Public Comments to CPSC on NIST Technical Note 

1781: Modeling and Measuring the Effects of Portable 

Gasoline Powered Generator Exhaust on Indoor Carbon 

Monoxide Level, dated February 2013

(as of June 12, 2013)
Secretary/Treasurer: 

THOMAS ASSOCIATES, INC.

1300 Sumner Ave. • Cleveland, Ohio 44115-2851 • 216-241-7333 • Fax 216-241-0105 

URL: www.pgmaonline.com E-mail: pgma@pgmaonline.com

 June 7, 2013 

Ms. Janet L. Buyer 

Project Manager 

Directorate for Engineering Sciences 

U.S. Consumer Product Safety Commission 

4330 East West Highway 

Bethesda, MD 20814 

SUBJECT: Comments to CPSC on NIST Technical Note 1781

Dear Ms. Buyer: 

The Portable Generator Manufacturers’ Association (PGMA) is pleased to offer its 

comments on the recently released NIST Technical Note 1781. 

PGMA is a trade association that seeks to develop and influence safety and performance 

standards for our industry’s products. As the history of both PGMA and the individual 

members of PGMA demonstrate, our commitment to safety is a sincere commitment, one 

backed by repeated actions and not simply empty words. Since our members include the 

major industry manufacturers of portable generators sold in North America and a 

significant majority of the industry, we are the recognized voice of the portable generator 

industry, particularly with respect to the paramount issue of the safety of our respective 

customers. 

Our member companies include: 

• American Honda Motor Company 

• Briggs & Stratton Power Products Group 

• Champion Power Equipment 

• Generac Power Systems 

• Pramac America 

• Subaru Industrial Power 

• Techtronic Industries, North America 

• Wacker Neuson Production Americas 

• Yamaha Motor Corporation USA 
PGMA shares with CPSC the goal of promoting and continuously improving the safe and 

proper use of portable generators. PGMA would note at the outset that, while the NIST 

Technical Note 1781 is a valuable contribution to the many efforts already expended by 

PGMA, CPSC, and others aimed at achieving this shared goal, the NIST Technical Note 

does not draw any specific conclusions or make any particular recommendations as to 

actions that should be taken to achieve the ultimate safety goal. It rather confirms by 

testing a point with which it would be hard for anyone to argue, that being that a device 

that emits a lower amount of Carbon Monoxide will result in a lower volume of Carbon 

Monoxide being present in the area in which the emitting device is located. In that sense, 

it is a bit difficult for PGMA to specifically respond to the NIST Technical Note. 

Nevertheless, PGMA offers the comments below in a spirit of cooperation and we look 

forward to working with you, NIST and others to make the use of our products even 

safer. 

It seems that a key premise of the NIST Technical Note is that reduced CO emission rates 

from common portable generators can provide additional critical time for consumers to 

recognize and escape, and thus reduce the number of CO deaths from portable generators. 

There is no documentation or study confirming the validity of that premise. Given the 

importance of the premise to the Technical Note, PGMA encourages CPSC and/or NIST 

to provide the documentation or study on which the premise is based or to conduct a 

study to validate it. While the proposition may seem intuitive, it could also be possible 

that someone experiencing minor symptoms from reduced CO emissions will be even 

less likely to attribute them to CO than someone exposed to emissions from an 

unmodified generator. Moreover, decreasing the rate of symptom onset would not 

benefit someone who is sleeping and could reduce awareness that a serious problem is at 

hand. 

There are no warning signs commonly and uniquely associated with carbon monoxide 

poisoning regardless of how quickly the carbon monoxide poisoning occurs or begins to 

occur. This is because the headache and nausea which are associated with carbon 

monoxide poisoning are such common, everyday occurrences for virtually everyone that 

it is questionable whether those symptoms would be recognized as being caused by 

carbon monoxide exposure. Empirical data would be extremely valuable, and probably 

necessary, to support the proposition that a consumer experiencing early reactions to 

carbon monoxide poisoning would realize the source of the symptoms as carbon 

monoxide and react in the manner desired, that is to quickly remove himself or herself 

from the area to a place where there was fresh, untainted air. 

