I have consulted the Health & Safety Authority on the technical issues raised by Deputy Fleming and am advised that the widespread use of slatted sheds for cattle housing makes slurry handling a major issue on Irish farms. In this regard, I am informed that during slurry handling, the vast majority of deaths and injury are, in fact, associated with the use of tractors and machinery. However, drowning in slurry and slurry gases also pose a major risk to farmers and farm families.
During storage, and as the slurry decays, an anaerobic reaction takes place which produces a cocktail of toxic and potentially lethal gases. These gases include Hydrogen Sulphide, Methane, Carbon Dioxide and Ammonia. The most dangerous of these gases is Hydrogen Sulphide (H2S) as it is extremely poisonous both to people and animals. It affects the nervous system and one lungful at high concentrations can cause death.
There have been many incidents in which people were overcome by slurry gases. Tragically, several people have been killed either by inhaling fumes or drowning associated with slurry pits. In relation to H2S, at very low levels over 3 ppm (parts per million), H2S has a distinctive smell of rotten eggs. Critically though, exposure to the gas at levels up to 150 ppm will quickly kill the sense of smell leading to the assumption that the gas has gone when, in fact, the levels may have become much higher and lethal.
When slurry is agitated, H2S is released at levels often in excess of 1,500 ppm which can cause immediate unconsciousness, H2S poisoning (pulmonary oedema), Acute Respiratory Distress Syndrome (ARDS), coma and death in just a few seconds. H2S, even at lower levels above 500 ppm, can cause unconsciousness after just a few breaths. One lung-full at high concentrations can cause instant death.
The highest risk occurs when slurry is being “agitated”. On such occasions, the gases trapped in the slurry, often beneath a crust, are released when it is mixed. Studies indicate that levels are greatest when slurry is stored for several months, when slurry is mixed in deep tanks, when slurry is mixed in cold weather or after silage effluent or other additives are involved.
In relation to animal bedding; straw, sand and woodchips/shavings/sawdust from virgin timber have often been used as a livestock bedding material. Furthermore, some waste materials may be suitable for use as bedding materials provided they do not pose a risk to the animals bedded on it or to human health. However, while waste plasterboard containing “Gypsum” may have been used in the past as a replacement bedding material, such use is now banned and is not known to occur in Ireland.
The Health & Safety Authority has informed me that a literature search was conducted in the UK to find evidence and scientific studies relating to the use of waste Gypsum and waste plasterboard as animal bedding and the likelihood of H2S being generated. Very little literature was found on the use of waste Gypsum or plasterboard as animal bedding and there appears to have been no studies into the possibility of H2S generation. Similarly, there have been no studies to determine if different bedding systems affect the likelihood of H2S, and if so, whether H2S generation can be prevented.
Gypsum - usually produced from re-cycled plasterboard - can be applied direct to agricultural land as a soil conditioner. In this regard, research is currently commissioned by Health and Safety Executive UK concerning Gypsum and its effect on H2S production in slurry and our Health and Safety Authority, in their regular contacts with their UK counterparts, await the results of that research which they expect within the next few months.
In conclusion, the critical message to farmers is that all slurry contains potentially lethal levels of toxic gases, whether additives are involved or not. In this regard, the recommended prevention strategies are: Never agitate slurry in still air conditions. Open all doors and outlets to provide a draught. Move all animals out of the shed before commencing. At least two people should be present at all times. Keep children and elderly persons away from the area when agitating. Never stand over slats or near tank access points when agitation is in progress. Avoid vigorous agitation in confined spaces. Do not allow slurry to rise within 300mm of the slats or tank covers. Keep all people away from the agitation point for 30 minutes after starting agitation. Never enter the slurry tank (even an empty tank) unless you are wearing suitable breathing apparatus and/or a harness attached to a lifeline controlled by at least two other adults positioned outside of the area. Where possible agitate from the outside the building. Avoid smoking or the use of naked lights as slurry gases are highly flammable. Gases can build up and remain in partially emptied tanks above the slurry, never enter a tank for any reason. Put up warning signs to warn of the dangers when working with slurry. I trust the Deputy finds the foregoing information useful.