U.S. CONSUMER PRODUCT SAFETY COMMISSION 

DIRECTORATE FOR ENGINEERING SCIENCES

DEMONSTRATION OF A 

REMOTE CARBON MONOXIDE SENSING 

AUTOMATIC SHUT OFF DEVICE

FOR PORTABLE GENERATORS 

August 2006 

Arthur Lee 

Electrical Engineer 

Division of Electrical Engineering 

Directorate for Engineering Sciences 

This report was prepared by the CPSC staff and has not been reviewed or approved by, 

and may not necessarily reflect the views of, the Commission.
ii August 2006 

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August 2006 i

Executive Summary 

Gasoline-powered portable generators are widely used to provide back-up electrical 

power during extended power outages. One of the exhaust by-products from portable generators 

is carbon monoxide (CO), a colorless and odorless but highly lethal gas. In recent years, the 

proliferation and increased availability of portable generators at the consumer level have resulted 

in an increase in the number of CO related deaths. This increase is particularly evident in areas 

that have lost electrical power for extended periods due to severe weather. 

In an effort to mitigate the CO hazards associated with the use of portable generators, in 

2005, the U.S. Consumer Product Safety Commission (CPSC) staff conducted a proof-ofconcept demonstration to integrate a CO detection system with a portable generator. The 

concept utilizes wireless technology combined with CO detection devices and off-the-shelf 

circuitry designed to provide an automatic shut off feature on portable generators. If elevated 

levels of CO accumulate in occupied areas of a household, the CO detection device sends a 

command to shut off the generator, thus eliminating the CO source. The following report details 

the design and testing of the demonstration system. 
ii August 2006 

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August 2006 iii

Table of Contents

Executive Summary .......................................................................................................................................i

1.0 Introduction.............................................................................................................................................1

1.1 CO Alarms...........................................................................................................................................1

1.2 Possible Technical Solution for Shutting Off a Portable Generator....................................................3

1.2.1 CO detection at the source............................................................................................................ 3

1.2.2 Remote CO detection .................................................................................................................... 5

2.0 Wireless Communication with CO Alarms and Portable Generators.....................................................6

2.1 Test Setup and Instrumentation...........................................................................................................7

2.2 Incorporating a Wireless Transmitter in a CO Alarm .......................................................................10

2.3 Incorporating a Wireless Receiver on the Portable Generator ..........................................................12

3.0 Testing of the Remote CO Detection System .......................................................................................15

3.1 Test Button Testing ...........................................................................................................................16

3.2 Elevated CO Testing .........................................................................................................................17

4.0 Observations/Improvements .................................................................................................................23

4.1 Power.................................................................................................................................................23

4.2 Relays................................................................................................................................................24

4.3 CO Detection Unit.............................................................................................................................24

4.4 Supervised System ............................................................................................................................25

4.5 Wireless Range..................................................................................................................................25

4.6 Feed-Back Indicators.........................................................................................................................25

4.7 Self-Check.........................................................................................................................................25

4.7.1 CO Detection Unit ...................................................................................................................... 26

4.7.2 Shut Off Unit............................................................................................................................... 26

4.8 Cost....................................................................................................................................................26

5.0 Summary...............................................................................................................................................27

APPENDIX A Standard Operating Procedures for Assuring Minimum Carbon Monoxide Exposure 

During Demonstration of a Remote Carbon Monoxide Detection Shut Off Device for a Portable 

Generator ..................................................................................................................................................... A
iv August 2006 

List of Figures

Figure 1. CO alarm helps detect elevated levels of CO in the home ............................................................2

Figure 2. Portable generator located in confined spaces or near an open window .......................................3

Figure 3. Portable generator located in the garage of an attached home ......................................................4

Figure 4. Portable generator located outside in a semi-confined space ........................................................5

Figure 5. CO detection device to remotely shut off the generator ................................................................5

Figure 6. Block diagram of a shut off device on a portable generator..........................................................7

Figure 7a. Example of a CO detection unit in a small home ........................................................................9

Figure 7b. Example of multiple CO detection units in a larger home ........................................................10

Figure 8. RF transmitter installed in a CO alarm........................................................................................11

Figure 9. Schematic of CO alarm and RF transmitter.................................................................................11

Figure 10. Block diagram of receiver unit operation ..................................................................................13

Figure 11. Wireless receiver and shut off unit ............................................................................................14

Figure 12. Schematic of shut off unit and generator...................................................................................14

Figure 13. Wireless receiver/shut off unit on the generator........................................................................15

Figure 14. Adapter Response......................................................................................................................16

Figure 15. Voltage response for remote shut off using the test button .......................................................17

Figure 16. Test 1 set-up with remote CO detection/shut off unit in the garage ..........................................18

Figure 17. Remote CO detection/shut off unit in the garage disabling the generator.................................19

Figure 18. Test 2 set-up with remote CO detection/shut off unit in the hallway ........................................20

Figure 19. Remote CO detection/shut off unit in the hallway disabling the generator...............................21

Figure 20. Test 3 set-up with remote CO detection/shut off unit in the kitchen.........................................22

Figure 21. Remote manual shut off of the generator from the kitchen .......................................................23

Figure 22. Powering the receiver unit.........................................................................................................24
August 2006 1

1.0 Introduction 

 

Gasoline-powered portable generators are widely used to provide back-up electrical 

power during extended power outages. The popularity and availability of these devices began to 

increase during pre-Y2K (year 2000) as consumers prepared for possible long-term power losses 

associated with the Y2K conversions. Although portable generator sales peaked in 1999*, their 

relatively low cost and availability at the retail level continued even after year 2000. Following 

the Northeastern blackout of August 2003, many consumers considered generators to be a 

necessity in an emergency, similar to candles, flashlights, batteries, and bottled water. Major 

home improvement chains shipped thousands of additional generators to stores in affected areas 

within days after power was restored.† 

Most portable generators use a single cylinder, gasoline-fueled, internal combustion 

engine equivalent to a lawnmower engine. Although robust and rugged, these engines are 

inefficient and contain no emission controls to mitigate harmful exhaust, thus making them 

significant producers of carbon monoxide (CO), a colorless and odorless but highly lethal gas. 

Available data show that CO-related deaths occur when portable generators are improperly 

located in enclosed spaces or inadequately vented locations‡

 such as garages or near open 

windows and doors. Consumers locate generators indoors or close to houses for a number of 

reasons, including fear of theft and concerns that direct exposure to precipitation may damage 

the unit. 

One concept to address the CO hazard is to incorporate a control system into the 

generator to shut it off or prevent it from starting if CO levels constitute a significant risk to 

occupants in an area being monitored. The approach is to use a standard residential CO alarm 

with a wireless link that will communicate with a transmitter/receiver affixed to the portable 

generator. In the event that the CO alarm senses elevated concentrations of CO, the wireless link 

will communicate with, and automatically shut off, the generator. 

Figures, illustrations, and test setups shown or descriptions of tests conducted in this 

report show a generator that has purposely been improperly located in order to evaluate the 

effectiveness of the experimental system in sensing accumulated CO. The CPSC recommends 

that portable generators never be operated in a confined space, such as a garage. Portable 

generators should be operated and maintained as specified by the manufacturer. 

