# Investigating the Utility of Global Positioning System (GPS) Technology to Mitigate the Carbon Monoxide (CO) Hazard Associated with Portable
Generators

– Proof of Concept Demonstration

June 2013

Han Lim
Division of Combustion and Fire Sciences
Di rectorate for Engineering Sciences

U.S. CONSUMER PRODUCT SAFETY COMMISSION 4330 East West Highway, Bethesda, MD 20814

This report was prepared by CPSC staff and it has not been reviewed or approved by, and may not necessarily reflect the views of, the Commission.EXECUTIVE SUMMARY

The CPSC Directorate for Engineering Sciences’ Division of Combustion and Fire Sciences ( ESFS ) staff has conducted a limited, exploratory exercise to demonstrate the feasibility of using Global Positioning Syst em ( GPS ) technology to distinguish indoor and outdoor environments, with the intent of shutting down portable generator operation
when a generator is used indoors. Through a series of experiments, ESFS staff demonstrated that a modified, off

- the

- shelf, co mmercially available GPS receiver unit,
with a staff

- developed electromechanical shutoff system installed on a portable generator

, can distinguish indoor and outdoor environments and shut off the generator accordingly

, with the exception of a dense tree cover scenario.

If ultimately proven effective and reliable, this technology may not suffice as a sole carbon monoxide ( CO ) mitigation technology because it does not protect against all generator use scenarios that pose a CO poisoning risk. To protect against CO poisoning resulting from outdoor operation near an opening into a home, as well as to minimize CO accumulation from a generator operating indoors before the GPS receiver/shutdown
system can shut it off, additional technology would be needed to red uce the generator’s engine CO emission rate. As noted in Reference [1], page 5, deaths have occurred when generators were operating outside the home, near open windows, doors, or vents. CO emission reduction is CPSC staff’s primary strategy to reduce the generator CO poisoning hazard; and staff has demonstrated that current emission control technology adapted onto a prototype generator is effective in greatly reducing portable generator CO emissions in generator indoor use scenarios that are commonly fatal. The high CO emission rate of current generator designs can rapidly create an unsafe exposure in the space where the generator is operating, as well as in adjoining spaces. Implementation of a shutoff strategy, without requiring a reduced CO emission r ate, can create a hazardous

CO exposure if the generator runs for even a brief period of time before indoor operation
is detected

. Therefore, CPSC staff views a GPS receiver shutoff strategy as a supplemental means of further reducing the risk of CO poisoning [1].

The issue of dense tree cover requires further exploration by GPS technology experts.

ESFS staff believes that the challenge posed by the scenarios in this study that involv ed
dense trees can be met as GPS receiver technology continues to evolv e and become more sophisticated. However, ESFS staff recommends that the appropriate experts in the GPS/radio frequency (RF) engineering community explore the issue of dense tree cover

or any additional situational limitations, as they influence this uniq ue engineering challenge.TABLE OF CONTENTS

BACKGROUND ................................................................................................................1

THE CONCEPT .................................................................................................................2

IMPLEMENTATION .......................................................................................................3

The Candidate GPS Receiver Unit ...................................................................................3

Preliminary Considerations and Experiments ..................................................................5

Generator Shutdown System Demonstration Package .....................................................6

Plan for Evaluation for the Demons tration Package ........................................................8

RESULTS AND DISCUSSION ........................................................................................8

Preliminary Test Data .......................................................................................................8

Test Data from Seven Indoor and Outdoor Environments ...............................................9

Verification of the Shutdown System Functionality ......................................................11

Testing at NIST Test House ...........................................................................................12

POSSIBLE FUTURE PROTOTYPE .............................................................................15

CONCLUSION ................................................................................................................16

ACKNOWLE DGEMENTS ............................................................................................16

REFERENCES .................................................................................................................171 BACKGROUND

In support of the CPSC Portable Generator Rulemaking activity, ESFS staff explored the application of GPS technology to differentiate between indoor and outdoor portable generator operation. The goal was to determin e if existing GPS receiver

- based technology could be used to sense when a generator is operating in an enclosed location

, and then, in combination with an electromechanical shutoff system, shut off the generator to prevent continued unsafe operation and mi tigate the carbon monoxide (CO) hazard.

