prospective study. A Coleman Dual Fuel 533 stove was used to 

heat pans of water to boiling point, with CO concentration monitored every 30 seconds for 5 

minutes. The stove was inside a partially ventilated 200-L cardboard box model that was inside an 

environmental chamber at −6°C. Water temperature, water volume, and flame characteristics were 

all standardized. Ten trials were performed for each of 2 pan diameters (base diameters of 165 mm 

[small] and 220 mm [large]). Results There was a significant difference (P = .002) between the 

pans for CO levels at each measurement interval from 60 seconds onward. These differences were 

markedly larger after 90 seconds, with a mean difference of 185 ppm (95 % CI 115, 276 ppm) for 

all the results from 120 seconds onwards. Conclusion This study has shown that there is 

significantly higher CO production with a large-diameter pan compared with a small-diameter 

pan. These findings were evident by using a camping stove to heat water to boiling point when a 

maximum blue flame was present throughout. Thus, in enclosed environments it is recommended 

that small-diameter pans be used in an attempt to prevent high CO levels.

Palke, D. R. and M. A. Tyo (1999). The Impact of Catalytic Aftertreatment on Particulate Matter 

Emissions from Small Motorcycles. Warrendale, PA, SAE International.

This paper presents the results of an exploratory study examining the production of particulate 

matter (PM) by 2-wheel vehicles and the impact of catalytic aftertreatment on these emissions. 

Information is presented demonstrating the efficacy of catalytic aftertreatment for significantly 

reducing not only hydrocarbons (HC) and carbon monoxide (CO), but also PM emissions from 

motorcycles equipped with small 2-stroke engines. The generation of PM by 5 test vehicles during 

realistic driving conditions is discussed and the impact of catalyst performance characteristics on 

the reduction of these releases is examined. Vehicle based test data, obtained with a mini-dilution 
17

tunnel, clearly demonstrates the benefits to the environment achievable through the use of catalytic 

aftertreatment.

Phipps, R., et al. (2006). Not just hot air: Methods and preliminary results for the intensive 

monitoring of emissions and by-products from two types of domestic heaters, International 

Society of Indoor Air Quality and Climate. Proceedings of Healthy Buildings 2006

Intensive air quality measurements were made for up to a week in a sample of 33 homes drawn 

from a 500 home Heating, Housing and Health interventional community trial. Measures include 

nitrogen dioxide, formaldehyde, carbon monoxide and dioxide, fungi, moisture, temperature and 

heater usage. Families with an asthmatic child and where their primary means of heating was a 

plug-in electric or unflued gas heater were enrolled in the trial. Baseline measures were completed 

in 2005 and in 2006 a randomly selected 250 households will be given a heat pump, flued gas 

heater or pellet wood fire. All environmental measures will be repeated in 2006.

Priest, M. W., et al. (2000). "Emissions from in-use lawn-mowers in Australia." Atmospheric 

Environment 34(4): 657-664.

Concern over the levels of pollutants emitted from small engines has led to recent legislation in 

the United States that regulates exhaust emissions from lawn and garden equipment. Particular 

attention has focused on the high levels of hydrocarbons emitted by these engines. The present 

study establishes emission factors for lawn-mowers in use in Australia. The estimates were 

calculated on the basis of a series of controlled emission tests conducted on commonly used lawnmowers. Ten two-stroke and six four-stroke lawn-mower engines were operated under simulated 

power requirements while fuel usage and gas emissions were monitored. Fuel consumption rates 

from the tests were compared to those ascertained under actual mowing conditions in field tests 

conducted on 19 two-stroke and ten four-stroke lawn-mowers. Basic emission factors were 

established for CO, CO2, CH4, NMHC and NOx, and combined with data on machine population 

and annual usage collected in a survey of lawn care practices and lawn-mower usage conducted in 

the Newcastle area. When compared to transport sources in the Newcastle study region, lawnmowers contribute 5.2 and 11.6% of CO and NMHC emissions, respectively.

Schwartz, R. B., et al. (2001). "A comparison of carbon monoxide levels during the use of a multifuel camp stove." Wilderness & Environmental Medicine 12(4): 236-238.