1.1 CO Alarms 

Alarms to detect elevated levels of CO in the home have been available to consumers 

since the early 1980s. In 1992, Underwriters Laboratories (UL) published the first edition of UL 

2034, Standard for Safety for Single and Multiple Station Carbon Monoxide Alarms. Initially, 

 

*

 Donaldson, Mary, Portable Generators, CPSC Memorandum to Janet Buyer, Project Manager, U.S. Consumer 

Product Safety Commission, Washington, D.C., August 22, 2005. 

† Generators: Power in a Pinch, Consumer Reports, Consumers Union of U.S., Inc, November 2003. 

‡

 Marcy, Natalie and Debra Ascone, Incidents, Deaths, and In-Depth Investigations Associated with Carbon 

Monoxide and Engine-Driven Tools, 1990-2004, CPSC Memorandum to Janet L. Buyer, Project Manager, U.S. 

Consumer Product Safety Commission, Washington, D.C., December 1, 2005. 
2 August 2006 

CO alarms were plagued with reliability challenges, particularly false alarms. In response to 

these concerns, UL 2034 was modified to improve the reliability of residential CO alarms. 

CO alarms allow the detection of elevated levels of CO in a home from fuel burning 

appliances, as shown in Figure 1. The early detection of elevated levels of CO is critical to 

ensuring that affected occupants have sufficient time to evacuate, before being overcome by 

dangerous levels of CO. Some jurisdictions in the U.S. require the installation of CO alarms for 

homes containing fuel-burning appliances. Others, such as Mecklenburg County in North 

Carolina, require them in homes regardless of whether they contain fuel-burning appliances in 

response to CO deaths that occurred in a December 2002 ice storm due to portable generators 

and burning charcoal. Most homes in the U.S. that use fuel-burning appliances are not required 

to have CO alarms installed. 

CO alarm

Source of CO - Misaligned exhaust pipe

Figure 1. CO alarm helps detect elevated levels of CO in the home 

The three basic types of CO sensors used in residential CO alarms are biomimetic, metal 

oxide, and electrochemical. Biomimetic (chemioptic) sensors are designed to mimic the way the 

body responds to carbon monoxide. These sensors use gel-coated discs that darken in the 

presence of CO, thus tripping the alarm. There are several advantages to biomimetic sensors. 

They are inexpensive and require very little electricity. The sensors typically do not nuisance 

alarm in the presence of common household gases. However, CO alarms equipped with these 

sensors may false alarm if there are high or low temperatures and/or relative humidity levels in 

the home. 

The first residential CO alarms on the market used metal oxide or tin oxide sensors. 

These sensors use heated tin dioxide, which reacts to carbon monoxide, to determine the level of 

CO. These units use more electricity than the biomimetic or the electrochemical sensors because 

the tin oxide has to be heated every few minutes. Metal oxide sensors respond quickly to CO, 

but may sometimes nuisance trip from exposure to common household chemicals. High 
August 2006 3

humidity can also be a problem, since the sensors degrade slightly each time they are exposed to 

moisture.§

 

Electrochemical technology uses three platinum electrodes in an electrolyte solution. The 

sensor generates energy when exposed to CO. These alarms respond quickly to CO, but their 

sensors have a shorter life than the other sensor types. 

1.2 Possible Technical Solution for Shutting Off a Portable Generator 

Deaths have occurred in scenarios in which portable generators were placed inside or too 

close to a home, as shown in Figure 2. Since portable generators produce significant amounts of 

CO, the build-up of lethal concentrations of CO in a home can occur in a short amount of time. 

Source of CO - Generator located

 in the garage

Source of CO - Generator located

 in basement

Source of CO - Generator located

near open window

Figure 2. Portable generator located in confined spaces or near an open window 

Before sending a shut off signal to the generator, the level of CO in the affected area(s) 

must be monitored. There are at least two possible techniques to measure the CO produced by 

the generator. One method is to detect the level of CO in the vicinity of the generator (at the 

source). If levels near the generator become elevated, an auto shut off device can disable the 

generator. Another method is to monitor the CO level in the vicinity of the occupants in the 

home (remote detection). If elevated CO levels are detected in the home, an auto shut off device 

can disable the generator. There are advantages and disadvantages to each method. 

1.2.1 CO detection at the source 

Mounting a CO detection device on the generator allows fast detection of elevated CO in 

a confined space as shown in Figure 3. Even though this method may be ideal for fast detection 

of CO, there are some design obstacles. Generators are typically used outside, which can cause 

the CO sensors to become contaminated or dirty. The difficulty lies in designing a housing to 

shield the sensor from contaminants, but which will also allow air to enter the sensor chamber. 

In addition to withstanding the environmental conditions, the electronics and sensor(s) must also 

 

§

 Phillips WG. Carbon monoxide detectors: What you need to know. Popular Science. 1998 Jan:76-81 
4 August 2006 

withstand the conditions produced from the generator, such as continuous vibration present with 

most generator engines. 

CO sensor located on generator

detects elevated levels of CO 

CO cloud

CO cloud for illustration purposes. CO is colorless and odorless

Figure 3. Portable generator located in the garage of an attached home 

The location of the sensor on the generator and the sensor’s sensitivity will be critical in 

preventing false alarms and still allowing the sensor to detect elevated levels of CO. Depending 

on objects adjacent to the generator, such as a wall, bushes, car, or shed, small pockets of CO 

may be trapped. An effective CO alarm should be able to discriminate between a small 

temporary pocket of CO and a potentially lethal cloud. Small pockets of CO may cause the 

sensor to alarm and shut off the generator even though CO has not entered the home. Wind 

direction may also cause the CO sensor to shut off the generator, causing nuisance tripping of the 

generator. 

Even though CO levels are not elevated in the home, CO levels may be elevated near the 

generator, which may present a risk to the consumer. The generator may be located outside in a 

semi-confined space, such as a carport, that may cause elevated levels of CO only near the 

generator. The consumer may be within the hazardous CO cloud during refueling or operation of 

the generator as shown in Figure 4. 
August 2006 5

CO cloud

CO cloud for illustration purposes. CO is colorless and odorless

 Figure 4. Portable generator located outside in a semi-confined space 

1.2.2 Remote CO detection 

Locating a CO sensor remotely allows monitoring the level of CO where the 

concentrations are most critical, as shown in Figure 5. One advantage of placing the CO sensor 

in the living space near the occupants is that it reduces the likelihood of the sensor being 

compromised by exposure to harsh environments. The alarm will also be more audible to the 

occupants, alerting them to elevated levels of CO. If the sensor unit contains a visual display of 

CO concentration, such as parts per million (ppm), it will provide occupants with an indication 

of the level of CO to determine if it is rising or stable. If occupants observe rising CO levels, 

they could remotely shut off the generator without having to approach it, thereby potentially 

reducing exposure to higher CO levels that may be present closer to the generator. A 

disadvantage to remote sensing is that the CO sensing unit might not be located in the same part 

of the house in which occupants are located. In such a case, the level of CO near the occupants 

could be elevated, but the CO sensing unit may not detect it because it is in a different part of the 

home. 

