The dangers of farm slurry tanks

The terrible events of the weekend highlight again the awful dangers of underground slurry tanks. A father and his two sons dead within minutes, one of them a rising rugby star, and his daughter in hospital after the effect of fumes. No doubt there is much more to learn about this tragic event, but early reports suggest that father entered the tank to rescue the family dog which had fallen in. Father got into trouble, his eldest son tried to save him to be followed by younger brother trying to save them both. Noel, Graham and Nevin Spence have all tragically died trying to save each other with who knows what consequences for their remaining family and the farm.

This is yet another reminder of the dangers of farm slurry tanks. A number of gases can accumulate in these tanks and have been responsible for the deaths of both people and cattle before. Anybody working on farms or advising farmers needs to be aware of these dangers. The atmosphere in an underground tank can be a heady mixture of methane, carbon dioxide, ammonia, and hydrogen sulphide. In the right concentrations this can be explosive. But the far bigger danger is from the hydrogen sulphide – it seems almost certain that this is what the Spences will have succumbed to.

Hydrogen sulphide (H2S) (sulfide in US spelling) has a variety of other names, including Sewer Gas. It is familiar to most of us from its characteristic smell of rotten eggs. However, this odour is deceptive as we only detect it in low concentrations. As concentrations rise the gas itself starts to affect the nervous system, effectively switching off the sense of smell as the nerves from the nose are paralysed. At these levels a few breaths of the gas are enough to kill. At 50 ppm of the gas, the effects of short exposure can include shock, coma, convulsions and death.

“H2S is classed as a chemical asphyxiant, similar to carbon monoxide and cyanide gases. It inhibits cellular respiration and uptake of oxygen, causing biochemical suffocation” (SafetyDirectory.Com H2S factsheet).

H2S is also 19% heavier than air, so it collects in tanks and low places, adding further to the danger. Workers who routinely work in these environments have to wear breathing and gas detection equipment, with roped harnesses attached to winches overseen by two colleagues. This is certainly not ‘health and safety red tape’ but very sensible protection. The continuing tragedy is that farmers and their workers continue to expose themselves to these dangers.

During the 1980’s I advised a lot of farmers on slurry storage and management, and always tried to emphasise these dangers – the production of gas can be particularly active when silage effluent is mixed with slurry for example. I hope that readers who work in similar areas will continue to be alert to these dangers – this is an area where there really is a point to an accurate risk assessment and the careful deployment of safe working practices and protective equipment. The Health and Safety Executive website is a good place to start: www.hse.gov.uk . Take care.

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