According to the police, a build-up of methane gas in the shed was responsible for an explosion in a cattle shed in the German municipality of Rasdorf, in which the roof was blown off and one cow was injured. The gas was thought to have accumulated from the ninety flatulent cows in the shed. But researchers at Wageningen UR think that this methane gas explosion may have been caused by something else.
When digesting grass and other feed into milk, cows produce methane in their fore-stomachs. But 98% of this ‘enteric’ methane production does not enter the shed’s atmosphere via flatulence, but via belching. The exact amount of methane a cow produces depends on diet composition, but is roughly 500 litres per day.
Air becomes explosive when it contains 6 to 16% (= 60,000-160,000 ppm) methane. Usually, explosive concentrations like this do not occur in cowsheds. Under normal circumstances in Dutch dairy cowsheds, the average amount of methane does not exceed 50 ppm (only 0.08% of the lowest explosive limit). Housing standards for dairy cattle ensure that the volume of the shed is large enough to minimise the methane concentration. Moreover, most dairy cowsheds are partially open and therefore well ventilated.
Explosive mixture from slurry
Another source of methane in the cowshed is the psychrophilic digestion (‘cold digestion’) of manure organic matter under predominantly anaerobic conditions in the slurry storage. Methane production from the manure storage is normally lower than from the animals, but in some situations (feed spillage, mixing of the manure) the methane production in the storage can be temporarily increased. Some manure pits start foaming, entrapping the methane gas in air bubbles.
Researchers from Wageningen UR therefore think it to be more likely that the explosive mixture developed from the manure pit underneath the shed in combination with insufficient ventilation. News stories about methane gas explosions caused by foaming manure and mixing have been reported regularly, but more often feature pigsties.
Conclusion: flatulent or belching cows were probably not to blame for the explosion in the German cattle shed. It is more likely to have been caused by an incident in the manure storage under the shed, possibly combined with insufficient ventilation.
Wageningen UR is currently conducting research into methane gas formation in cattle (firstname.lastname@example.org), cow shed layouts (email@example.com), gaseous animal shed emissions (firstname.lastname@example.org) and foaming manure (email@example.com). Communication; Hans Bothe +31 (0)317487148.