Generator shuts-off

remotely

Remote unit detects

elevated levels of CO

Figure 5. CO detection device to remotely shut off the generator 
6 August 2006 

Both types of CO detection/shut off concepts, either at the source or remotely, would 

require the CO sensing unit to operate with a battery or secondary power supply during a power 

outage. However, the “source” CO sensor located at the generator could switch to AC generator 

power once the generator has started. 

2.0 Wireless Communication with CO Alarms and Portable Generators 

CPSC staff evaluated the concept of using a remote CO detection device to detect 

elevated CO concentrations and remotely shut off the portable generator. In a December 2003 

joint effort with the Naval Research Laboratory (NRL) under contract to CPSC (CPSC-I-02-

1290), the feasibity of incorporating wireless technology in battery-powered smoke alarms and 

having the alarms “communicate” with each other was demonstrated. 

Under the 2003 contract with NRL, transmitter and receiver circuits were successfully 

integrated into existing residential smoke alarms using wireless technology. If any smoke alarm 

activated, it transmitted a signal to the other smoke alarms so that they would activate 

“sympathetically.” Each receiving smoke alarm also acted like a repeater; thus, a smoke alarm 

that may have been too far away to be activated by the initiating smoke alarm could be activated 

by a closer smoke alarm that was transmitting an alarm signal. Maximizing battery power was a 

key factor in selecting the transmitting range and the rate at which the receiver checked for an 

alarm signal. 

The demonstration described in this report uses wireless technology with a CO alarm to 

trigger a shut off device on the portable generator. The remote CO alarm was designed to 

initially check the CO level in the home before allowing the occupant to start the generator. This 

feature may also be beneficial in helping prevent the occupant from restarting the generator when 

there are elevated levels of CO in the home. 

A wireless transmitter that triggers a shut off device on the portable generator was 

incorporated into a conventional CO alarm. A shut off device was located on the generator 

where it will shut off the engine in the event of elevated CO levels in the home. Figure 6 shows 

a block diagram of a remote CO sensing shut off system. The user would be required to depress 

an enable button before the generator would be allowed to start. The enable button would 

prevent the operator(s) from starting the generator when an elevated level of CO may already 

exist in the home. 
August 2006 7

Check for CO

User attempts

to start generator

Power remote

CO unit

CO below

threshold

CO above

threshold

Disable safety

interlock switch

for xx minutes

Safety interlock

switch enabled 

for xyz minutes

< xx minutes > xx minutes

User presses

enable button

Timer

>xyz minutes <xyz minutes

Figure 6. Block diagram of a shut off device on a portable generator 

2.1 Test Setup and Instrumentation 

CPSC staff conducted tests using a UL listed CO alarm, AC-powered with battery backup and electrochemical sensing, as the sensing device to signal the controls to shut off a 

generator. For this testing, the CO alarm was powered only from a battery (no AC power) to 

enhance the portability of the system. The CO alarm also incorporated an interconnect feature 

that would allow multiple CO alarms to sound when any one of the units alarmed. This feature 

increases alarm audibility throughout the home. For the purposes of the staff testing, the 

interconnect signal was used to trigger the wireless transmitter that was installed in the CO 

alarm. 

 A data acquisition system consisting of a current meter, an analog-to-digital signal 

converter (ADC) unit, a gas analyzer, and a computer was used. The current meter was used to 

measure the load on the generator during the tests. The ADC unit was used to record load 

current, CO alarm interconnect signal, CO level, and generator operating status (whether or not it 

was running). The CO alarm and gas analyzer (CO sampling device) were moved to different 

locations in the home to record CO levels. 

 Below is a list of the equipment used in the staff testing. CPSC does not endorse the 

equipment and instrumentation used in the tests nor state that the equipment and instrumentation 
8 August 2006 

used are the best or only products for this application. The product and company names listed 

are trademark or trade names of their respective companies. 

Alarm Source Residential Carbon Monoxide Alarm 

AC powered with 9-volt battery back-up 

Sensor Type - electrochemical 

UL listed 

CO Sampling NOVA Gas Analysis Equipment 

 Model 310WP 

 Sensor Type – electrochemical 

 Aspirated air sampling 

 Range: 1% of full scale, 0-2000 ppm 

 Response time: 20-30 seconds for 90% of step change 

 Last calibrated – August 2002 

Digitizing System Data Translation 

 Model DT9834 

16 bit A/D 

Computer Laptop 

 3GHz processor 

 1G RAM 

Current Probe Fluke 

 Model 80i-110s 

 Rated 10 milliamps to 100 Amps 

Transmitter and Receiver Wireless Automator 

 Programmable relays 

6 relays rated at 3 amps @ 12V 

High Current Relay Type - SPDT Form "C" heavy duty dry contacts 

Contact rating 7A @ 30VDC, 10A @125VAC 

Input trigger 9-12VDC 30mA 

Portable Generator 5250 watt 

 Fuel - Gasoline 

 Pull start 

The transmitter and receiver units were part of an off-the-shelf remote-controlled relay 

unit that can control power for up to six 5-ampere appliances. The transmitter had three channels 

with a range of 150 ft. The receiver unit included six relays that were opened or closed by a 

signal from the transmitter. Depending on which push button(s) was depressed on the 

transmitter, the receiver unit could operate different relays. 
August 2006 9

The receiver unit was mounted on the generator to control a relay that was incorporated 

into the generator ON/OFF circuit as a shut off device. Since the receiver unit could receive 

multiple programmed signals from transmitters, multiple CO alarm transmitter units could be 

located throughout a home to increase the number of areas monitored for CO accumulation. 

Monitored areas might include individual bedrooms and each level of the home. The number of 

CO transmitter units installed in a home would, in part, depend on the location of occupants in 

the home, and the size and configuration of the home. Figure 7a shows an example of a small 

home, which may require only one remote CO unit. A larger home may require multiple remote 

CO units as shown in Figure 7b. In this example, the master bedroom is separated from the other 

three bedrooms. A remote CO detection unit would be needed in both areas if each area 

contained occupants. An additional remote CO unit might also be needed in the family room. 

For the purposes of this test program, only a single CO alarm transmitter unit was used. 

Living Room

Dining

Room

Kitchen

Bedroom 2 Bedroom 3

Bedroom 1

DN

Generator located outside back door

Figure 7a. Example of a CO detection unit in a small home 
10 August 2006 

Kitchen Family Room

Living Room

Dining Room Master

Bedroom

Breakfest Screened Porch Room

Utility/

Laundry

Room

Garage

Remote CO Detection Unit

Vaulted

Ceiling

UP

First Floor

Bedroom 2 Bedroom 3

Bedroom 4

Loft

Attic storage

Vaulted

Ceiling

Open to

 below

DN

Second Floor

Generator located outside screened porch

Figure 7b. Example of multiple CO detection units in a larger home 

For staff testing, a 3,900 ft2

 home was used as the test structure. The home had an 

attached three car garage. The home had two levels and a basement. Each level was 

approximately 1,300 ft2

. The home contained central heating and air conditioning, which were 

turned off during the testing. All the external windows and doors were closed during the testing. 

