NIOSH alert explains hazards of manure pits.
Eisma
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D000062:Accidents, Occupational; D000293:Adolescent; D000328:Adult; D000368:Aged; D000383:Agriculture; D006256:Hazardous Waste / Q000009:adverse effects*; D006801:Humans; D008372:Manure; D008697:Methane / Q000009:adverse effects* / Q000633:toxicity; D009314:National Institute for Occupational Safety and Health, U.S.; D014481:United States
D006256:Hazardous Waste; D008372:Manure; D008697:Methane