Objective The use of camp stoves in an enclosed or poorly ventilated space is clearly not 

recommended due to the risk of carbon monoxide (CO) poisoning. Instances may arise, however, 

when use for a limited time is necessary. We sought to find differences in CO levels between 

various fuels used to power a commercially available camp stove. Methods A comparison was 

made between unleaded gasoline, kerosene, and white gas (Coleman fuel). The stove, fuels, and 

CO detector were all purchased from local retailers. A 0.4-m3 space was constructed with a 

cardboard box. Three trials were performed using each fuel in which water was heated over the 

stove for 5 minutes. Measurement of the CO level within the box was taken every 30 seconds. 

Results Kerosene created CO levels of 714 (SD = 113.5) parts per million (ppm) at 2 1/2 minutes 

but was out of the measurable range of >999 ppm within 4 minutes on each of its trials. White gas 

burned the cleanest, with an average of 212 ppm (SD = 27.8) at 2 1/2 minutes and 348 ppm (SD = 
18

76.0) at 5 minutes. Unleaded gasoline created 305 ppm (SD = 27.1) at 2 1/2 minutes and 464 ppm 

(SD = 31.6) at 5 minutes. Conclusion All of the fuels created a high level of CO in a short period 

of time. White gas burned the cleanest and would be preferred to unleaded gasoline or kerosene in 

the event that the unvented use of a camp stove was necessary.

Thomassen, Ø., et al. (2004). "Carbon monoxide poisoning while using a small cooking stove in a 

tent." The American Journal of Emergency Medicine 22(3): 204-206.

Carbon monoxide (CO) is formed wherever incomplete combustion of carbonaceous products 

occurs.(1) CO is the leading cause of poisoning in the United States, and common sources of CO 

poisoning include housefires, automobile exhaust, water heaters, kerosene space heaters, and 

furnaces.(2) Stoves used for cooking and heating during outdoor activities also produce significant 

amounts of CO. Mountain climbers have been reported to succumb to fumes generated by small 

cook stoves.(3) The aim of this study was to investigate if burning a cooking stove inside a tent is 

a potential health hazard. Seven healthy male volunteers used a cooking stove inside a small tent 

for 120 minutes. CO levels in the ambient tent air were measured in addition to hearth rate (HR) 

and pulse oximetry (SpO2). Venous blood samples were obtained every 15 minutes for 

measurement of carboxyhemoglobin (COHb). After 2 hours, all the subjects had significant CO 

levels in their blood (mean COHb = 21.5 %). Mean SpO2, also fell from 98 % to 95.3 % (P <.05),

whereas mean HR increased from 63 to 90 beats/min (P <.05). Kerosene camping stoves do 

produce CO when burned in a small tent. The concentration is high enough to cause significant 

COHb levels in venous blood after 120 minutes' stay in the tent.

Traynor, G. W., et al. (1985). "Indoor Air Pollution Due to Emissions from Unvented Gas-Fired 

Space Heaters." Journal of the Air Pollution Control Association 35(3): 231-237.

Operation of an unvented combustion appliance indoors can elevate pollutant concentrations 

Under laboratory conditions, oxygen consumption rates and pollutant emission rates of CO, CO2, 

NO, NO2, HCHO and submicron suspended particles emitted from eight unvented gas-fired space 

heaters operated with well adjusted air shutters at partial and full fuel consumption rates were 

determined in a 27-m3 chamber. Emission rates were also determined for some heaters operating 

under poorly tuned conditions. Four of the eight heaters were subsequently tested in a 240-m3

research house with 0.36-1.14 air changes per hour. Based on measurements near steady state, 

steady state pollutant and oxygen levels were projected: 1930-11,100 ppm for CO2, 1.0-26 ppm 

for CO (under well-tuned conditions), 0.40-1.46 ppm for NO2, and 19.1-20.7% for O2. 

Concentrations of CO2, CO, and NO2 sometimes exceeded outdoor or occupational guidelines. 

Analysis showed that CO, NO, and NO2 emission rates can vary with time and that, while shortterm emission rates derived from laboratory tests were consistent with initial emission rates 

observed in the field, they did not always correspond to steady state emission rates.

Tutupalli, L. V., et al. (1997). Standard test method for the measurement of emissions from the 

combustion of manufactured fireplace logs in zero-clearance fireplaces, Air & Waste Management 

Assoc.

A standard test method is developed for measuring emissions from the combustion of 

manufactured fireplace logs in zero-clearance fireplaces. In order to be reliable and cost effective, 
19

the test method followed the EPA method 5G very closely. However, in addition to the particulate 

matter, CO measurement is incorporated into the protocol because CO is a criteria pollutant for 

which there are ambient air quality and indoor level standards. The test method includes 

automated data collection, and data processing to produce final reports similar to those of the EPA 

method.

