Manure and animal manure: safe storage, stirring and life-threatening gas

Manure is one of agriculture's most important nutrient sources, but it is also one of the most underestimated hazards on a farm. Every year serious and sometimes fatal accidents occur in connection with manure channels, sumps and tanks, and according to the Labour Authority manure gas is one of the known causes of both people and animals dying in the stable. The hazard is particularly insidious because the gas is often invisible and can knock a person unconscious in just a few breaths.

§The dangerous gases in manure

When slurry is stirred or set in motion, a series of gases are released that are otherwise bound in the liquid. The two main ones to know are hydrogen sulfide (H2S) and ammonia (NH3), but carbon dioxide (CO2) and methane (CH4) can also accumulate and displace oxygen in a closed room.

§When is the danger greatest

According to the Working Environment Authority's guidance on safe work with slurry and hydrogen sulphide, the acute danger typically occurs when the slurry is put in motion — for example by stirring, pumping or when a slurry robot or scraper sets the mass in motion in a channel under a slatted floor shed. The gas, which has been bound in the slurry, is then released quickly and can rise through the slats to rooms occupied by both animals and people.

• 01Upon start-up of stirring or pumping especially after prolonged stoppage.
• 02When working near open hatches, grilles or ventilation openings on slurry tanks.
• 03Upon entry to empty or partially empty slurry tanks and pits.
• 04In poorly ventilated stables with ducts under slatted floors, where gas can accumulate.

§Safe work procedure for stirring

Good practice is to start stirring carefully and gradually so gas is released slowly, while there is good ventilation in the shed. Animals should be removed or kept away from the area if possible while stirring, and people should not spend unnecessary time near open hatches or grating while the process is ongoing.

• 01Ensure maximum ventilation — open doors and windows and use mechanical ventilation if necessary.
• 02Remove or move the animals from the area if practically possible.
• 03Start stirring slowly and stay away from open hatches and ventilation openings for the first few minutes.
• 04Never work alone on tasks where manure can release gas in large quantities — always have another person within earshot.

§Floating layer covering and environmental requirements

Alongside safety the environmental rules set requirements for how slurry is stored. Slurry tanks should generally have solid coverage floating coverage (floating layer) or another approved solution that limits ammonia evaporation to the air. An intact floating layer — for example of straw or naturally formed crust — is therefore both an environmental requirement and part of the overall management of the tank which the municipality supervises.

“Most accidents with manure do not occur because people are ignorant that gas can be dangerous — but because you underestimate the situation 'just this one time'.”

— The Labour Authority about safety during manure work

§If the accident is out

If a person or animal is surprised by slurry gas, the instinct is often to hurry to the rescue — but that is precisely the reaction that has cost several lives because the rescuer themselves becomes poisoned. Call 112, keep your distance, ensure maximum ventilation, and only enter the area with supplied air breathing apparatus and safety line attached to a person outside. If the farm has slurry channels, sumps or closed containers, a fixed emergency plan should be drawn up and instruction given to everyone working there so that everyone knows the risk and the correct reactions before something goes wrong.