The questions and answers found in this document were developed from a number of federal agencies, such as the Consumer Product Safety Commission (CPSC), U.S. Department of Energy's Pacific Northwest Laboratory (PNL), and the U.S. Environmental Protection Agency (EPA); the American Lung Association (ALA); and peer-reviewed scientific literature.

The primary source for each question and answer is specified and users are encouraged to obtain and review these references.

Since this a draft, the author would appreciate suggestions and comments to be sent to him at 1985 Buford Avenue (240), St. Paul, MN 55108-6134 or fax 612-625-3113 or E-mail wangell@che2.che.umn.edu

While the shortcomings of this document are the responsibility of the author, he thanks the following colleagues for their critique and suggestions: Tracy Washington Enger, U.S. Environmental Protection Agency (EPA); and Liz Wortman, American Lung Association of Hennepin County, Minnesota.

What is carbon monoxide (CO)?

Carbon monoxide (CO) is a colorless, odorless, and tasteless gas that is produced from the incomplete combustion of a fuel containing carbon such as charcoal, coal, kerosene, liquid petroleum (LP) gas, natural gas, oil, tobacco, and wood. It combines with hemoglobin (Hb) in the blood and prevents oxygen from being carried to the tissues of the body, causing asphyxiation. The attraction between CO and Hb is 200 times stronger than that of oxygen and Hb. The half-life of CO in the body is about five (5) hours.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003 and U.S. Environmental Protection Agency [1980] Significant Harm Levels for Carbon Monoxide, Research Triangle Park, NC, Office of Air Quality Planning and Standards).

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What are the effects or symptoms of CO poisoning?

Symptoms of carbon monoxide exposure at:
lower concentrations in healthy people include headaches, decreased alertness, dizziness, flu-like symptoms, nausea, fatigue, rapid breathing, confusion, disorientation, impaired judgment, and weakness as well as decreased learning ability in school children; lower concentrations in people with chronic heart disease include chest pain; and higher concentrations include coma and death.

The effects depend on the concentration of CO, the duration of the exposure, and the individual's activity level and health status as well as sensitivity. The elderly, fetuses, and persons with cardiovascular and pulmonary diseases are especially sensitive to elevated CO. Commonly, CO health effects are considered in terms of the percentage of CO in blood's hemoglobin, which is expressed as percent carboxyhemoglobin (% COHb). In the average nonsmoker, COHb is 1.5% or less (0.7% due to metabolism) while heavy smokers' COHb may be as high as 10%. Environmental tobacco smoke can raise COHb in a nonsmoker to 2 to 3%. No adverse health effects have been reported below 2% COHb. A level of 2.5% COHb will cause chest pain in persons suffering from angina pectoris and it can result from CO exposure at 50 parts per million (ppm) for 90 minutes or 15 ppm for 10 hours.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003; U.S. Environmental Protection Agency [1980] Significant Harm Levels for Carbon Monoxide, Research Triangle Park, NC, Office of Air Quality Planning and Standards; National Research Council [1977] Carbon Monoxide, Washington, DC, National Academy of Science, Committee on Medical and Biologic Effects; U.S. Environmental Protection Agency [1993] The Inside Story: A Guide to Indoor Air Quality, Washington, DC, EPA and Consumer Product Safety Commission, EPA 402-K-93-007; and U.S. Environmental Protection Agency, Indoor Air Pollution: An Introduction for Health Professionals, Washington, DC, EPA, American Lung Association, Consumer Product Safety Commission, and American Medical Association).

What are the health effects according to the concentration of CO?

First, for reference, 9 ppm average over 8 hours and 35 ppm average over 1 hour are the National Ambient (or outdoor) Air Quality Primary Standards in the U.S. In a healthy non-smoker, the approximate health effects of carbon monoxide exposure may be summarized as follows:

(Original source not specified; secondary source: Greiner, T.H. [1995] Carbon Monoxide Concentrations, Ames, IA, Iowa State University).

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Someone said there are no effects from 10% COHb; is this true?

This statement may relate to a study of active, healthy adults conducted by the U.S. Army and published in the early 1970s. As cited in Ritchie (1991), no health effects have been reported under 2 % carboxyhemoglobin (% COHb). Thus, the low range of COHb from 2 to 10 % carries some risk, especially in populations at greater sensitivity than healthy, active adults. The Army data may be summarized as follows:

-10 % COHb no effect
-15 % COHb slight headache
-20 % COHb headache
-25 % COHb headache and nausea
-30 % COHb drowsy
-35 % COHb vomiting
-40 % COHb collapse
-45 % COHb coma and permanent brain damage
-50 % COHb permanent brain damage, death

(Primary citation not available; secondary source: Patty, P. [1995] Carbon Monoxide Detectors, On The Mark, Northbrook, IL, Underwriters Laboratory, Fall: 9-14 and Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003).

What should be done if someone suspects they are exposed to elevated indoor CO?

