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Unintentional Carbon Monoxide Poisoning from Indoor Use of Pressure Washers -- Iowa, January 1992-January 1993

On January 18, 1993, the Iowa Occupational Health Nurses in Agricultural Communities (OHNAC) * project was notified that an Iowa farmer (index case) had died of carbon monoxide (CO) poisoning while using a gasoline-powered pressure washer -- a device that produces a high-pressure water spray -- to clean his swine farrowing (birthing) barn. OHNAC staff subsequently reviewed hospital records and data from the Sentinel Project Researching Agricultural Injury Notification System (SPRAINS) ** and identified four other farmers treated since January 1992 for CO poisoning after operating gasoline-powered pressure washers. This report summarizes the investigation of these incidents. Index Case

On January 15, 1993, a 33-year-old farm owner died while using an 11-horsepower (HP) washer to clean inside a 3420-cubic-foot (ft3) swine farrowing area within a larger wooden structure. He was working alone, the door was closed, and there was no other ventilation on this cold day (outside temperatures ranged from -7 F to 20 F {-21.7 C to -6.7 C}). An investigation by the local medical examiner's office indicated that, based on the amount of work he had completed, he had been overcome in approximately 30 minutes. His postmortem carboxyhemoglobin (HbCO) level was 75.6% (normal values: less than or equal to 2% for nonsmokers, less than or equal to 9% for smokers {1}). He had recently insulated the farrowing room and replaced his electric pressure washer with a gasoline-powered model. Case 2

On December 30, 1992, a farm owner found his 12-year-old son unconscious near the door of a swine farrowing building (estimated volume: 4480 ft3). The boy had been working alone while using a rented 11-HP gasoline-powered washer for approximately 30 minutes. Because outside temperatures had ranged from -2 F to 30 F (-18.9 C to -1.1 C), the washer had been placed inside the building approximately 5 feet from the door. His HbCO level was 50% at the time of initial medical treatment. He required mechanical ventilation and received hyperbaric oxygen therapy; he was discharged following an 8-day hospitalization. Case 3

On November 3, 1992, a 35-year-old farm owner was found by her husband to have extreme weakness, confusion, and slurred speech. She had been working alone inside a 4480-ft3 room used for raising calves. During a 7-hour period (most of the time alone) she had intermittently been cleaning the room with a 4-HP gasoline-powered washer. Outside temperatures ranged from 30 F to 34 F (-1.1 C to 1.1 C). She had set the machine inside the building approximately 5 feet from an open doorway. All three doors to the room were open, and an exhaust fan of unreported size was in operation. When found, although obviously confused, she insisted she was only tired. Her HbCO level obtained approximately 90 minutes postexposure was 18.8%. She was treated with oxygen at the local hospital and released. Case 4

On April 18, 1992, a 32-year-old farm owner was found by her husband in a 5148-ft superscript 3 swine farrowing building she had been cleaning. She was confused, weak, dizzy, and nauseated and reported a severe headache and diffuse muscle pain; she subsequently stated she believed she had been unconscious. She had worked alone intermittently for 6-1/2 hours, with three exhaust fans of unreported size and capacity in operation and a 13-HP gasoline-powered washer located in an adjacent room (outside temperatures ranged from 46 F to 69 F {7.8 C to 20.5 C}). CO apparently entered the work area when the door leading to the room containing the washer blew open sometime during the final hour of work. An HbCO level obtained 5 hours postexposure and after 30 minutes of oxygen therapy was 9.2%. Case 5

On January 2, 1992, a 37-year-old farm owner was found by his wife in their house; he was dizzy, extremely weak, and somewhat confused. He had been working for approximately 30 minutes in an unventilated, 6480-ft superscript 3 swine farrowing building (outside temperatures ranged from 28 F to 33 F {-2.2 C to 0.6 C}) using a borrowed 9-HP gasoline-powered washer. His symptoms began while he attempted to refuel the washer, which had been placed inside the building. He crawled to the house, where he was found and taken to a hospital, treated with oxygen, and released. An HbCO level obtained 2 hours postexposure was 27.5%. Investigation by OHNAC

The four surviving persons were interviewed by OHNAC investigators and reported that sudden onset of dizziness, weakness, extreme difficulty walking, and difficulty thinking had inhibited their ability to recognize the hazard, exit the hazardous environment, and seek help. All reported being unaware that the sudden onset of symptoms is characteristic of CO poisoning, that they can be poisoned in a short time, and that CO can remain hazardous in areas with open doors and ventilation fans in operation.