The scope of portable generators examined for this study i s limited to a class of internal combustion engine- driven generators rated at 15 kW (20 hp) or less, 250 V or less, which contain receptacle outlets for al ternating current (AC) output circuits. Marine generators, recreational vehicle generators, and stationary generators are excluded from the scope [4]. Portable generators generally are equipped with wheels for ease of transport. The stated class of port able generators also come s in smaller sizes, where those generators are equipped with handles for hand carrying.

This investigation was conducted to perform the following : ( 1) determine if there is utility in pursuing this GPS receiver strategy, and if initial field tests with a modified GPS
system proved hopeful, ( 2) develop a prototype shutoff system with the ability to sense that a generator is running indoors and to shut the generator down. This exploratory
exercise was not intended to demonstrate eve ry possibility / scenario ; it was strictly limited to documenting the concep t’s utility. CO emission tests were not conducted; nor was
there an attempt to analyze the time needed to shut down the generator.

I f ultimately proven effective and reliable, th is technology may not suffice as a sole CO mitigation technology because it does not protect against all generator use scenarios that pose a CO poisoning risk. To protect against CO poisoning resulting from outdoor operatio n near an opening into a home, a s well as to minimize CO accumulation from a generator operating indoors before the GPS receiver/shutdown system can shut it off

, additional technology would be needed to reduce the generator’s engine CO emission

rate . As noted in Reference [1], page 5, deaths have occurred when generators were operating outside the home, near open windows, doors, or vents. CO emission reduction
is CPSC staff’s primary strategy to reduce the generator CO poisoning hazard ; and staff
has demonstrated that current emission c ontrol technology a dapted onto a prototype generator is effective in greatly reducing portable generato r CO emission s in generator
indoor use scenarios that are commonly fatal . The high CO emission rate of current
generator designs can rapidly create an u nsafe exposure in the space where the generator is operating, as well as in adjoining spaces. Implementation of a shutoff strategy, without requiring a reduced CO emission rate, can create a hazardous CO exposure if the generator runs for even a brief per iod of time before indoor operation is detected

. Therefore, CPSC s taff views a GPS receiver shutoff strategy as a supplemental means of further reducing the risk of CO poisoning [1].2 CPSC staff has explored another shutoff system alternative. CPSC sta ff contracted work

to the University of Alabama (UA) to develop a shutoff system onto a prototype
generator using sensors such as intake air temperature and manifold air pressure and an algorithm to detect and shutdown the generator, as described in Refere nce [1], Tab G. The UA approach differs substantially from the GPS receiver approach. The GPS receiver approach , as discussed in this paper, presents another supplemental alternative to the UA shutoff strategy.

THE CONCEPT

GPS receiver technology is ubiquitous, portable, and relatively inexpensive. Generally, GPS receiver units do not function properly indoors because the indoor structure s attenuate the satellite signals the unit uses to identify its location . When this happens,

some GPS receiver unit s activate a visual “ Poor Satellite Reception” display to alert the

user. ESFS staff hypothesized that it may be possible to exploit this feature and
evaluated a commercially available GPS receiver unit in a variety of indoor and outdoor settings to inves tigate the capability to discriminate between indoor and outdoor operation. The degree of satellite signal attenuation will vary from receiver unit to
receiver unit.

ESFS staff anticipates that certain use scenarios will present challenges and that the G PS

receiver based concept will have limitations. Notw ithstanding the above, ESFS staff
believes that the GPS receiver technology may prove useful as an adjunct to CO emission reduction technologies to extend protection into enclosed spaces. T herefore, the use of

GPS receiver technology merits investigation.