First, they and anyone else in the space should get fresh air outdoors immediately. However, victims may need help since it is often difficult for them to respond in rational ways due to the decreased alertness, dizziness, fatigue, confusion, disorientation, impaired judgment, and weakness that is brought on by exposure to carbon monoxide. Next, the victims or responders should contact a health care provider as soon as possible---even if the victims are feeling better--- and inform the provider that they suspect the victims have symptoms of carbon monoxide poisoning. Prompt medical attention is needed for proper diagnosis of CO poisoning. If a victim is unconscious, perform CPR. The health care provider may take a blood sample to measure carbon monoxide in the victim's blood. Finally, have combustion appliances in the home inspected and serviced if a problem is suspected.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, CPSC, U.S. Environmental Protection Agency, and American Lung Association).

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What is the concentration of CO commonly found indoors?

The indoor concentrations of carbon monoxide vary widely depending on sources and occupant patterns of use. Concentrations of 1 to 2 parts per million (ppm) may be found in houses with a normally operating gas furnace to well over 1,000 ppm in houses with a faulty furnace. Thirty-five (35) to 120 ppm have been reported after 20 minutes of operation of four burners on a gas stove. Kerosene space heaters can produce over 20 ppm. An unvented gas heater in a 1,150 square foot test house was found to produce almost 90 ppm.

(Ritchie, I.M. and Oatman, L.A. [1983] Residential Air Pollution from Kerosene Heaters, Journal of the Air Pollution Control Association, 33, 91: 879-881; Sterling, T.D. and Sterling, E. [1979] Carbon Monoxide Levels in Kitchens and Homes with Gas Cookers, Journal of the Air Pollution Control Association, 29, 3:238-241; and Traynor, G.W., Girman, J.R., Allen, J.R., Apte, A.R., Carruthers, J.F., Dillworth, J.F. and Martin, V.M. [1983] Indoor Air Pollution Due to Emissions from Unvented Gas-Fired Space Heaters, Berkeley, CA, Lawrence Berkeley Laboratory, LBL-15878).

What is the concentration of CO commonly found outdoors?

Unless next to a major highway or street, outdoor carbon monoxide generally will not exceed 1 or 2 ppm* (at the lower limit of detectability for many measurement methods). EPA's National Ambient Air Quality Standard (NAAQS) for carbon monoxide is that 9 ppm should not be exceeded more than once a year.

(U.S. Environmental Protection Agency National Primary and Secondary Ambient Air Quality Standards, Code of Federal Register, Title 40, Part 50 (40CFR50), Washington, DC, EPA).

A large portion of the population over 40 years old, as much as half, has heart conditions that leave them susceptible to adverse health effects associated with carbon monoxide commonly found in urban air (note: ambient air carbon monoxide concentrations have significantly declined over time and this proportion has likely declined significantly).

(U.S. Environmental Protection Agency [1980] Significant Harm Levels for Carbon Monoxide, Research Triangle Park, NC, Office of Air Quality Planning and Standards).

Is there an association between outdoor carbon monoxide levels and heart failure?

Yes, according to an epidemiological study of daily hospital admissions for congestive heart failure among Medicare recipients over the four-year period from 1986 through 1989 and the maximum daily ambient carbon monoxide in seven U.S. cities selected to reflect different climate and pollution patterns. The relative risks of hospital admissions for congestive heart failure for a 10 ppm increase in the daily maximum outdoor concentrations of carbon monoxide were: +36% in Los Angeles; +29% in Chicago and Milwaukee; +24% in Detroit; +17% in Philadelphia; +11% in Houston; and +10% in New York.

(Morris, R.D., Naumova, E.N. and Munasinghe [1995] Ambient Air Pollution and Hospitalization for Congestive Heart Failure among Elderly People in Seven Large US Cities, American Journal of Public Health, 85, 10 [October]: 1361-1365.)

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Are pets effected by CO in the home?

Yes, pets require oxygen just like humans and their health may be adversely by exposure to carbon monoxide. Often pets spend more time in the home than their human companions and therefore may show symptoms of carbon monoxide poisoning before humans, although they can't verbalize their symptoms. However, I have not searched the literature on this question and I would welcome any input from colleagues.

How many people die of CO poisoning each year in the United States?

The answer to this question is uncertain since the number of deaths will vary from year to year and some carbon monoxide related deaths may not be diagnosed as such. For example, heart failure is diagnosed as the leading cause of death in the U.S. and unknown portion of these may be directly or indirectly be due to carbon monoxide, such as congestive heart failure among the elderly. According to an examination of National Center for Health Statistics death certificate reports from 1979 to 1988, the 10-year average of carbon monoxide deaths was 5,613 per year.

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 [August 7], 659-663 and U.S. Environmental Protection Agency [1980] Significant Harm Levels for Carbon Monoxide, Research Triangle Park, NC, Office of Air Quality Planning and Standards).

What are the causes of CO deaths in the U.S.?

Investigators examined 56,133 National Center for Health Statistics death certificate reports from 1979 to 1988 that implicated carbon monoxide as a contributing cause of death and found that the classifications were that:

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

Where does CO rank compared to other unintentional deaths from poisoning?

In the 10-year period from 1979 through 1988, there were 40,424 U.S. death certificate reports for all poisonings of which carbon monoxide was the largest (11,547 or 29%) followed by heroin overdoses (5,948 or 15%).

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

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What are the causes of unintentional and nonfire-related CO deaths in the U.S.?

