Suffocation from grain is the leading cause of grain bin deaths, but oxygen-deficient atmospheres are another serious danger.

Confined spaces on farms pose a serious suffocation or asphyxiation risk to farmers, employees and family members. Examples of potentially dangerous confined spaces on farms include grain bins, silos, manure pits, slurry tanks, water tanks and wells.

These confined spaces produce toxic, oxygen-deficient atmospheres that can quickly overcome anyone who enters — causing almost-instant death or serious bodily injury.  

Suffocation hazards

Grain bins

Grain engulfment is the leading suffocation hazard, but suffocation or asphyxiation also occurs when workers are overcome by toxic gases caused by spoiled or deteriorating grain, machinery in use in or near grain bins or other problems. If the grain being held in storage is out-of-condition, the potential for carbon monoxide is high due to decomposition of the grain. If the grain has visible mold growth or there is a musty smell in the bin, one should not enter the bin.

In the absence of visible grain decay, hazardous carbon monoxide build-up is still possible when out-of-condition grain is hidden underneath good grain. That’s why it’s important not to rely on “warmer-than-expected temperatures” or “higher levels of moisture” as primary indicators. The best and recommended indicator of the atmospheric condition inside a grain bin is to utilize a personal oxygen monitor that accurately tests air quality and warns you of unsafe oxygen levels.

Grain bin hazards are not limited to suffocation or engulfment. See other grain bin hazards and other grain bin accidents.


Highly toxic nitrogen dioxide is produced by the natural fermentation of chopped silage. In small amounts, the gas can cause severe irritation to the nose and throat and may lead to inflammation of the lungs. Very high concentrations will cause immediate distress resulting in a person collapsing and dying within minutes.

Manure pits

The decomposition of animal waste produces an oxygen-deficient, toxic and explosive environment. It’s not uncommon for manure pit incidents to result in multiple fatalities when family or co-workers enter the pit to perform a rescue — only to meet the same fate. Don’t run in to rescue. Plan ahead by developing an emergency action plan.

On July 25, 2015, an Iowa father and his son died from manure pit fumes. Early that same month, a Wisconsin father and son were killed in a manure pit while trying to retrieve a piece of equipment that had fallen into the pit.

Oxygen levels

The following table shows how oxygen levels effect us:

% oxygen in atmosphere Health effects
21 (normal oxygen content in air) None
19.5 (minimum oxygen level for safe entry) None
16 Impaired judgment and breathing
14 Faulty judgment, rapid fatigue
6 Difficult breathing, death in minutes
Source: NIOSH [1987].

Safety best practices

The best approach for preventing tragic accidents is simple: keep out of confined spaces, unless absolutely necessary. This means performing all work from outside of the confined space, whenever possible. It’s essential that the seriousness of these hazards are clearly communicated to all workers and family members. Always keep children out — children and grain handling don’t mix.

Grain bins

  • Maintain proper grain management, more specifically proper aeration and cooling of stored grain to prevent spoiled or deteriorating grain – the leading cause of grain bin entry.
  • Use a pole from the outside of the grain bin to break up crusted grain. (Keep away from power lines.)
  • Follow safe bin-entry procedures, such as using a grain bin-entry permit, de-energizing and locking out equipment and testing bin atmosphere.
  • Restrict bin-entry to proper trained entrants — 18 years of age or older.
  • Encourage young workers to Stand T.A.L.L.

Atmospheric testing and ventilation

If grain bin entry is absolutely necessary, the entrant must test the air for the presence of combustible gases, vapors and toxic agents – before entry. If an insufficient oxygen level is identified, ventilation must be provided until the unsafe condition is eliminated; and it must be maintained if there’s a chance for the condition to redevelop while the worker is inside. No entry is permitted until a sufficient oxygen level has been reached.


  • Avoid silo during the critical period when gases are forming.
  • Wear a self-contained breathing equipment with oxygen-supplying tanks during entry.
  • Restrict entry to proper trained entrants — 18 years of age or older.

Manure pits

  • Never enter a manure pit, especially during or just after agitation.
  • If absolutely necessary to enter a manure pit, always wear a self-contained breathing equipment with oxygen-supplying tanks
  • Always wear a safety line and work with at least two other people outside the pit.
  • Restrict entry to proper trained entrants — 18 years of age or older.
  • Remove all people and all animals from buildings over pits before pit agitation.
  • Provide maximum ventilation when agitating or pumping manure.
  • Do not smoke or have any other fire or ignition source around manure pits.

Nothing that is dropped into any of these spaces is so important that you cannot take a few extra minutes to think about how to enter safely or just replace the item and not enter. If the reason for entry is to work on something located in the area, it’s very important to ensure proper ventilation is provided to the area. Also verify that the oxygen content is high enough that the person entering is safe.

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