The graphic below shows how GPS receiver technology can be integrated into a portable generator to detect indoor operation and shut down the generator. The concept is rather simple: once the GPS rece iver cannot track the required number of satellites (from which one can infer that the generator may be operating indoors ), an actuation circuit will disable the engine from running. Otherwise, the indoor-outdoor detection system
concludes that the genera tor is running outdoors and the generator will run as intended.3 Figure 1 - Concept of GPS-Based Generator Shutdown System

IMPLEMENTATION

The Candidate GPS Receiver Unit

The worldwide GPS uses a system of 24 satellites that o rbit the earth twice a day sending
data to earth. A GPS signal contains three components of information–a pseudorandom code, time data , and date data. Th ese components of information identif y the satellite, its current status, date, and time , as well as pinpoint where it is located at any given time

.

ESFS staff initially evaluated two GPS receiver units that were commercially available

. ESFS staff compared the relative strengths of a 2005 GPS receiver and a 1998 receiver selected by ESFS staff for the exploratory exercise. The 2005 GPS unit, without an
external antenna

, was readily able to receive clear reception in every room of a detached

, single family home. ESFS staff acquired a 1998 model GPS receiver equipped with an external antenna that could be modified to obtain the optimal “balance” to discriminate
between indoor and outdoor environments.

The 1998 GPS receiver used in this study must continuously receive signals from at least
three satellites to calculate the GPS receiver’s location and track the receiver’s movement [2]. At times, additional satellites may be needed to determine its location. The GPS receiver can only process radio signals from satellites that are above the horizon and4 provide adequate radio signal strength to the GPS receiver’s antenna

. Once the GPS receiver is initialized to a location, it will compute a position in a few minutes. Shortly
after the 1998 GPS receiver is turned on, a flashing triangle with a question mark first

appears , indicating that it is locating the required satellites to determine its location. After several minutes, the GPS receiver will either display its location, complete with longitudinal, latitudinal, and elevation coordinates, or display an error message , depending on whether the GPS rece iver unit has adequate reception.

The GPS receiver requires an unobstructed view of the sky for optimal performance
because GPS satellite signals are generally weak and cannot travel through rock materials, metal, or heavy tree cover. If the GPS receiver does not detect the required number of satellite signals, it will display the error message

, “Poor Satellite Reception” [2].

To improve the receiver’s ability to discriminate between indoor and outdoor locations, i t was necessary to make the receiver les s sensitive to satellite reception

. ESFS staff chose
to use the receiver intact as a “black box ,” rather than attempt to modify the proprietary internal components of the 1998 GPS receiver unit. Using the above approach greatly simplified concept evaluat ion. For example, if a new method or adjustment was made to
attenuate the GPS receiver signal by partially shielding the antenna, the only output for
evaluation was either the presence or absence of an error signal on the GPS receiver’s screen displaying “Poor Satellite Reception .”

V arious signal attenuation approaches using metal shields on the receiver’s antenna were evaluated : mesh steel wire cage , aluminum foil, and copper tubing. The above three materials are known for attenuating radio frequency signals. A fixed length of copper tubing gave promising results during the initial screening evaluations and was chosen as a shield.

As mentioned in the background section, there may be instances where the location, nearby structures, and terrain, for exa mple

, may impede the reception of satellite radio frequency signals. To understand some of these effects, ESFS staff evaluated the 1998
GPS receiver unit in various homes and surrounding spaces, such as the front yard and back yard

.

According to the owne r’s manual [2], the 1998 GPS receiver unit determines in approximately 5 minutes whether the required number of satellites is not detected. If the appropriate number of satellites is not detected , the unit displays a “Poor Satellite Reception” message . T he decision time of 5 minutes is particular to this 1998 receiver

, and a shutoff system could be designed to make the decision more quickly. However , it
would be at the risk of shu tt ing the generator down while it is properly being operated
outdoors. D eaths have occurred where generators were operated outdoors, near the home, near open windows, doors, or vents [1]. This tradeoff would have to be carefully
considered because t he utility of a generator and, possibly, acceptance of the GPS
receiver controlled shutoff system by the consumer could be negatively impacted by a system that shuts the generator off when used properly outdoors.5 A section of copper tube was used to reduce the sensitivity of the 1998 GPS receiver