Volckens, J., et al. (2008). "Carbonaceous species emitted from handheld two-stroke engines." 

Atmospheric Environment 42(6): 1239-1248.

Small, handheld two-stroke engines used for lawn and garden work (e.g., string trimmers, leaf 

blowers, etc.) can emit a variety of potentially toxic carbonaceous air pollutants. Yet, the 

emissions effluents from these machines go largely uncharacterized, constraining the proper

development of human exposure estimates, emissions inventories, and climate and air quality 

models. This study samples and evaluates chemical pollutant emissions from the dynamometer 

testing of six small, handheld spark-ignition engines—model years 1998–2002. Four oil–gas 

blends were tested in each engine in duplicate. Emissions of carbon dioxide, carbon monoxide, 

and gas-phase hydrocarbons were predominant, and the PM emitted was organic matter primarily. 

An ANOVA model determined that engine type and control tier contributed significantly to 

emissions variations across all identified compound classes; whereas fuel blend was an 

insignificant variable accounting for <5% of the observed variation in emissions. Though 

emissions rates from small engines were generally intermediate in magnitude compared with other 

gasoline-powered engines, numerous compounds traditionally viewed as motor vehicle markers 

are also present in small engine emissions in similar relative proportions. Given that small, 

handheld two-stroke engines used for lawn and garden work account for 5–10 % of total US 

emissions of CO, CO2, NOx, HC, and PM2.5, source apportionment models and human exposure 

studies need to consider the effect of these small engines on ambient concentrations in air polluted 

environments.

Wang, J., et al. (1988). "Remote Measurement of Motorcycle Exhaust Using Fourier Transform 

Infrared System." Spectroscopy Letters 21(9-10): 935-946.

We have explored the basic theory and quantitative methods for the measurement of motorcycle 

exhaust using a Fourier transform infrared interferometer system. Remote sensing direct 

measurements were made and the species carbon monoxide, carbon dioxide, nonmethane 

paraffinic carbon(CHx) and unburned additional harmful species in motorcycle exhaust were 

determined. Typical concentrations observed in absorption for carbon monoxide, carbon dioxide 

and nonmethane paraffinic carbon were about 1.11 %, 1.91 %, 0.54 % respectively. Furthemore, 

this paper describes the remote sensing Fourier transform infrared spectrometer system. The 

system covers the infrared spectral region from 700 to 6000 cin−1 at a maxim resolution of 0.06 

cm−1 for beamsplitter of gerrniuiirun coated zinc selenide and receiver telescope with zinc selriide 

leis. For air multipollutant monitoring the analytica1 methods have the potential and become 

important. The remote measurements using the Fourier transform infrared spectroscopy could 

become more practical.
20

APPENDIX B: Draft Test Method

Equipment and Test Procedures to Perform Generator Emission Rate Test in a Chamber at 

Reduced Oxygen Level

Warning: Carbon monoxide is a poisonous gas. Operating an internal combustion engine in a 

confined space can create an accumulation of carbon monoxide and unburnt hydrocarbons. 

These procedures are not intended to address the safety concerns associated with their use. 

Appropriate safety measures need to be taken by those using these procedures before, during, 

and after testing.

A. Equipment

1. Chamber: Emission tests shall be performed in a single zone test chamber. (Note: The actual 

chamber size needed will depend on meeting the test requirements of Section C and on the 

size of the engine that is powering the generator being tested, among other factors. See 

Appendix 1 for guidance on selecting chamber size and ventilation rate.) The chamber shall be 

constructed of materials that are non-reactive for the engine exhaust gasses and that are 

acceptable for use at a sustained temperature of 90 °C (200 °F). The chamber shall be 

constructed to be sufficiently airtight such that the chamber ventilation fan (see subsection 

A.2) can maintain a negative pressure differential between the chamber and its surroundings 

of at least 2.5 Pa at all chamber operating conditions. Mixing fans may be provided as needed 

to meet the uniformity requirements of Part B below. 

2. Chamber ventilation fan and measurement: The chamber shall be ventilated by an exhaust 

fan capable of providing a range of ventilation rates sufficient to satisfy the requirements of 

Section C for the generators to be tested. Means shall be provided to measure the chamber 

ventilation rate with an accuracy of ±5 %. The volumetric airflow rate may be directly 

measured in the duct of the exhaust fan. Alternatively, the air change rate may be measured 

using a tracer gas decay test in compliance with ASTM Standard E741-11 Standard Test 

Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution.