None of the machines involved in these incidents had labels warning of the risk for CO exposure or directing that the equipment not be used indoors, although one engine operator's manual advised that the pressure washer should not be started or run inside a closed area (2). However, none of the four farmers had read the operating manuals; the two who had used rented or borrowed equipment had not been provided with manuals. All machines were reported to be properly maintained at the times of the respective incidents. Reported by: M Kahler, W Kuhse, LA Wintermeyer, MD, State Epidemiologist, Iowa Dept of Public Health. Surveillance Br, Div of Surveillance, Hazard Evaluations, and Field Studies, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: CO is an insidious health hazard because it accumulates rapidly (even in seemingly well-ventilated areas), cannot be detected (it is odorless and colorless), and produces weakness and confusion in persons exposed to toxic levels. Because CO absorption is proportionate to respiratory effort, persons engaged in vigorous physical activity -- such as during use of a pressure washer -- are at increased risk for adverse health effects when exposed to CO (1).

Levels of CO increase rapidly in closed environments and settings with limited ventilation. The average volume of the structures investigated in this report was approximately 150% that of a typical two-car garage. The risk for CO poisoning associated with operation of automobile engines in poorly ventilated spaces is well known; however, the findings in this report underscore the hazards of CO exposure when smaller gasoline-powered engines are operated inside buildings. Based on data collected in the field investigations, it is estimated that a 3-11-HP pressure washer operated in a 4700-ft superscript 3 space will produce dangerous CO levels within minutes (CDC, unpublished data, 1993) ***. In addition, there are no practical means to determine reliably whether ventilation is adequate for safe indoor operation of even small engines. In this report, the three farmers who were working in unventilated buildings had onset of CO toxicity within 30 minutes of exposure, while the two who were working intermittently in spaces with open doors and windows and with exhaust fans in operation were poisoned despite these precautions. Therefore, even brief indoor use of gasoline-powered pressure washers is hazardous, particularly for persons with preexisting cardiac or respiratory conditions (1,4).

In the United States, 81% of the approximately 243,000 swine farms house swine for farrowing, and pressure washers are used for cleaning on approximately 63% (5,6). Eleven other recent cases of CO poisoning associated with use of gasoline-powered pressure washers have been identified in four states. In Iowa, OHNAC has identified two cases in 1991 and two cases related to flood clean-up efforts in July 1993. In Kentucky, OHNAC identified one case occurring in April 1993. Finally, as a result of information disseminated by OHNAC programs about this hazard, family members have reported four more cases to OHNAC -- one in 1989 in North Carolina and three in Minnesota during 1991-1993.

As demonstrated in this report, farm workers can be poisoned by CO when operating gasoline-powered washers inside buildings. Preventing CO poisoning requires operating any gasoline-powered equipment outdoors at all times. Because pressure washers are used frequently during the winter months when freezing water is a problem, an approach to safe operation under these conditions includes moving the washer indoors when it is not operating and back outdoors before restarting or draining water from the machine when the washer is turned off. Alternative approaches, such as building separate structures to isolate the washer or attaching specially designed hoses to the exhaust pipe, may be inadequate or pose unique hazards (e.g., high CO exposure on entrance into the isolation structure or leaks or breaks in the hose).

In addition to gasoline-powered pressure washers, CO poisonings among persons on farms have been associated with unvented or inadequately vented space heaters and indoor tractor maintenance, underscoring that gasoline engines, irrespective of size, should not be operated indoors. Although warning labels and operator's manuals often advise against operating gasoline-powered equipment without "adequate" ventilation, adequate ventilation cannot be safely determined. Therefore, these labels and manuals should clearly indicate the CO hazard associated with indoor operation and prohibit any indoor use. In addition, equipment owners should ensure that manuals are provided when equipment is rented or borrowed and that operators read and understand these manuals before operation.


  1. Amdur MO, Doull J, Klaassen CD. Casarett and Doull's toxicology: the basic science of poisons. 4th ed. New York: Pergamon Press, 1991:264-8.

  2. Honda Motor Company. Owner's manual for GX-240, GX-270, GX-340, GX-390. Duluth, Georgia: Honda Motor Company, 1990:3.

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

  5. US Department of Agriculture. Technical report: national swine survey -- data collection: 1990. Fort Collins, Colorado: US Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services, 1992 (revised April 1993).

  6. US Department of Commerce, Bureau of the Census. 1987 Census of agriculture. Vol 1. Washington, DC: US Department of Commerce, Bureau of the Census, 1989:30.

* OHNAC is a national prevention program conducted by CDC's National Institute for Occupational Safety and Health (NIOSH) that has placed public health nurses in rural communities and hospitals in 10 states (California, Georgia, Iowa, Kentucky, Maine, Minnesota, New York, North Carolina, North Dakota, and Ohio) to conduct surveillance of agriculture-related illnesses and injuries that occur among farmers and their family members. These surveillance data are used to assist in reducing the risk for occupational illness and injury in agricultural populations. 

**SPRAINS is a statewide active and passive surveillance system in Iowa funded initially by CDC and currently maintained by the Iowa Department of Public Health. Injury data from Iowa farms are analyzed by county of occurrence. 

*** The NIOSH recommended exposure limit for CO is 35 parts per million (ppm) (as an 8-hour, time-weighted average), with a ceiling limit of 200 ppm (3).

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