The Dangers of Hydrogen Sulphide

Working with slurry is an extremely dangerous activity if it is not managed safely. Sadly, too many people have needlessly lost their lives by asphyxiation, drowning and accidents involving the PTO when handling slurry.
Considering that most farmers know that one lungful of slurry gas can kill, it astonishes me that many farmers still continue to agitate slurry with cattle in sheds. There are three main hazards you should risk assess and manage when handling slurry. They are: slurry gases; slurry tank openings; and the slurry tanker/the PTO.

Slurry Gases

A number of highly toxic and flammable gases are produced during the bacterial decomposition of slurry and high levels of these gases are released during the agitation of slurry. Inhaling these gases, which include hydrogen sulphide, ammonia, methane, and carbon dioxide, can be lethal. Because hydrogen sulphide and carbon dioxide (CO2) are heavier than air they can displace oxygen and, therefore, present a suffocation hazard in tanks and poorly ventilated areas. In particular, hydrogen sulphide is extremely poisonous both to people and animals. Hydrogen sulphide is colourless and it has a ‘rotten egg’ smell at low levels but cannot be smelled at higher levels. Repeated or prolonged exposures may cause eye inflammation, headache, fatigue, irritability, insomnia, digestive disturbances, and weight loss. To prevent the risk of being overcome by hydrogen sulphide gas you should always follow the golden rules around ventilation, evacuation and agitation.

Ventilate: where possible, choose a windy day as this will allow the gas to disperse quickly; open all shed doors and outlets.

Evacuate: all persons and all animals.

Agitate: 

• do not stand on or near slats or the agitation point;
• agitate from outside the shed if at all possible (for sheds with internal agitation points you should strongly consider moving the agitation points to an external area);
• do not attempt to enter the shed until at least 30 minutes after agitation has finished, remember toxic gases are being released even if you cannot smell them
• two people should be present if possible;
• do not smoke or use a naked flame within the vicinity of the shed being agitated, as slurry gases are highly flammable;
• never enter the slurry tank unless you are trained and competent in working in confined spaces and are wearing suitable breathing apparatus and a harness attached to a lifeline controlled by at least two other adults positioned outside of the area.

Slurry Tank Protection

Many children, farmers and contractors have drowned in unprotected slurry tanks. All open slurry tanks must be fenced off with an unclimable safety wall or fence at least 1.8m in height, and locked gates of the same standard should be fitted at the access point. For all other tanks, the first step is to provide safety manhole access covers at the agitation points. 

If the tank does not have a safety manhole access cover, additional precautions need to be taken. Temporary covers or guardrails must be used to protect the opening and warning signs should be put in place. However, this is not an ideal situation and these slats should be replaced with safety access covers. 

Remember that slats can degenerate over time, and fail. With this in mind, it is imperative that slats are regularly inspected and replaced if damaged.

Beware of the PTO

Extreme caution must be taken when operating the PTO, as entanglement in it can lead to loss of life and limb. Exposed bolts, universal joints or other projections on rotating components can grab clothing, resulting in instant entanglement. Always ensure that the PTO is fully guarded with a PTO-shaft guard, U guard and O guard. 

By following these simple precautions you will minimise the risks associated with slurry.  

Stop taking risks. Always think safety first.