3. Gas concentration measurement of CO and O2

a. Gas concentration measurement equipment shall be provided to measure CO and O2

gas concentrations with a manufacturer’s specified accuracy of 1 % of range. The peak 

CO concentration during a test must reach at least 25 % of instrument range being 

used during that test. 

b. Sampling: Gas concentration sample lines shall be made of non-reactive materials and 

shall be located to enable verification of the uniformity requirements of Part B.3. 

Particle and water filtration of gas sample lines may be provided to meet the 

specifications of the CO and O2 measurement equipment. Note: Ensure that any 

filters used do not interfere with concentrations of any gases being measured. Gas 

concentrations shall be measured and recorded at least once per minute.
21

4. Air temperature and humidity: Air temperature and humidity sensors shall be provided with 

accuracies of ± 1 °C and ± 5 % RH or better, respectively. Recommended locations are on two 

opposite walls at the midpoint of the chamber height.

5. Load bank and power meter: An AC electric resistor load bank shall be used to simulate 

electric loads on the generator. The load bank shall be capable of meeting the generator’s 

rated continuous output at ambient oxygen and standard temperature and pressure 

conditions. The load bank shall be capable of a load setting that is within 5 % of each specified 

load condition. The delivered load may decrease during the test, but the load bank setting 

shall not be adjusted. A power meter shall be provided to measure the actual electrical load 

delivered by the generator with an accuracy of ± 5 %. 

6. Fuel and lubricants: Generators shall be tested with a full tank of fuel. Fuel and lubricants 

meeting manufacturer’s specifications for the generator being tested shall be used.

B. Experimental Set-up Verification

1. Calibration: All test equipment shall be calibrated per manufacturer’s instructions. Proper 

operation of test equipment (including a zero and span check with calibrated gas and a leak 

test of the gas sampling system) shall be verified for each test per manufacturer’s 

instructions.

2. Volume: The chamber volume may be determined by direct measurement if it is a single, 

unchangeable volume. If the chamber volume is modified, the volume shall be determined in 

accordance with Appendix X5 of ASTM E741-11 Standard Test Method for Determining Air 

Change in a Single Zone by Means of a Tracer Gas Dilution. 

3. Gas concentration uniformity: Gas concentrations at representative locations (a minimum of 

three evenly spaced locations) throughout the chamber shall differ by less than 10 % of the 

average gas concentration in the chamber. Uniformity shall be verified during testing at least 

once for each chamber volume, ventilation rate, and generator loading combination.

C. Test Procedure [Repeat steps 1 through 9 for two load conditions –rated continuous output at 

ambient oxygen and standard temperature and pressure conditions and 50 % of the generator’s 

rated continuous output at ambient oxygen and standard temperature and pressure 

conditions.]

1. Setup and confirm normal instrumentation function per manufacturer’s instructions.

2. Establish an initial chamber air temperature of 20 °C ± 10 °C and relative humidity of 50 % ±

15 % RH at start of test. Note: temperature and humidity do not need to be controlled during 

the test, however, maintaining near ambient temperature conditions during the test may aid 

in stability and repeatability.

3. Verify initial air concentrations in the chamber and in ventilation air are at ambient conditions 

(< 5 ppm CO and 20.9 % O2) within instrument accuracy.
22

4. Place generator in center of chamber, activate chamber ventilation system, start generator 

and operate until warm per manufacturer’s instructions. Turn off the generator and continue 

to ventilate the chamber until chamber returns to ambient conditions. The post warm-up 

chamber ventilation rate can be greater than the test ventilation rate to achieve the desired 

initial conditions more quickly. The generator may instead be warmed up outside of the 

chamber.

5. Set test ventilation rate of chamber. See Appendix 1 for guidance on selecting ventilation 

rate.

6. Start generator and within 2 minutes apply desired setting on load bank.

7. Operate the generator with constant load setting at least 60 minutes and until the equilibrium 

CO concentration (defined as occurring when the concentration at the end of a 30 minute 

period is within 10 % of the concentration at the beginning of that 30 minute period) is 

reached, or for 180 minutes. 

a. If O2 level decreases below 17.5 % in less than 30 minutes, the test (steps 1 through 7) 

shall be repeated with a higher ventilation rate (see Appendix 1 for guidance). 

b. If O2 level does not decrease below 18.5 %, the test (steps 1 through 7) shall be 

repeated with a lower ventilation rate (see Appendix 1 for guidance). 

i. Exception: for partial load settings at or below 1 kW, the test does not need 

to be repeated if the O2 level reaches below 19.5 %.

c. If the temperature within the test chamber rises above 90 °C (200 °F) prior to 

achieving CO concentration equilibrium, the test must be aborted and performed 

with a ventilation rate or chamber volume sufficient to prevent the temperature from 

exceeding 90 °C (200 °F).

