The six workers who died in August at a dairy east of Keenesburg were killed by exposure to hydrogen sulfide gas, the Weld County Coroner confirmed Thursday afternoon.

On Aug. 20, Oscar Espinoza Leos, 17; Carlos Espinoza Prado, 29; Noe Montanez Casanas, 32; Jorge Sanchez Pena, 36; Ricardo Gomez Galvan, 40; and Alejandro Espinoza Cruz, 50, were found dead at Prospect Valley Dairy, 32063 Weld County Road 18.

The Southeast Weld Fire Protection District had originally responded to a confined space rescue. When first responders arrived, they noted the men with possible high levels of hydrogen sulfide, according to archived radio transmissions.

Hydrogen sulfide occurs naturally in crude petroleum and natural gas, but is also produced from decomposing manure. Low doses of exposure to the gas,

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