antenna s trength to obtain the optimum balance of “strong enough to detect outdoors” and “weak enough not to detect indoors.” While the copper tube was a somewhat better
alternative to aluminum foil or mesh steel wire cage , the copper tubing had limitations.
ESFS staff tried several leng ths of tubing to fine-tune the amount of attenuation . Various evaluations were done using 17 mm and 15 mm long copper tubes. As noted previously, the only output for evaluation was either the presence or absence of an error signal on the GPS receiver’s screen displaying “Poor Satellite Reception.” After conducting many trials in various indoor and outdoor environments, such as an ESFS staff’s house and parks with heavy tree cover, it appeared that the 15 mm copper tube did not provide
sufficient shieldin g. Ultimately, ESFS used the 17 mm copper tube. Further fine -tuning was attempted by positioning the 17 mm copper tube on different locations of the antenna (held i n place with a set screw). After several trials (approximately five to six different positions on the antenna), the optimum position was obtained. Figure 2 shows the GPS
receiver with the 17 mm copper tube in its optimum position. The GPS receiver show s an error message indicating “ Poor Satellite Reception ”, as illustrated in the right-side photograph of Figure 2 when the GPS receiver cannot track the required number of
satellites . The change in luminosity (from light to dark) in the area inside the “optical sensor target” box (illustrat ed in Figure 2 ) is what is detected by the optical sens or to trigger t he shutdown function.

Figure 2 - GPS Receiver with External Antenna and Copper Tube for Signal Attenuation; (L eft): LCD Screen Does Not Show Error Message in this view (R ight) : LCD Screen Shows Error Message

Preliminary Considerations and Experiments

Stray electromagnetic interference (EMI) can disrupt the proper operation of the GPSbased shutoff circuit. Current GPS designs effectively shield interference from many

sources , such as radio and television antennae, garage door operators, and more . One source that may pose a particular challenge for a GPS receiver unit mounted onto a
generator is the EMI that is rad iated from the alternator in the generator. A few limited evaluations were conducted to gauge if such sources could have a n adverse effect (interference) on the GPS receiver’s ability to sense indoor versus outdoor environments.6 ESFS staff deemed that interference did not exist if the “ Poor Satellite Reception ” error message did not display on the LCD screen when positioned near the alternator of an operating engine . Evaluating for interference was done by tests with the GPS receiver inches away from a parked car alternator and an unloaded 1 portable generator alternator

. There did not appear to be interference in these two t rials. However, it is unknown whether trials with a generator supplying an electrical load (a configuration that was not
tested in this study ) may give different results. A third trial consisted of placing a television antenna with a booster amplifier a few inches from the 1998 GPS receiver ; again , no interference was observed. Although adverse EMI effects were not observed with this limited testing, further investigation may be needed to determine whether these effects will ever pose a problem.

Genera tor Shutdown System Demonstration Package

The demonstration system consists of three main components: the GPS receiver, the photo sensor activation circuit, and a portable generator. The generator

, which was used in emissions testing for the CPSC staff s tudy in reference [1], is hereafter referred to as

“ SO1 ” (short for shutoff generator 1). While the GPS receiver determine d indoor or outdoor status, an actuation system was developed by Engineering Sciences, Division of Electrical Engineering ( ESEE ) staf f that would interface the generator to the GPS receiver. A circuit that would recognize a change in state from normal GPS receiver operation (with satellite reception) to poor satellite reception was developed. This circuit

was not integrated into the a ctual GPS receiver unit; rather a separate external circuit box was constructed. An error message that appears on the LCD screen was the trigger

source. A relatively simple circuit was employed to sense the “Poor Satellite Reception” error signal on the GPS receiver’s screen and deactivate the generator as shown schematically in Figure 3. Figure 4 shows the fully assembled physical circuit layout

.

Figure 3

- Schematic Diagram for Phot o Sensor Activation Circuit for Shutdown System

1 A n electrical receptacle panel was not connected to the generator, so the generator was not electrically loaded, although the alternator was being energized.7 The SO1 prototype generator already had a remote engine shutoff switch installed, and it was activated by a remote control ler

. This feature was used quite often for the testing conducted at the National Institute for Standards and Technology ( NIST ) [1] to shut off the generator safely using the remote control feature. ESEE staff decided to make use of this existing generator shutoff feature . Figure 5 shows the components that comprise the shutdown system: modified GPS receiver, actuation circuit box, and remote controlle r.