 

2.2 Incorporating a Wireless Transmitter in a CO Alarm 

To demonstrate this application using wireless technology, CPSC staff used off-the-shelf 

universal radio frequency (RF) transmitter and receiver units. The RF transmitter circuit board 

was removed from its plastic housing and installed in a CO alarm, as shown in Figure 8. The 

transmitter circuit board was 1.25 inches x 1.5 inches, which allowed it to fit in the 9-volt battery 

compartment. A separate 9-volt battery terminal was used to power the CO alarm. The 

transmitter circuitry used one 12-volt battery. 
August 2006 11

 

Wireless transmitter

mounted in the battery

compartment

CO alarm with start-up safety interlock button

Emergency Shut-Off

Press Test Button

Figure 8. RF transmitter installed in a CO alarm 

The interconnect signal on the CO alarm was used to trigger the transmitter, which is 

normally activated by the pushbuttons on the transmitter. Staff fabricated a circuit to interface 

the transmitter with the CO alarm’s interconnect output signal. Figure 9 shows the schematic of 

how the wireless circuitry was incorporated into the CO alarm. The transmitter could send two 

different commands to the receiver. One command would initiate the allowable period for 

starting up the generator, and the other command was used to shut off the generator if the CO 

alarm went off. 

CO Alarm

Wireless Circuit

Interconnect

Alarm

Signal

Channel 1

Channel 2

9 V battery

Push button to enable

generator

Figure 9. Schematic of CO alarm and RF transmitter 
12 August 2006 

2.3 Incorporating a Wireless Receiver on the Portable Generator 

The receiver/shut off unit was installed on a portable generator. The unit contained a 

wireless receiver, a separate shut off relay, and a rechargeable battery. Figure 9 shows a block 

diagram for the operation of the receiver unit and its integration with the generator. 

The receiver unit is normally in a “stand-by” mode, waiting for a wireless start-up signal 

from the CO detection unit. The generator start-up sequence begins when the user presses a 

button on the remote CO detection unit to transmit a start-up signal. When a signal is received, 

the receiver unit closes relays, which prepares the generator for start-up and operation. The startup relay is closed for approximately 20 minutes, which gives the user time to go outside to the 

generator and continue the starting sequence, such as pull starting the engine. When the 

generator starts, the power to maintain closure of the relay (initially battery power) is replaced by 

the generator. If 20 minutes has elapsed and the generator has not been started, the relay opens 

and disables the generator. The user would have to press the start-up button on the CO detection 

unit again before attempting to start the generator. 

Once the generator has been started, if elevated CO levels are detected by the CO 

detection unit, the CO detection unit transmits an RF signal to the receiver unit. Upon receiving 

the signal, the receiver unit removes power from the relay, causing it to open and disable the 

generator. The generator will be disabled until the CO levels drop and the detection unit stops 

sounding/transmitting. Once the CO levels have declined, the start-up button can be pressed, and 

the user will be able to start the generator within the 20 minute window. 
August 2006 13

Receiver determines

if start-up signal

or

elevated CO signal

Elevated CO

signal Start-up

signal

Timer

20 minutes

User attempts

to start generator

High Current

Relay

Powered by

generator

High Current

Relay

Opens

Timer expires

Generator Stops Generator Running

Disconnect Power

to Relay

Power Relay

Timer

1 minute

Generator Starts Programmable

Relay Programmable Closes

Relay

Opens

Reciever/Shut-off

Unit awaiting signal

Figure 10. Block diagram of receiver unit operation 

The receiver and shut off system were packaged in an 8 x 3 x 2 inch box, which also 

contained the back-up battery, high current relay, and a small circuit board. The wireless 

receiver with the programmable relays was mounted on the outside of the box as shown in Figure 

11. The wireless receiver had a 10-inch antenna and required 12 volts input to power the 
14 August 2006 

circuitry. An AC/DC connector was used to allow charging of the back-up battery by either 

plugging the adapter into a household 120 VAC receptacle or into the generator’s 120 VAC 

receptacle. Another connector was used to connect the shut off relay to the generator’s manual 

ON/OFF switch. For prototype designing and testing, this set-up allowed easy removal of the 

receiver/shut off unit. Figure 12 shows the schematic of the wireless circuitry incorporated in the 

test generator. 

Receiver Unit and Shut-off Circuitry

Battery Back-up and High Current Relay Wireless Circuitry and

Programmable Relays

Wireless Receiver and

Programmable Relays

Battery Back-up and

High Current Relay

Receiver Antenna

AC/DC Adapter/Charger

Connector to Generator Switch

Programmable Relays

High Current Relay

Battery Back-up

 Figure 11. Wireless receiver and shut off unit 

Figure 12. Schematic of shut off unit and generator 
August 2006 15

 The wireless receiver/shut off unit was mounted on the generator and connected to the 

generator’s manual ON/OFF switch as shown in Figure 13. The generator’s ON/OFF switch 

remained in service and allowed the user to shut off the generator by turning the switch to the 

OFF position. The generator also could not be started unless the switch was in the ON position. 

The receiver unit’s relay was connected in parallel with the manual ON/OFF switch. (The 

ON/OFF switch is open in the ON position and closed in the OFF position, so either switch can 

be used to shut off the generator.) This arrangement allowed either the user to manually shut off 

the generator or the receiver unit to shut off the generator. 

Manual Shut-Off Switch

Receiver Antenna

Connector for 

battery back-up

AC/DC Adapter/Charger

Connector to Generator Switch

Wireless Receiver 

and Shut-Off Unit

Manual Shut-Off Switch AC/DC Charger

Wireless Receiver and Shut-Off Unit Mounted on Generator

Figure 13. Wireless receiver/shut off unit on the generator 

The shut-off relay current capacity was determined by measuring the current through the 

ON/OFF switch when the switch was turned from ON to OFF with the generator running. The 

peak current was less than 2 amps, and the pulse width was less than 0.5 seconds. The current 

through the generator’s manual ON/OFF switch was less than the maximum current rating for 

the high current relay selected for the shut off unit. 

3.0 Testing of the Remote CO Detection System 

Several tests were conducted to determine the functionality of the CO detection and shut 

off system. The testing was conducted using the test button on the CO detection unit and the 

receiver unit mounted on the generator. Several tests were conducted to allow the CO detection 

unit to be exposed to elevated levels of CO and then shut off the generator automatically. The 

elevated levels of CO were generated by operating the portable generator in a confined space 

(6993 ft3

 garage). As previously noted, testing conducted with the portable generator in the 

garage was for test purposes only and is not consistent with correct and safe operation of a 

portable generator. The CPSC recommends against operating a portable generator in a garage. 

Portable generators should be operated and maintained as specified by the manufacturer. 
16 August 2006 

For all the tests, an AC/DC (120 VAC/5VDC) transformer was plugged into the 

generator’s 120 VAC receptacle and used as a monitoring source to indicate that the generator 

was running. Figure 14 shows the response of the AC/DC adapter when power is removed. The 

voltage slowly decays after a delay of approximately 3 seconds. The delay and decay are caused 

by internal adapter capacitance. 

