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Unintentional Carbon Monoxide Poisonings in Residential Settings -- Connecticut, November 1993-March 1994

Carbon monoxide (CO) gas is an environmental hazard, and unintentional CO poisonings have occurred in multiple settings, including residences, motor vehicles, and workplaces. In 1993, exposure to CO produced by a malfunctioning natural gas furnace in a Suffield, Connecticut, home resulted in the deaths of three children and hospitalization of four other family members. Publicity resulting from this and other CO poisoning incidents prompted concern that gas furnaces have been a primary cause of residential CO poisonings in Connecticut. To determine the sources of residential CO poisonings in Connecticut, the Connecticut Department of Public Health (CDPH) surveyed persons with cases of CO poisoning during November 1993-March 1994. This report presents the survey findings.

CDPH reviewed the daily telephone logs of the Connecticut Poison Control Center (CPCC) to identify potential nonfatal CO poisonings during November 1993-March 1994. To determine whether potential cases met the case definition for a CO poisoning and whether the source of CO was residential, nurses from the CPCC collected additional details about poisonings through telephone interviews. A case was defined as two or more symptoms consistent with CO poisoning (i.e., headache, nausea, diarrhea, dizziness, dry mouth, drowsiness, or vomiting) or CO poisoning diagnosed by a physician and a carboxyhemoglobin (COHb) level greater than 10% (normal concentration: less than 2% for nonsmokers, 5%-9% for smokers). A 32-item questionnaire was administered by CDPH to one adult respondent in each household to obtain information about demographics and socioeconomic status for each person in the household with CO poisoning, as well as information about symptoms, potential CO sources, details of the investigation and remediation of CO in the home, and the respondent's knowledge of CO poisoning before the incident.

A total of 197 records of potential nonfatal CO poisonings were identified; of these, 139 (71%) contained both the name and telephone number of persons with potential cases. Overall, 61 (44%) persons could be contacted, and 51 (84%) were considered to have had CO poisoning resulting from exposure to a residential source of CO. These 51 persons ranged in age from 1 to 71 years (median: 32 years); most (83%) were aged 20-49 years. Persons with CO poisoning resided in 36 households: 19 (53%) single-family dwellings, 11 (31%) multifamily dwellings, four (11%) apartments, and two (6%) dwellings classified as other.

The most common source of CO in these 36 homes was heating systems: oil heating systems (16 households), gas heating systems (11), and kerosene heaters (three). Gas appliances and fireplaces were identified as the CO source in six households.

Reported symptoms for the 51 patients included headache (88%), dizziness (83%), nausea (75%), drowsiness (75%), dry mouth (44%), diarrhea (17%), and vomiting (11%). For 28 (55%) patients, the first symptom noted was headache; for eight (16%), dizziness; for seven (13%), nausea; for five (10%), dry mouth; and for three (6%), drowsiness. Twenty-two (43%) patients consulted a physician. Of the 33 patients who suspected they were experiencing CO poisoning, 10 (30%) became concerned because of information obtained previously from television news media; eight (24%), because of prior knowledge of CO poisoning; eight (24%), because of information previously learned from others; four (12%), because of an odor from a malfunctioning appliance; two (6%), because of a CO detector; and one (4%), because of some other reason. For 32 cases, data were available about the interval between onset of symptoms and the time at which the patient first considered CO as the cause of symptoms: for 10 (31%), the interval was less than 1 hour; for three (9%), 1-12 hours; for five (16%), 24.1 hours-4 days; for one (3%), 4.1-7 days; and for 13 (41%), greater than 7 days.

The 36 respondents also were asked about possible methods to prevent CO exposure: 22 (61%) provided one method, eight (22%) provided two, and one (3%) provided three; five (14%) were unable to list any method. Prevention methods included appropriate maintenance of appliances (16), use of a CO detector (14), proper ventilation of the room (five), public education (three), and other actions (three).

