Mike Broderick farms just outside Portumna in Co Galway. A part-time dairy farmer, he is used to agitating and spreading slurry, having carried out the task for over 22 years on the farm incident-free. Re-living a day back in April 2014, when he lost two animals and almost lost his own life, Mike shares with us the chain of events that ultimately led to a slurry gas accident.
Overfull tanks
“I went down to look at the heifers in the shed that morning; everything was fine except for the slurry was very full in the tanks and coming up through the slats. I decided that the best way to get over this until the weekend came, was to stir it up with the agitator. I had carried out this job before and the levels of slurry always dropped down a few inches in the slats. I dropped the agitator into the tank and the slurry started to swirl a little. It looked like the job was going to work and the slurry drop down in the tank.”
Open sided shed
“The animals were left inside. In my mind it was fine to do this as the shed was open with good air movement. The hydrogen sulphide gas found in all tanks normally stays low to the ground as it is heavier than air. I looked down the shed and one of the heifers appeared to be staggering. That’s when all hell broke loose as four animals dropped to the ground. I knew I had a big problem on my hands.”
Focused on getting animals out
“All the advice is to get out and stay out if you suspect slurry gas to be a problem. That was not the case for me – my natural instinct to save the animals took over. Adrenalin was flowing and I ran down opened the gates to let the animals go. Reaching down I managed to pull the heads of the other two animals up off the slats and on to the top of the two dead animals. I physically pushed another animal over the timber barrier out of the shed. I had lost two heifers. I went to ring a neighbour for help and realised I had no phone. I ran back to the house and I noticed my chest tightening, dizziness and a shortness of breath. I got to the back door where my wife met me and I was hardly able to speak. From there I was rushed to hospital. My wife thought I was dying along with the animals. I had inhaled a percentage of the gas every time I bent over to help an animal. Luckily I did not inhale one complete mouthful or I was a goner. A few more seconds is all the time I had left. Leaving the phone behind that day may be the one thing that actually saved me.
Having carried out this type of work for 22 years, Mike never had a problem. So why did it happen this time? We look at some of the factors.
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 is recognisable as the characteristic smell of rotten eggs. The problem is however, that you rapidly lose your ability to smell it, so you may think it is not present. Exposure to concentrations above 500ppm causes confusion, disorientation, rapid collapse and it can kill in seconds where concentration is above 700ppm. Such concentrations are not uncommon at slat level within animal enclosures.
The gas release is greatest in the first 10-15 minutes of mixing. The concentrations are particularly high where the slurry has been stored and decomposing over a number of months and a crust has been trapping the gases pre-agitation.
Slurry gas detectors
The HSA does not recommend the use of devices like these. Concerns exist over calibration levels, and the use by individual operators who wear the devices while at work. It may well be too late to take any remedial action to get away from the toxic gas when the alarm sounds, if it can be heard over the tractor and agitator.
Mike’s plans to make agitating slurry safer
Shed design needs to be looked at according to Mike, having a holding bay outside that allows the animals to be collected easily and held while agitation is in progress.
Internal gas detectors could work very well if installed correctly. Fitting them at the right height and protected from animals is a must. The alarm warning should be very audible like a security alarm that can be heard over a tractor in the yard.