Investigators examined 11,547 National Center for Health Statistics death certificate reports from 1979 to 1988 that implicated carbon monoxide as a contributing cause of death and that were classified as unintentional as well as not fire-related and found that motor vehicle exhaust caused 6,552 deaths (57%), most of which were stationary automobiles (5,452 or 83% of 6,552); and nonvehicle sources caused 4,995 deaths (43%) including 2,302 deaths (46% of 4,995) for which the source is not specified.

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

Within the home, is there a profile of the types of combustion appliances and fuels that have been associated with CO deaths?

Of the 2,693 unintentional, nonfire-related, and nonvehicle-related deaths reported by Cobb and Etzel from 1979 through 1988:

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

Another perspective is provided by Girman who analyzed Consumer Safety Product Commission (CPSC) in-depth investigations of 121 carbon monoxide deaths and 254 injuries from October 1991 through September 1992.

Girman found that 68% of the deaths and 96% of the injuries were in permanent residences including apartments, houses, and mobile homes, while 32% of the deaths were in temporary residences including vehicles, tents, and cabins. In temporary residences, the source of the CO was a heater or a stove used to heat and not vehicle exhaust.

Overall, 81% of the deaths were due to furnaces and room heaters and 82% of the injuries were due to furnaces and water heaters; in comparison, 56% of the deaths in permanent residences were due to furnaces and 25% were due to room heaters. Victims were generally located in bedrooms or living rooms and many were overcome in their sleep and never got out of bed.

(Girman, J. [1994] Perspectives on CO Poisoning in the U.S., Paper Presented at Workshop on Carbon Monoxide Detectors, Washington, DC, U.S. Environmental Protection Agency (June 2) and Long, K. and Saltzman, L. (1995) Nonfire-Related Carbon Monoxide Incidents: Morbidity and Mortality Related to the Use of Household Appliances, Washington, DC, U.S. Consumer Product Safety Commission).

Girman also profiled the percentage of 252 carbon monoxide deaths by fuel and combustion appliances in 1991 in California:

27% gas space heater
5% wood or coal stove
1% oil heat
21% gas furnace
4% gas water heater
1% solid fuel generator
14% solid fuel grill
3% coal furnace
1% gas refrigerator
9% gas stove
2% gas lantern
9% kerosene heater
2% chimney

(Girman, J.R., Chang, Y., Hayward, S.B. and Liu, K. (1993) Causes of Unintentional Deaths from Carbon Monoxide Poisonings in California, Berkeley, CA, California Department of Health Services).

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Are some people more affected by exposure to CO than others?

Although the extent to which anyone is affected depends on physiology, exercise, and exposure patterns, those persons with conditions of pre-existing oxygen debt (e.g., anemia, asthma, angina, and the unborn) and heart disease as well as smokers are among those at greater risk of carbon monoxide exposure.

(U.S. Environmental Protection Agency [1980] Significant Harm Levels for Carbon Monoxide, Research Triangle Park, NC, Office of Air Quality Planning and Standards).

Males, blacks, and people over 75 years of age have higher rates of unintentional and nonfire-related deaths from carbon monoxide in the U.S. between 1979 and 1988. While the death rate for the overall population averaged 0.51 per 100,000 people per year, the rate was:

0.78 for males and 0.26 for females;
0.63 for blacks and 0.51 for whites; and
0.9 to 1.2 for people 75 and older compared to 0.17 for children under 15 years of age.

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

Also, male deaths were twice those of females in Consumer Safety Product Commission (CPSC) in-depth investigations of 121 carbon monoxide deaths and 254 injuries from October 1991 through September 1992. In cabins, tents, vehicles and other temporary residences, the number of deaths for males was 15 times greater than that of females.

(Long, K. and Saltzman, L. (1995) Nonfire-Related Carbon Monoxide Incidents: Morbidity and Mortality Related to the Use of Household Appliances, Washington, DC, U.S. Consumer Product Safety Commission).

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Do unintentional, nonfire-related CO deaths vary by geographic region of the U.S.?

The highest unintentional, nonfire-related carbon monoxide death rate from 1979 through 1988 was in the cold, plains, and high altitude states while the lowest rate was in the Atlantic, Gulf, and Pacific coast states. Alaska had the highest rate (2.72 per 100,000) while Hawaii (0.05) had the lowest followed by California (0.25). Georgia ranked 24th from the lowest death rate (0.5) while New Jersey ranked 8th (0.34) and Minnesota ranked 39th (0.78).

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

Do unintentional, nonfire-related CO deaths vary by season of the year?

The pattern of unintentional, nonfire-related CO deaths in the U.S. was strongly seasonal from 1979 through 1988 with an average of four times as many deaths in January (181) as July (44).

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

A similar pattern, but with a December peak, was observed over a 10 year period in California especially for combustion appliances including wall and floor heaters, space heaters, furnaces, and water heaters as well as vehicle exhaust and grills or hibachis.

(Girman, J.R., Chang, Y., Hayward, S.B. and Liu, K. (1993) Causes of Unintentional Deaths from Carbon Monoxide Poisonings in California, Berkeley, CA, California Department of Health Services).

Is there a trend in overall CO fatalities? Is the number of CO deaths increasing or decreasing?