Sources of CO were identified primarily by heating-system technicians (48%) or a resident (38%). Sources also were identified by fire department personnel (10%) or building officials (3%). Methods of identification were visual inspection of the furnace or heating system (63%), process of elimination (18%), CO meters (11%), and other (7%). Actions taken to correct the CO emissions included replacing the furnace; ventilating the room; and/or cleaning, repairing, or discontinuing use of the malfunctioning appliance.

Reported by: RL Miller, Town of Coventry Health Dept; BF Toal, K Foscue, Div of Environmental Epidemiology and Occupational Health, Connecticut Dept of Public Health; H Hansen, MD, M Bayer, MD, School of Medicine, Univ of Connecticut, Farmington. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Unintentional CO poisonings result in approximately 600 deaths annually in the United States (1). A surveillance system implemented by the Colorado Department of Health in 1985 has helped to characterize the epidemiology of fatal and nonfatal CO poisonings (2). Findings from this system indicate that, during 1986-1991, the primary sources of 1149 CO poisonings in Colorado were furnaces in residential settings (40%), automobile exhaust (24%), and fires (12%). Furnaces were the source of CO in 46% of nonfatal CO poisonings but only 10% of fatal poisonings, suggesting that the primary sources of CO associated with nonfatal poisonings differ from those for fatal cases. In addition, findings from the Colorado surveillance system indicate that mortality data may underestimate the importance of furnaces as a source of CO in residential settings.

Other studies also have documented that furnaces are important sources of CO in residential CO poisonings. For example, of the 38 residential CO-related episodes investigated in West Virginia during 1978-1984, furnaces or space heaters were implicated in most (89%) incidents (3); 94% of the faulty units were fueled by methane or butane. In Connecticut, although most (75%) CO poisonings were caused by faulty furnaces, oil-fueled furnaces were the source of CO more often than natural gas -- possibly reflecting a higher percentage of oil- or kerosene-fueled furnaces in homes in New England (51% in homes in New England compared with 6% in the Midwest, 7% in the South, and 2% in the West) (4). In addition, based on the 1990 census, the distribution of furnace types identified as sources of CO in this survey is representative of the distribution throughout Connecticut (gas furnaces, 28%, and oil or kerosene furnaces, 54%) (4).

CDPH is using the findings in this report to educate the public about sources of CO and strategies to prevent CO poisoning. Prevention of CO poisoning requires that 1) homeowners and renters recognize that all combustion appliances must be professionally installed to ensure both complete combustion of the fuel and adequate ventilation of combustion products (4); 2) combustion appliances be maintained and inspected annually; 3) fuels not be burned in confined spaces (e.g., tightly closed rooms); 4) public education efforts highlight the early manifestations of CO intoxication; 5) homeowners and renters be informed about the availability of low-cost CO detectors and public health agencies document the effectiveness of these devices; and 6) health-care providers -- particularly emergency department personnel -- consider the possibility of poisoning from residential exposure to CO in patients reporting typical symptoms (e.g., headache, nausea, vomiting, and malaise). Additional information about CO detectors is available from the Consumer Product Safety Commission hotline (800) 638-2772 or (301) 504-0220.


  1. Cobb N, Etzel RA. Unintentional carbon monoxide-related deaths in the United States, 1979-1988. JAMA 1991;266:659-63.

  2. Cook M, Simon PA, Hoffman RE. Unintentional carbon monoxide poisoning in Colorado, 1986 through 1991. Am J Public Health 1995;85:988-90.

  3. Baron RC, Backer RC, Sopher IM. Fatal unintended carbon monoxide poisoning in West Virginia from nonvehicular sources. Am J Public Health 1989;79:1656-8.

  4. Bureau of the Census. 1990 Census of population and housing: summary of social, economic, and housing characteristics -- United States. Washington, DC: US Department of Commerce, Economic and Statistics Administration, Bureau of the Census, 1992; document no. 1990 CPH-5-1.

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