Confined spaces are an invisible hazard

Clardale manure pit
An earthen manure pit at Clardale Farms in Stark County. Farm and Dairy file photo.

By Haley Zynda and Dee Jepsen | Ohio State University Extension

As we continue to process the tragedy that occurred in western Ohio last week, when three farmers died after being overcome by fumes in a manure pit on their livestock farm, our hearts and prayers go out to the affected family. 

Confined spaces on farms are hazards, and difficult ones to recognize, at that, because of the normalcy of their presence on both grain and livestock operations. 

Confined spaces are defined as an area that is large enough for a person to enter and perform work but has limited or restricted means for entry or exit. These spaces have unfavorable ventilation and often contain or produce dangerous air contaminants. Examples include upright silos, manure pits and grain bins.


There are four primary dangers for working in confined spaces, the major risk being chemicals and gases that displace or consume oxygen, causing breathing difficulty for the worker. Another danger is the presence of toxins that can damage the respiratory and nervous systems and even cause death. 

Fires and explosions, typically caused by the presence of methane, physical dangers from moving parts and equipment or falls from or within the structure are the other three dangers of working in confined spaces. 

Each confined space has its own specific dangers as well. For example, hazards specific to manure pits include hydrogen sulfide gas, oxygen displacement by gases and drowning.  Meanwhile, in silos, the specific hazard is the displacement of oxygen by nitrogen dioxide gas. All other hazards of confined spaces can still occur in manure pits and silos. 

dairy excel table


Even with the danger that confined spaces pose, unfortunately, we often enter them. The most frequent reason workers enter a confined space is to conduct repairs or maintenance. The second reason they may enter is to rescue another person entrapped or overcome by gases.

The gases in manure pits and silos pose a particularly difficult hazard because they are invisible. We have a hard time responding to dangers we cannot see or touch. 


If you were to map the gases in a manure pit, you would see they appear in layers; they stratify based on weight compared to atmospheric air. Heavier gases sink to the bottom, while those lighter than atmospheric air will be found at the top. 

Hydrogen sulfide, carbon dioxide, carbon monoxide and methane are all gases found in manure pits. Going back to our air map, we would see hydrogen sulfide near the bottom, carbon dioxide between the hydrogen sulfide and air, carbon monoxide mixing with air because of their similar weights and methane above atmospheric air. 

Of the manure pit gases, hydrogen sulfide and carbon monoxide are the only truly toxic gases, whereas carbon dioxide and methane have displaced and used oxygen for their formation, depriving the “air” in a manure pit of oxygen for respiratory use. However, all have maximum concentration thresholds that can be found in the accompanying table. 

Silo gases, although different in chemical makeup, still pose the same invisible threat. Nitrogen dioxide gas causes respiratory distress and can cause death within minutes if present in great enough concentration. It is also heavier than air, so it will settle near the silage surface. 


Confined spaces are a necessity on grain farms and livestock operations. Maintaining these spaces is necessary. And safety, for ourselves, our families and our workers, is also a necessity. Talking to and educating people associated with the farm can be the first step in preventing confined space emergencies. Stay safe, and prayers to Mercer County, Ohio. 

(Haley Zynda is an extension educator in Wayne County and can be reached at 330-264-8722. Dee Jepsen is a professor and the state leader of the OSU Extension Agricultural Safety and Health Program. She can be reached at 614-292-6008.)


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