The number and rate of unintentional, nonfire-related carbon monoxide deaths in the U.S. from 1979 through 1988 appear to be decreasing from 1,513 or 0.67 per 100,000 persons to 878 or 0.39 per 100,000. This trend was found for both vehicle and nonvehicle causes.

(Cobb, N. and Etzel, R.A. [1991] Unintentional Carbon Monoxide-Related Deaths in the United States, 1979 Through 1988, JAMA, 266, 5 (August 7), 659-663).

How many people are poisoned from CO each year?

According to 1993 data from 64 poison control centers serving about 70% of the U.S. population in 43 states and the District of Columbia, there were 12,879 exposures to carbon monoxide of which 12,553 were unintentional. Of the 12,553 unintentional CO exposures there were 11 deaths which suggest that carbon monoxide exposure may be 1000 times more common than carbon monoxide deaths.

(Litovitz, T.B., Clark, L.R. and Soloway, R.A. 1993 Annual Report of the American Association of Poison Control Centers Toxic Exposure Surveillance System, American Journal of Emergency Medicine, 12, 5: 546-584).

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What about idling automobiles in attached garages and carports?

It would be wise to avoid warming up automobiles or running lawn mowers, snowblowers, and other fuel burning appliances or equipment in attached carports and garages---even with the garage door open. Also, it would be wise to weatherstrip doors between the house and attached carport and garage as well as to caulk other openings between the house and the garage or carport.

How can CO problems be prevented through combustion appliance maintenance?

You should have your combustion appliances regularly inspected, serviced, and maintained. Combustion appliances are those that burn natural gas, liquid petroleum (LP) gas, oil, kerosene, coal, oil, or other fuel for heating, cooking, light, power, and decorative purposes including space heaters, ranges, ovens, stoves, fireplaces, furnaces and boilers, water heaters, clothes dryers, lanterns, grills, lawn mowers, snow blowers, generators, and other small engines. In addition, have the chimney or flue inspected when replacing or adding vented appliances---those that use a chimney, flue, or other means to carry combustion pollutants out of the home.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

How can CO problems be prevented through combustion appliance selection?

The U.S. Consumer Product Safety Commission, U.S. Environmental Protection Agency, and American Lung Association recommend that you consider a number of factors when selecting appliances that burn natural gas, liquid petroleum (LP) gas, oil, kerosene, coal, oil, or other fuel for heating, cooking, light, power, and decorative purposes including space heaters, ranges, ovens, stoves, fireplaces, furnaces and boilers, water heaters, clothes dryers, lanterns, grills, lawn mowers, snow blowers, generators, and other small engines.

1.Choose vented over nonvented appliances whenever possible.
2.Buy appliances that are certified to meet current safety standards by groups such as the Underwriters Laboratory (UL) or the American Gas Association (AGA).
3.Make sure vented gas heaters have an industry required carbon monoxide shut-off device.
4.If you are considering buying an unvented space heater, check to see if they are allowed by your building, fire, and housing codes.
5.Although it is best to buy vented appliances whenever possible, if you do buy an unvented space heater, purchase one manufactured after 1982 which has an oxygen depletion switch (ODS).
6.If buying a gas appliance, purchase one with an electronic ignition rather than pilot lights.
7.If buying a heater, make sure it is the correct size for the area you wish to heat.
8.If you are buying a wood stove, make sure it is EPA-certified to limit pollution.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

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What is an oxygen depletion sensor (ODS)?

An oxygen depletion sensor (ODS) is a safety device designed to shut a space heater off when there is limited amount of oxygen to support combustion without producing large amounts of carbon monoxide. ODSs are found in space heaters manufactured after 1982. Generally, older space heaters do not have this safety device.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

How can CO problems be prevented through proper combustion appliance installation?

Combustion appliances should be installed by a professional following installation instructions, industry standards, and relevant building and mechanical codes. With vented appliances, chimneys, flues, and vents should be inspected and the appliance should be checked for backdrafting and unacceptable combustion spillage.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

What is combustion spillage and what amount of combustion spillage is acceptable?

Combustion spillage is the unintended flow of products from a combustion appliance or its venting system into the occupied space. Spillage is common at the start-up of traditional appliances that rely upon thermal buoyancy to carry combustion products up a chimney or flue (sometimes called vents). The length of time that is required to establish proper drafting of combustion products out of the home should be as brief as possible. However, there is no explicit definition for how much spillage is acceptable. Combustion spillage is uncommon with properly installed closed combustion or draft-induced combustion appliances.

(Nagda, N.L., Krug, R.W., Koontz, M.D. and Stoltz, S.V. [1995] Depressurization, Backdrafting and Spillage from Vented Gas Appliances--A Literature Review, Chicago, IL, Gas Research Institute).

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What is backdrafting?

Backdrafting is the unintended flow of outdoor air down a chimney or vent due to depressurization of the space where the combustion appliance is located in relation to the top of the chimney or flue resulting in the spillage of combustion products indoors. Backdrafting is uncommon with properly installed closed combustion or draft-induced combustion appliances. Backdrafting is more common when the combustion appliance has been off and the chimney or flue is cold.

