That's Gas! - The importance of gas concentration in farm buildings



There is no doubt that intoxication by gas is dangerous. On-farm gases have caused many deaths in both humans and livestock. Gases can be aggravating to the health of humans and animals and also to the environment.


There is some evidence that sub-lethal concentrations of the gas can cause respiratory disease, and ascites which is common in poultry has also been linked with poor air circulation and the accumulation of ammonia.


Gas concentration in livestock buildings may also have a negative impact on livestock production by:

  • Reducing feed consumption

  • Lowering growth rates

  • Increasing the animals' susceptibility to invasion by pathogenic micro-organisms

Awareness of the gases and their management is key to ensuring human and animals stay healthy and safe.


The main culprit gases from stored manure are:

  1. carbon dioxide

  2. ammonia

  3. hydrogen sulphide

  4. methane

The limit of concentrations for these gases is called the Threshold Limit Value (TLV) and is expressed in parts per million (ppm).


Carbon Dioxide - TLV 5000ppm


To put the TLV in perspective, fresh air has about 300ppm. A standard ventilated controlled environment on-farm has around 2000ppm of carbon dioxide.


Measuring carbon dioxide is a good way to measure ventilation because even though it is not a toxic gas, carbon dioxide in large amounts can lead to oxygen deficiency and asphyxiation.


Ammonia - TLV 50ppm


The TLV is set at 50ppm because at this level humans can experience eye and respiratory tract irritation.


Up to 100ppm can be inhaled with little effect for many hours with little effect in some cases, but up to 200ppm can cause sneezing, loss of appetite and salivation. Chickens are affected at this rate by similar symptoms and therefore their growth rate also suffers.


Ammonia is released from fresh manure and during the anaerobic decomposition of manure. It is one of the most significant gases in animal housing.

Because it is highly soluble in water it's not as much of a problem with slatted flooring as it is with solid flooring.


Hydrogen Sulphide - TLV 10ppm


It is from the decomposition of manure under anaerobic conditions. This is the one gas that smells like rotten eggs!


The TLV for this is set at 10ppm as it is seriously toxic. When the slurry is agitated, concentrations can get extremely high (800ppm have been found). At these high levels, humans can die from respiratory paralysis.


Carbon Monoxide - TLV 50ppm


It isn't likely that carbon monoxide will be a problem in most settings but problems can happen in scenarios where brooding poultry need extra heat but ventilation may be poor and there isn't enough oxygen for the burners, so instead of producing carbon dioxide, they produce carbon monoxide.


This could also happen if burners aren't getting the right oxygen supply because they aren't cleaned and maintained as they should be.


Scrub up on keeping safe with gases


The Health and Safety Authority in Ireland has some helpful videos and tips on keeping safe with slurry and other farm hazards here.


I also find the UK government information on this topic quite useful - this can be found here.