Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Carbon Monoxide Levels During Indoor Sporting Events -- Cincinnati, 1992-1993

Carbon monoxide (CO) produced by internal combustion engines is an indoor health hazard. High CO levels can occur during indoor sporting events -- such as tractor pulls *-- that involve vehicles modified to achieve high horsepower. In January and March 1992 and January 1993, the Cincinnati Health Department evaluated CO levels during tractor pulls, monster-truck jumps, and a mud race event held in an indoor arena with a seating capacity of approximately 16,000 persons. This report summarizes findings from the evaluations.

The engines of vehicles involved in the events in Cincinnati used a variety of high-octane fuels and had limited exhaust systems but no emission-control devices. During each of these events, 10-15 vehicles were operated -- usually one at a time -- during the 2-3-hour event. In addition, approximately 3-4 other support vehicles were used for towing and resurfacing grounds. For each of the three events, attendance was approximately 40% of the arena's capacity; in addition, the ventilation system's supply and exhaust operated maximally, and the ground level commercial truck entrance was opened completely. CO levels were recorded in the arena at approximately 15-minute intervals before each event and during the event. Measurements were recorded at different elevations in the public seating area; most recordings were obtained at the midpoint elevation (area of the maximal seating occupancy by the audience).

In January 1992, during a monster-truck jump and tractor pull, CO levels averaged 13 parts per million (ppm) before the event (monitored from 6 p.m. to 8 p.m.) and 79 ppm (peak level: 140 ppm) during the event (8 p.m.-10 p.m.). In March 1992, during a monster-truck jump and mud race, CO levels averaged 23 ppm before the event (monitored from 6 p.m. to 8 p.m.) and 106 ppm (peak level: 250 ppm) during the event (8 p.m.-10:10 p.m.). In January 1993, during a monster-truck jump and tractor pull, CO levels averaged 14 ppm before the event (monitored from 6:30 p.m. to 8 p.m.) and 140 ppm (peak level: 283 ppm) during the event (8 p.m.- 9:08 p.m.). Measured levels of CO varied inversely with seating level within the arena.

Because the existing ventilation system could not supply a quantity of fresh air sufficient to eliminate excess levels of CO produced by the internal combustion engines operated during events, at the midpoint of each event the time interval was increased between each run to lower CO levels. However, this measure did not lower concentrations of CO.

Additional engineering and administrative controls to reduce CO levels during future events are being considered by the arena management, event promoter, local health department, municipal fire division, and municipal legal division. A public assembly permit application has been written requiring that indoor CO levels not exceed a 15-minute time-weighted average of 35 ppm and that levels not exceed 200 ppm of CO for any two consecutive samples (1). Reported by: DR Boudreau, Cincinnati Health Dept; MP Spadafora, MD, Univ of Cincinnati School of Medicine; LR Wolf, MD, Wright State Univ School of Medicine, Dayton; E Siegel, PharmD, Cincinnati Drug and Poison Information Center. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Because CO is colorless, tasteless, odorless, and nonirritating, it is difficult to detect with the senses. Exposure to CO concentrations of 80-140 ppm during 1-2 hours can result in blood carboxyhemoglobin (COHb) concentrations of 3%-6% in healthy, resting adults (normal concentration: less than 2% for nonsmokers, 5%-9% for smokers) (2). COHb levels of 3%-6% may decrease exercise tolerance and precipitate angina attacks and cardiac arrhythmias in susceptible persons (2); at levels of 10%-20%, headache, nausea, and mental impairment generally appear, and at COHb levels of 30%- 60%, more profound central nervous system effects, coma, and death can occur (3). The risks of CO poisoning are greater for fetuses, infants, pregnant women, and persons with underlying cardiovascular or pulmonary disease. Although more than 500 persons die each year in the United States from unintentional CO poisoning, the epidemiology of nonfatal CO poisoning is not well defined (4).

Any combustion process occurring indoors may result in the accumulation of CO, particularly when ventilation is inadequate, as demonstrated in Cincinnati. Indoor exposures to even small gasoline-powered engines have been fatal (5). Common sources of indoor CO include automobile exhaust in garages, ice resurfacing machines, blocked chimneys, faulty home heaters, other home cooking and heating appliances, and tobacco smoke. Elevated CO levels have been documented previously in Canada at sporting events similar to those monitored in Cincinnati (6). Although ambient air quality standards for outdoor air have been established by the U.S. Environmental Protection Agency for CO (9 ppm over 8 hours and 35 ppm over 1 hour {2}), there are no such national standards for the indoor environment.

Treatment of CO poisoning requires removing the patient from the source of exposure and initiating therapy with 100% oxygen; hyperbaric oxygen therapy has been recommended for severe poisonings (COHb level greater than 40%) and for pregnant women with symptoms or COHb levels greater than 10% (7,8). Adverse health effects from exposure to CO can be prevented by ensuring adequate maintenance and cleaning of gas-fired stoves, furnaces, and appliances and by using appropriate ventilation and emissions-control devices at indoor sporting events such as those described in this report. In addition, CO levels at such events should be monitored routinely to enable detection of hazardous levels and prompt intervention.


  1. City of Cincinnati. Public assembly permit: conditions for the use of internal combustion engines. Cincinnati: Cincinnati Department of Safety, 1993.

  2. US Environmental Protection Agency. Air quality criteria for carbon monoxide. Washington, DC: US Environmental Protection Agency, Office of Research and Development, 1991; publication no. EPA-600/8-90/045F.

  3. Llano A, Raffin T. Management of carbon monoxide poisoning. Chest 1990;97:165-9.

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

  5. CDC. Unintentional carbon monoxide poisoning from indoor use of pressure washers -- Iowa, January 1992-January 1993. MMWR 1993;42:777-9,785.

  6. CDC. Carbon monoxide levels in indoor tractor-pull events -- Manitoba, Canada. MMWR 1990;39:743-5.

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

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

    • A "tractor" is a vehicle modified to look like a farm tractor (e.g., large rear wheels and smaller front wheels) and powered by a variety of units (e.g., aircraft turbines and supercharged car engines). During a typical pull, approximately 12 tractors compete in dragging a 40- to 50-ton sled across a dirt surface in the fastest time. In a monster-truck jump, trucks with oversized wheels, high horsepower engines, and four-wheel drive accelerate up slight inclines and jump over a series of cars with the goal of achieving height, distance, and dynamic show when crushing the cars. Mud races use a smaller vehicle that pulls a weighted sled through a mudded area to achieve the fastest time while flinging mud.

Disclaimer   All MMWR HTML versions of articles are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the electronic PDF version and/or the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to

Page converted: 09/19/98


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/2/01