ADC Adapter voltage curve

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Time (seconds)

Voltage

Powering the adapter

Power removed

adapter response

approximately 3 s delay before decay

Figure 14. Adapter Response 

The NOVA Gas Analyzer used in the testing was last calibrated in 2002 so the measured 

values were only used for monitoring purposes in the course of these tests. The purpose of using 

the CO gas analyzer was to roughly monitor the CO build-up during the test. The reading was 

also used to determine when the CO level in the home had reached near zero before starting the 

next test. The unit was zeroed before each test. A data acquisition system was used to record 

CO levels, the CO detection unit’s interconnect signal, and the output of the AC/DC transformer 

plugged into the generator. The sampling rate was 0.1 seconds unless noted otherwise. 

3.1 Test Button Testing 

 Initial testing was conducted using the test button on the CO alarm. This test was 

conducted outdoors. The CO detection unit was placed approximately 20 feet from the 

generator. The test button on the CO unit was depressed, which enabled the generator to be 

started. The generator was started successfully and, after 20 minutes, the relay timed out but 

remained closed utilizing power from the generator. No external load was connected to the 

generator. 

 After 30 minutes, the test button on the CO detection unit was depressed. The receiver 

unit received the signal and opened the relay, causing the generator to stall and shut off. Figure 
August 2006 17

15 shows the voltage response curves for the interconnect signal and the generator power 

shutting off. The sharp peaks show the interconnect signal triggering the wireless transmitter. 

Approximately 0.5 seconds later, the power at the generator’s 120 V receptacle was 

discontinued. The adapter response delay and decay are also shown in the figure. 

Interconnect Signal and Generator Shut-Down

-1

0

1

2

3

4

5

6

7

8

9

Time (0.25 second per tick)

Voltage

Generator power Alarm interconnect

Generator engine stops

Wireless interconnect

signal transmitted 

Indicator of 

generator running

Indicator of wireless

interconnect signal

Generator begins

shut-down

adapter response

Generator engine stops

Generator begins

shut-down

Figure 15. Voltage response for remote shut off using the test button 

3.2 Elevated CO Testing 

The generator was located in a three car garage attached to a two-story (with basement) 

single family home. The CO detection unit was placed in various locations in the home for each 

test. The home has an open floor plan and 9 ft ceilings. The family room has cathedral ceilings 

to the second floor, and the foyer is two stories high. Together, the first floor, second floor, and 

basement are approximately 3,900 ft2. The three car garage is approximately 31.5 feet x 18.5 

feet x 12 feet high. The generator was placed in the middle bay of the three car garage, and all 

the garage doors were closed for all the tests. The generator was placed with the exhaust 

directed towards the middle garage door. The garage did not contain any vehicles, but the 

miscellaneous items in the garage occupied approximately 1/12 of the garage’s volume. The 

garage has a door leading to a hallway. The adjoining hallway includes an open staircase down 

to the basement, an interior door to the general living area and an exterior door to the outside. 

The home’s heating and air conditioning system was off for all the tests. All the 

windows and external doors were closed for all the tests. During the testing, the ambient 

temperature varied from 70° F to 76° F, and the winds were variable from 5 to 10 mph. 
18 August 2006 

For the first test, the CO detection unit was placed in the garage near the door to the 

hallway. The remote detection/shut off unit was approximately 14 feet from the generator and 3-

1/2 feet from the floor. The door to the hallway was closed. The test was conducted with no 

load. The gas analyzer was placed at the same location as the CO detection unit. Figure 16 

shows the setup for the testing. 

Open

Closed

Closed

Garage door

closed

Garage door

closed

Garage door

closed

CO

CO Detection Unit

Gas Analyzer

Data Acquisition System

Generator with

Shut-off Unit

To living area

To basement

No Load Test

approximately 14 ft

both units approximately

3.5 ft from the floor

Figure 16. Test 1 set-up with remote CO detection/shut off unit in the garage 

 

The start button on the CO detection unit was depressed, which enabled starting of the 

generator. The generator was pull-started successfully and the operator monitored the testing 

from an outdoor location. After the start of the generator, the CO detection unit detected 

elevated CO levels in approximately 8 minutes. At this time, the CO detection unit transmitted a 

wireless signal. The receiver unit received the signal and shut off the generator. The gas 

analyzer indicated approximately 732 ppm, and the CO detection unit’s digital display indicated 

598 ppm when the generator shut off. Figure 17 shows the interconnect signal from the CO 

detection unit, the generator running power indicator, and the CO gas analyzer over a 15 second 

period. 

The garage and exterior doors were opened and CO levels were allowed to drop to near 

zero before the operator re-entered the structure. The gas analyzer was zeroed before the next 

test. 
August 2006 19

Test 1 Generator Shut-Down - Remote in Garage

0

2

4

6

8

10

12

495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510

Time (seconds)

Voltage

700

710

720

730

740

750

760

770

CO Level (ppm)

Alarm Interconnect Signal Generator Power CO Level

Generator engine stops

Gas Analyzer

Figure 17. Remote CO detection/shut off unit in the garage disabling the generator 

 

In the second test, the CO detection unit and CO gas analyzer were moved to the hallway, 

adjacent to the garage. As shown in Figure 18, the CO detection unit and the CO gas analyzer 

were approximately 4 feet from the door leading from the garage to the hallway. The door was 

ajar approximately 3/8 inch to allow an extension cord from the generator to be connected to a 

refrigerator in the kitchen. The door from the hallway to the living area was closed with the 

extension cord to the refrigerator routed under the door air gap, which was approximately 1 inch 

high. The load on the generator varied from near 0 amps to 2 amps, depending on whether the 

refrigerator’s compressor was operating (which amounted to approximately 4.5% of its rated 

load capacity). The sampling rate of the data acquisition system was set at 1 second. 
20 August 2006 

Closed

Partially

closed

Garage door

closed

Garage door

closed

CO

CO Detection Unit

Gas Analyzer

Data Acquisition System

Generator with

Shut-off Unit

Extension cord

to refrigerator

To living area

To basement

Closed

both units approximately

3.5 ft from the floor

Garage door

closed

Distance 4 feet from the door

Figure 18. Test 2 set-up with remote CO detection/shut off unit in the hallway 

 The start button on the CO detection unit was depressed, which enabled starting of the 

generator. The generator was pull-started successfully. After about 17 minutes, the gas analyzer 

measured approximately 532 ppm in the hallway. At this time, the CO detection unit began to 

alarm, which caused the unit to transmit a signal to the receiver unit. The receiver unit received 

the signal and the generator stalled and shut off, as shown in Figure 19. In examining Figure 19, 

the graph makes it appear as though the generator began to shut off before the CO detection unit 

triggered the transmitter. This was because the digitizing system sampling rate of 1 second was 

not frequent enough to capture the first pulse signal from the CO detection unit. The CO 

detection unit’s LED indicated 520 ppm when the generator was shut off. 

