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Carbon Monoxide Poisonings Associated with Snow-Obstructed Vehicle Exhaust Systems -- Philadelphia and New York City, January 1996

On January 9, 1996, CDC was notified about carbon monoxide (CO)-related morbidity and mortality associated with the blizzard in the northeastern United States. Most of these poisonings occurred among children and elderly persons and resulted from exposures in idling automobiles with exhaust pipes blocked by snow. This report summarizes three cases of CO poisoning reported to Philadelphia's Poison Control Center on January 8-9, and 22 cases reported in New York City on January 8-9. Philadelphia Case 1. A 4-year-old girl who had accompanied her family while they were digging their car out of a deep snow embankment became cold; to warm the child, she was placed in the car with both the engine and heater running while deep snow surrounded the rear of the automobile. The child's grandmother and sister also were in the car but exited the vehicle after a few minutes when the grandmother became dizzy and lightheaded. The child was believed to be napping and was allowed to remain in the car for approximately 30 minutes before she was found to be unconscious and could not be awakened. On arrival at the Children's Hospital of Philadelphia emergency department, she was awake but drowsy and complained of a headache. She initially was treated with 100% oxygen by nonrebreather mask and soon became alert and oriented; she was then transferred to the hyperbaric oxygen unit for a standard treatment regimen. She was discharged on January 9. Case 2. A 63-year-old man was brought to the Hospital of the University of Pennsylvania emergency department by paramedics after being found unconscious in his car with the engine running. Approximately 1 hour before being found, the patient informed his wife he was going to test the car to ensure it would run after the severe storm. He made no attempt to remove any snow surrounding the car before starting the engine. At the hospital, he was treated with 100% oxygen and then a standard hyperbaric regimen. Although his clinical status improved markedly after hyperbaric oxygen therapy, residual deficits in short-term memory persisted. Case 3. An 81-year-old man was found unconscious and could not be awakened in his car in a suburb outside of Philadelphia. The engine had been running, and the car was surrounded by deep snow. On their arrival at the site, paramedics declared the man dead. A qualitative test for carboxyhemoglobin was positive. New York City

During January 8-9, a total of 21 persons were admitted directly to the Jacobi Medical Center or transferred from other hospitals for hyperbaric oxygen therapy because of CO poisoning. In addition, one fatal case of CO poisoning was reported in which the victim was not admitted to the hospital. The cause of the CO poisonings was directly related to exposure to automobile exhaust from vehicle exhaust systems blocked with snow. The 21 persons admitted to the hospital were found unconscious inside automobiles with engines running. Of these blizzard-related cases, eight were aged less than 16 years and 12 were aged greater than 50 years (range: 4-81 years). Of the 21 persons, 17 were discharged within 24 hours of admission and four remain hospitalized.

Reported by: F Henretig, MD, Dept of Pediatrics, Univ of Pennsylvania School of Medicine, F DeRoos, MD, K Hardy, MD, Hospital of the Univ of Pennsylvania, Philadelphia; D Contostavlos, MD, Delaware County; R Levenson, MBA, Philadelphia Dept of Health; J Logue, DrPH, Div of Environmental Health Assessment, Pennsylvania Dept of Health. M Touger, MD, Jacobi Medical Center/Albert Einstein College of Medicine, Bronx; BA Mojica, MD, New York City Dept of Health. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Each year in United States, approximately 500 deaths are attributed to unintentional CO poisoning (1). CO is an insidious poison that is a naturally occurring byproduct of the incomplete combustion of carbon-based fuels. Because CO is colorless, tasteless, odorless, and nonirritating, its presence usually is not detected. CO is a component of vehicle exhaust, and CO can seep into the cabin of a vehicle through leaks or cracks in the floorboard if the exhaust pipe is obstructed. The CO poisonings described in this report resulted from inhalation of exhaust by persons sitting in idling automobiles with exhaust pipes obstructed by snow.

CO poisoning is not easily diagnosed because early symptoms are nonspecific (e.g., headache, dizziness, weakness, nausea, visual disturbances, and confusion) (2,3). Consequently, CO poisoning may be misdiagnosed as influenza or other acute, self-limited illnesses (4). Three important factors associated with carboxyhemoglobin levels and symptoms are 1) the concentration of CO in the environment; 2) the duration of exposure; and 3) the interval between exposure and clinical assessment. Normal carboxyhemoglobin concentrations are less than 2% for nonsmokers and 5%-9% for smokers. Treatment of CO poisoning requires termination of exposure and initiation of therapy with 100% oxygen; hyperbaric oxygen therapy has been recommended for patients with neruologic or cardiac symptoms, pregnant women, and children when higher cortical function cannot be measured (2,5).

The epidemiology of CO poisonings in the United States is characterized by seasonal increases during winter months (1) -- particularly because of the risks for exposure to the exhaust from vehicles and combustion appliances during periods when heating appliances are in use and ventilation is more likely to be inadequate (6). The findings in this report also underscore that heavy snowfalls are associated with particularly hazardous conditions in areas where vehicles are parked outdoors. Following heavy snowfalls, the public should be reminded to inspect vehicles to ensure that exhaust pipes are cleared of snow before engines are started. Other precautions to prevent CO poisoning include avoiding running automobile engines in enclosed spaces (e.g., garages), inspecting furnaces each year, using space heaters only in well-ventilated rooms, and inspecting exhaust systems of all combustion appliances that vent to the outside to ensure that vents have not been damaged or blocked with snow.


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

  2. Thom SR, Keim LW. Carbon monoxide poisoning: a review. Clin Toxicol 1989;27:141-56.

  3. Meredith T, Vale A. Carbon monoxide poisoning. Br Med J 1988;296:77-8.

  4. Baker MD, Henretig FM, Ludwig S. Carboxyhemoglobin levels in children with nonspecific flu-like symptoms. J Pediatr 1988;113:501-4.

  5. Viccellio P, ed. Handbook of medical toxicology. Boston: Little, Brown and Company, 1993.

  6. CDC. Unintentional carbon monoxide poisoning following a winter storm -- Washington, January 1993. MMWR 1993;42:109-11.

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