Agricultural Engineering Safety Lesson Plan: Hazardous Gases


Learn about the various toxic gases found in and around agricultural buildings (especially silos, manure pits, and grain bins) and what precautions should be taken to minimize exposure to and/or damage done by these hazardous gases. Also to identify the specific kinds of protective equipment needed when working in confined spaces and the differences in respiratory protective equipment.


Air-purifying respirator, powered air purifier, gas mask, air supplied respirator.


  1. Five toxic gases of major concern can be found in manure pits and silos. They are: Hydrogen sulfide (H2S), ammonia (NH3), carbon dioxide (CO2), methane (CH4), and nitrogen dioxide (NO2).
  2. The primary hazards of these gases are:
    • Toxic or poisonous reactions in people or animals
    • Oxygen depletion which can result in asphyxiation
    • Explosions that can occur when oxygen mixes with the gases (primarily a problem with methane)
  3. Characteristics of hydrogen sulfide (H2S)
    • Most dangerous gas associated with waste decomposition
    • Distinct rotten egg smell
    • Heavier than air
    • After breathing this gas a short time, sense of smell becomes fatigued and you can no longer detect an odor
    • At low concentrations H2S irritates the eyes and respiratory tract; at moderate levels exposure causes headache, nausea, and dizziness; at high concentrations H2S causes death
  4. Characteristics of ammonia (NH3)
    • Distinct, sharp, penetrating odor detectable at very low concentrations
    • Heavier than air
    • At moderate levels of concentration, can irritate eyes and respiratory tract; at high concentrations can cause ulceration to the eyes and severe irritation to the respiratory tract.
  5. Characteristics of carbon dioxide (CO2)
    • Odorless, heavier than air, difficult to detect
    • Replaces oxygen in air and acts as an asphyxiant
    • At moderate concentrations causes shortness of breath and dizziness
    • A major contributing factor to animal deaths by asphyxiation in confinement buildings with faulty ventilation
  6. Characteristics of methane (CH4)
    • Odorless and lighter than air, so it tends to accumulate at the top of manure pits
    • Considered an asphyxiant at extremely high concentrations. Main hazard is its flammable, explosive nature
  7. Characteristics of nitrogen dioxide (NO2)
    • Pungent, sweetish odor, even at low concentrations. Has reddish-brown color, visible only in extremely high concentrations
    • Heavier than air and can settle at the bottom of enclosed spaces
    • One of the most hazardous lung irritants, however, the effect is so subtle that the victim may not realize the serious nature of the exposure until it is too late. Can cause bronchitis, chemical pneumonia, a severe fibrosis-type of pneumonia, severe lung damage than can be fatal in two to 10 days; or acute pulmonary edema that can be fatal in less than 48 hours.
  8. When working in agricultural buildings provide as much ventilation as possible, especially around manure pits during the agitation of waste. No workers should be near a manure pit or in the building during the agitation process. If possible, remove all animals from the building.
  9. Avoid entering a manure pit at any time, it at all possible. Even if the pit has been emptied, it still may be lacking in oxygen or have high concentrations of toxic gases.
  10. Always keep at least one toot of space between the highest manure level and the slats. This protects animals who lie on the slats and inhale the gases that accumulate at the surface of the pit.
  11. Do not allow anyone to enter a silo during the tilling process until the blower has run for at least 30 minutes.
  12. Never enter a silo or manure pit area without someone on the outside monitoring your activity.
  13. Do not allow anyone to enter a silo for seven to 10 days after the filling process is complete because the fermentation process produces toxic gases.
  14. Select the specific type of respiratory protective equipment necessary for the hazards present and the amount of filtering necessary. Regardless of the type that is chosen, however, all respiratory protection must be approved by the National Institute for Occupational Safety and Health (NIOSH).
  15. Air purifying respirators remove contaminants from the air, but can be used only in an environment that has enough oxygen to sustain life. Do not use air purifiers to provide protection from the dangers of oxygen-limited environments. There are two general types of air purifying respirators; those with mechanical filters and those with a chemical cartridge. Mechanical filter purifiers are not for use around toxic gases.~ Chemical Cartridge respirators protect against certain gases and all but the most toxic organic vapors.
  16. Powered air purifiers can be mechanical filter, chemical cartridge, or a combination of both. They cannot be used in oxygen-limited environments.
  17. Gas masks are more effective than chemical cartridge respirators against high concentrations of toxic gases. Gas masks should not be used in oxygen-limited environments.
  18. Supplied-air respirators are for use in oxygen-deficient areas such as manure pits, silos containing silo gas, airtight silos, or bins containing high moisture grain. The two main types of supplied-air respirators are the hose mask with blower and emergency air supply, and the self-contained breathing apparatus (SCBA).

Kansas State University Cooperative Extension Service, Manhattan, Kansas.

The KSU Cooperative Extension Service provides practical, research-based information and educational programs to address critical issues facing individuals, families, farms, businesses and communities.

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