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Manure Pit/Silo Hazards with Balloons and Role Playing Exercise

By Linda Fetzer


Hazard Overview

Many instances of someone being overcome by manure or silo gases resulting in multiple fatalities have been recorded when someone or several people decide to go into the manure pit or silo to rescue a victim. This role playing activity can demonstrate what can happen related to exposure to dangerous gases. Common hazards related to silos and manure storage are listed below:

  • Upright silo dangers include climbing/falls, silo gases, turning parts (e.g., silo unloader), and dust.
  • Bunker/horizontal silo dangers include cave-ins and tractor rollovers while packing.
  • Manure storage dangers include gases and drowning.

Silo Gas Hazards

In an upright silo, a variety of gases are formed through the natural fermentation process of chopped forages. The type of silo is important in determining which gas will be predominant. For example, in sealed, oxygen limiting silos both nitrogen and carbon dioxide gases are created, but carbon dioxide is produced in far greater amounts which is beneficial because high carbon dioxide levels help maintain high quality silage. However, carbon dioxide is odorless, colorless, and very dangerous because it displaces the silo's oxygen, and in high concentrations, gives a person little warning that they are about to be overcome. Because of this hazard, sealed silos are designed in such a way that entering them is unnecessary.

A variety of gases can be formed in conventional silos but generally, nitrogen dioxide is the most prevalent type of gas. This gas is characterized by a strong bleach-like odor and under certain conditions can be visible as a fog from a distance (sometimes mistaken for smoke). Unlike carbon dioxide, nitrogen dioxide levels reach a peak about three days after harvesting and rapidly begin to decrease thereafter, particularly if the silo is ventilated. After two weeks it is unlikely that more gas will be produced, although some hazard remains if the gas has not been able to escape the silo.

Nitrogen dioxide is harmful because it causes severe irritation to the nose and throat and may lead to inflammation of the lungs. Individual reactions to silo gas depend on the concentration of inhaled gas and length of exposure. Very high concentrations of gas will cause immediate distress resulting in a person collapsing and dying within minutes. When gas levels are this high, typically the individual will not be able to withstand the symptoms felt and will quickly vacate the area. However, this gas is dangerous because a low level exposure may be accompanied by only a little immediate pain or discomfort, and more severe reactions may be delayed for several hours.

Manure Gas Hazards

The breakdown of manure is a biological process, and environmental factors such as temperature, humidity, and air flow can impact the release rate of gases produced during this process. High temperature, lack of air exchange, and humidity can increase the levels of manure gases that are produced and released. The following hazardous gases form naturally in manure storage areas and are difficult to detect because of their properties, impact on a person's sense of smell, and similarity to other odors on a farm or ranch:

  • Ammonia is found in manure pits or above-ground tanks used for manure storage and has a strong odor that can irritate a person's eyes or respiratory system.
  • Carbon dioxide is a colorless and odorless gas associated with animal respiration and manure decomposition. Carbon dioxide can replace the oxygen in a confined space. If you breathe in air that contains high levels of carbon dioxide, this gas can replace the oxygen in your bloodstream and may result in headaches, drowsiness, and death (after prolonged exposure). Carbon dioxide is heavier than air, so it can easily accumulate in low-lying areas of confined spaces.
  • Hydrogen sulfide is a colorless gas that smells like rotten eggs at low levels but can overcome a person's sense of smell at levels of 100 ppm and higher. Exposure to hydrogen sulfide can cause eye and nose irritation, headache, nausea, and immediate death at high levels). Hydrogen sulfide is heavier than air, so it can easily accumulate in low-lying areas of confined spaces.
  • Methane is a colorless and odorless gas produced during the decomposition of manure in storage. This gas is flammable and potentially explosive, especially when captured in foam that can form on the surface of stored manure. Methane is lighter than air, so it does not accumulate in low-lying areas of confined spaces.

Learning Objectives for the Demonstration

  • To reduce the risk of injury and fatality from manure pit and silo gas exposure through a role playing exercise demonstrating what happens when a family member or other untrained rescuers enter these hazardous environments.

Materials Needed

  • 10 - 12 small square bales
  • Plastic tarp for under bales
  • 2 balloons (one filled with air and one filled with helium)

Demonstration Steps and Key Discussion Points

Prior to the demonstrations, survey the group/class with the following questions:

  1. How many have a silo at home?
  2. Is the silo an upright or trench silo?
  3. Have you ever climbed up into an upright silo?
  4. Have you ever played games in the silo area?
  5. Do you have manure storage at home?
  6. Is the manure storage underground, in the ground, or above ground?
  7. Have you ever heard of a fatality happening in a manure pit or silo? What happened?
  8. What are the dangers of silos and manure storage?
i. Have students list as many as they can for later discussion.
ii. Discuss each danger listed the by students.

Demonstration Option 1: Gas Properties

  1. Discuss with the students how manure and silo gases will displace oxygen and the problem that this causes since humans need oxygen to breathe.
  2. Discuss with the students that gases/vapors can be odorless, colorless, and heavier or lighter than air.
  3. Show the students the concept of heavier/lighter than air by using the balloons. The balloon filled with air (air + weight of balloon will fall to the floor) represents heavier than air. The balloon filled with helium show a gas that is lighter than air and will float.

Key discussion points: Discuss the location of where gases would settle and how that should impact ventilation and doing activities near a silo or manure pit.

Demonstration Option 2: Role Playing Activities

  1. Place the tarp on the floor with bales in a circle on the edge of the tarp to represent manure storage.
  2. Ask for a volunteer from the group to be a victim and provide directions for the role playing activity. Secretly tell the volunteer that they must lie perfectly still and become dead weight during the role playing activity.
  3. Have the volunteer lie down on the ground (plastic tarp) inside the straw bale circle.
  4. Select a person to be 'Rescuer #1'. Instruct them to take 5 big breathes and then hold their breath while trying to lift the victim to the edge of the bales. If they cannot, hold their breath, they become the second victim and they are to then lie perfectly still like the first volunteer.
  5. Repeat step 4 with another volunteer.

Key discussion points: Discuss with the students that the first person at the scene should have contacted 911 and provide the following information: description of emergency/incident, location, and number of people involved. Discuss how multiple deaths/injuries have occurred because people attempt a rescue rather than contacting first responders.

Take-Home Points for the Demonstration

  • Students understand that gases can be lighter or heavier than air and how that impacts manure or silo gases.
  • Students understand the first thing they should do in an emergency situation involving manure or silo gases.

Additional Classroom Activities/Assignments

  • Develop a plan on how to prevent manure and silo storage injuries and fatalities.
  • Develop manure and silo emergency response plans with local emergency responders.


We have provided a one page evaluation  which has been designed to be used with participants after each lesson. The answer key is offered below.

Evaluation Questions Answer Key

  1. D
  2. D
  3. Contact 911 and provide the following information: description of emergency/incident, location, and number of people involved.
  4. (student response)
  5. (student response)
Source :

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