Gas, not slurry, is the real danger when it comes to tank dangers

Michael Flynn’s letter on escape routes for slurry tanks (Sept 19) makes a number of very valid points on escape routes and designs for slurry tanks.

These are very valid for open tanks and lagoons, however, drowning is not the only issue. The Spence family died in only about four feet of slurry. This is shallow enough for most adults to be able to stand in and wade toward an escape route, but the killer in this instance was due to gas in the area.

The biggest danger with underground tanks is not drowning but lack of oxygen. The breakdown of manure like other organic waste (septic tank for house or in council water treatment plant) creates gases; during the time animals are housed the gas escapes in small amounts. When the animals are not being housed the top of the slurry hardens as there is no longer waste falling into the tank, and forms a crust trapping the gas under it. When it comes to emptying the tank the crust is broken and the concentrated gas escapes.

The guidelines for emptying the tank are to carry out the work with no animals in the shed, with all the doors open and when a breeze is blowing, combined with the regulations that all agitation points must be outside the shed reduces the effect of the concentrated gas affecting the person working on it. The gases from slurry are heavier then the oxygen in the air so will push the breathable air away, and can bring about unconsciousness very quickly.

The effect of gas in tanks is not confined to slurry. This can be in any tank where there is only a small entry point, especially if that is on the top. CO2 in air is also heavier than the oxygen and will settle in the bottom of an empty tank, meaning there might not be enough oxygen to breath for someone standing inside. Even an empty tank can be lethal. A portable gas monitor can be used to check the readings before entering, and can be clipped onto someone working inside to warn them if the area is dangerous, giving enough time to get out. If any good can come from the recent tragic events, it will be to make people more aware of the dangers, and to only carry out work when they are fully aware of all the dangers so that the deaths of the Spences will not be in vain.

Tom Coleman

Leamlara

Co Cork