An additional concern raised by the low CO technology is the potential for users to 

believe that portable generators are safe for indoor use and whether the implementation 

of a low CO technology could result in users being more likely to use the product 

improperly. The potential for such additional misuse should be evaluated by CPSC. 

We continue to support the statement in the CPSC’s Press Release for the report on its 

study of low CO portable generators that recognizes that a carbon monoxide (CO) hazard 

would continue to exist even if the technology applied to the prototype generator that was 

the subject of the report and now the NIST Technical Note, were applied to commercially 

available generators, and that educating owners about the proper use of their generators 

needs to remain the first line of defense: 
“The CPSC continues to urge consumers to never run their portable 

generators in their attached garages, in or even near their houses, including 

avoiding placement near windows or vents. Generators should only be used 

outside, far away from homes. CPSC cautions that even if portable gasoline 

powered generators were to incorporate this technology, they would still need 

to be used outside, far from the home. The technology does not make them 

safe for indoor use.” (CPSC Press Release #12-278, September 14, 2012). 

PGMA continues to encourage CPSC and/or NIST to conduct a study that includes a 

human factors analysis to determine the effectiveness of the existing CPSC mandated CO 

warning adopted in 2007. In any event, PGMA encourages CPSC to revise the mandated 

warning to incorporate the standards and format in ANSI Z535.3-2011 and Z535.4-2011. 

THE NIST Technical Note further demonstrates that CO levels are affected by numerous 

variables creating a high degree of uncertainty as to how they interact, and an inability to 

draw reliable conclusions from the demonstration testing performed. The NIST 

Technical Note is further support for CPSC’s previous statement regarding the use of CO 

alarms: 

[CPSC] also recognizes that “[a]nother important line of defense against CO 

poisoning is having CO alarms on each level of the home and outside sleeping 

areas. Based on available alarm data, 93 percent of CO-related deaths involving 

generators take place in homes with no CO alarms. Much like smoke alarms 

designed to alert consumers about smoke or fires, CO alarms are designed to alert 

consumers to dangerous CO levels and give them time to get out of the house 

before becoming incapacitated.” (CPSC Press Release #12-278, September 14, 

2012). 

States and local communities throughout the United States have recognized the role CO 

monitors play in protecting consumers from the multiple sources of CO present in 

everyday life – furnaces, space heaters, and charcoal grills to name a few. As a result, the 

number of states adopting mandatory CO monitor laws and codes has increased 

significantly over the last 5 years. PGMA encourages the adoption of such a requirement 

in every state as a cost effective means of significantly reducing the CO hazard from 

multiple sources. CPSC and NIST could use their influence to further promote the 

adoption of statutes, regulations and building codes requiring the use of CO monitors in 

living spaces as a means of implementing the objective of protecting users. PGMA also 

encourages CPSC or NIST to analyze the data collected on CO poisoning and deaths to 

develop a public awareness campaign that is targeted based on use conditions and user 

groups, similar to what has been done with hazards such as fires and severe weather. 

PGMA would support such an effort by CPSC and/or NIST. 

With respect to the Technical Note, if the electronic fuel injectors and closed loop air/fuel 

ratio control used in conjunction with catalytic converters employed on the prototype 

generator were installed on currently available generators, it would result in significant 

changes to the product that is on the market today. The Technical Note appears to simply 

repeat the statement from the CPSC Low CO Portable Generator Study concluding that 

the control technology is commercially available without an evaluation of the changes to 

the product that would be necessary in order to replace the product currently in the 

market place and perform comparably to it. As we and others have pointed out 
previously, the road from prototype to commercial viability is typically as long and 

fraught with as many issues as the initial stages of development. 

One of the most significant concerns related to the incorporation of the employed 

technology is the effect of the increase in high combustion temperatures which are 

detrimental to air-cooled engine durability and performance. In addition, the durability 

impact varies significantly on engines of different sizes, designs, applications, and rated 

speeds thus making it difficult, if not impossible for the results from a single product to 

be generally applicable to the entire category of portable generators. The breadth of 

product in the portable generator category and the scalability of the employed technology 

in terms of cost, performance and efficiency will vary significantly between 50 cc and 

500 cc sized engines. 

