What is the sulfur dioxide IDHL value?

• A. 100 ppm
• B. 50 ppm
• C. 150 ppm
• D. 200 ppm

Answer: (A)

IDHL values mark the concentration at which air is immediately dangerous to health and life, guiding emergency response and respirator choices. For sulfur dioxide, that threshold is 100 parts per million. Reaching this level means the gas can cause rapid, severe irritation and potentially life‑threatening respiratory effects, so a respirator with an independent air supply (such as an SCBA or supplied‑air respirator) is required and evacuation is indicated. Exposures below this limit can still irritate the airways, but 100 ppm is the established point where immediate danger to health and life is considered present.