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Carbon Monoxide Poisoning at an Indoor Ice Arena and Bingo Hall -- Seattle, 1996

On March 16, 1996, paramedics and fire department personnel were requested to evaluate complaints of illness among persons exposed to exhaust fumes in an indoor ice skating facility in Seattle. Indoor-air measurements detected elevated levels of carbon monoxide (CO), prompting evacuation of the building. An investigation of the cluster of CO poisonings related to the exposure was conducted March 16-18, by a pulmonary and hyperbaric medicine physician who treated one of the ill persons. This report summarizes the investigation findings, which underscore the importance of adequate maintenance of machinery equipped with internal combustion engines that are operated at indoor ice arenas and of proper ventilation of such arenas.

The skating facility comprised two adjoining ice rinks on the lower level and a bingo hall on the upper level. On the evening of March 16, the ice in both rinks was smoothed with a 20-year-old ice-resurfacing machine powered by a propane engine. Immediately after the first rink was resurfaced, skaters in that rink had onset of fatigue, headache, and dizziness. Because several persons complained of these symptoms, paramedics and fire department personnel were requested to evaluate the symptoms. After measurements by fire department personnel indicated maximum CO levels of 354 ppm inside the ice arena, the approximately 300 persons in the building were evacuated.

Outside the building, paramedics evaluated, triaged, and treated the exposed persons. Two persons were intubated at the site because of acute respiratory distress. A total of 67 persons were transported to emergency departments (EDs) of nine different area hospitals by 22 emergency medical units and one city bus. Persons transported to EDs included those who had been in either of the ice rinks or in the bingo hall at the time of building evacuation. In addition to those referred to EDs from the scene, some persons independently sought medical evaluation.

Overall, 78 persons were evaluated in EDs; 47 (60%) were female. The median age was 14 years (range: 6 years-70 years). Based on data for 17 persons, the average carboxyhemoglobin (COHb) level was 8.6% (range: 3.3%-13.9%). One 15-year-old patient was referred for hyperbaric oxygen therapy for symptoms of possible myocardial ischemia. All other patients were treated in the EDs and discharged. Some returned to skate the following day when the rink was reopened after CO levels had decreased to 2 ppm.

Based on the investigation, the source of CO was determined to be a malfunction of the ice-resurfacing machine (the only source of combustion in the arena). The building's ventilation system, which alternates with a dehumidifier, may have been off during operation of the machine. An open access door from the ice arena to the bingo hall probably permitted CO to diffuse throughout the facility.

Use of the ice-resurfacing machine was discontinued, and the machine was replaced by a newer model. Until a CO detector system is installed in the arena, ambient CO levels are monitored after each ice resurfacing. To assist in preventing future CO poisonings at the arena, the Seattle-King County Health Department advised the arena manager to submit a CO-monitoring plan to the health department.

Reported by: NB Hampson, MD, Virginia Mason Medical Center, Seattle. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: CO is a colorless, odorless gas produced by the incomplete combustion of carbon-based fuels. CO induces toxic effects by tightly binding to hemoglobin to form COHb and reducing the oxygen-carrying capacity of blood; by binding with mitochondrial cytochrome oxidase, CO also interferes with cellular respiration (1). Because CO can induce toxicity through different pathways and because COHb levels begin to decrease as soon as exposure ceases, COHb levels indicate exposure but do not correlate consistently with either symptoms or prognosis.

Because early symptoms of CO exposure are nonspecific (e.g., headache, dizziness, weakness, and confusion) (1,2), CO poisoning may be misdiagnosed as acute, self-limited illnesses (e.g., upper respiratory tract infection and food poisoning). Four factors are associated with COHb levels and the severity of symptoms: 1) concentration of CO in the environment, 2) duration of exposure, 3) the activity level of those exposed, and 4) interval between exposure and clinical assessment. In general, however, exposure to CO concentrations of 80 ppm-140 ppm for 1-2 hours can result in blood COHb levels of 3%-6% (the normal COHb concentration is less than 2%; concentrations in smokers frequently may be 5%-9%) (3); this concentration may be associated with decreased exercise tolerance and, in persons who are otherwise at risk, can precipitate angina pectoris and cardiac arrhythmias (3). Clinical manifestations associated with CO concentrations of 105 ppm-205 ppm and COHb levels of 10%-20% include headache, nausea, and mental impairment. Manifestations associated with COHb levels of greater than 20% include more profound central nervous system effects, coma, and death (2).