Any conclusions regarding the durability of the prototype product used in the study are 

necessarily limited in scope as the testing was not conducted in accordance with EPA test 

procedures and was conducted on EPA Phase 2 certified product. EPA Phase 3 has been 

in effect since 2011, with more stringent emission standards and a useful life category 

which is now double for the study prototype. To better understand and assess the impact 

of the employed technology in the NIST study additional information on how and where 

the thermocouples for measuring temperature were installed should be provided for both 

the modified and unmodified test units. PGMA is requesting that this information be 

made available for review. 

Even if the technical challenges could be overcome, one would not be surprised to find 

that there is a significant delta between the cost to manufacture the product on the market 

today and products that incorporate the technology used with the prototype model. The 

portable generators on the market today perform a valuable function for consumers, 

especially during power outages. The limited availability of new product or a significant 

cost delta will result in this option no longer being a viable alternative for many 

consumers. 

As the leading trade association of manufacturers of portable generators, PGMA is 

engaged in many activities promoting the safe use of its products. For example, PGMA 

has worked with the National Association of Regulatory Utility Commissioners to 

standardize the CO message being delivered via the utility industry’s various forms of 

communication so that it can be clearly and efficiently provided to consumers. Reducing 

the number of portable generator related CO incidents that occur after a utility company 

shuts off the power, due to nonpayment for example, shows promise and this effort could 

be enhanced by the CPSC’s participation. We invite CPSC to work with PGMA 

collaboratively as other opportunities arise. 

 

Very Truly Yours, 

 

 JOHN H. ADDINGTON 

 Executive Director 

 PGMA 

JHA/jlb 

pgma 
From: CPSC-OS,

To: Buyer, Janet

Subject: FW: Comments to CPSC on NIST Technical Note 1781

Date: Wednesday, May 29, 2013 11:42:50 AM

Attachments: image001.png

image002.png

Importance: High

Todd Stevenson

Director, The Secretariat

(Office of the Secretary)

Office of the General Counsel

US Consumer Product Safety Commission

(301) 504-6836, Fax (301) 504-0127

From: Jim Nice [mailto:jim.nice@kiporpowersystems.com] 

Sent: Tuesday, May 28, 2013 11:27 AM

To: CPSC-OS,

Subject: Comments to CPSC on NIST Technical Note 1781

Importance: High

Comments to CPSC on NIST Technical Note 1781

Always use generators outdoors, away from doors, windows and vents.

NEVER use generators in homes, garages, basements, crawl spaces, or other

enclosed or partially enclosed areas, even with ventilation.

Follow manufacturer's instructions to operate generators in a well-ventilated

area.

Install battery-operated or plug-in (with battery backup) carbon monoxide (CO)

alarms in your home, following manufacturer's instructions.

Test CO alarms often and replace batteries when needed.
Even with the “modified” generators, which was never thoroughly explained what or

how the generators were modified; the CO levels were still excessive. It would have

been interesting to see a comparison of the generators being operated in a proper

manner outdoors and see what the CO levels were within the house.

In considering any “rule-making” changes, one of the major considerations should be

the cost to the manufacturer and eventually to the end user. Perhaps the most

economical and beneficial changes would be to have a reasonable sized decal (label)

place on the unit with contracting colors, warning of the danger of operating the

generator in enclosed spaces.

Respectfully,

Jim Nice

National Technical Services Manager

Kipor Power Systems

12021 NE Airport Way, Suite G

Portland, OR 97220

503-445-0197 X 304

www.kiporpowersystems.com
1

6/7/13

Comments to CPSC on NIST Technical Note 1781

From Albert Donnay, MHS, adonnay@jhu.edu

Submitted to cpsc-os@cpsc.gov

Thank you for making this report available for public comment.

It is my professional opinion as a certified CO analyst [BPI], environmental health engineer and 

consulting toxicologist that this NIST study and the Technical Note that describes its results 

should not be relied upon by CPSC for any rulemaking related to portable generator safety. 

The primary problem with the NIST study is that it only tested CPSC’s modified and unmodified 

portable generators in a single 1500 sq ft pre-manufactured house whose design, layout and 

construction are not representative of most US single family housing [SFH]. 

Although over 75% of SFH in USA have attached garages [AG] according to the National 

Association of Home Builders, they are very different from that built by NIST for CPSC. 

