The National Institute for occupational Safety and Health (NIOSH) requests assistance in preventing deaths of farm workers in manure pits. An urgent need exists to inform farm owners and workers about the dangers of entering such pits, where oxygen-deficient, toxic, and/or explosive atmospheres often result from fermentation of the wastes in confined areas. These hazards have been known for several years. However, recent NIOSH investigations conducted under the NIOSH Fatal Accident Circumstances and Epidemiology (FACE) Program suggest that farm workers are unaware of the danger, and many deaths continue to occur as a result of entry into manure pits.
This Alert describes seven deaths from asphyxiation (suffocation) that occurred during two incidents involving entry into manure pits. The recommendations included in this Alert should be followed by all farm owners and operators who have manure pits on their property. Editors of appropriate trade journals, agriculture extension agents, farm owners and operators, and those in the agricultural trades are requested to bring the recommendations in this Alert to the attention of all workers who re at risk.
Inside the pit, the manure undergoes anaerobic digestive fermentation to form fertilizer. The digestive process can generate four potentially dangerous gases:
The accumulation of these gases within the confined space of the manure pit can produce an oxygen-deficient, toxic, and/or explosive environment.
The National Traumatic Occupational Fatality (NTOF) Data Base indicates that from 1980 through 1985, 16 deaths resulted from the asphyxiation (suffocation) of workers in manure pits or similar waste tanks [NIOSH 1989a]. These deaths resulted from nine separate incidents, but five of them involved multiple fatalities. Because the NTOF Data Base includes only work-related deaths of U.S. workers aged 16 or older, it may underestimate the number of deaths resulting from entry into manure pits during 1980-85.
Under the Fatal Accident Circumstances and Epidemiology (FACE) Program, NIOSH investigated the two 1989 incidents described in this Alert. These two incidents resulted in seven fatalities and suggest that many farm workers are unaware of the hazards of entering manure pits. These pits are designed as confined spaces with limited means of entry and unfavorable ventilation. The gases generated by the bacterial decay of the manure may accumulate sufficiently to create deadly oxygen-deficient ( less than 19.5% oxygen), toxic, and/or explosive atmospheres [NIOSH 1987].
In these two incidents and in those reported earlier, the fatalities often involved more than one victim. Two or more workers often died when rescue was attempted without appropriate safety equipment and procedures. Such a chain of events is consistent with the findings of other FACE investigations, which show that 39% of the victims in confined space incidents were coworkers or others who attempted to rescue the initial victim [Manwaring and Conroy (in press)].
NIOSH has published a criteria for a recommended standard for working in confined spaces [NIOSH 1979], an Alert on confined space hazards [NIOSH 1986], and a guide for working in confined spaces [NIOSH 1987].
|Table 1. Health effects associated with various percentages of oxygen in the atmosphere*|
|% oxygen in atmosphere||health effects|
(normal oxygen content in air)
(minimum oxygen level for safe entry)
|16||impaired judgement and breathing|
|14||faulty judgement, rapid breathing|
|6||difficult breathing, death in minutes|
|* - Source: NIOSH |
Methane Methane (CH4) is an odorless gas that is flammable or explosive at concentrations of 5% to 15% by volume of air [NIOSH 1985b]. At high concentrations, methane can displace enough oxygen to cause death by suffocation. Because this gas is lighter than air, it occurs near the top of the pit. Methane should be expected to be present in manure pits.
Hydrogen Sulfide Hydrogen sulfide (H2S) is a highly toxic gas with a "rotten egg" odor at low concentrations [NIOSH/OSHA 1981]. At high concentrations, hydrogen sulfide can paralyze the olfactory senses [NIOSH 1979]. Because this gas is heavier than air, it can settle near the bottom of the manure pit. Hydrogen sulfide is a severe eye irritant and may cause tissue damage [NIOSH/OSHA 1981]. At low concentrations, this gas can cause dizziness, headache, nausea, and irritation of the respiratory trait. At high concentrations, hydrogen sulfide can cause unconsciousness, respiratory failure, and death within minutes. In addition, hydrogen sulfide may be explosive at a wide range of concentrations in air-4.3% to 46% by volume [NIOSH 1985a].
Carbon Dioxide Carbon dioxide (CO2) is an odorless gas that is normally present in the atmosphere [NIOSH/OSHA 1981]. Because this gas is heavier than air, it can settle near the bottom of the manure pit. At low concentrations, carbon dioxide can result in labored breathing, drowsiness, and headache. At high concentrations, carbon dioxide can displace enough oxygen to cause death by suffocation.