The photo resistor, Rp, senses the change in the brightness of the LCD panel when the “Poor Satellite Reception” message is displayed. This signal is sent to the operation amplifier (triangular shape d symbol in Figure 3 ) turn ing on transistor Q1, which, in turn, activates relay K1. T he relay contacts of K1 were connected to the “lock” button on the remote control, and when activated

, the remote control sends a signal to shut off the generator’s engine. Shutting off the generator is achieved by ground ing the engine’s spark plug.

Figure 4 - Top View of Photo Sensor Activation Circuit

Figure 5 - Components of the Shutdown System, from Left to Right: Remote Controller, Photo Sensor Activation
Circuit Box

, and GPS Receiver8 Plan for Evaluation of t he Demonstration Package

As mentioned in the background section, the GPS receiver is not immune to external
influences

. Varying t ree cover is a potential issue. ESFS staff investigated to what degree trees may affect the GPS reception of the particular 1998 GPS receiver used in this exploratory exercise. Originally, E SFS planned to test the demonstration system (generator plus shutdown system) in many different indoor and outdoor locations, such as homes, buildings, front yards, and back yards. However , since generator shutdown system depends upon the generation of the “ Poor Satellite Reception ” message on the GPS receiver’s LCD screen, only the GPS receiver was u sed for these evaluations

.

As presented in the results and discussion section, a variety of home types, with and without garages, and with and without basements, were evaluated

.

RESULTS AND DISCUSSION

The data and discussions are presented in the chronological order that the evaluations
were conducted. The 1998 modified GPS receiver is her eafter referred to as GPS
receiver.

Preliminary Test Data

To test the feasibility of using the GPS receiver unit, ESFS staff initially evaluated the effectiveness of the GPS’s ability to differentiate indoor and outdoor environments. During these initia l steps, the exact locations of the GPS receiver unit ( e.g ., middle of the room, near a window) were not noted. While these exact locations are important, ESFS staff conducted these limited, estimated experiments to determine if the GPS’s ability to
diffe rentiate indoor and outdoor environments would work. Table 1 below shows the
results.

The evaluations, as indicated in Table 1

, led to further investigation of the feasibility of using GPS receiver technology for differentiating indoor and outdoor environments. The data shown in Table 1 did not specify particular locations in the various rooms, but
rather

, they were merely collected to determine if further study should commence. Therefore, a detailed evaluation was conducted on more homes, and the GPS receiver was placed in a variety of specific locations (see Tables 2 and 3). The office building indicated in Table 1 is CPSC’s National Product Testing and Evaluation Center (NPTEC), 5 Research Place, Rockville, Maryland 20850.9 Table 1 – Preliminary Data from Two Homes and a CPSC Office Building

Location Room Does the G PS Receiver Get Satellite Reception Using the
Modified Antenna?

Single Family

Home with

2- Car Garage office room NO

2

- car garage, near garage door NO

2

- car garage, near back wall NO

B a sement NO

back yard deck YES

front yard YES

Single Family

Home with

1- Car Garage living room NO

1

- car garage NO

2nd floor bedroom NO

s unroom NO

back yard deck YES

front yard YES

CPSC Office Building (NPTEC) c ubicle NO

parking lot YE S

Test Data from Seven Indoor and Outdoor Environments

Seven homes of CPSC Engineering Sciences and Laboratory Sciences personnel were evaluated to help characterize the reception qualities of the selected GPS receiver. T here were a variety of home types, with all but one having garages of various types and one home was a townhome. Homes with garages were of particular interest, as some
fatalities occurred when the generators were run in the garage and CO infiltrated into the homes [1]. It should be noted that t his list of homes is not intended to represent any particular cross -section of homes in the United States; rather

, it is a limited list of homes that were available at the time of this study.10 Table 2