Most SFH with AG were designed and built simultaneously by the same builder using the same 

materials with plans from the same architect. As a result, the wall they share is an interior one

with no windows, little or no insulation, and sometimes even unfinished on the garage side with 

studs showing. The connecting door is commonly also of interior quality, rarely solid, and not as 

tightly sealed as doors leading outside. 

If one story, the house and garage commonly share the same roof line, and if without basement, 

they commonly share the same floor, although the house floor is usually raised at least a few 

inches if not feet to prevent spills from entering the rest of the house. 

In sharp contrast, the AG in the NIST test house was added in 2007, 5 years after the original 

home was built for a different study that involved greatly ‘tightening’ the house against air leaks 

to the outside (Nabinger and Persily 2008, NISTIR 7478). 

It was added onto an external endwall that already had a tight window, tight exterior door, and 

exterior siding. Instead of matching the end wall and roof line, however, it was built with a 

higher floor, narrower width, and taller roofline. 

This NIST note [#1781], like Emmerich’s interim report to CPSC of July 6, 2011, gives only the 

square footage and volume for the garage and house, from which the average heights of each 

can be calculated by simple division as 2.5 and 2.4 meters respectively, but the graphics in 

figure 2 of NIST note 1637 [Wang and Emmerich 2009] clearly show the shared wall is much 

higher than this, with the garage roof extending more than 0.1m above the roof of the house. 

Why was it not built to match? NIST refused multiple requests to answer this question, and also 

refused to release any photo of the shared wall from within the garage. The report does show 

pictures of the inside of the shed, so why not the inside of the garage?

Any CO rising in the garage would naturally rise higher than the house and result in less CO 

diffusing into other rooms or the attic than if they shared a wall that was the same height and 

width from floor to ceiling. The higher garage floor also would reduce the opportunity for rising 

CO to enter the house since the critical floor/wall seam on the house side was below the level of 

the garage floor. 

The NIST test house is thus not a sufficiently representative design for such an important 

evaluation upon which the lives of all Americans with portable generators may depend. 
2

COMMENTS OF DONNAY ON NIST 1781, PAGE 2 OF 2

The second problem is that CPSC’s portable generators were tested without any reference to 

whether the engines were hot or cold when started. 

The authors told me that they did not control for engine startup temperature, and so it is 

impossible now in retrospect to know which of their experimental runs were done with 

appropriately cold engines [representative of the most likely worst case exposure scenario for 

the home user] and which were done with done with already warm or hot engines [whose CO 

emissions would be lower].

I also note with great concern that the authors never measured how long it took for the COcontaminated test house to return to the baseline CO level with only natural ventilation, as 

would be the case in most SFH during generator use when no other source of electricity is likely 

available, but instead turned on mechanical ventilation to speed up the process. Without this 

information, it is impossible to estimate how long the occupants of a SFH whose portable 

generator had just automatically shut off might be exposed to just how much CO while they 

waited [without mechanical ventilation] for the CO in their garage and other rooms to return to a 

safe level.

Finally, and most critically, the CO levels reported in Appendix C on Additional Garage Tests 

clearly document that even when the shutoff algorithm worked, the maximum CO level in the 

garage was in the range of hundreds of ppm. This is far above all levels considered safe by all 

federal agencies, including the:

1) 9 and 35ppm avg limits of EPA [for 8 and 1 hour exposures, respectively, equivalent to 

72 and 35ppm-hours]; 

2) 35 ppm avg limit recommended by NIOSH for healthy workers and the level at which 

most fire departments in USA require firefighters to put on their self contained breathing 

apparatus and order the evacuation of any building

3) 50 ppm avg limit allowed by OSHA 

4) 70 ppm limit allowed by CPSC

Rather than continue to pursue this complicated, expensive and ultimately ineffective approach 

to shutting off portable generators, I urge CPSC to require only a CO-sensing shut off device. 

Staff have already tested such an approach [2006] and CPSC should release their report so that 

their findings can be evaluated by the public and portable generator manufacturers before any 

new rule or is proposed. 

Given that over 25 million high quality long lasting CO-sensing switches are sold to the auto 

industry ever year for approximately $5 each and have been for over a decade, it is outrageous 

that CPSC has still not even studied the potential of these devices. 

