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Most people can readily smell hydrogen sulfide at a level of about 10 parts per billion (10 micrograms per cubic meter) in air. This would be equivalent to a thimble of hydrogen sulfide in a movie theater full of air. Persons with a keen sense of smell can detect the gas at concentrations slightly below 1 part per billion in air. NOTE: Hydrogen sulfide concentration in water is not noticeable to many people until it reaches a level of at least 500 ppb, equivalent to 0.5 mg/L or parts per million (ppm). |
