Fatality Assessment and Control Evaluation (FACE) Program
Hog Farmer Dies from Asphyxiation after Manure Pit Agitation
In the fall of 2003, a 42-year-old farmer was killed in a hog confinement building after he was overcome by toxic gases arising from agitation of the manure pit beneath the facility. Working alone very early in the morning, the farmer prepared the manure for removal by agitating the pit with a manure pump attached to a tractor power take off (PTO). After starting the agitation process, the farmer entered the building to retrieve a dead hog that he had noticed inside of the building (Photo 1). The mechanical ventilation system in the building was not in use and the building was totally enclosed at the time of his entrance. Later in the afternoon the farmer was found lying face down in the center of the building by his fiancé, who immediately called 911 for help. Upon arrival, emergency rescue personnel donned appropriate personal protective equipment and removed the farmer from the confinement building. Examination of the farmer revealed that he had been deceased for several hours prior to the discovery of his body.
Recommendations based on our investigation are as follows:
In the Fall of 2003, a 42-year-old male farmer was killed in an animal confinement building in northwest Iowa after agitation of the manure pit beneath the building resulted in the release of toxic gases. The Iowa FACE program was alerted to this incident by a local newspaper article and began an investigation. Information for this report was derived from a Sheriff’s Office report, Medical Examiner’s report, newspaper articles, and interviews with family members.
The farmer was a co-owner with his brother in this swine production operation. After loading hogs at one of their hog confinement sites for transport to a processing plant, the farmer drove seven miles to the incident site. He began to agitate the manure pit beneath the floor of one of the buildings in preparation for taking a sample to analyze for nutrient levels. The hogs from this building had been removed two days earlier, and at that time, a dead hog had been seen inside the building. The farmer appeared to have entered the building to remove the hog while the pit was being agitated. With no added mechanical ventilation inside the enclosed building, the farmer was overcome by suffocating gases coming from the pit during agitation. The farmer was found dead several hours later.
Through manure management courses provided by the Iowa Extension Service, both the victim and his brother were aware that toxic gases are produced by decomposing manure, and that it was dangerous to enter unventilated manure pits. However, both farmers casually enter and exit these confinement buildings every day, and a strong ammonia smell inside of the buildings was considered normal.
The farm produced approximately 12,000 hogs per year. The farmer and his brother had been in partnership since 1995 and also produced cattle and grew corn and soybeans. The farmer had grown up on the farm where he died and had been involved in farming operations since he was a small boy.
In the fall of 2003, sometime between 3:45 AM and 1:00 PM, a 42-year-old male farmer died in a hog confinement building after he was apparently overcome by toxic gases. During the night the farmer and his brother, who was his business partner, had finished loading hogs at one of their production sites for shipment to a processing plant. His brother believed that immediately after loading the hogs, the farmer drove seven miles to the confinement building located at another site. All hogs had been removed from that confinement building two days before the incident, with the exception of one dead hog noticed during the loading process.
The farmer planned to collect a manure sample from the pit beneath the confinement building to have its nutrient level analyzed by the Iowa Department of Natural Resources. Prior to collecting this sample, it was necessary to agitate the pit, and the brothers had positioned a large row-crop tractor with a waste removal system attached to its power take off, and inserted this into the pit to stir the manure (Photo 2).
The victim’s fiancé had driven to the confinement building searching for the farmer, because she was concerned that no one had seen him all morning. Upon arriving at the confinement building at 1:00 PM,, she saw the man lying face down in the center aisle with a small puddle of blood on the floor beneath his face. The tractor was out of fuel and the manure pump no longer agitating the pit. The dead hog with a six-foot (1.8 m) piece of rope tied around its right hind leg, was approximately 10 feet (3.0 m) from where the farmer was lying. His fiancé immediately called 911 for help.
Upon arrival at the scene, the emergency rescue personnel donned air packs and entered the confinement building to remove the farmer. Examination of the farmer in the ambulance revealed that his body showed signs of stiffness and lividity, with a body temperature less than 80° F (27° C), indicating that he had died several hours earlier. He had pulled the hog approximately 60 feet (18 m) from where it had been seen lying the previous day, and he was only 20 feet (6 m) from the door of the building.