They function reliably for 10-15 years, even in cars that are left outdoors all the time, and could 

easily prevent not just the CO deaths caused by portable generators but also the no doubt much 

higher number of CO poisonings that clearly cannot be prevented if relying only on electronic 

emission controls and non-CO sensors. 

Thousands of Americans have died needlessly since CPSC started this project 7 years ago. 

Please do not allow this to continue. 

# # #
1

Written Comments of the Manufacturers of Emission Controls Association (MECA)

on the National Institute of Standards and Technology’s (NIST) Report, “Technical Note 

1781: Modeling and Measuring the Effects of Portable Gasoline Powered Generator 

Exhaust on Indoor Carbon Monoxide Level”

June 7, 2013

The Manufacturers of Emission Controls Association (MECA) is pleased to provide our 

comments to the U.S. Consumer Product Safety Commission (CPSC) on the National Institute of 

Standards and Technology’s (NIST) report, “Technical Note 1781: Modeling and Measuring the 

Effects of Portable Gasoline Powered Generator Exhaust on Indoor Carbon Monoxide Level.” 

MECA is a non-profit association of the world’s leading manufacturers of emission control 

technology for motor vehicles and stationary internal combustion engines. Our members have 

nearly 40 years of experience and a proven track record in developing and manufacturing 

emission control technology for a wide variety of on-road and nonroad vehicles and engines. A 

number of our members have extensive experience in the development, manufacture, and 

commercial application of carbon monoxide (CO) emission control technologies for stationary 

engines, as well as expertise in applying catalyst technologies to small, spark-ignited engines less 

than 25 hp.

MECA has been engaged in CPSC’s efforts to improve the safety of portable generators 

in marine and domestic applications by reducing the level of CO emitted by these small, sparkignited four-stroke engines. MECA has previously provided comments to CPSC about the 

available technology for portable generator applications in response to CPSC’s request for 

information on techniques to reduce CO from gasoline portable generators (MECA letter dated 

April 28, 2006), MECA’s written comments on CPSC’s ANPRM on portable generators 

(comments dated February 11, 2007), and MECA’s written comments on CPSC’s September 

2012 test report, “Technology Demonstration of a Prototype Low CO Emission Portable 

Generator” (comments dated November 7, 2012). Our comments below mirror the comments 

we submitted to CPSC back in November.

The new report by NIST describes a series of tests performed for CPSC on generators in 

commercially available and modified low CO emission prototype configurations to determine 

their CO emission and oxygen consumption rates while operating in a single-zone enclosed 

space. For two different unmodified commercially available generators (i.e., with carbureted 

engines lacking CO-emission controls), CO emissions ranged from a low of around 500 grams 

per hour (g/hr) at near ambient oxygen levels to a high of nearly 4000 g/h as oxygen approached 

17%. Tests of two modified, low CO emission prototype generators (i.e., commercially available 

units adapted with closed-loop electronic fuel injection and a small catalyst integrated into the 

muffler) showed CO emissions reductions of over 90% with most CO emission rates well below 

500 g/hr, and no trend toward higher emission rates was seen as the oxygen level dropped.

Like CPSC’s September 2012 test program, the results of the NIST study support the 

experience of catalyst manufacturers and the recommendations provided by MECA on the 

effectiveness of the use of catalysts to reduce CO emissions and improve the safety of portable 

generators. Catalyst technology is a cost-effective technique for substantially reducing CO 
2

exhaust emissions from spark-ignited, gasoline portable generators. Catalyst technology for 

small gasoline engines like those used in portable generators draws from nearly 40 years of 

successful experience in the U.S. with catalytic converters applied to light-duty gasoline cars and 

trucks. Similar catalyst technology has been successfully applied to a wide variety of smaller, 

two-stroke and four-stroke gasoline engine applications, including handheld equipment (e.g., 

chainsaws, leaf blowers, string trimmers), non-handheld equipment (e.g., lawn mowers), motor 

scooters, motorcycles, marine engines, and forklift trucks. In many cases, these catalyst systems 

have been engineered to provide high reductions of CO emissions as well as reductions in 

hydrocarbon (HC) and NOx emissions. The U.S. EPA in its small engine test program that was 

completed in advance of their Phase 3 small engine regulations (published in October 2008) 

clearly demonstrated that catalysts can be safely incorporated on Class 1 and Class 2 gasoline 

engines without any significant increase in muffler surface temperatures. MECA and MECA 

members were active participants in EPA’s small gasoline engine test program.