Depressurization may result from a number of variables, such as

1.use of another combustion appliance such as a fireplace or woodburning stove;
2.use of a high power range exhaust fan and/or a combination of exhaust devices such as clothes dryers, central vacuum systems, and attic fans; and
3.leaky ducts in forced air heating and cooling systems.

(Dumont, R.S. and Snodgrass, A. [1990] Investigation of Chimney Backflow Conditions: A Case Study in a Well-Sealed House, ASHRAE Transactions, 96, 1, 3305 and Fugler, D.W. [1989] Canadian Residential Combustion Spillage Monitoring, ASHRAE Transactions, 95, 1, 3209).

Is there any special concern about backdrafting of fireplaces?

There are several concerns about fireplaces that users should consider. First, a roaring fire requires a lot of oxygen to support the combustion. In airtight houses that do not have combustion air supplied from the outdoors directly to the fire, there is a risk that the combustion air for the fireplace could come down the flue or chimney of the furnace or boiler and water heater. In these cases, the furnace or boiler and water heater could backdraft and spill combustion products indoors. Second, when the fire burns down to coals, it produces less heat to support venting combustion products to the outdoors and it becomes a very effective producer of carbon monoxide. Thus, the fireplace is more likely to backdraft and to spill carbon monoxide indoors. This risk increases if the damper is partially or completely closed before the fire is completely out.

If there is combustion spillage or backdrafting, is there a carbon monoxide problem?

Simple combustion spillage or backdrafting induced spillage does not necessarily produce an indoor carbon monoxide problem. However, simple spillage or, more importantly, backdraft induced spillage establishes one of the conditions that can produce a carbon monoxide problem. The other condition that is required is that the burner must actually be producing carbon monoxide.

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How can CO problems be prevented through appliance use?

Read and follow the instructions and warning labels for all combustion appliances in your home. For example, some unvented space heaters will caution you to use them only in a well-ventilated area. If you use a kerosene heater, use the correct fuel: ASTM 1-K kerosene. In fireplaces or wood stoves, use seasoned hardwoods that burn cleaner and produce less creosote and smoke than softwoods or unseasoned wood. Never close the damper on a fireplace before the coals are completely burned out. The coals are effective carbon monoxide producers. Never burn preservative treated wood or painted wood, plastics, charcoal, or colored paper in a fireplace or stove. Never use a gas stove, oven, or clothes dryer to heat your home. Never use an unvented space heater overnight or in a room where you sleep.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

Are there any special considerations for the use of unvented space heaters?

It is better to use vented combustion appliances to heat your home rather than unvented space heaters. However, if you do use an unvented kerosene space heater, use one manufactured after 1982 which has an oxygen depletion switch (ODS). Also, in order supply air for combustion and to dilute combustion pollutant concentrations, always keep doors open to the rest of the house or apartment and crack a window open in the room where you are using the unvented gas or kerosene heater. In addition, you should never use an unvented combustion heater overnight or when you are sleeping.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

Are there any special concerns about the use of a gas range and/or oven for space heating?

You should never use gas range or oven for space heating---even in a power outage.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

Are there any special concerns about the use of unvented gas clothes dryer to heat or humidify the home?

You should never use a clothes dryer to heat or humidify your home for at least two reasons: first, the products of combustion as well as vaporized laundry products are dumped indoors where occupants may be exposed; and second, significant amounts of water vapor are released indoors which increases the chances of damage and mold contamination from excessive condensation.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

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What signs might indicate improper appliance operation or other CO problems?

Sometimes, an increase in window condensation may indicate a combustion spillage problem. Also, with oil or wood burning appliances---but not usually gas-fired appliances---the odor of combustion may indicate a problem. Other signs may include subtle health symptoms that occur only in the home (or car) and that decrease when you or other household members leave the home and redevelop when you return, for example: headaches, dizziness, sleepiness, watery eyes, coughing, or nose or throat irritation.

(U.S. Consumer Product Safety Commission [1994] What You Should Know About Combustion Appliances and Indoor Air Pollution, Washington, DC, U.S. Environmental Protection Agency and American Lung Association).

What are the EPA, CPSC, and other federal agencies doing about CO?

The U.S. Environmental Protection Agency (EPA) has worked with states and local units of government as well as automobile and wood stove manufacturers to significantly reduce ambient or outdoor levels of carbon monoxide. Also, the EPA has initiated an indoor air program that emphasizes control of pollutants such as tobacco smoke. Since 1989, the Consumer Product Safety Commission (CPSC) has encouraged the Underwriters Laboratory (UL) to develop a standard for nonindustrial carbon monoxide detectors. Since 1992, CPSC has encouraged installation of carbon monoxide detectors in every home. For more than two decades, the CPSC has monitored and investigated the safety of combustion appliances used in the home and has advocated improvements in the design and use of these appliances. Both the EPA and CPSC are working with various groups on voluntary standards for carbon monoxide alarms. The U.S. Department of Energy (DOE) has supported a building-related research effort that includes indoor air quality and combustion safety in energy-efficient housing.

What are the limitations of medical diagnosis?

