Measuring manure gases. Solutions for working with them more safely

What are manure gases and what are their dangers?

Most people are by now aware that hazardous gases can be released in the agricultural sector. Which gas is actually the most dangerous seems to us less important — none of these gases should be underestimated. What does matter is knowing which properties the manure gases have and what you must take into account at all times.

1. Hydrogen sulphide

This gas – mainly known for its rotten-egg smell – is also known as H2S or hydrogen sulphide. It is a putrefaction gas produced during a natural decomposition process and therefore occurs in large quantities in the agricultural sector. H2S is slightly heavier than air (relative vapour density = 1.19), which means it can linger in confined spaces such as manure cellars, silos or tanks. SO ALSO AFTER VENTILATING. Moreover, at around 100 ppm the gas paralyses your sense of smell and only then does it become truly dangerous.

2. Methane

Methane, or CH4, is the main component (~80%) of the natural gas most people use at home for heating and cooking. You have guessed it: methane is flammable. However, that is not the greatest danger. If methane builds up to higher concentrations because it accumulates, it can be explosive. In explosions in a manure cellar, for example, methane is often the culprit. Like H2S, methane is a putrefaction gas, so the two often occur together. The main difference is that methane is lighter than air and therefore collects higher up in tanks, silos or manure cellars. The advantage of this is that it disappears more quickly in a well-ventilated barn, but that is no guarantee. While mixing in a manure cellar an explosive environment can therefore be created in an instant, because the gas has accumulated beneath the crusted top layer of the slurry. As well as being flammable, methane can also be explosive. This can be measured with an LEL sensor; if you would like to know more about that, please consult our other articles.

3. Ammonia

Ammonia, or NH3, is not released from every type of manure and often occurs in far lower concentrations than the gases above. It therefore poses an acute danger less quickly. However, it remains a toxic gas that must be taken into account and on exposure can lead to watering eyes, irritation of the airways, red and painful skin, etc.

4. Hydrogen cyanide

Also known as HCN or prussic acid gas. The vapour is colourless to very pale blue with a smell of bitter almonds. The gas is just slightly lighter than air (relative vapour density = 0.94) and therefore mixes well with air. Like H2S it is an acidic gas which on acute exposure can cause headache, confusion, dizziness, fatigue, shortness of breath, nausea and vomiting. With large doses of prussic acid, immediate unconsciousness occurs, followed by death. However, HCN is not present in all manure gases and often occurs in many times lower concentrations than the other gases.

5. Carbon dioxide

Carbon dioxide, or CO2, is formed during the breakdown of organic matter such as manure or animal feed. It is therefore also one of the main components of biogas; for more on working in biogas, read our blog on biogas installations and occupational health and safety law. CO2 is present in outdoor air in low concentrations (400-600 ppm) — after all, we breathe it out. But in high concentrations it is toxic. It is an odourless and colourless gas that is heavier than air. In the context of manure gases, CO2 is less of a problem gas. In the barn it is usually diluted quickly so that it does not become dangerous. Because the gas is heavier than air it can nevertheless accumulate in the manure cellar, even if that has been standing empty for some time. If the milking parlour is openly connected to the barn, the CO2 can also concentrate in the milking pit. Some caution is certainly called for — for example, do not milk while slurry is being stirred.

What does Dutch legislation say about working with manure gases?

Working with manure gases is not addressed specifically. There is, however, clear legislation on working in confined spaces. This article goes into that in more depth: Measuring gas in confined spaces. For now, in brief: working with manure gases is working with hazardous gases, and in addition manure cellars, silos, tankers, etc. all count as confined spaces. Before anyone enters, he or she must carry out a clearance measurement with a gas detector fitted with a pump. It is very important to measure at various heights, since gas can be heavier or lighter than air. On entering, it is also important — and mandatory — to wear a personal detector. Smaller personal gas monitors are available for this, which can be worn on the chest.