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Carbon Monoxide Exposures at an Ice Skating Rink -- Colorado

In April 1984, the Pitkin County (Colorado) Health Department (PCHD) asked the National Institute for Occupational Safety and Health (NIOSH) to evaluate the potential hazard associated with carbon monoxide (CO) exposure at an indoor ice skating rink during the operation of gasoline-powered ice-resurfacing machines (1). A previous survey done by the PCHD had shown that the CO concentration in air was an 8-hour time-weighted average (TWA) of 53.8 parts per million (ppm) and a 1-hour reading of 80.5 ppm. The Occupational Safety and Health Administration (OSHA) maximum acceptable level for CO exposure is an 8-hour TWA of 50 ppm. The NIOSH-recommended level is an 8-hour TWA of 35 ppm, with a 200 ppm ceiling limit.*

NIOSH investigators collected air samples during the operation of both an old and a new resurfacing machine. CO measurements were made with an Ecolyzer** CO analyzer and direct-reading detector tubes. Air samples collected at the edge of the rink showed CO concentrations of 55 ppm and 65 ppm when the new ice resurfacer was run and concentrations of 90 ppm when the old resurfacer was in operation. Measurements taken with sampling equipment located on the machines themselves showed peak levels of 250-400 ppm (average 140-175 ppm) for the new machine and 500 ppm (average 200 ppm) for the older machine.

CO exposures for individual workers were monitored by determining concentrations of CO in expired air. Six workers and two county sanitarians were monitored. An initial test was performed before the first ice resurfacing of the day (8 a.m.), and afternoon tests took place between 1 p.m. and 2 p.m. The worker who operated the ice-resurfacing machines was given several tests in between. Workers were also asked about their smoking habits and current symptoms. Of the eight persons monitored, six were nonsmokers, and the other two--an occasional cigarette smoker and a pipe smoker--had not smoked on the day of the test.

Initial CO concentrations in the exhaled air of the eight subjects averaged 12.1 plus or minus 2.5 ppm, which corresponds to 2.3% plus or minus 0.7% carboxyhemoglobin (COHb). (The average COHb level for a nonsmoker is 1.0% (2).) CO concentrations in expired air rose during the day for all eight subjects. The smallest rise--equivalent to 1.0% COHb--was for an individual who arrived after the first resurfacing. The highest--4.7%--was for the worker who operated the resurfacing machines. Concentrations of exhaled CO at the end of the day averaged 26.3 plus or minus 4.7 ppm for the seven individuals who were in the building all day. This corresponds to 5.7 plus or minus 1.0% COHb and represents a rise in COHb of 3.3% plus or minus 1.2%. None of these values differed significantly from the average level at the 95% confidence interval. Reported by Pitkin County Health Dept, Aspen NIOSH Region 8 Office, Denver, Colorado; Div of Surveillance, Hazard Evaluations, and Field Studies, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: The principal toxic effect of CO is tissue hypoxia (3). Inhaled CO causes hypoxia by binding tightly with circulating hemoglobin to produce COHb, thus reducing the capacity of the blood to transport oxygen (4,5). The heart and brain are the tissues most severely affected by CO-induced hypoxia. A considerable body of evidence links CO exposure to altered hemodynamics. Exercise studies in normal adult subjects show that venous oxygen tension is decreased during exposure to CO and that heart rate, cardiac output, and coronary artery blood flow are all increased compared with preexposure values (6,7).

While nonsmokers who have not been exposed to other sources of CO have an average COHb level of 1% (2), nonsmokers who are exposed to 50 ppm CO (the OSHA standard) for 6-8 hours have COHb levels of 8%-10%. NIOSH bases its recommended exposure limit of 35 ppm for an 8-hour TWA and its ceiling of 200 ppm on the concentration needed to produce a COHb level of 5% or less. These recommendations do not take into account the smoking habits of the workers. COHb levels in smokers have generally been found in the 4%-5% range but may run as high as 10%-15% in heavy smokers. Thus, moderate smokers with blood levels of 5% who are then exposed to an average concentration of 35 ppm CO in a workplace may have a total COHb concentration of about 10%.

At the time of this study, no health complaints could be attributed to CO exposure. However, at least one worker had some respiratory complaints that may have been related, in part, to exposure to resurfacer exhaust. Because individual exposures to CO were slightly higher than desirable (average COHb by the end of the day was over 5%), NIOSH investigators made the following recommendations:

  1. The room in which the ice-resurfacing machine is stored should be fitted with an exhaust system; this should include a flexible hose that can be attached to the machine exhaust during warm-up.

  2. The resurfacing machines should be well maintained to keep CO emissions as low as possible.

  3. The operator of the resurfacing machine should be very familiar with its use, thus making the procedure quicker and helping to eliminate some CO exposure.

  4. Fresh air should be forced into the rink area toward the exhaust fan, particularly after each resurfacing. The problem of CO exposures associated with ice skating rinks has

been reported previously (8,9). Because 10,000 persons in the United States seek medical attention each year after exposure to CO gas, and because approximately 1,500 persons die of CO poisoning (10), the monitoring of CO levels at such rinks would be a prudent public health measure.


  1. National Institute for Occupational Safety and Health. Health hazard evaluation report no. HETA 84-299-1524. Cincinnati, Ohio: National Institute for Occupational Safety and Health, 1984.

  2. National Institute for Occupational Safety and Health. Criteria for a recommended standard: occupational exposure to carbon monoxide. Cincinnati, Ohio: National Institute for Occupational Safety and Health, 1973. (DHEW (NIOSH) publication no. 73-11000).

  3. Haldane JBS. The dissociation of oxyhemoglobin in human blood during partial carbon dioxide poisoning. J Physiol 1912;45:22.

  4. Turino GM. Effect of carbon monoxide on the cardiorespiratory system. Carbon monoxide toxicity: physiology and biochemistry. Circulation 1981;63:253A-59A.

  5. McGrath JJ, Barnes CD, eds. Air pollution--physiological effects. New York: Academic Press, 1982.

  6. Vogel JA, Gleser MA. Effect of carbon monoxide on oxygen transport during exercise. J Appl Physiol 1972;32:234-9.

  7. Ayres SM, Gianelli S Jr, Mueller H. Myocardial and systemic responses to carboxyhemoglobin. Ann NY Acad Sci 1970;174:268-93.

  8. CDC. Carbon monoxide intoxication associated with use of a gasoline-powered resurfacing machine at an ice-skating rink--Pennsylvania. MMWR 1984;33:49-51.

  9. Davis BP, Drenchen A. Carbon monoxide of concern in ice arenas. J Environ Health 1979;42:120-2.

  10. CDC. Carbon monoxide fact sheet. Atlanta, Georgia: Centers for Disease Control, 1979.

*The NIOSH-recommended exposure level should be lowered appropriately at very high altitudes--5,000-8,000 feet above sea level--to compensate for a decrease in the available oxygen. **Use of trade names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.

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