The reported number of emergency room treatments for nonintentional and nonfire-related carbon monoxide poisoning is widely believed to under-represent the incidence of the problem for a variety of reason. Many victims associate their symptoms with the flu or a cause other than CO and medical attention may focus upon the more immediate symptom, such as heart failure, and not the underlying cause.

(Brennan, T. [forthcoming] Report on a Search of the Medical Literature for Topics Related to Indoor Carbon Monoxide, Richland, WA, U.S. Department of Energy-Battelle Pacific Northwest Laboratories).

What are the limitations of diagnosis by service technicians?

Some carbon monoxide events may be very transient, for example caused by a very specific series of factors such as: wind direction and speed; operation of various exhaust devices; operation of combustion cooking appliances; closing or opening of various doors in the home; outdoor temperature; and combinations of these factors. For example, the Underwriters Laboratory indicated it has received reports that the number of carbon monoxide alarms is significantly higher on days when wind is gusty (and chimney or combustion appliances backdraft). Thus, it is possible that a technician may not detect a problem even though it exists; this is called a "false negative."

(Patty, P. [1995] Carbon Monoxide Detectors, On The Mark, Northbrook, IL, Underwriters Laboratory, Fall: 9-14).

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What are the standards for CO? Is there a safe level of CO?

Professional standards and government guidelines call for carbon monoxide during any 12-month period to be less than 9 ppm (0.0009%) for exposures in living areas for an 8-hour average; and not to exceed an 35 ppm (0.0035%) average during any one-hour period.

These guidelines may not provide sufficient protection for individuals who are chronically ill with lung or heart problems. Although there is no known safe level of carbon monoxide, there are background levels in the outdoors that are beyond the individual's immediate control.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003).

How can CO be detected or measured?

There are a variety of measurement methods available including electrochemical where electrical changes caused by chemical reactions are measured, and colorimetry where the color of a reagent changes by chemical reaction.

The costs for carbon monoxide monitors range from a few dollars for disposable colorimetric badges to thousands of dollars for some portable scientific monitors. A summary of measurement methods, costs, and manufacturers is found in Ritchie, 1991.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003).

What proportion of deaths could be prevented by CO detectors and at what cost?

In California, Girman, et al. estimated that a carbon monoxide detector in every residence would reduce unintentional CO deaths by 35% at an estimated cost of $14 million per life saved and that a carbon monoxide detector in every vehicle would reduce unintentional CO deaths by another 35% at an estimated cost of $27 million per life saved.

(Girman, J.R., Chang, Y., Hayward, S.B. and Liu, K. (1993) Causes of Unintentional Deaths from Carbon Monoxide Poisonings in California, Berkeley, CA, California Department of Health Services).

What CO detectors are available for use in the home?

Before buying a carbon monoxide detector, remember a detector does not reduce the importance of a regular inspection of heating system by a qualified serviceperson. There are a number of carbon monoxide detectors intended for home or recreational vehicle use that have come on the market in the past few years. There are both 110-volt AC (plug-in and hard-wired) and battery powered detectors that sound an 85 decibel alarm in the presence of certain concentrations of CO over pre-set periods of time, for example according to Underwriters Laboratory Standard 2034 effective October 1, 1995, within 90 minutes at 100 ppm, within 35 minutes at 200 ppm, and within 15 minutes at 400 ppm.

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Has "Consumer Reports" tested CO detectors that are available and what do they cost?

Yes, Consumer Reports tested carbon monoxide detectors and reported their test results in May 1994 on pages 334-336. The criteria that Consumer Reports used included: response time to various levels of carbon monoxide; response time when re-exposed to low concentrations of carbon monoxide; the ease to manually silence the alarm the cost and/or difficulty of replacing sensors if needed; Underwaters Laboratory listing; and warranty. The cost of the detectors Consumer Reports tested were in the $50 to $80 range. Since that time, changes may have been made in the detectors, so use the article as only one piece of information. One important change is that some detectors have digital displays of carbon monoxide levels.

There is a July, 1995 Consumers Report update on carbon monoxide detectors (pages 466-467). The highest rated detector cost $40 and it was an 110-volt AC-powered plug-in unit with a digital display of carbon monoxide levels. However, none of the detectors listed in the July, 1995 Consumers Report article meet the revised Underwriters Laboratory Standard 2034 effective October 1, 1995.

What about battery-powered versus AC-powered detectors?

The two options have both advantages and disadvantages. For example, a battery-operated but not an AC-powered detector has the ability to detect carbon monoxide during power outages. However, a battery-operated detector will not perform if batteries are removed or rundown batteries are not replaced; this is not an issue of AC-powered detectors. A CO detector that uses AC with a battery back-up would offer an advantage over a detector that is solely AC or battery.

Are there less expensive detectors and, if so, what are their limitations?

Yes, there are passive (meaning no power required) colorimetric sensors that are intended to change color when exposed to high levels of carbon monoxide. These sensors cost from about $5 to $15. However, Consumer Reports exposed three colorimetric sensors to 100 ppm of carbon monoxide for two hours and only one changed color. Also, none of the passive sensors sound alarms and, thus, none are capable of alerting someone who may be asleep or in another area of the home. Consumer Reports rated the three passive sensors as unacceptable for home use.

(Carbon Monoxide Detectors: Alerts to a Deadly Gas, Consumers Reports, May, 1994, 334-336).