– Detailed Evaluation of the Modified 1998 GPS Receiver in Seven Homes

Home Indoor
Detection Front Yard (Outdoor)
Detection Back Yard (Outdoor)
Detection

S ingle family detached home with 2

- car

garage (HOME A) YES YES YES

Townhouse with 1

- car garage (HOME B) YES YES YES

S ingle family detached hom e with 4

- car

garage (HOME C) YES NO* YES

Single family detached home with 1

- car

garage (HOME D) YES YES YES

Single family , one level detached home with detached garage (2- car garage ) (HOME E) YES YES YES

Single family detached home with 1

- car

garage (H OME F) YES YES NO*

Single family, detached one

- level home , no

garage (HOME G) YES NO* NO*

* GPS receiver failed to properly detect outdoor status, possibly due to dense tree canopies

. However, the following observations were made: HOME C detected outdoor status in the back yard 18 ft from the sunroom HOME F detected outdoor status 9 ft from the front yard stoop
HOME G detected outdoor status 27 ft from front yard stoop [side walk], which is not considered part of homeowner’s property
Additional notes : On e- level homes were indicated as such. Other homes listed either had a full second floor or split

- level foyer type of second level.

Table 3 – Specific Areas of the Seven Homes That Were Evaluated

Indoor Rooms Tested: garage, basement, bedrooms, living r oom, kitchen, sunroom/enclosed porch, dining

room – all near windows to maximize the opportunity for the GPS receiver to obtain
satellite signal s Outdoor Areas Tested: decks, open grassy fields, varying distances from the front yard stoop

For indoor det ection, a “YES” indicates that the GPS receiver generated a “ Poor Satellite Reception ” error message , which means that the GPS receiver correctly sensed indoor

status . For outdoor detection , a “YES” indicates that the GPS receiver was able to obtain
its l ocation coordinates and did not generate an error signal, which means the GPS receiver correctly detected outdoor status. For outdoor detection, a “NO” indicates that
the “ Poor Satellite Reception ” error signal appeared which means the GPS receiver
incorr ectly detected indoor status. As the data tables show, the GPS receiver unit did not have any problems detecting indoor status. However, the 1998 modified GPS receiver had difficulty detecting outdoor areas in three homes with dense tree cover. See Figure 6.11 In contrast, homes with fewer trees did not exhibit problems obtaining a clear satellite signal outdoors . See Figure 7.

Figure 6 – Three h omes that had difficulty receiving a satellite signal outdoors; l eft (Single family, detached one- le vel home, no garage ); middle (4

- car garage home –only had difficulty in the front yard); and right (1- car garage home –only had difficulty in the back yard)

.

Figure 7 – Three homes that did not have difficulty receiving a satellite signal outdoors; left (townhouse); middle (1- car garage home); and right (2

- car garage home)

.

ESFS staff observed that if the GPS receiver was located where a roof

- type structure was over it, even a clear , tempered glass sunroom (of Home C) provided sufficient shielding
to detect that t he GPS receiver was located indoors. One caveat to this observation is that
it is not clear whether the indoor detection was due solely to the glass ceiling, or if surrounding trees or other obstructions played a role.

Verification of the Shutdown System Functionality

ESFS and ESEE staff verified the physical functionality of the shutdown system after installing the GPS receiver -photo sensor activation shutdown system on to the SO1
generator . This verification was independent of the indoor and outdoor GPS receiver
evaluations. Using the GPS receiver -based shutdown circuit, ESFS and ESEE staff demonstrated successful shutdown of a generator within 2 minutes after having started the engine. This demonstration was conducted in the all- terrain vehicle (ATV) laboratory

at NPTEC . All safety checks were conducted prior to running the verification, such as securing the generator to the floor and connecting the engine exhaust pipe to the exhaust snorkel. Figure 8 shows the generator fitted with the shutdown system. The successful shutdown system operation was captured on video.12 Figure 8 - Shutdown System Fitted onto SO1 Generator at NPTEC