The building in which the farmer died was 50 ft. wide by 160 ft. long and 7.5 ft. high [approximately 60,000 ft.3 (1700 m3)]. The building was used for raising 1000 hogs. Six ventilation fans were in one end of the building—two 20” (500 mm) fans and four 24” (610 mm) fans. These fans were capable of moving approximately 30,000 cubic feet per minute (850 m3/min.) of air through the building. Curtains, which could be lowered during warm weather, lined both sides of the building. These curtains on the side of the confinement building were closed, and the ventilation fans were not operating. An electronic control system automatically raised the side curtains and started the ventilation fans when the temperature in the building reached 58° F (14.5° C). Inspection of the control system revealed that it was operating properly, but because of the cool temperatures (minimum 24, maximum 52, average 38° F; -4.5, 11.1, and 3.3° C respectively, according to the nearest weather reporting station) on this particular day, the curtains and fans had not been engaged. The fiancé and the emergency crew noted a very strong ammonia odor when they entered the building, but did not notice the “rotten-egg” odor associated with hydrogen sulfide.
Manure pit systems are commonly used on livestock farms to allow for easy cleaning of animal confinement buildings and storage of large amounts of raw manure. The manure pit on this farm was 8 ft. (2.4 m) deep beneath a slatted floor running the entire width and length of the confinement building. Large areas of the confinement building could be efficiently cleaned by washing manure and debris through the slats and into the pit. At the time of the incident, the pit was approximately 75% full. Inside pits such as this, manure undergoes anaerobic digestive fermentation. This process can generate four potentially dangerous gases: methane, hydrogen sulfide, carbon dioxide, and ammonia (Table 1). Accumulation of these gases within the confined space of the manure pit can produce an oxygen-deficient, toxic environment.
Oxygen levels below 16% lead to impaired judgment and breathing; levels below 6% lead to death within minutes. Methane is a colorless odorless gas which is explosive at concentrations between 5% and 15%, and at high concentrations can displace oxygen causing suffocation. The atmospheric concentration of carbon dioxide is generally 0.035%; higher concentrations may displace oxygen causing labored breathing, drowsiness, headache, and suffocation. Ammonia has a sharp, pungent odor, and can irritate the eyes and respiratory membranes. High concentrations may cause pulmonary edema and suffocation. Hydrogen sulfide has a “rotten egg” odor at concentrations between 0.02 to 0.13 ppm, but odor perception is unreliable as a warning because rapid olfactory fatigue may develop at concentrations above 100 ppm. Hydrogen sulfide is a metabolic toxin, blocking the cellular respiration in the mitochondria (cytochrome electron transport chain). Hydrogen sulfide concentrations above 1000 ppm may cause rapid unconsciousness and death. With hydrogen sulfide being heavier than air, the oxygen is displaced just above the emitting manure surface. With agitation, a large amount of hydrogen sulfide is emitted, replacing the oxygen at the level of a pig before affecting an adult in the upright, standing position.
Table 1: NIOSH Recommended Exposure Limits (RELs)
Cause of Death
The official cause of death from the Medical Examiner’s report
was, “asphyxiation, due to
Recommendation #1: Hazards of working in and around manure pits should be regularly and effectively communicated to farmers.
Discussion: The anaerobic digestion of manure below animal confinement facilities causes the generation of four potentially dangerous gases—methane, hydrogen sulfide, carbon dioxide and ammonia. In particular, agitation of the manure pit may produce hydrogen sulfide in the atmosphere above the pit. The accumulation of these gases within the confined space of the manure pit can produce an oxygen-deficient, toxic environment. Entering such an environment can be lethal and death can occur from the lack of oxygen or from the toxic effects of these gases. Livestock producers and other agricultural workers should be made aware of these hazards through training via extension service programs, trade journal announcements, producer meetings, and other communication campaigns. These education, outreach, training, and communication efforts should be continued and repeated periodically to inform new workers and remind experienced workers. While the number of manure pit asphyxiation fatalities may be on the decline, the potential for fatal injury still exists whenever agitating and handling liquid manure.
Many hog farmers are aware of the dangers associated with manure pits, and take appropriate precautions when working in or around the pits. However, farmers are naturally more casual with the confinement building interior space, since they enter and exit these buildings several times every day. Farmers must remember that these two areas share a common exchange of air through slats on the floor, and that agitation of the manure pit will cause gas levels to rise in the entire building. Farmers may assume they will notice something unusual if high concentrations of toxic, suffocating gases are present in their hog buildings, but this is not the case, and farmers must always be disciplined to take necessary precautions whenever they agitate a manure pit.