Intensively managed farming systems have resulted in a move towards predominantly slurry-based manure management systems, where animals are housed on slatted floors over a storage tank, with no bedding material. Because grazing animals do not use the nutrients they ingest very efficiently, the fertilising value of the slurry produced in these systems is appreciable but can be highly variable. Variation results from a number of factors including the class of stock, their diet and water intake, dilution of slurry by washing water as well as gaseous losses during storage and agitation.

Gases are produced from the bacterial decomposition of slurry in storage and released during slurry agitation. They include ammonia, carbon dioxide, methane and hydrogen sulphide. All are unpleasant gases which damage the environment. Some can result in a financial loss from the system and some are highly inflammable. However, by far the most deadly to animals and humans is hydrogen sulphide.

Hydrogen sulphide is a clear gas that is slightly heavier than air. This means that it will not disperse but stays low to the ground, especially when there is no air movement. At low concentrations of fewer than 50 atmospheric parts per million (ppm), the gas has the characteristic smell of rotten eggs. The problem is that you rapidly lose your ability to smell it, so you may think it is not present but it is and in very high concentrations. Exposure to concentrations above 500ppm causes confusion, disorientation, rapid collapse and it can kill in seconds where concentrations exceed 700ppm. Such concentrations are not uncommon at slat level within animal enclosures.

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The gas release is greatest in the first 15-30 minutes of mixing. The concentrations are particularly high where the slurry has been stored and has been decomposing over a number of months and a crust has been trapping the gases pre-agitation. Mixing silage effluent with slurry also increases the risk of the gas being produced and because the gas is so heavy, deep tanks are likely to hold the gas, even when empty and particularly when agitated in cold weather, with little air movement.

The single most important safety protocol when agitating slurry is to remove yourself, all personnel and all livestock from buildings above or adjacent to the slatted tank before you start and stay out of any buildings for, at least, the first hour of agitation. Ensure children are kept away and always inform someone of what you are doing, but ideally have two people present.

Open all available ventilation to provide a through draught, especially at floor level, and always try to agitate and spread slurry on a day where there is good air movement. Obviously outdoor agitation points are preferable but when in confined spaces, try to avoid very vigorous agitation and never enter a tank without either suitable breathing apparatus (check manufacturer’s instructions) and/or a harness attached to a lifeline controlled by at least two other adults standing outside. Also, when agitating avoid naked lights, as the gas mixture can be highly flammable.

Slurry drowning

However, while asphyxiation from slurry gases is a serious danger at this time of year, it is not the only one related to slurry on farms. The fatal farm accident data available from the Health and Safety Authority (HSA) indicates that 75% of farm accident victims drown in slurry as opposed to gassing. The fatal accident data available from the HSA is based on the outcome of a coroner’s inquest, so it is the best information available. The sad reality is that children are often the victims in such accidents. According to the HSA, drowning is the most common slurry-related farm death and between 2000-2010, 30% of child fatal accidents on farms and 8% of deaths to elderly farmers were caused by drowning in slurry or water. It is important to look at the farmyard, the types of slurry storage facilities and the precautions that are in place to prevent any such accident.

Whether slurry tanks are covered or uncovered, warning signs are central to securing the farmyard and should be highly visible. Any dangers should be pointed out to visitors and particularly children, and when agitating and spreading slurry, children must be excluded from the farmyard. Surfaces around agitation points should be free of obstacles that may act as a trip hazard and the surfaces should be kept clean while working to prevent slips or falls.

When slats or manhole covers are lifted or removed for agitation or when emptying the tanks, ensure that there is adequate temporary protection of such openings and where possible, safety access manhole covers should be fitted.

In the case of slurry lagoons or open tanks, a childproof safety wall or security fence of at least 1.8m in height with equally high-locked access gates should be fitted. Safeguard any scrape holes that have developed and be aware of dangers surrounding the lagoon, such as platforms or the tank wall, to ensure there are adequate protections. For example, a guard rail may be necessary

The HSA has recently stated they have changed their policy and go to prosecution where slurry tanks are left open or in an unguarded state without adequate justification. This new approach should motivate farmers to examine their approach to covering tanks.

The mechanics of agitating and spreading the slurry also brings its own risks and when operating machinery the usual rules apply. Firstly, know where your children are and again, exclude them from the farmyard during such operations.

The importance of having the machine in good working order cannot be understated, with safety covers on the PTO shaft and tankers fitted with braking systems. Then during land application, drive at an appropriate speed to the terrain you are working on, showing due diligence to low-lying electrical cables where relevant.

Farm safety scheme

The scheme has a number of measures related to slurry and effluent including safety fencing with gates and solid covers for external agitation points or manholes. Damaged slats whether single, twin or gang can be replaced. Tank end walls can be replaced and provision made for external agitation. Simple slurry aeration systems and a circulation pipe for agitation can be installed.

The Farm Safety Scheme will close on 9 January 2015 and details are available on the DAFM Website. The amount grant aided is from €2,000 to €20,000 with a 40% grant rate. Both Teagasc advisers and agricultural consultants can provide further advice on the scheme.

If managed appropriately, slurry is a valuable asset on any farm, rich in nutrients and organic material.

If not managed appropriately, slurry related facilities and operations can lead to an accident which can destroy a family and community for many years, if not forever.

As we prepare to enter the busy slurry spreading season, take the time to examine your own operation.

The slurry facilities and slurry related practices on the farm, should be safe, not only for the people involved but also for the uninvited guest, such as a curious child or public visitor.

Slurry safety information

Further Information on safety with slurry is available from ww.hsa.ie and www.teagasc/health_safety/. A DVD series on the dangers of slurry can be viewed on the HSA and Teagasc YouTube channels. The Northern Ireland Branch of the Institution of Agricultural Engineers held a technical meeting with the title The Slurry Gas Problem – an Engineering Perspective. A comprehensive report of the proceedings has been produced and is available to download from www.iagre.org/brgp/15 .