Manure pit injuries: Rare, deadly, and preventable.

A male worker entered an underground manure pit and lost consciousness. His coworker tried to rescue him and also lost consciousness in the pit. Emergency service arrived in minutes and removed both of them from the pit. Both men suffered anoxic brain injury and died in the hospital. Cases from Iowa Fatality Assessment and Control Evaluation Program Data Base program were reviewed. Occupational mortality rate was found to be 7.4 per 10,000 per year for occupational deaths related to agriculture compared to 3.1 per 10,000 per year for deaths not related to agriculture. In most of the cases associated with sewage or livestock waste handling, victims died of asphyxiation. While manure pit injury is rare, it has an extremely high fatality rate. The most effective strategy to decrease mortality is active prevention.

INTRODUCTION

Agriculture ranks among the most hazardous industries in the United States (US),[1] with the livestock manure storage facility being a major hazard in the agricultural workplace. Livestock manure storage facilities pose several risks, including falls, toxic gas inhalation and asphyxiation, aspiration of liquid manure, infection, and explosion. There have been numerous instances where a farmer, employee, or family member has died from exposures associated with livestock manure storage facilities.[2-6] These events are relatively rare but result in a disproportionate share of fatalities, with many incidents involving multiple fatalities.[34] Many of the deaths are associated with toxic gas inhalation.[4] Common gaseous by-products of organic decomposition include hydrogen sulfide (H2S), ammonia (NH3), methane (CH4), and carbon dioxide (CO2). H2S is considered the most dangerous of these by-products and is one of the leading causes of sudden death in the workplace.[78]

We present a case of a double fatality resulting from toxic gas inhalation involving two men entering a hog manure pit. In addition, we present our findings from our evaluation of the Iowa fatality assessment and control evaluation (FACE) Program database for agriculture-related deaths and deaths resulting from exposure to manure and sewage handling facilities. Finally, we provide a discussion and recommendations for agriculture livestock manure storage and for the treatment and prevention of injuries and fatalities related to sewage handling.

CASE PRESENTATION

Two male farmers, ages 52 and 23, were working at a swine confinement facility on a warm spring day. The older man entered an underground manure pit that had been drained. He quickly lost consciousness and became unresponsive. The younger man went for help, and the 911 emergency response system was activated. The 23-year-old returned and entered the pit to attempt rescue. He also quickly lost consciousness and became unresponsive. Emergency service personnel arrived in minutes and removed the two men from the manure pit. Both men underwent endotracheal intubation at the scene and were taken to a local emergency department, where advanced life support protocol was initiated. The men were subsequently transferred to a tertiary trauma center. Upon arrival, both men were unresponsive with Glasgow Coma Scale of 3 in total score. The 52-year-old man's vital signs and arterial blood gas were within normal limits, with an elevated lactic acid at 3.0 meq/L. He was transferred to the surgical intensive care unit (SICU) for further resuscitation. The 23-year-old man arrived in sinus tachycardia with rate of 150 bpm. He was found to be acidotic with an arterial blood pH of 7.15, hypercarbic with PCO2 of 61 torr, and hypoxic with PaO2 of 40 torr. He had a base excess of –10 meq/L and elevated lactic acid of 6.5 meq/L. His chest X-ray was consistent with severe pulmonary edema, and hypoxemia continued with maximal ventilator settings. He then developed hypotension that was refractory to fluid administration and required vasopressor administration. He was transferred to the SICU and placed on high-frequency oscillating ventilation, and his PaO2 level improved with blood pressure stabilization. In the SICU, both men developed evidence of anoxic brain injury. The older man died on the 4th hospital day and the younger man died on the 14th hospital day.

EPIDEMIOLOGY

We reviewed the Iowa FACE Program Database, which includes all occupational fatalities that occurred in the state of Iowa from 1995 through 2003. The Iowa FACE Program defined an occupational fatality as “any fatal event that occurs at work. The victim may be an employer, employee, or self-employed person, farmer or family member helping with business.” It further states that “each case in the program has been investigated and results were verified. Occupation fatalities must be work-related; death from natural causes is not included.” The total agricultural workforce in Iowa from 1995 through 2003 was obtained from the US Department of Agriculture (USDA) National Agricultural Statistics Service. The incidence of occupational fatalities in Iowa was then derived using USDA workforce data and is illustrated in Figure 1.

Figure 1

Shows the yearly distribution of occupational deaths per 10,000 Iowa from 1995 through 2002. The frequency of occupational deaths per year was found to be significantly higher among agriculture workers (P=0.002)

A total of 671 occupational deaths were documented by the Iowa FACE Program from 1995 through 2003, with 399 of these deaths not associated with agriculture and 272 of the deaths associated with agriculture-related occupations. Figure 1shows the annual distribution of occupational deaths per 10,000 Iowa workers among the total workforce, occupational deaths not related to agriculture, and occupational deaths related to agriculture. Occupational deaths per 10,000 workers were consistently higher among agricultural occupations each year. Over this time period, the mean±standard deviation of occupational deaths among 10,000 workers per year was 4.0±0.67 for the total work force, 3.1±0.58 for occupational deaths not related to agriculture, and 7.4±1.8 for occupational deaths related to agriculture. The incidence of occupational-related deaths per year was significantly higher among agriculture workers (P=0.002). During this period, seven incidents occurred, resulting in nine deaths associated with livestock manure and sewage-handling facilities [Table 1], accounting for approximately 1% of all reported occupational fatalities. Five of the nine deaths involved agricultural workers working in or around hog manure storage facilities, with one of these deaths secondary to an unsuccessful rescue attempt. The remaining four deaths were among sewage plant workers; two of the deaths occurred in the same incident.