8. If the generator stalls or drops the load during the test prior to meeting the end condition 

above, the test can be restarted up to 4 times (a higher ventilation rate may be used – see 

Appendix 1 for guidance). 

9. Redo test if instrumentation fails or if the peak CO concentration exceeds the analyzer range.

D. Calculation Procedures.

1. Excluding the 2 minutes allowed for the generator to be operating without the load applied, 

calculate the CO emission rate in g/h using Equation 1:

Equation 1: A t

out CO,t 2

CO out 1 e

0.001A VC

S − ∆ − =

where the nomenclature is per Table 1:
23

Table 1 Nomenclature for Equation 1

Aout Air change rate of chamber (volumetric flow rate through the chamber divided 

by chamber volume), h-1

CCO, t2 Equilibrium CO concentration (concentration at beginning of 30 minute 

equilibrium period or at end of 180 minute test period if equilibrium is not 

achieved), ppm(v)

SCO CO emission rate, g/h

V Chamber volume , m3

∆t Time interval to reach initial equilibrium CO concentration condition (or 3 

hours if equilibrium is not achieved), h

2. Sample calculations

a. For a given test, the chamber volume is 30 m3 and the ventilation rate is measured to be 2.0 h-1

. 

The measured CO concentration reaches 1250 ppm(v) after one hour. Thirty minutes later, the 

concentration is 1325 ppm(v). Since 1325 ppm(v) is within ± 10 % of 1250 ppm(v), equilibrium is 

considered to have been reached at one hour. From Equation 1, the CO emission rate is

87

1 e

0.001* 2.0* 30* 1250 SCO 2.0*1 = − = − g/h of CO 

b. For a given test, the chamber volume is 40 m3 and the ventilation rate is measured to be 2.5 h-1

. 

The measured CO concentration reaches 2250 ppm(v) after three hours. The CO concentration 

increased more than 10 % over the previous 30 minutes and the O2 level has dropped to 18 %. 

The CO emission rate may be calculated at the three hour mark. From Equation 1, the CO 

emission rate is

225

1 e

0.001* 2.5* 40* 2250 SCO 2.5*3 = − = − g/h of CO 

References

ASTM. 2011. ASTM E741-11 Standard Test Method for Determining Air Change in a Single Zone 

by Means of a Tracer Gas Dilution.
24

Appendix 1 – Guidance on selecting chamber size and ventilation rate

Known O2 Consumption Rate

If the portable generator’s O2 consumption rate is known (e.g., calculated from theoretical 

engine characteristics, determined from a previous test or estimated from tests of similar 

equipment), the suggested initial test chamber ventilation rate (in h-1) for an O2 target of 18 %, 

can be calculated from the O2 consumption rate (in g/h) and chamber volume (in m3

) according 

to equation A1.

Equation A1: 35V

S A O2

i =

Sample calculation

For a given portable generator test, the chamber volume is 30 m3 and the O2 consumption rate is 6000 

g/h. From Equation A1, the suggested initial ventilation rate to achieve the target O2 concentration is:

5.7

35* 30

6000

35V

S A O2

i = = = h-1 

Unknown O2 Consumption Rate

If the portable generator’s O2 consumption rate is unknown, the suggested initial test chamber 

ventilation rate (in h-1

) to achieve the target O2 concentration may be estimated by dividing the 

generator load setting (in W) by 25 times the known chamber volume (in m3). See Table A1 for 

example results depending on load setting which can be used to specify chamber and initial 

ventilation rate or to choose ventilation rate for a given chamber size. [Note: This approximation 

is for a generator operating at near stoichiometric air to fuel ratio (AFR), and the needed 

ventilation rate is expected to be higher for generators operating at richer AFR.]

Table A1 

Load Setting (W) Chamber Volume (m3) Ventilation Rate (h-1)

2000 10 8

2000 20 4

6000 20 12

6000 40 6

10000 40 10

10000 60 5