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Carbon Monoxide Poisoning from Use of Gasoline-Fueled Power Washers in an Underground Parking Garage -- District of Columbia, 1994

On June 17, 1994, five workers in the District of Columbia were treated in an emergency department for carbon monoxide (CO) poisoning following exposure to the exhaust from two gasoline-fueled power washers (i.e., pressure washers), which they had used in an empty underground parking garage. These cases were identified by The George Washington University (GWU) Division of Occupational and Environmental Medicine (DOEM) through ongoing surveillance for work-related injuries among construction workers treated in the GWU emergency department (1). This report summarizes the results of an investigation by DOEM of this incident.

At 11 p.m. on June 16, four laborers and a foreman (age range: 22-39 years) began preparing to resurface the floor of an underground parking garage that had been closed for business when the crew began work. At approximately 12:30 a.m., the workers started two power washers equipped with 8-horsepower, gasoline-fueled engines. A pedestal fan used previously in such situations was not operable. In addition, the garage exhaust fan was not in operation, and the main door of the garage (located approximately two levels above the work site) was closed.

At approximately 3:30 a.m., a worker collapsed. His three co-workers and the foreman assisted him out of the garage and remained outside with him for a few minutes before they returned to the garage and resumed work. A second worker then collapsed; the co-workers immediately turned off the washers, evacuated the garage, and contacted the District of Columbia Fire Department. Onsite evaluation by fire department officials indicated that all five men had acute symptoms including dizziness, confusion, headache, and nervousness. The two workers who had collapsed were transported by ambulance to a local emergency department. At the hospital, carboxyhemoglobin (COHb) levels, obtained from the workers at 5:10 a.m., were 20% and 17%, respectively (normal: less than or equal to 5%-10% for smokers and less than or equal to 1% for nonsmokers {2}). Carbon monoxide poisoning was diagnosed, and they were treated with hyperbaric oxygen and released later that day. The three other workers were transported to the hospital where their COHb levels, obtained at 7:15 a.m., were 10.3%, 13.4%, and 7.9%, respectively. They were administered 100% oxygen and released.

At 4:14 a.m., the fire department's hazardous materials team responded to investigate the incident. Based on measurements using a hand-operated air pump and indicator tube approximately 1 hour after the washers had been turned off, the concentration of CO was 648 parts per million (ppm). * The only identified source of CO was the exhaust from the gasoline-powered washers.

Reported by: L Nessel-Stephens, MSS, LS Welch, MD, JL Weeks, ScD, KL Hunting, PhD, J Cardenas-Amaya, MD, Div of Occupational and Environmental Medicine, The George Washington Univ, Washington, DC. Div of Surveillance, Hazard Evaluations, and Field Studies, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: CO is a potentially lethal gas with nonspecific warning properties. Levels of CO uptake vary among persons and are a function of air concentration, level of exertion and ventilatory rate, and duration of exposure. For example, among workers engaged in light work and who were exposed to a CO concentration of 700 ppm, COHb levels were 20% after 35 minutes and 40% after approximately 1 hour (4). In general, COHb levels greater than 20% are associated with symptoms; dizziness and unsteady gait may result from levels greater than 30% (5).

Based on estimates of the Bureau of Labor Statistics (BLS), in 1992 CO exposure accounted for 867 nonfatal work-related CO poisonings in private industry in the United States that resulted in days away from work (BLS, Survey of Occupational Injuries and Illnesses, unpublished data, 1992) and for 32 fatal work-related CO poisonings (BLS, Census of Fatal Occupational Injuries, unpublished data, 1992). The occurrence of nonfatal work-related CO poisonings probably is underestimated because workers with mild symptoms may not seek treatment, medical providers may not recognize nonspecific symptoms as manifestations of CO poisoning, and some correctly diagnosed cases may not be reported as work-related.

Since November 1990, DOEM has identified four other cases of CO poisoning among construction workers; all required emergency medical treatment (1). Two cases involved use of gasoline-powered forklifts in an enclosed warehouse, and two involved use of gasoline-fueled saws. Similar incidents have been reported among workers in other industries, including farmers using gasoline-fueled pressure washers to clean structures housing animals (6; NIOSH, unpublished data, 1993) and workers using liquid propane-powered floor burnishers to clean floors in a retail establishment (7). During January 1985-February 1995, the Colorado Department of Public Health and Environment (CDPHE) received reports of 147 cases of occupational CO poisoning related to the use of gasoline-powered equipment; of these, 13 (9%) were associated with use of pressure washers (CDPHE, unpublished data, 1995).

The investigation described in this report and other incidents indicate that many workers may not be aware of the risks of CO poisoning associated with gasoline-fueled engines and may not be able to assess accurately whether ventilation is adequate for their safe use. For example, in 1993, to characterize risk awareness and behavior related to the indoor use of small engines, NIOSH surveyed 416 persons involved in flood-cleanup activities in Missouri. Of those who had ever used a gasoline-powered pressure washer, 38% reported bringing the engine component of the washer inside a building (NIOSH, unpublished data, 1993).

For many construction projects, CO exposure cannot be consistently controlled because of the involvement of multiple contractors. The employer of the laborers involved in the incident described in this report has discontinued use of the gasoline-powered pressure washers in underground parking garages and now uses electric- or diesel-powered washers. However, other contractors routinely use gasoline-powered equipment in maintaining and resurfacing parking garage floors -- often without additional ventilation. Alternatives to gasoline-powered equipment (i.e., electric and diesel equipment) are associated with other potential hazards (e.g., improper use of electric equipment can result in electrocution, and unfiltered diesel exhaust contains hazardous particulates). Even though diesel equipment and well-maintained gasoline-fueled equipment that are fitted with catalytic converters emit less CO, the reduced levels may be too high for safe indoor use.

The risk for CO exposure to workers can be reduced through improved ventilation. In addition, however, risk-reduction efforts must include air monitoring for CO levels. Reliable air monitoring includes the requirement for persons who have been trained to perform the monitoring and for equipment that has been properly calibrated and maintained. Training and warning labels can increase awareness among contractors and workers about the risks associated with use of gasoline-fueled equipment in enclosed spaces.


  1. Hunting KL, Nessel-Stephens L, Sandford SM, Shesser R, Welch LS. Surveillance of construction worker injuries through an urban emergency department. J Occup Med 1994;36:356-64.

  2. Smith R. Systemic toxicology. In: Amdur MO, Doull J, Klassen CD, eds. Casarett and Doull's toxicology: the basic science of poisons. 4th ed. New York: Pergamon Press, 1991:264-8.

  3. NIOSH. Pocket guide to chemicals. Cincinnati: US Department of Health and Human Services, Public Health Service, CDC, 1990; DHHS publication no. (NIOSH)90-117.

  4. Forbes WH, Sargent F, Foughton FJW. The rate of CO uptake by normal man. Am J Physiol 1945;143:594-608.

  5. Seger DL, Welch L. Carbon monoxide. In: Sullivan JB, Krieger GR. Hazardous materials toxicology: clinical principles of environmental health. Baltimore: Williams and Wilkins, 1992: 1160-4.

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

  7. CDC. Carbon monoxide poisoning associated with a propane-powered floor burnisher -- Vermont, 1992. MMWR 1993;42:726-8.

    • The NIOSH recommended exposure limit for CO is 35 ppm (as an 8-hour time-weighted average), and the recommended ceiling limit is 200 ppm (3).

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