Table 1

Case series associated with sewage or livestock waste handling

DISCUSSION

Agriculture is one of the most hazardous industries in the US. Deaths related to work in agriculture have been demonstrated to be higher than any other sector, including the mining industry.[1] While the absolute number of occupational deaths was less among agriculture-related occupations than non-agriculture occupations, the fatality rate for agriculture-related occupational deaths per 10,000 workers annually is twofold higher than that of occupational deaths not related to agriculture.

Toxic gas inhalation leads to more work-related fatalities than any other route of chemical exposure in sewage management.[9] The nature of these fatalities is a very rapid onset. An individual exposed to toxic gas will become incapacitated in seconds to minutes depending on the gas concentration. Rescuers without proper protective gears often succumb to toxic gas inhalation. This case report describes two fatalities consistent with toxic gas inhalation involving a worker entering hog manure pit and the unsuccessful rescue attempt by a coworker. Evaluation of the Iowa FACE Program database identified seven additional deaths related to toxic exposure associated with livestock manure and sewage handling facilities, which accounted for 1% of the total occupational deaths. One of the incidents involving sewage workers resulted in the deaths of two workers. The high fatality is not only unique to the sewage handling business; a published review of construction-related fatalities demonstrated 1.3% were due to toxic inhalation.[10] In that review article, water and sewer workers had the highest risk for occupational deaths due to poisoning. Ten percent of the fatalities involved coworkers who were attempting rescues and were incapacitated. Moreover, a review of 77 livestock manure storage-related fatalities between 1975 and 2004 found that 22% of the deaths involved unsuccessful rescue attempts by coworkers.[4] Therefore, although these incidents are relatively rare, multiple fatalities are not uncommon because many deaths occur during rescue attempts.

Common gaseous by-products of organic decomposition include H2S, NH3, CH4, and CO2. H2S is considered the most dangerous of these byproducts[78] and is one of the leading causes of sudden death in the workplace.[1112] NH3 is corrosive and can be rapidly fatal at high concentrations (>5,000 ppm);[13] however, the usual levels in manure pits only cause irritation to the eyes and respiratory tract. CH4 and CO2 act as physical asphyxiants, producing anoxia by displacing oxygen in an enclosed space. In contrast, H2S acts as a chemical asphyxiant, interfering with cytochrome oxidase and aerobic metabolism, similar to hydrogen cyanide. Additionally, carbon monoxide (CO) has been attributed to occasional sewer-related deaths.[10] However, CO is a byproduct of combustion rather than decomposition and was more commonly associated with deaths in which gasoline-powered tools were used in an unventilated sewer.[10]

H2S is classically associated with deaths occurring in sewers.[4] H2S is a metabolic poison to the cellular mitochondrion. It inhibits cytochrome oxidase and leads to blockage of the electron transport chain and inhibition of cellular respiration. During exercise, low level exposure (5–10 ppm) can cause a shift to anerobic respiration, leading to increased production of lactic acid.[8] The US National Institute for Occupational Safety and Health (NIOSH) recommended maximal exposure limit of H2S is 10 ppm for no more than 10 min. H2S concentrations of 5 ppm have been documented in swine barns during normal operations;[14] however, H2S concentrations of nearly 1000 ppm have been recorded when various procedures associated with manure storage tanks are performed.[14] H2S has an unpleasant and intense odor (“rotten eggs”) at levels of 10-30 ppm, with olfactory fatigue and olfactory nerve paralysis developing at 100-150 ppm. Additionally, pulmonary edema and apnea are associated with H2S levels of 300-500 ppm and with near-instant respiratory paralysis and coma associated with levels of 1000 ppm and greater.[15] High concentrations of H2S will inactivate respiratory centers in the brain, causing respiratory arrest. Additionally, prolonged exposure to even lower concentrations of H2S can lead to pulmonary edema and congestion.[7]

Treatment of patients exposed to livestock manure storage and sewage handling facilities involves a safe rescue, immediate administration of an antidote in the field, and supportive respiratory care. Upon entering a livestock manure storage or sewage handling facility, rescuers should use a self-contained breathing apparatus and wear a safety harness for the safe rescue of victims because rescuers may become victims. Additionally, as with any critically ill patient, appropriate airway management and administration of high-flow oxygen should be performed. The production of methemoglobin results in competitive binding of the H2S anion.[7] Inhalation of amyl nitrite ampules or intravenous administration of sodium nitrite is used to produce methemoglobin. Other supportive care measures also include vasopressors for hypotension and benzodiazepines for seizure control. Additionally, hyperbaric oxygen has been used for H2S toxicity in patients with neurological compromise and patients with refractory acidosis.[16-18]

Many of the deaths and injuries associated with livestock manure storage and sewage handling facilities are often preventable. Entering a manure storage or sewage handling facility may not be safe even if it has been entered uneventfully in the past. Individuals entering a manure storage facility should use a self-contained breathing apparatus and wear a safety belt or harness with line attached. An observer capable of retrieving the individual inside the facility should also be available outside the facility in the event of a toxic exposure.

CONCLUSIONS

Agriculture is an extremely hazardous industry, with occupational deaths significantly higher than nonagriculture-related deaths. Manure pit injury has an extremely high fatality rate; also, it is often preventable. Active prevention is the most effective strategy to decrease mortality. Improved engineering and design of manure facilities should decrease the severity and incidence of toxic exposure. Treatment options are inadequate due to delays common to rural settings.

Although these deaths are rare, multiple fatalities are not uncommon, as many deaths occur during rescue attempts of individuals from manure storage and sewage-handling facilities. These deaths can be prevented by using a self-contained breathing apparatus, a safety cable, and having at least one observer capable of pulling individuals out of these facilities. Specific measures such as resuscitation per advanced life support protocols, administration of a methemoglobin-inducing agent, and hyperbaric oxygen treatment may increase chances for survival.