Are there standards that CO detectors must meet?

Since 1992, there has been voluntary standard UL 2034 developed by Underwriters Laboratory in consultation with industry. In some cases, this standard may be required by some local ordinances or state statutes. UL 2034 establishes maximum response times at three different concentrations intended to be equivalent to 10 % COHb, for example: 100 ppm for a maximum of 90 minutes; 200 ppm for a maximum of 35 minutes; and 400 ppm for a maximum of 15 minutes. In addition, UL 2034 requires that UL-listed CO detectors ignore carbon monoxide concentrations of 15 ppm for 30 days (an unhealthy level that may occasionally occur in urban outdoor air in violation of national ambient air standards). Also, UL 2034 requires that CO detectors not sound an alarm when exposed to 35 ppm of carbon monoxide for one hour followed by exposure to six hours of "fresh" air and then another hour of 35 ppm. This requirement is intended to avoid alarms related to high CO concentrations near highways during "rush hour."

(Patty, P. [1995] Carbon Monoxide Detectors, On The Mark, Northbrook, IL, Underwriters Laboratory, Fall: 9-14).

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Where should a CO detector be located?

The Consumer Product Safety Commission (CPSC) recommends that every home have at least one carbon monoxide detector, preferably located outside the bedrooms. Some manufacturers recommend one CO detector for each floor of the home. The Underwriters Laboratory recommends placing CO detectors within the hearing range of each sleeping area, near but not directly above combustion appliances such as furnaces and water heaters, near fireplaces, and in the garage. CO detectors should not be located within five (5) feet of kitchen stoves and ovens. The detector may be placed near the floor or near the ceiling since CO has nearly the same density as air. The detectors are sensitive to common household chemicals such as cleaners and bleach and, thus, should not be placed near where these chemicals are stored or used.

(Patty, P. [1995] Carbon Monoxide Detectors, On The Mark, Northbrook, IL, Underwriters Laboratory, Fall: 9-14).

If I have a smoke detector, do I really need a CO detector?

Smoke detectors and CO detectors are designed to protect against different hazards; therefore, you should notfeel one is a substitute for the other.

Do CO detectors require any maintenance?

Yes, carbon monoxide detectors should be regularly cleaned and tested as recommended by the manufacturer. In addition, if the detector is battery powered, the batteries should be replaced yearly or when recommended by the manufacturer.

Would providing passive combustion air supply to a fireplace, furnace or boiler, wood stove, or water heater to prevent backdrafting?

Some building codes require that passive (meaning no fan) outdoor air be supplied to traditional fireplaces, furnaces, boilers, wood stoves, and water heaters that rely on the heat from combustion instead of a fan to carry combustion products outdoors. While passive combustion air supplies can help in many cases, they are not always sufficient in very airtight houses when the wind is blowing on the side of the house opposite the intake for the combustion air supply. Also, many passive combustion air supplies are blocked by occupants for a variety of reasons including thermal discomfort. White, for example, estimates 80% of Ottawa, Ontario, Canada homes have combustion air supplies blocked during several months of the beginning of the heating season. Many building scientists believe it is preferable to spend slightly more for higher efficiency, closed combustion or induced draft combustion appliances when possible (both use a fan to exhaust combustion products outside the home).

(White, J.H. [1994] Combustion Spillage: A Primer, Minneapolis, MN, Minnesota Building Research Center).

Why should I spend more to buy a closed combustion furnace or boiler compared to a conventional furnace or water heater?

Closed combustion furnaces, boilers, and water heaters offer a number of advantages: 1) they are more energy-efficient and will reduce your energy costs year after year; and 2) they are safer since they remove combustion from the air you breath in your home.

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Will residential air cleaners or high-efficiency filters correct a CO problem in a home?

No, residential air cleaning devices and filters are commonly used to remove particles and usually have no effect on gaseous contaminants such as carbon monoxide. Source control is the strategy that should be used to prevent or to correct a carbon monoxide or related combustion pollutant problem.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003; U.S. Environmental Protection Agency [1993] The Inside Story: A Guide to Indoor Air Quality, Washington, DC, EPA).

In general, why should I care about the quality of air in my home?

In the last few years, there has been increasing scientific evidence that the air in our homes can be more seriously polluted than the outdoor air in industrialized cities. Furthermore, we spend, on the average, about 90 percent of our time indoors with the greatest portion of this time in our homes. Thus, the risk to health due to air pollution is, for most people, greater indoors than outdoors. In addition, some people who are most likely to be exposed to indoor pollutants for the longer periods of time are often those more susceptible to the effects of air-borne pollutants. Populations at higher risk include infants and young children, the elderly, and the chronically ill.

What does it take to have an indoor air quality problem?

It takes a combination of three factors to have an indoor air quality problem and if you remove any of the factors you resolve the problem: 1) there must be a source of the pollutant; 2) there must be an occupant to be exposed; and 3) there must be a pathway and physical driving force that connects pollutant source and the occupant. Some indoor air professionals refer to these three factors as the indoor air quality triangle.

Besides CO, are there other common combustion pollutants?