Testing at NIST Test Home

While evaluations of the seven houses provide a rough sketch of how the GPS r eceiver performed in those scenarios, ESFS staff also evaluated the GPS receiver at the National Institute for Standards and Technology ( NIST ) test home (Building 423 - NIST Indoor Air Quality House , see Figures 9 and 10). This building was designed for t esting indoor air quality of a single story home. This test home i s furnished like a resident ial home complete with bedrooms, bathrooms, fireplace, window curtains, kitchen appliances, such

as a range, and the building has been used for a multitude of indoor air quality related projects, including recent emission testing programs for the Prototype Generator testing [1].13 Figure 9 - Floor Plan of NIST Indoor Air Quality Building 423

Figure 1 0 – Aerial View of NIST Building 42314 Table 4 – GPS Receiver Evaluations Conducted at NIST Indoor Air Quality House Building 423, July 23, 2012

INDOORS

Room Approximate Time s (MM:SS) for “Poor Satellite Reception” Error Message to Display

Location K*

– Middle of the Garage 5:13

Locati on J**

– Window of the Garage 1:48 // 1:52 // 1:48 // 5:05 // 1:56 Family Room 1:42

Kitchen 1:09 Dining Room 1:34 Living Room 1:55

Master Bedroom 1:54

Bedroom 2 1:30

Bedroom 3 5:30

OUTDOORS

Location Approximate Times (MM:SS) for Indicating GPS Acq uired All Necessary
Satellites

Location A*

– Grass field 15 ft from window 1:58

Location B*

– Grass field 15 ft from window 3:09

Location L*

– Grass field 15 ft from window 3:12

Location M*

– Grass field 15 ft from
window 1:42

NOTES:
* Refer to the specific lettered locations in Figure 9 ** Since the garage area was of interest and with time permitting at the NIST facility , five trials were
conducted at Location J

T he results in Table 4 show that the GPS receiver unit was capable of distinguishing
indoor from outdoor environments. The “indoor” times in Table 4 represent the time
from the moment the GPS receiver unit was powered on, to when the “ Poor Satellite Reception ” error message appeared. The “outdoor” times represent the time from the moment the GPS unit is powered on, to indicating that the GPS receiver has acquired the
minimum number of satellites for proper operation . The GPS receiver then displays its

exact location, complete with longitude, latitude , and elevation coordinates. When the

GPS receiver unit is powered on, a triangle with a question mark flashes continuously
until either a location is determined or an error occurs (“ Poor Satellite Reception ”

message appears ). One caveat is that Building 423 had only a few surrounding trees. The perimeter of the building has grassy fields and open spaces.

ESFS staff observed that, on occasion, the GPS required somewhat longer times to detect
the indoor environment status. 2 This observation regarding longer times is believed to be

2 The times were approximate, as the staff’s reaction times to the start and stop events were performed with an electronic stopwatch.15 due to the complicated attenuation of the GPS radio signal from the satellites because of the interaction of varying terrain, tree cover, building materials, building structure, and location within the building, among other variables. The above- mentioned factors make GPS shutdown time challenging to predict.

It is necessary to keep in mind that the GPS receiver was treated like a “black box,” and staff was only monitoring the output (error “ Poor Satellite Reception ” signal or no error signal). Also, the selec ted GPS receiver unit was manufactured in the 1998 timeframe, and there have been many improvements and refinements in GPS circuitry and software since then. Additionally, the shutdown times are somewhat irrelevant because GPS technology is evolving. The se times only reflect how this particular GPS receiver performed, and they are not necessarily indicative of how a future GPS receiver, designed specifically for the generator shutdown feature, could function. However, i t was more important to discover wh ether the GPS receiver was capable of correctly identifying whether it was operating indoors or outdoors.

The demonstration supplements the work performed on the reduced

- CO generator by

U niversity of Alabama (UA) , and it is not in place of the UA work. E SFS staff
recommends that GPS technology experts and generator manufacturers creatively explore the feasibility of possible solutions (on the indoor-outdoor detection aspect).