The garage and exterior doors were opened and CO levels were allowed to drop to near 

zero before the operator re-entered the structure. The gas analyzer was zeroed before the next 

test. 
August 2006 21

Test 2 - CO Detection Unit in Hallway

(generator located in garage)

-1

0

1

2

3

4

5

6

7

8

9

0 100 200 300 400 500 600 700 800 900 1000 1100

Time (seconds)

Voltage

-100

0

100

200

300

400

500

600

CO Level (ppm)

Generator power Alarm interconnect CO (Nova)

Gas Analyzer

Figure 19. Remote CO detection/shut off unit in the hallway disabling the generator 

In the third test, the CO detection unit and CO gas analyzer were moved to the kitchen, 

adjacent to the hallway to the garage. The door leading from the garage to the hallway was 

opened 3/8 inch to allow the extension cord from the generator to be connected to the 

refrigerator. The door leading from the hallway to the kitchen was opened fully. Figure 20 

shows the setup for the testing. 
22 August 2006 

Closed

Partially

closed

Garage door

closed

Garage door

closed

CO

Generator with

Shut-off Unit

Extension cord

to refrigerator

To living area

To basement

To basement open

both units approximately

3.5 ft from the floor

Garage door

closed

To foyer

To dining

room

Kitchen

Open to family room

Refigerator

CO Detection Unit

Gas Analyzer

Data Acquisition System

Distance 5 feet from the exterior door

closed

To second f ol or

Figure 20. Test 3 set-up with remote CO detection/shut off unit in the kitchen 

The start button on the CO detection unit was pressed, which enabled starting of the 

generator. The generator was pull-started successfully. After almost 1 hour of generator 

operation, the CO gas analyzer measured 90 ppm in the kitchen. Note that the CO levels in the 

kitchen did not reach the threshold level for the alarm to activate. To test the remote manual shut 

off of the generator, the test button was pressed on the CO detection unit, causing it to transmit a 

shut off signal. The receiver unit received the signal, causing the generator to shut off as shown 

in Figure 21. The LED display on the CO alarm displayed 82 ppm when the generator had shut 

off. The remote manual shut off of the generator allowed the tester to stop the generator without 

entering the garage which, based on earlier testing, most likely contained elevated levels of CO. 

In the first test, the CO levels in the garage measured over 700 ppm in 8 minutes. For this test, 

the generator was operating for almost 60 minutes before being shut off. The actual CO level in 

the garage was not measured. 

As demonstrated in test 3, the remote shut off device could be very beneficial in that it 

could allow the user to shut the generator off remotely (without having the user enter the area 

near the generator, which may contain high levels of CO). 

 
August 2006 23

Test 3 - CO Detection Unit in Kitchen

-1

0

1

2

3

4

5

6

7

8

9

1500 1700 1900 2100 2300 2500 2700 2900 3100 3300

Time (seconds)

Voltage

-40

-20

0

20

40

60

80

100

120

CO Level (ppm)

Generator power Alarm interconnect CO (Nova)

Manual remote shut-down signal. 

Generator shuts down shortly after.

Gas Analyzer

Figure 21. Remote manual shut off of the generator from the kitchen 

4.0 Observations/Improvements 

The demonstration of the experimental CO detection/shut off system showed that it is 

possible to incorporate an auto shut off system on a generator. The design of the experimental 

unit was based primarily on functionality and, therefore, was not optimized for considerations 

such as cost, complexity, size, usability, and reliability. After building and testing the system, 

staff concluded that there are features and technological improvements that could be 

incorporated in the CO detection and shut off system that would increase the reliability, reduce 

the number of components, and simplify the system. 

4.1 Power 

The demonstration system tested used a rechargeable battery to power the receiver unit 

before it received AC power from the generator. The system allowed the user to plug the 

AC/DC charger adapter into a regular household receptacle to charge the battery until needed. 

When needed, the user would unplug the AC/DC charger from the household receptacle and plug 

it into the generator’s 120 VAC receptacle as shown in Figure 22. This setup allowed the battery 

to be fully charged at all times so that the wireless circuit would always be energized, regardless 

of the ON/OFF status of the CO detection unit. 

A much simpler method, which could significantly reduce both the size and cost of the 

receiver unit on the generator, would be to use a 9-volt battery to power a receiver unit equipped 
24 August 2006 

with an ON/OFF power switch. The 9-volt battery would be used to power the receiver unit until 

the generator started. The usage life of the battery would be similar to its shelf life because of 

the short duration of the usage period just prior to generator start-up. Typically, an alkaline 

battery can have a 5-year shelf life, which may vary with extremes in temperature. 

Household receptacle

Stand-By Mode

User wants to

start generator

(example - loss of household power)

User starts

generator

AC/DC Charger

Generator Start-Up Mode

Receiver is powered

by battery back-up

AC/DC Charger

Generator Running Mode

Generator with

Shut-off Unit

Back-up battery

being charged Receiver is powered

by generator and

recharges battery

back-up

AC/DC Charger

Figure 22. Powering the receiver unit 

4.2 Relays 

The demonstration system had six standard relays available and an additional high 

current relay. The six relays were programmed and controlled by the wireless circuitry. Each 

relay could be programmed separately. The relays could be programmed to be momentary, 

latched, validity**, 30-second timed, 1-minute timed, 5-minute timed, 20-minute timed, or 

strobed (repeated ON/OFF). Each relay could be used normally open (N.O.) or normally closed 

(N.C.) and was rated for 3 amps at 12 VDC. The shut off system used only two of the six relays 

on the circuit board. The two relays were used to control the high current relay, which was rated 

at 7 amps at 30 VDC or 10 amps at 125 VAC. 

The number of relays needed can be reduced, and it is possible the high current relay 

could be eliminated. The six relay circuit board could also be reduced to one or two relays 

depending on the programming capabilities of the relay circuit. Reducing the number of relays 

would also drastically reduce the size and cost of the receiver unit. 

4.3 CO Detection Unit 

A residential CO alarm was integrated with a wireless transmitter. The CO alarm used 

AC power with battery back-up. In the testing, only the battery back-up power source was used. 

Since the alarm was originally designed for household plug-in as the primary power, the alarm 

had an LED display, which required a significant amount of power. Most battery-only powered 

CO alarms use an LCD display to help minimize current usage. 

 

** Only ON when pressed and OFF when released. 
August 2006 25

4.4 Supervised System 

The demonstration system utilized an unsupervised wireless system. The shut off unit on 

the generator and the remote CO detection unit did not incorporate an additional check for 

communication integrity. The disadvantage of such a system is that it would allow a user to 

disable the CO detection unit after starting a generator, thus leaving occupants unprotected in the 

event of a CO build-up. 

A supervised system would allow each of the units, CO detection and shut off units, to 

monitor each other. The CO detection and shut off units would each have a transmitter and 

receiver, or a transceiver. If the shut off unit on the generator did not receive a periodic check 

signal from the CO detection unit, the shut off unit would disable the generator. If the CO 

detection unit did not receive a periodic check signal from the shut off unit, the CO detection unit 

would sound an alarm, indicating that it was out of range or the shut off unit had malfunctioned. 

4.5 Wireless Range 

The maximum range tested for the demonstration unit was approximately 50 feet through 

one wall or door. The minimum required reliable wireless range between the CO detection unit 

and generator would need to be determined to ensure that the CO detection unit and generator 

work as intended for consumers. 

4.6 Feed-Back Indicators 

The demonstration unit did not contain any feed-back indicators to indicate that the 

system was operating correctly. Indicator lights on the shut off unit would allow the user to 

know the system status. 

