Gypsum bedding impact on operator exposure to hydrogen sulfide from dairy manure storages

Anecdotal reports have linked Injury and death to dangerous levels of gas emissions released from dairy manure storages containing gypsum-based bedding. Recycled gypsum products are used as a cost-effective bedding alternative to improve animal welfare in the stall environment and agronomic benefits to manure recycled back to the land. Sulfur contained in Gypsum (calcium sulfate) can contribute to hydrogen sulfide (H₂S) formation under the anaerobic storage conditions typical of dairy manure slurry. Disturbance of stored manure during agitation releases a burst of volatile gases that may contain dangerously high concentrations of H₂S. On-farm monitoring was conducted to document conditions during manure storage agitation relative to gas concentration emissions and operator safety. Observations at ten farms from three dairy bedding management categories were compared: (1) traditional organic bedding; (2) gypsum bedding, and (3) gypsum bedding plus manure treatment thought to reduce H₂S formation/release. Portable meters placed around the perimeter of dairy manure storages recorded H₂S concentrations prior to and during nineteen agitation events. A detailed farm characterization documented factors affecting manure storage management. The primary objective reported here was to provide observations of operator exposure to hydrogen sulfide gas levels during manure storage agitation. Results show that manure storage agitation at farms using gypsum bedding produced significantly higher H₂S emission concentrations than farms using traditional bedding. In many cases, gypsum-containing manure storages produced H₂S levels above recognized safe thresholds for both livestock and humans.Farm operators were most at risk during activities in close proximity of the manure storage during the first 60 minutes of agitation.