The published experience of catalyst performance on four-stroke gasoline engines 

indicates that high efficiencies for reducing CO emissions are strongly influenced by the air/fuel 

stoichiometry in the exhaust upstream of the catalyst. Maximum reduction efficiencies for all 

three regulated pollutants (HCs, CO, NOx) can be obtained if the air/fuel ratio of the exhaust 

stream is controlled to be near the stoichiometric ratio of reducing and oxidizing components in 

the exhaust stream. At or near this stoichiometric air/fuel ratio, catalyst efficiencies can be well 

in excess of 90% for all three pollutants provided that the catalyst temperature is above its 

activation temperature (typically 350o

C or higher), and that a reasonable catalyst volume relative 

to the volumetric flow of exhaust gas is contained in the system. Catalyst formulations can be 

optimized for these small engine applications to deliver maximum CO reductions and/or NOx 

reductions depending on the final emissions target. Precious metal costs for these small engine 

catalysts are typically less than half the total cost of the finished catalyst. The addition of a 

catalyst to a small engine would have only a very small impact on the cost of a gasoline 

generator.

The most widely used method for accurate, and cost effective, air/fuel ratio control is 

through the use of fuel injector technology in combination with a closed-loop control strategy 

that employs a simple engine control unit (ECU) and an oxygen sensor present in the exhaust, 

upstream of the catalyst. The sensor provides a feedback loop to the engine’s intake air and fuel 

metering system. The combination of closed-loop, electronic fuel injection with a catalyst 

reduces engine-out emissions and ensures consistent engine operation. This more stable, reduced 

engine-out emissions operation reduces the thermal stress on the catalyst and improves the 

catalyst durability. Such an approach has been applied to a whole range of spark-ignited engines 

from passenger cars to handheld lawn and garden equipment, and this is the same approach that

was effectively demonstrated on the two modified, low CO emission prototype generators in the 

NIST study, as well as on the small gasoline-powered portable generator in CPSC’s previous 

demonstration program.

MECA is aware of two manufacturers of four-stroke, gasoline generators that are already 

using properly designed exhaust systems with catalysts to reduce CO emissions by more than 

90% compared to uncontrolled levels: Westerbeke Corporation and Kohler Power Systems. 

Both of these companies have targeted marine applications for these ultra-low CO emission 
3

generators. The same strategy is applicable to portable generators for home use. MECA 

believes that the ultra-low CO emission generators offered by Westerbeke and Kohler employ 

the same type of strategy (controlled exhaust air/fuel ratio near the stoichiometric point) to 

achieve high CO conversion efficiencies across a catalyst as documented in the subject report.

In summary, similar to CPSC’s September 2012 test program, the commission has 

effectively demonstrated in the NIST study that catalyst-based exhaust emission controls are a 

proven, cost-effective, durable, and safe strategy for reducing CO emissions from small, fourstroke gasoline engines like those used in portable generators. The combination of precious 

metal-based, three-way catalyst formulations and precise air/fuel control has been shown to 

provide CO conversion efficiencies well in excess of 90% on a small, four-stroke gasoline 

engine in a portable home generator. We commend the commission on its ongoing work to 

demonstrate the effectiveness of state-of-the-art combustion controls in combination with 

catalyst technologies to reduce CO emissions from these generators. MECA continues to 

strongly support CPSC’s efforts in urging portable generator manufacturers to voluntarily 

implement these cost effective strategies to reduce CO emissions and improve the safety of home 

portable generators. In addition, in the absence of a voluntary standard, MECA believes that

EPA should strongly consider adoption of a mandatory, low CO emission standard for gasoline 

generators.

CONTACT:

Joseph Kubsh

Executive Director

Manufacturers of Emission Controls Association

2200 Wilson Boulevard

Suite 310

Arlington, VA 22201

Phone: (202) 296-4797 x107

E-mail: jkubsh@meca.org