The Agricultural and Biological Engineering group of Penn State University is currently conducting a research project on hydrogen sulfide releases from manure pits, with a focus on farms using gypsum products as bedding for dairy cows. (Industrial Scientific Corporation photo)

Agricultural Safety, Sometimes Forgotten

There must be ongoing education of farmers, their families, and hired hands on the dangers of gases on farm properties.

One industry in the United States that many people take for granted is the farming industry. Agriculture and agriculture-related industries contributed $75.8 billion to the U.S. Gross Domestic Product in 2012, a 4.8 percent share. Of that amount, American farms contributed $166.9 billion, or about 1 percent. That translates into 16.5 million full- and part-time jobs, accounting for about 9.2 percent of total U.S. employment. More than 2.6 million of those jobs are directly connected to U.S. farms.

Why all the stats? Agricultural deaths in 2012 totaled 475, making the death rate 21.2 per 100,000 full-time workers. And to make matters worse, in 2013, the number of deaths to 479 and the rate increased to 22.2 deaths per 100,000 workers. These numbers shouldn't be accepted by anyone.

Having spent time on farms, I have seen several unsafe acts involving different age groups. On family farms, the "young ones" are always helping out, from driving tractors and combines to working closely with the animals.

Of the many safety hazards that exist on a farm, the atmospheric hazards often go unaccounted for or are simply forgotten. This is due to either lack of caring or just being unaware of the potential gas hazards on a farm. Because of this, an increasing number of farmers and their family members are dying from gas exposures.

Areas in a farm that should be of concern are silos, outbuildings, barns, and manure pits. The most hazardous of these locations, by far, is manure pits. Some of the gases that can be found on a farm are hydrogen sulfide (H2S), nitrogen dioxide (NO2), methane (CH4), chlorine (Cl2), and ammonia (NH3). In addition to these hazardous gases, another threat is the depletion of oxygen (O2), which is a very common problem.

The areas where these gases appear on a farm's property are numerous. For example, ammonia is used as a fertilizer, while nitrogen dioxide can be found when corn and other crops along with silage are stored in silos, while methane and hydrogen sulfide are present in manure pits. The list goes on.

Manure Pit Gas Hazards
As mentioned, the most hazardous area on a farm is the manure pit. Look at any fatality report regarding farming, and you’ll see that the manure pit generally gets top billing as one of the most dangerous locations. Why are manure pits so dangerous? A typical dairy cow that produces approximately 2,000 gallons of milk per year also produces more than 7,000 gallons of liquid manure. The manure requires storing and overall managing by the farmers.

The Agricultural and Biological Engineering group of Penn State University is currently conducting a research project on hydrogen sulfide releases from manure pits, with a focus on farms using gypsum products as bedding for dairy cows. The gypsum bedding is being used for the animals' welfare in that it improves the dairy cows' living conditions. The gypsum absorbs moisture better, reducing the bacteria count, and it is pH neutral. In result, the cows are healthier. Later, as the manure is spread on the fields, the effects on the soil are low carbon additions with added sulfur.

(This study was principally funded by a grant from the United States Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS). It is being conducted by Mike Hile, a Ph.D. candidate at Penn State University, and overseen by Eileen Fabian Wheeler, Professor, Air Quality. They are located in University Park, Pa., and can be contacted as follows: Mike Hile, [email protected]; Eileen Wheeler, [email protected].)

Before gypsum was introduced to the dairy industry, there needed to be an understanding of the working of the manure pits and the dangers associated with them. The cow manure is moved from the barn into a manure pit either by a built-in conveyor system or manually by the farmer, depending on the size of the dairy operation. For example, one farm included in the research study has 275 dairy cows and a 1 million-gallon manure pit. The pit is emptied twice a year, with the manure spread over the fields for fertilizer. Typically this is done late fall after the crops have been harvested, and then again in the spring before the crops are planted.

This long storage time of the manure allows it to go anaerobic (without oxygen) and allows the bacterial action to produce hydrogen sulfide. Sometimes a "crust" forms on the top of the manure, acting as a lid trapping the gases. The danger occurs when the farmer needs to "stir" the manure pit to prepare for the disposal or spreading of the manure. The stirring of the manure releases the hydrogen sulfide that is trapped, along with any methane. The presence of these gases also can contribute to low-oxygen atmospheres. There are numerous accidents on record of farmers and members of their families who have been overcome by these deadly gases.

While gypsum benefits the welfare of cows, it increases the presence of hydrogen sulfide. Gypsum is a sulfur-based ore. Also known as calcium sulfate, CaSO4, it provides a sulfate source within the manure storage that reduces to form H2S. The research that Penn State is conducting is focused on the use of gypsum as bedding and its contribution to the increased levels of H2S. When farms using gypsum were studied, H2S was detected at life-threatening levels.

OSHA has a Permissible Exposure Limit (PEL) of 20 ppm and that is stated as the ceiling level, with an Immediately Dangerous to Life or Health (IDLH) level of 100 ppm. When the manure pits containing gypsum were stirred, levels as high as 500 ppm were encountered. A breath or two at these levels could have serious effects on a farmer, including respiratory distress and/or unconsciousness, potentially leading that farmer to fall into the manure pit. This could lead to higher gas exposures, asphyxiation, and even drowning.

One farm visited during the study experienced a very close call related to the safety of the family's two young boys. Playing slightly downhill from the manure pit one day during a stirring process, the boys were observed by their father to be lying next to their bikes. Thinking that the boys were just playing, he continued his work. A short time elapsed and he noticed the boys were in the same position. The two young boys had been overcome by hydrogen sulfide. He immediately attended to the boys and was able to revive them. No long-term damage occurred, but the younger of the boys was kept overnight at the hospital for observation.

Scenes like this are repeated several times a year on farms, sometimes with tragic outcomes. There must be ongoing education of farmers, their families, and hired hands on the dangers of gases on farm properties, and there also must be additional studies like the one being done by Penn State. Only then will the 479 deaths that occurred during 2013 in agriculture be reduced to eventually zero.

1. U.S. Bureau of Labor Statistics; USDL-14-1674
2. Centers for Disease Control (CDC) NIOSH Publication NIOSHTIC-2
3. Occupational Safety & Health Administration (OSHA); NEWS Release: 13-1921-NAT (234)


This article originally appeared in the December 2014 issue of Occupational Health & Safety.

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