4.7 Self-Check 

The demonstration unit did not conduct a self-check of the circuitry. Similar to a 

supervised system for wireless communication, the self-check would determine that the 

remainder of the circuitry in the CO detection and shut off units was functioning. 

 
26 August 2006 

4.7.1 CO Detection Unit 

Self-check the CO sensor sensitivity

A periodic check of the CO sensor sensitivity to determine if the sensor has become 

more or less sensitive than manufacturer specifications would help prevent the CO 

alarm from nuisance alarming or not alarming when elevated levels are present. 

Low battery check

A low battery check in the CO alarm unit would allow the user to change the battery 

before the system becomes nonfunctional. 

Transceiver circuitry is functioning

 

A self-check of the transceiver circuitry would determine if the circuitry is functioning 

correctly. 

4.7.2 Shut Off Unit 

Self-check the relay circuitry

A self-check of the relay circuitry would determine if the circuitry is functioning 

correctly. 

Low battery check

A low battery check in the receiver unit would allow the user to change the battery 

before the system becomes nonfunctional. 

Transceiver circuitry is functioning

A self-check of the transceiver circuitry would determine if the circuitry is functioning 

correctly. 

Continuity with the manual ON/OFF switch

A continuity check of the manual ON/OFF switch would determine if the receiver unit 

is connected to the generator and has not been disabled or bypassed. 

4.8 Cost 

Off-the-shelf components used in the demonstration included an AC-powered CO alarm 

with battery back-up, which retails for approximately $52. The CO alarm cost would be lower if 

it was only battery powered and contained an LCD instead of an LED display. The off-the-shelf 
August 2006 27

wireless transmitter and receiver system cost approximately $100 (retail). The system contained 

more features than were actually required in the demonstration unit and more features than 

would be required in a production unit. For example, the unit was programmable, which was a 

useful feature for prototyping but unnecessary for production units. Additionally, although the 

demonstration unit contained six relays, only two were used in the system. This number could 

probably be further reduced to one relay with careful circuitry design and programming. The 

high current relay used in these tests cost approximately $12 (retail), which could have been 

omitted in the design. For the circuitry and the other associated hardware discussed above, the 

engineering staff estimates that a production unit could add an additional $100 to the cost of a 

portable generator. The average cost of a retail CO alarm is approximately $30 and the wireless 

circuitry would be an additional $50 to $70. The additional cost would depend on many factors, 

such as the manufacturer’s approach and previous experience in using wireless technology, 

technique for interfacing the shut-off circuitry with the generator, and type of CO alarm. In 

addition, there could be additional costs in producing a final product that makes the system 

reliable, consumer friendly, and other factors that were not examined in this demonstration. 

5.0 Summary 

In recent years, the proliferation and increased availability of portable generators at the 

consumer level have resulted in an increase in the number of carbon monoxide (CO) related 

deaths. To help mitigate the CO hazards associated with the use of portable generators, the 

CPSC staff successfully demonstrated a concept to incorporate an auto shut off device on a 

portable gasoline-fueled engine generator that activates when elevated CO levels are detected in 

the home. A method of monitoring CO levels at a single location away from the generator was 

explored. If elevated CO levels are detected in the home, an auto shut off device can disable the 

generator. 

A demonstration system was designed and built to evaluate the concept of shutting off a 

generator from a remote location when elevated levels of CO are detected. For the 

demonstration system, a wireless transmitter was incorporated into a CO alarm that was used as 

the initiating device to signal a shut off of the generator. A wireless receiver and relays were 

used to shut off the generator. 

Several tests were conducted to determine the functionality of the CO detection and shut 

off system. Testing was conducted using the test button on the CO detection unit with the 

receiver unit mounted on the generator. Several tests were conducted to allow the CO detection 

unit to detect elevated levels of CO and shut off the generator remotely. In all the tests, the 

generator shut off when the CO detection unit transmitted a shut off signal. The CPSC staff 

viewed this program as a successful demonstration of the CO detection/automatic generator shut 

off concept. 

The study was limited to proof-of-concept and did not consider issues such as life 

expectancy, reliability, usability, and environmental conditions. All of these factors would need 

to be considered in developing a remote CO detection/shut-off system for portable generators for 

consumer use. 
28 August 2006 

No Text on This Page 
December 2005 DRAFT A

APPENDIX A 

Standard Operating Procedures 

for Assuring Minimum Carbon Monoxide Exposure During Demonstration of 

a Remote Carbon Monoxide Detection Shut Off Device 

for a Portable Generator 
DRAFT December 2005 

No Text on This Page
December 2005 DRAFT A-1

Standard Operating Procedures 

for Assuring Minimum Carbon Monoxide Exposure During Demonstration of a Remote 

Carbon Monoxide Detection Shut Off Device for a Portable Generator 

Prepared by Arthur S. Lee 

Electrical Engineer 

Division of Electrical Engineering 

U.S. Consumer Product Safety Commission 

August 2005 

 

Version 2 
Page 2 of 7 

Version 1 

Date : August 2005 

Standard Operating Procedures 

For Assuring Minimum Carbon Monoxide Exposure 

Title: Guidelines and Procedures for Demonstration of a Remote Carbon 

Monoxide Detection Shut Off Device for a Portable Generator

A-2 DRAFT December 2005 

1.0 PURPOSE:

The purpose of this document is to specify appropriate procedures and safeguards 

for test personnel to follow to protect them from exposure to potentially-harmful 

concentrations of carbon monoxide during testing of a prototype remote CO detection/ 

automatic shut off system installed on a portable generator running indoors in an actual 

residence. The nature of the testing is to intentionally reproduce an inappropriate (albeit 

foreseeable) application of a portable gasoline-fueled electric generator (operating it 

indoors) to evaluate the effectiveness of the prototype system. 

2.0 DEFINITIONS:

For purposes of this document, the following definitions apply: 

Standard Operating Procedures 

The recognized, acceptable criteria which serve as support for methods or 

manners of fulfilling a function or functions. 

 CO

Carbon Monoxide. The CO in this testing will be one of the components of the 

exhaust gasses produced by the portable generator. 

 Portable Generator

The gasoline-powered engine-driven, electric generator that was outfitted with a 

radio-frequency (RF) receiver controlling an engine shut off device. 

 Remote Carbon Monoxide Detection/Shut Off Unit

The carbon monoxide detection unit that was outfitted with an RF transmitter to 

send a signal to the receiver unit on the generator. 

PPM

Parts per million. Units representing the concentration of carbon monoxide. 

Manual Remote Shut Off Device

A hand-held transmitter that can be used to shut off the generator from a location 

where accumulated CO is below hazardous levels. 
Page 3 of 7 

Version 1 

Date : August 2005 

Standard Operating Procedures 

For Assuring Minimum Carbon Monoxide Exposure 

Title: Guidelines and Procedures for Demonstration of a Remote Carbon 

Monoxide Detection Shut Off Device for a Portable Generator

December 2005 DRAFT A-3

Gas Analyzer

A portable unit that measures the level of carbon monoxide with an accuracy 

better than 1% of the instrument’s full scale based on a 0-2000 ppm range and a 

response time of at most 30 seconds for a 90% step change; the unit must also be 

capable of remote monitoring. 