Yes, in addition to heat and light, fuel combustion gives off a wide range of contaminates including those that are irritants, carcinogens, teratogens, and mutagens. The combustion of natural gas primarily produces carbon dioxide, water vapor, and nitrogen oxides as well as carbon monoxide. In addition, the combustion of kerosene also produces sulfur and particulates including polycyclic aromatic hydrocarbons. The combustion of coal, tobacco, and wood adds aldehydes, various polycyclic aromatic hydrocarbons, and other pollutants to those already listed.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003).

What are the health effects of carbon dioxide?

Carbon dioxide (CO2) is a colorless, odorless gas that can cause asphyxiation at high levels and headaches, dizziness, and nausea at lower concentrations.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003).

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What are the health effects of nitrogen dioxide?

Nitrogen dioxide (NO2) is produced from combustion of fossil fuels. It is a corrosive and highly oxidizing gas that has a pungent odor that is a deep lung irritant. NO2 may adversely effect lung functioning in asthmatics and individuals with lung disease as well as increase risk of respiratory infections, especially in young children.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003; and U.S. Environmental Protection Agency, Indoor Air Pollution: An Introduction for Health Professionals, Washington, DC, EPA, American Lung Association, Consumer Product Safety Commission, and American Medical Association).

What are the health effects of particles from combustion?

Airborne particulates can be important in homes where there is environmental tobacco smoke (ETS) or where kerosene or wood is burned. Particulates in ETS have been associated with impaired breathing, lung disease, aggravation to existing lung and heart diseases, changes to the immune system, and lowered defenses against inhaled particles. Polynuclear or polycyclic aromatic hydrocarbons (PAH) are produced when kerosene or wood is burned. They are potentially cancer causing in humans.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003; and U.S. Environmental Protection Agency, Indoor Air Pollution: An Introduction for Health Professionals, Washington, DC, EPA, American Lung Association, Consumer Product Safety Commission, and American Medical Association).

What are the health effects of sulfur dioxide?

Sulfur dioxide (SO2) is a colorless gas with a strong pungent odor. It is a strong eye and upper respiratory tract irritant. Brief SO2 exposure creates breathing problems for asthmatics at low concentrations and for healthy persons at higher concentrations.

(Ritchie, I. [1991] Introduction to Indoor Air Quality: A Reference Manual, Washington, DC, U.S. Environmental Protection Agency, EPA/400-3-91-003; and U.S. Environmental Protection Agency, Indoor Air Pollution: An Introduction for Health Professionals, Washington, DC, EPA, American Lung Association, Consumer Product Safety Commission, and American Medical Association).

What are the health effects of water vapor from combustion?

Vast amounts of water vapor are produced from combustion (for example, 10 gallons of water from 1000 cubic feet of gas burned!) and, while water vapor is generally not considered a pollutant, it can cause excessive humidities that support the growth of biological pollutants such as dust mites and molds. Biological contaminates can produce a number of adverse health reactions including upper and lower respiratory irritations and difficulties, exacerbation of asthma, and allergic reactions.

(U.S. Environmental Protection Agency, Indoor Air Pollution: An Introduction for Health Professionals, Washington, DC, EPA, American Lung Association, Consumer Product Safety Commission, and American Medical Association).

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What are the health effects of unburned hydrocarbons and aldehydes?

I haven't found anything to speak of in the literature about the health effects of unburned hydrocarbons and aldehydes. Hydrocarbons include methane (natural gas) and other organic compounds that contain only carbon and hydrogen. Aldehydes are highly reactive organic chemical compounds.

Dwellings

Are apartments more likely have higher concentrations of carbon monoxide?

Good question, but I'm not aware of literature that directly addresses this question. There is, however, evidence that outdoor or ambient concentrations of carbon monoxide are the highest adjacent to the busiest streets where it is more likely locate apartments and other multi-family dwellings. Thus, it makes sense to believe apartment and other residents of multi-family dwellings could have greater exposure to carbon monoxide.

Do apartments over garages have higher concentrations of carbon monoxide than other apartments?

Once again this is a good question for which I am not aware of published data that provide a strong answer. There is clearly a source of carbon monoxide in this situation: automobile emissions. However, there is usually a fair amount of effort made to isolate the garage from the living space for fire protection. Despite any such effort, we know that unplanned pathways are built into almost all buildings, or they develop over time. In addition to having, ideally, an airtight barrier, enclosed garages are commonly ventilated in a way that both dilutes garage carbon monoxide and controls an important driving force by lowering the air pressure in the garage in relation to the apartments. However, fans are not always maintained or they are shutoff and thus this protection may be lost.

Are apartments that are next to boiler rooms more likely to have higher concentrations of carbon monoxide than other apartments?

There are no published data to answer this question, although I know of a case where a resident in an apartment, which was located above a boiler room in a building with steam or hot water heat, had carbon monoxide poisoning while residents with apartments away from the boiler room had no apparent symptoms.

What if I have no choice but to use my gas stove for heat since the landlord will not provide sufficient heat?

Most cities have housing codes that require that landlords to provide a minimum amount of heat during the heating season. If the landlord fails to respond to requests to provide heat, you should contact your city's housing inspections department or use an electric heater rather than using a gas kitchen stove or oven for heating.

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