Many heating appliances rely on combustion of carbon-based fuels and therefore are potential sources of health-threatening indoor air pollution. Most combustion heating appliances are vented to the outside of buildings to facilitate removal of the products of combustion, which include carbon monoxide (CO), carbon dioxide, nitrogen dioxide, and water vapor (1). However, some combustion heating devices may be unvented (e.g., kerosene- and propane-fueled space heaters, some gas-fueled log sets, and cooking devices used improperly for heating), and the use of such unvented devices in closed settings may be associated with risks for exposure to toxic gases and other emissions. This report presents an analysis of data from the Third National Health and Nutrition Examination Survey (NHANES III) to estimate the number and regional distribution of adults using unvented residential heating appliances and stoves or ovens misused as heating devices in the United States during 1988-1994. The findings indicate that the percentage of adults using these devices was higher in the South, among low-income groups, among blacks, and among rural residents, and underscore the need for public education about the health risks associated with exposure to elevated levels of combustion by-products.

NHANES III collected data from approximately 20,000 adults about household characteristics, including the prevalence of various types of residential heating appliances, the use of unvented combustion space heaters, and use of stoves or ovens specifically for heating during the previous year. NHANES weights (2) were used to obtain national estimates based on these responses. Because responses by race/ethnicity other than for whites and blacks were too small for reliable estimates, responses from all others were combined. National Estimates

During 1988-1994, an unvented combustion space heater was used by an estimated 13.7 million adults, and electric space heaters were used by 23.1 million adults; space heaters were not used by 150.4 million adults. Unvented combustion space heaters were used more commonly by adults living in rural areas than by those living in urban areas (10.0 million {10.6%} compared with 3.7 million {4.0%}), by adults with an annual household income less than or equal to $20,000 (low income) than by adults with an annual household income greater than $20,000 (high income) (9.3% compared with 6.3%), and by black adults (11.0%) than by white adults (7.0%) or by adults of all other races (3.7%). In each income group, household use of these devices was reported more commonly by blacks than whites (low income: 12.2% compared with 9.1%; and high income: 9.6% compared with 6.1%).

Of the estimated 83.1 million adults who used a gas stove or oven for cooking, approximately 7.7 million (9.3%) had used the stove or oven for heat at least once during the previous year. Improper use of the stove or oven as a heating device was more common among rural than among urban residents (12.2% compared with 7.4%). Stoves or ovens were used for heating in approximately 14.5% of low-income households compared with 6.1% of high-income households. Use of gas stoves and ovens as heating devices was reported more commonly by black adults (15.6%) than by white adults (8.1%) or by adults of other races (9.2%). Regional Estimates

Unvented combustion space heaters were used by an estimated 13.2% of adults in the South; 5.9%, in the Midwest; 4.2%, in the Northeast; and 2.5%, in the West. * The types of fuel used in combustion space heaters also varied by region (Figure_1), with propane being used predominantly in the South. Low-income households in the South and West used unvented combustion heating appliances more frequently than did high-income households in those regions (in the South: 16.3% compared with 11.2%; and in the West: 3.8% compared with 2.0%). Use of unvented combustion heating appliances was similar in low-income households and high-income households in the Midwest and Northeast (in the Midwest, 6.0% compared with 5.8%, and in the Northeast, 4.2% compared with 4.2%).

Use of a gas stove or oven as a heating device was higher among adults in the South (14.4%) than in any other region (West, 8.7%; Northeast, 7.6%; and Midwest, 5.9%). In all regions, the use of such devices in low-income households was approximately twice that in high-income households.

Reported by: HH Slack, Region 4, US Environmental Protection Agency. MA Heumann, Center for Disease Prevention and Epidemiology, Health Div, Oregon Dept of Human Resources. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Unvented combustion appliances and gas stoves or ovens improperly used as heating devices often produce levels of combustion by-products that exceed acceptable limits (1,3), degrade indoor air quality, and may cause unnecessary exposure to toxic gases such as CO. Unintentional, nonfire, nonautomobile poisonings from CO exposure in permanent dwellings result in approximately 200 deaths and 5900 injuries (treated in emergency departments) annually (K. Long, U.S. Consumer Product Safety Commission, memorandum to E. Leland, September 4, 1996). Symptoms characteristic of CO poisoning include headache, nausea, fatigue, weakness, abdominal pain, and confusion. Severe poisoning may result in seizures, coma, and death (4).

The findings in this report indicate that, although the use of unvented combustion heating appliances is common throughout the United States, the percentage of adults using these devices is higher in the South, among low-income groups, among blacks, and among rural residents. Because these estimates are based on adults reporting usage of these appliances and may not reflect the true prevalence of household use, the number of persons potentially exposed may be underestimated. The increased race-specific usage among blacks reflects, in part, a higher percentage of blacks living in the South (18.2%) compared with the Northeast (9.9%), Midwest (9.4%) and West (5.4%). These findings also indicate that the use of gas stoves and ovens as heating devices is common, especially among low-income and rural residents, even though these appliances were not designed or intended for such purposes (2).

Since 1992, use of unvented combustion heaters has increased because in many states, regulations prohibiting the use of these devices have been rescinded. As of November 1997, five states prohibit the use of unvented gas-fueled or liquid-fueled heaters (Alaska, Massachusetts, and Minnesota; and Colorado and Utah at high altitude only) (M. Carson, Vent-Free Gas Products Association, personal communication, December 2, 1997). Manufacturers recommend that these devices be used for short periods of time with a nearby window open for ventilation (5; M. Carson, Vent-Free Gas Products Association, personal communication, December 2, 1997). Failure to follow these instructions could result in elevated levels of combustion by-products.

Both unvented and vented heating appliances must be properly maintained to reduce the risk for associated health hazards. Persons who use unvented combustion space heaters should follow manufacturers' recommendations and use these devices only for short periods in well-ventilated areas to prevent the accumulation of toxic gases in living spaces. Other prevention strategies include conducting media campaigns detailing the potential hazards of unvented combustion space heaters during the colder months and encouraging the proper use of CO detectors in homes.

References

1. New York State Energy Research and Development Authority. Critique of guidelines on use of unvented gas space heaters. Albany, New York: New York State Energy Research and Development Authority, 1997.

2. National Center for Health Statistics. Plan and operation of the third National Health and Nutrition Examination Survey, 1988-94. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1994; DHHS publication no. (PHS)94-1308. (Vital and health statistics; series 1, no. 32).

3. Tsongas G, Hager WD. Field monitoring of elevated carbon monoxide production from residential gas ovens. In: Proceedings of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc, Indoor Air Quality '94 Conference. Atlanta, Georgia: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc, 1994.

4. Ilano AL, Raffin TA. Management of carbon monoxide poisoning. Chest 1990;97:165-9.

5. DeWerth DW, Borgeson RA, Aronov MA. Development of sizing guidelines for vent-free supplemental heating products -- topical report. Arlington, Virginia: Gas Appliance Manufacturers Association and Gas Research Institute, 1996.

* Northeast=Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont; Midwest=Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin; South=Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia; and West=Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.

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