Exposure to H2S concentrations of 50-500 ppm causes which effects?

• A. Respiratory irritation, coughing and labored breathing
• B. Systemic poisoning
• C. Rapid collapse
• D. No effect

Answer: (A)

Hydrogen sulfide affects the body in a dose-dependent way. When exposure is in the 50–500 ppm range, the main impact is irritation of the respiratory tract. This irritates the nose, throat, and lungs, which triggers coughing and makes breathing feel difficult or labored as the airways react to the irritant. At this level, systemic poisoning or rapid collapse isn’t the typical immediate outcome—that happens at higher concentrations (or with longer exposure) when the gas can affect cellular respiration and the nervous system. Also, don’t rely on the smell to gauge danger, because H2S can dull or block its own odor at higher concentrations. So the best description for this exposure range is respiratory irritation with coughing and labored breathing.