CO intoxication is the most common form of unintentional poisoning in the United States (1). Although most unintentional exposures involve small numbers of persons and typically occur during the winter, episodes such as that described in this report (i.e., during indoor public gatherings) can occur throughout the year. For example, elevated ambient levels of CO and nitrogen dioxide have been documented at indoor sporting venues including arenas for tractor pulls, monster-truck jumps, and ice rinks (4-6). Production of CO in ice arenas has been attributed to ice-resurfacing machines, with rink CO levels of up to 150 ppm measured in simulation tests during operation of the machines (4), and CO levels as high as 117 ppm have been detected during ice hockey games in six arenas surfaced by propane-fueled machines (6). Some episodes of indoor CO exposure during sports events have been associated with substantial morbidity requiring acute medical evaluation of patients (4,7).

Skaters especially may be at risk for CO poisoning because they are engaged in strenuous activity that increases total lung ventilation and oxygen consumption. To ensure that COHb levels are less than or equal to 2% among nonsmoking skaters, the CO level for enclosed ice skating rinks should be less than or equal to 20 ppm (6). Workplace standards for CO exposure have been established by the Occupational Safety and Health Administration, and the permissible exposure limit for CO is 50 ppm as an 8-hour time-weighted average (8). In addition, CDC's National Institute for Occupational Safety and Health recommended exposure limit for CO is 35 ppm as a time-weighted average, and the maximum exposure of 200 ppm should not be exceeded at any time. Workplace standards were developed to protect generally healthy working-aged persons; therefore, these standards may not be applicable to children, the elderly, or persons with preexisting cardiopulmonary disease -- all of whom might attend events at public arenas. In the arena involved in the investigation in this report, CO levels substantially exceeded workplace standards because of the combination of a malfunctioning ice-resurfacing machine and inadequate ventilation.

Although recommendations to help minimize CO accumulation in ice rinks have been published (4), routine monitoring of indoor-air quality in ice arenas is not required in most states (9). Because of the potential for mass exposure to and intoxication with CO in indoor ice rinks, public health agencies in jurisdictions with indoor ice rinks should ensure that 1) operators of ice arenas are educated about prevention of CO poisonings, 2) routine monitoring of CO levels is conducted, 3) routine testing and maintenance of CO detectors are performed, 4) ice-resurfacing machines and heating systems are properly maintained, 5) battery-operated resurfacing equipment is used if available, and 6) air-circulation systems capable of exchanging air are used throughout the arena, locker rooms, and any other rooms. In addition, organizations (e.g., hockey leagues and figure skating clubs) should require periodic CO monitoring at the arenas they rent for practices and games.


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

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

  3. 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.

  4. CDC. Nitrogen dioxide and carbon monoxide intoxication in an indoor ice arena -- Wisconsin, 1992. MMWR 1992;41:383-5.

  5. CDC. Carbon monoxide levels during indoor sporting events -- Cincinnati, 1992-1993. MMWR 1994;43:21-3.

  6. Lee K, Yanagisawa Y, Spengler JD, Nakai S. Carbon monoxide and nitrogen dioxide exposures in indoor ice skating rinks. J Sports Sci 1994;12:279-83.

  7. Paulozzi LJ, Satink F, Spengler RF. A carbon monoxide mass poisoning in an ice arena in Vermont. Am J Public Health 1991;81;222.

  8. NIOSH. NIOSH pocket guide to chemical hazards. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, CDC, 1994.

  9. Hedberg K, Hedberg CW, Iber C, et al. An outbreak of nitrogen dioxide-induced respiratory illness among ice hockey players. JAMA 1989;262:3014-7.

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