POSSIBLE FUTURE PROTOTYPE

ESFS staff envisions an efficient “black box” that u ses GPS receiver technology with a specifically designed antenna (internal or external) to detect indoor or outdoor status only. This simple detection scenario means that there is no need for populating maps, generating complex algorithms to log routes, o r any of the other auxiliary computationdemanding tasks found in common consumer GPS receivers , thereby

, minimiz ing demands on the chip processing power, circuit complexity, and costs. These design parameters would enable the ease of a GPS receiver

- based shutdown solution for integration into the generator.

A true production model would have a fully integrated design. GPS receiver circuitry could be housed safely in a weather

- resistant enclosure , with only the antenna exposed;

or, the manufacturer could opt to design an internal antenna. It should also be designed to be tamper

- resistant so that a consumer is unlikely to defeat this safety feature. This safety feature could be used in conjunction with mandatory labeling/packaging to the
effect : “This product will not operate indoors. ” This feature may actually help consumers
heed the warning : “do not use indoors.” Depending on how the power configuration is designed, the GPS receiver unit could be powered by a battery or super capacitor that is
internal to

, and charged by

, the alternator. The options are limitless, but quite achievable

, given the ubiquitous nature of GPS receiver technology found in everyday electronics, such as cellular phones and tablet computers.

Looking ahead, CPSC staff envisions a robust test method that will ensure the shutoff
system performance has the following characteristics: (a) produce repeatable16 performance in the variety of indoor environments that generators have been reported to be operated in ; (b) tamperproof (the g enerator will not start if the shut off system has been removed or bypassed) ; (c) durable after prolonged exposure to a generator’s typical storage and operating environments; and (d) features a fail

- safe mechanism (prevents the generator from starting) wh en the shutoff system is not functioning for some reason or its battery/supercapacitor is discharged or does not sustain charge

.

CONCLUSION

ESFS staff has conducted a limited

, exploratory exercise to demonstrate the feasibility of using GPS receiver tech nology to distinguish indoor and outdoor environments, with the intent of shutting down portable generator operation when used indoors. ESFS staff
demonstrated that a modified off- the

- shelf, commercially available GPS receiver unit can distinguish indoor and outdoor environments, with some exceptions where there were
dense tree cover scenarios. The issue of dense tree cover requires further exploration by GPS technology experts. The above scenarios can be addressed as the GPS receiver technology continue s to evolve and become more sophisticated.

ACKNOWLEDGEMENTS

Don Switzer (ESFS) provided oversight and his breadth of knowledge to help facilitate this exploratory exercise. Mark Gill (ESEE) developed the photo sensor a ctivation

c ircuit system and was instrumental in demonstrating the concept of this exploratory
exercise.

The author thanks the n umerous staff who have contributed and provided support :

CPSC Staff: Patricia Adair, Director for Division of Combustion and Fire Sciences (ESFS) Janet Buyer , ESFS, Project Manager for Portable Generators Susan Bathalon, Directorate for Hazard Identification and Reduction (EXHR)
Brian Baker

, Laboratory Sciences staff for his assistance in the ATV laboratory Stephen Patterson

, Laboratory Sciences staff for fabr icating the GPS receiver antenna modification components
Andrew Trotta

, Director for Division of Electrical Engineering (ESEE)

CPSC staff who have volunteered their homes for the various GPS experiments

NIST Staff : Steve Emmerich (Energy and Environment Division, Engineering Laboratory)
Dan Greb (Energy and Environment Division, Engineering Laboratory)17 REFERENCES

1. Buyer, J et al. “Technology demonstration of a Prototype Low Carbon Monoxide Emission Portable Generator,” August 2012. Source: http://www.cpsc.gov/library/foia/foia12/os/portgen.pdf

2. [brand name removed] Corporation, “GPS Receiver Unit Owner’s Manual and Reference Guide,” May 1998.

3. Marks, L, “Standard Handbook for Mechanical Engineers Tenth Edition,” 1996

McGraw

- Hill Companies

. 4. Underwriters Laboratories Inc. “UL 2201 – Standard for Safety

– Portable Engine

Generator Assemblies,” March 4, 2009.