3.0 SCOPE:

The testing is to demonstrate the prototype CO detection/shut off unit as 

incorporated with a generator by detecting CO and remotely shutting off the generator in 

an actual residence. The elevated levels of CO are to be generated by the portable 

generator in a confined space, such as a garage. The set-up and configuration of the 

testing to be conducted are for test purposes only and are inconsistent with correct and 

safe operation of a portable generator. 

4.0 GUIDELINES:

Monitored CO levels

 The level of CO in the test structure shall be monitored from the exterior of the 

test structure by two methods (residential CO alarm and a CO gas analyzer). The level of 

CO in the test structure shall be monitored in two areas of the test structure by residential 

CO alarms. 

 Operator(s)

 The operator(s) shall be at a minimum of 20 feet from the test structure during 

testing. The data acquisition system shall be located a minimum of 20 feet from the 

exterior of the test structure. The instrumentation and operator(s) shall be upwind or 

adjacent to the test structure during testing. DO NOT TEST if the instrumentation and 

operator(s) are downwind of the test structure. 

 Reentry

 The operator(s) shall reenter the test structure only when the CO concentration 

readings from both monitors are below 5 ppm. The operator(s) may enter CO monitor 

areas for less than 15 seconds if the CO levels are below 95 ppm. This 15-second period 

for concentrations below 95 ppm is within the OSHA PEL, NIOSH REL, and AGGIH 

TLV exposure limits for CO, as defined below. 
Page 4 of 7 

Version 1 

Date : August 2005 

Standard Operating Procedures 

For Assuring Minimum Carbon Monoxide Exposure 

Title: Guidelines and Procedures for Demonstration of a Remote Carbon 

Monoxide Detection Shut Off Device for a Portable Generator

A-4 DRAFT December 2005 

OSHA PEL 

The current Occupational Safety and Health Administration (OSHA) permissible 

exposure limit (PEL) for carbon monoxide is 50 parts per million (ppm) parts of air (55 

milligrams per cubic meter (mg/m(3))) as an 8-hour time-weighted average (TWA) 

concentration [29 CFR Table Z-1]. 

NIOSH REL 

The National Institute for Occupational Safety and Health (NIOSH) has established a 

recommended exposure limit (REL) for carbon monoxide of 35 ppm (40 mg/m(3)) as an 

8-hour TWA and 200 ppm (229 mg/m(3)) as a ceiling [NIOSH 1992]. 

ACGIH TLV 

The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned 

carbon monoxide a threshold limit value (TLV) of 25 ppm (29 mg/m(3)) as a TWA for a 

normal 8-hour workday and a 40-hour workweek [ACGIH 1994, p. 15]. 

 Remote Shut Off

 The generator shall be capable of being remotely shut off by two methods. One 

method must be a hand-held transmitter worn by the operator(s). 

 Effects of Carbon Monoxide

The operator(s) shall be familiar with the symptoms and effects of CO on a 

person. Signs and symptoms of acute exposure to carbon monoxide may include 

headache, flushing, nausea, vertigo, weakness, irritability, unconsciousness, and in 

persons with pre-existing heart disease and atherosclerosis, chest pain and leg pain. (U.S. 

Department of Labor, Occupational Safety & Health Administration) 

 Generator

 The gas tank will be filled with a maximum of 1⁄2 gallon of gas, limiting the run 

time to approximately 1 hour (7 gallons for 14 hours of operation) 

 Test Structure

 All doors to the test structure not visible by the operator(s) shall be locked to 

prevent persons from entering the test structure. The operator(s) shall carry keys to 

unlock any of the doors on the test structure. 

 
Page 5 of 7 

Version 1 

Date : August 2005 

Standard Operating Procedures 

For Assuring Minimum Carbon Monoxide Exposure 

Title: Guidelines and Procedures for Demonstration of a Remote Carbon 

Monoxide Detection Shut Off Device for a Portable Generator

December 2005 DRAFT A-5

5.0 PROCEDURES:

5.1 Initial Verification of Hardware Operation 

The operator(s) shall verify that the test instrumentation and prototype test 

units are operational. The gas analyzer shall not have a certification older than 5 

years. The wireless transmission of the shut off signal from the CO detection unit 

to the generator shall be tested by using the test button on the CO detection unit. 

The manual handheld transmitter for generator shut off shall be tested prior to any 

testing. 

5.2 Location of the CO source (generator) 

The portable generator shall be located in a test structure that allows easy 

ventilation of the test room, such as a garage. The test room or garage shall be 

equipped with remote ventilation, such as wireless garage door openers and 

fan(s). 

5.3 Location of the CO detection units 

The CO detection unit shall be located in areas of the test structure that 

provide accurate monitoring of CO levels in areas where operator(s) ingress and 

egress would result in potential exposures. 

5.4 Pre-Testing Safety Checklist 

a. Gas analyzer reading of CO level in the structure is below 5 ppm 

b. CO detection unit reading is zero 

c. Generator gasoline tank filled with maximum of 1⁄2 gallon of gasoline 

d. Instrumentation and data acquisition ready 

e. Verify no person in the test structure 

f. Zero gas analyzer before each test 

5.5 Post Testing Safety Checklist 

a. Generator has shut off 

b. Stop data acquisition 

c. Ventilate the test structure remotely 

d. Monitor CO levels in the test structure 
Page 6 of 7 

Version 1 

Date : August 2005 

Standard Operating Procedures 

For Assuring Minimum Carbon Monoxide Exposure 

Title: Guidelines and Procedures for Demonstration of a Remote Carbon 

Monoxide Detection Shut Off Device for a Portable Generator

A-6 DRAFT December 2005 

6.0 INSTRUMENTATION AND EQUIPMENT SET-UP:

The following is a list of instrumentations to be used in the testing: 

a. Residential Carbon Monoxide Alarm (AC powered with 9-volt 

battery back-up) 

b. NOVA Gas Analysis Equipment (Model 310WP) 

c. Data Translation (Model DT9834) 

d. Dell Laptop Computer (Model 5150) 

e. Fluke Current Probe (Model 80i-110s) 

f. Street Smart Technologies Wireless Automator (Model WA6R) 

g. Portable Generator (5250 watt) 

The following diagram is an illustration of the test set-up for testing the CO 

detection/shut off system and the portable generator. 

 

Closed

Ventilation Ventilation Ventilation

CO

CO CO

Data Acquisition System

Remote Ventilation System

Generator with

Shut-off Unit

CO Gas Analyzer

Display of CO

Levels

20 feet minimum

CO Detection Unit

Residential CO

Alarms

Viewing window of 

instrumentation

Test Structure
Page 7 of 7 

Version 1 

Date : August 2005 

Standard Operating Procedures 

For Assuring Minimum Carbon Monoxide Exposure 

Title: Guidelines and Procedures for Demonstration of a Remote Carbon 

Monoxide Detection Shut Off Device for a Portable Generator

December 2005 DRAFT A-7

7.0 EMERGENCY PROTOCOL:

Intervention for CO Poisoning

1. At first signs of CO poisoning symptoms, shut off the generator 

2. Go or move victim to a well-ventilated area 

3. Dial 911