Exposure to H2S concentrations greater than 1000 ppm causes which outcome?

• A. Rapid collapse followed by coma and death
• B. Respiratory irritation
• C. No effect
• D. Mild headache

Answer: (A)

High concentrations of hydrogen sulfide shut down cellular energy production by inhibiting mitochondrial cytochrome oxidase, so brain and vital organs are deprived of oxygen extremely quickly. That rapid loss of brain function leads to immediate collapse, followed by coma and death if the exposure continues. At these levels, the sense of smell can be lost because the olfactory nerves are paralyzed, so you can’t rely on smelling the gas to gauge danger. Lower exposures might cause irritation or headaches, but those effects aren’t the immediate life-threatening outcome seen with very high concentrations. This is why rapid collapse with coma and death is the best answer for exposure above 1000 ppm.