At this stage, the biggest majority of first-cut silage has been harvested and the countryside is being filled with a pungent smell, a smell which most people hate but personally I love it.

To me, it’s like cut grass, it always reminds me of summer. The smell is of course slurry.

Unfortunately, slurry spreading and agitation is a hazardous business, the news of farmers and family members being killed by slurry gases is becoming all too familiar.


Great care needs to be taken, especially during the agitation process.

Gases released during agitation include methane, carbon dioxide, ammonia and hydrogen sulphide, all of which are fairly unpleasant. These gases are produced by bacteria during the decomposition of slurry.

Hydrogen sulphide, in particular, is very poisonous to humans and animals. Hydrogen sulphide is actually more dangerous than hydrogen cyanide and at the high concentrations which exist in slurry is odourless, it also causes difficulty breathing and disorientation.

Collapse and death can occur within just a few breaths because it displaces air from your lungs and also affects the nervous system.


Hydrogen sulphide gas is formed within the slurry in the tank. Some gases may bubble to the surface but most remain dissolved within the liquid in a similar way to gas held within a bottle of fizzy drink.

When the slurry is mixed, the gas is released very quickly. The addition of other materials such as silage effluent may increase the quantity of gas produced.

Gas is released as soon as mixing starts. The rate is variable and difficult to predict which makes it all the more dangerous.

It is generally given off in large volumes very soon after mixing starts, the first half hour being the most dangerous.

The quantity of gas released reduces as mixing continues but as soon as the pump is repositioned to mix another part of the tank the gas concentration rises again and you should stay out of the shed for at least another 30 minutes.

Ten points to take on board when handling and agitating slurry

  • If possible, mix on a windy day.
  • Keep children away from the area at all times.
  • Take all animals out of the building before starting to mix slurry.
  • Open all doors to ventilate the area.
  • Use outside mixing points first.
  • If you are dealing with older sheds where the slats need to be lifted for agitation, be sure to cover exposed areas of the tank beside the mixer to stop anything falling in.
  • Start the mixer and then stay out of the shed for as long as possible – at least 30 minutes.
  • If you have to re-enter the shed, make sure there is another adult on site who knows what you are doing, stays outside the building and can get help if needed.
  • Avoid naked flames, as slurry gas is flammable.
  • Do not stand close to the pump exhaust of a vacuum tanker when it is being filled.
  • Always remember to put safety first.

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