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Epidemiologic Notes and Reports Fatalities Attributed to Methane Asphyxiain Manure Waste Pits -- Ohio, Michigan, 1989

In June and July 1989, a total of seven farm workers in two separate incidents died after they were asphyxiated by methane gas in manure pits. Brief reports follow.

Ohio. On June 26, 1989, a 31-year-old male dairy farmer and his 33-year-old brother died after entering a 25-foot-square by 4-foot-deep manure pit inside a building on their farm. A pump intake pipe in the pit had clogged, and the farmer descended into the pit to clear the obstruction. While in the pit, he was overcome by lack of oxygen and collapsed. His brother apparently saw him collapse and entered the pit in an attempt to rescue him. The brother, too, was overcome and collapsed inside the pit. Four hours later, another family member discovered the two men, and the local fire department was called to rescue them. The coroner's report attributed the cause of death in both cases to drowning, secondary to loss of consciousness from methane asphyxia.

Michigan. On July 26, 1989, five farm workers in one family died after consecutively entering an outdoor manure pit on a farm. The pit measured 20 feet by 24 feet by 10 feet deep. The victims were a 65-year-old male dairy farmer, his two sons (aged 37 and 28 years), a 15-year-old grandson, and a 63-year-old nephew. The index victim, the 37-year-old son, initially entered the pit by ladder to replace a shear pin on an agitator shaft. While attempting to climb out of the pit, he was overcome and fell to the bottom of the pit. The grandson then entered the pit to attempt rescue. He, too, was overcome and collapsed. One by one, the nephew, the younger son, and the dairy farmer entered the pit in attempts to rescue the others, were overcome by lack of oxygen, and collapsed. A carpet installer working at the farm then entered the pit as a rescuer and was overcome; however, he was rescued by his assistant and subsequently recovered. Finally, the owner of a nearby business arrived with two additional workers and, using a rope, extricated the five victims from the pit. When paramedics arrived, they began cardiopulmonary resuscitation. The nephew was pronounced dead at the scene, and the other four victims were transported to the emergency room of a nearby hospital. The dairy farmer and his younger son were pronounced dead on arrival at the hospital; the 37-year-old son died 1 hour after reaching the emergency room. The grandson was transferred by helicopter to a major trauma center but died within 6 hours of his removal from the pit. For the four older victims, the medical examiner attributed the cause of death to methane asphyxia. Assignment of the official cause of death for the grandson awaits completion of the autopsy report. Reported by: Industrial Commission of Ohio, Columbus. Water Pollution Control Federation, Washington, DC. Div of Safety Research, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: Acute traumatic occupational deaths* in the United States are monitored by the Division of Safety Research, National Institute for Occupational Safety and Health (NIOSH), CDC, through the National Traumatic Occupational Fatalities (NTOF) file (1). For 1980 through 1985, the NTOF data file includes 16 work-related deaths that involved asphyxiation of workers in manure pits (or similar waste tanks) on farms. These deaths resulted from nine separate incidents in nine different states (Figure 1). Five of these episodes resulted in multiple fatalities. Because NTOF only includes deaths of workers greater than or equal to 16 years of age that are clearly identified as work-related, these 16 deaths represent the minimum number of asphyxiation fatalities that occurred during this period among U.S. farmers, farm family members, farm workers, and others working in manure pits.

A farm manure waste pit is a confined space, defined by NIOSH (2) as a space that "by design has limited openings for entry and exit; unfavorable natural ventilation which could contain or produce dangerous air contaminants; and which is not intended for continuous worker occupancy." Manure pits are fermentation tanks where raw animal wastes undergo anaerobic bacterial decay. This bacterial action generates methane, hydrogen sulfide, and other gases. Methane is a colorless, odorless, and flammable gaseous hydrocarbon. It can displace oxygen in confined areas, resulting in an oxygen-deficient atmosphere. Hydrogen sulfide is a highly toxic, colorless gas that at concentrations of greater than or equal to 300 ppm can cause unconsciousness, respiratory failure, and sudden death (3). If these gases are not properly vented from a tank or other confined space, an oxygen-deficient or toxic atmosphere may be created. In industrial settings, the Occupational Safety and Health Administration (OSHA) limits permissible peak exposures to hydrogen sulfide to a ceiling of 50 ppm (for less than or equal to 10 minutes); NIOSH recommends a ceiling of 10 ppm (for less than or equal to 10 minutes) (4). There is no OSHA permissible exposure limit for methane. OSHA exposure standards are not enforceable on farms with less than or equal to 10 employees. The apparent tendency for episodes such as those described here to result in multiple fatalities is of major concern. Fatal incidents resulting from entry into manure pits often involve more than one victim; the deaths of any additional workers occur during rescue attempts conducted without use of appropriate equipment and safety precautions. Investigations performed by NIOSH as part of the Fatal Accident Circumstances and Epidemiology Project show that approximately 43% of confined-space-related deaths involved co-workers or other persons who were attempting to rescue the initial victim(s) (NIOSH, unpublished data). The hazards of confined spaces and improper rescue methods have been addressed in previous NIOSH publications, including a guide to safe work practices in confined spaces (2,5,6).

In the two events reported here, hot humid weather may have contributed to the generation of methane gas and increased the amount of gas in the manure pits. The possible connection between hot weather and increased gas accumulation in manure tanks is also suggested by the NTOF data (Figure 2). All 16 deaths identified in the NTOF file occurred in April through September, with the highest number occurring in August. Farmers should be made aware of the particular hazards of entering manure pits during the summer months.

NIOSH is preparing information for farm operators on the hazards of manure pits and recommendations for safely evaluating, ventilating, and entering (when absolutely necessary) manure pits. Recommendations will also be provided for the safe conduct of rescue operations in circumstances such as those described in this report. NIOSH will disseminate this information during the fall.


  1. National Institute for Occupational Safety and Health. National Traumatic Occupational Fatalities: 1980-1985. Morgantown, West Virginia: US Department of Health and Human Services, Public Health Service, 1989.

  2. National Institute for Occupational Safety and Health. Criteria for a recommended standard . . . working in confined spaces. Cincinnati, Ohio: US Department of Health, Education, and Welfare, Public Health Service, 1979; DHEW publication no. (NIOSH)80-106.

  3. National Institute for Occupational Safety and Health. Pocket guide to chemical hazards. Cincinnati, Ohio: US Department of Health and Human Services, Public Health Service, 1985; DHHS publication no. (NIOSH)85-114.

  4. CDC. NIOSH recommendations for occupational safety and health standards, 1988. MMWR 1988;37(no. S-7).

  5. National Institute for Occupational Safety and Health. Alert . . . request for assistance in preventing occupational fatalities in confined spaces. Cincinnati, Ohio: US Department of Health and Human Services, Public Health Service, 1986; DHHS publication no. (NIOSH)86-110.

  6. National Institute for Occupational Safety and Health. A guide to safety in . . . confined spaces. Morgantown, West Virginia: US Department of Health and Human Services, Public Health Service, 1987; DHHS publication no. (NIOSH)87-113. *International Classification of Diseases, Ninth Revision, E800-E999.

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