Manure Gas Safety

By John Tyson

Why should you worry or be concerned about manure gas safety? To be blunt, manure gases can and do kill. Unfortunately, throughout the year we see and hear reports of manure gases killing farmers, employees, animals, and even children.

To better understand manure gas safety, it is important to understand how and why these gases are produced and how they behave. Gases are produced naturally by microorganisms that are living within the manure, using manure nutrients as food, and producing the gases from respiration. While the gases may be able to be managed or controlled there is really no way to eliminate them from being produced.

There are four major gases of concern from manure: Ammonia (NH₃), Carbon Dioxide (CO₂), Methane (CH₄), and Hydrogen Sulfide (H₂S). Each of these gases has characteristics that need to be considered when working with manure.

Ammonia is formed by the bacterial degradation of nitrogen within manure. Manures with a higher nitrogen content have the potential of producing more ammonia. The gas is colorless; however, it has a sharp pungent smell that can cause eye irritation and respiratory issues. While typically not deadly, there can be long-term effects from extended exposure.

Carbon dioxide is a product of microbial respiration and is both colorless and odorless. While CO₂ is naturally occurring in the atmosphere around us, the concentration from manure is the concern. Carbon dioxide is heavier than normal air and as the concentration increases, it displaces the oxygen in the air. As you breathe in this higher CO₂ it then replaces the oxygen in the bloodstream and can lead to shortness of breath and dizziness. At high concentrations, this can cause asphyxiation.

Methane is formed by methane bacteria when manure is stored in anaerobic conditions like the bottom of a liquid manure storage. It is also colorless and odorless but is lighter than normal air. However, it can buildup in non-ventilated or confined spaces. Methane can also be trapped within the foam that can form on top of liquid manure under the right conditions. The major concern is the flammable/explosive potential that can be present with the right methane to oxygen mixture.

Hydrogen sulfide is the manure gas most often associated with deaths. It is produced continuously in manure storage systems under anaerobic conditions. While hydrogen sulfide is colorless it has a very distinct rotten egg smell. However, it very quickly will cause paralysis of the nerve cells in the nose causing a loss of smell. Therefore, even if the level of H₂S increases you will not be able to sense it by smell alone. If the concentration increases to over 700 ppm it will cause rapid loss of consciousness and death within minutes. Prolonged exposure to even low levels of hydrogen sulfide can cause delayed reactions up to 24 hours later and/or long-term neurological effects. Because H₂S is heavier than air and tends to stay at ground level, depending on topography wind directions and atmospheric conditions around the manure storage, it can cause issues for people and/or animals in the surrounding area. If workers and/or animals are located downslope or downwind from a manure storage during agitation and emptying, the gas can 'drain' into those areas and cause issues. During periods of manure agitation and removal surrounding areas need to be monitored to avoid issues.

Signs of exposure to these manure gases include feeling hot and clammy, loss of motor skills, irregular/fast heartbeat, tightness of chest, panting, nausea/vomiting, or anxiety. Basically, if you or other workers don't feel right, you need to remove yourself and others from the area and reevaluate the situation and develop another plan.

Using personal gas monitors when working around manure storages during agitation and emptying is always recommended. A personal gas monitor helps identify potentially hazardous environments and warns the user to escape and reevaluate the situation. More information and discussion about personal gas monitors can be found in Use Personal Gas Monitors to Avoid Exposure to Toxic Hydrogen Sulfide  .

Besides using a personal gas monitor, being aware of your environment and having a basic understanding and where these manure gases come from and how they behave can help increase your safety when working around manure and manure storages. Often one of the best Personal Protective Devices (PPD) you have is your mind and knowledge. Don't become complacent, just because you have done something in the past without issue doesn't make it safe.