Eastern Iowa custom cattle feeder Jason Johnson is concerned. After the deaths of his father and a worker on his family’s cattle farm near Andover in 2005 and a recent accident in which 20 cattle died, Johnson wants others to understand the dangers of hydrogen sulfide and the risks it poses not only to farm workers but also livestock.

Just last week, Johnson said a farm worker was pumping manure out of a deep-pitted cattle barn when the worker called to say 20 head of cattle collapsed and died.

The deep-pitted, gable-roofed structure was ventilated, Johnson said.

The farm worker, also a volunteer fire fighter, was able to get to the fire station to get an air pack...