Ammonia Ammonia (NH3) has the sharp odor characteristic of household ammonia [NIOSH/OSHA 1981]. This gas can severely irritate the eyes, nose, throat, and lungs. Exposure to high concentrations can be fatal.
Case No. 1: Two Fatalities On June 26, 1989, a 31-year-old male dairy farmer and his 33-year-old brother died after entering a 25-foot-square, 4-1/2-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 and collapsed. The victim's brother was standing at the entrance of the pit and apparently saw the victim collapse. He entered the pit in an attempt to rescue him. The brother as also overcome and collapsed inside the pit. Four hours later, another family member discovered the two victims inside the pit and called the local fire department to rescue them. The victims were pronounced dead at the scene by the coroner. The coroner's report attributed the cause of death in both cases to methane asphyxiation [NIOSH 1989b].
Case No. 2: Five Fatalities On July 26, 1989, five farm workers died after consecutively entering a manure pit on their farm. The pit measured 20 by 24 feet and was 10 feet deep. The victims were a 65-year-old dairy farmer, his two sons aged 37 and 28, a 15-year-old grandson, and a 63-year-old nephew. The younger son initially entered the pit to replace a shear pin on an agitator shaft. (NOTE: Agitation of the manure, which is required to facilitate transfer, causes a rapid release of the gases formed during decomposition.) While attempting to climb out of the pit, the initial victim was overcome and fell to the bottom. The grandson then entered the pit to attempt a rescue. He too was overcome and collapsed. The nephew, the older son, and the dairy farmer then entered the pit one at a time, attempting to rescue those already overcome. Each was overcome and collapsed in turn. A carpet installer working at the farmhouse then entered the pit to attempt a rescue. He too was overcome but was rescued by his assistant and subsequently recovered. Finally, the owner of a local farm implement business arrived on the scene wit two of his workers and, using a rope, extricated the five victims from the pit. When the local emergency rescue squad arrived on the scene approximately 20 minutes after the incident, they immediately began cardiopulmonary resuscitation. The nephew was pronounced dead at the scene. The remaining four victims were transported to the local hospital. The farmer and his younger son were pronounced dead on arrival, and the older son died an hour after reaching the emergency room. The grandson was transferred to a major trauma center by helicopter, but he died approximately 6 hours after his removal from the pi . Reports of the medical examiner cite methane asphyxiation as the cause of death for these five victims [NIOSH 1989c].
The decomposition of waste that occurs in manure pits can create oxygen-deficient, toxic, and/or explosive atmospheres. The anaerobic bacterial action that breaks down the manure can generate methane, hydrogen sulfide, carbon dioxide, and ammonia. These gases may produce toxic effects, but more important, they can displace oxygen in a confined space. Deaths can occur from lack of oxygen or from the toxic effects of these gases [Donham 1983; CES 19801. In addition, methane and hydrogen sulfide may present an explosion hazard.
The two incidents reviewed in this Alert occurred during hot weather, which may result in increased gas accumulation in manure pits. All 16 deaths identified in the NTOF Data Base occurred from April through September, with the highest number occurring in August. Although this information indicates that summer is the most dangerous period, the potential for an oxygen-deficient, toxic, and/or explosive atmosphere is always present in a manure pit.
In addition, a positive-pressure, self-contained breathing apparatus (SCBA) should be used by individuals entering the pit if an oxygen-deficient or toxic atmosphere is detected. However, because the required training and specialized equipment may not be readily available to farm workers, NIOSH recommends that they take the following MINIMUM precautions wherever manure pits are in use:
NIOSH further recommends that the following actions be taken by farm owners and operators as well as manufacturers and providers of equipment for animal waste pit systems:
Comments or questions concerning this Alert should be directed to Dr. Thomas R. Bender, Director, Division of Safety Research, National Institute for Occupational Safety and Health, 944 Chestnut Ridge Road, Morgantown, West Virginia 26505-2888, telephone (304) 291-4595.
Publication #: 90-103
This document is NIOSH Publication, 90-103 . Publication date: May, 1990.
National Institute of Occupational Safety and Health, Department of Health and Human Services, 200 Independence Avenue, SW, Washington, DC, 20201. Phone: (800) 356-4674.
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