Ammonia is a dangerous gas and is readily detectable at concentrations of ______.

• A. 5-15 ppm
• B. 20-50 ppm
• C. 10-30 ppm
• D. 100-120 ppm

Answer: (B)

Ammonia has a sharp, distinctive odor that most people can notice well before it reaches dangerous levels. In practical terms, a concentration in the tens of parts per million is when the smell becomes clearly noticeable in a typical environment, making 20–50 ppm the range where it’s readily detectable. Lower ranges around 5–15 ppm can be detectable, but they’re easy to miss in real-world settings. Very high concentrations, such as 100–120 ppm, are dangerous and cause rapid irritation, but that’s about hazard level, not the point at which the odor becomes readily detectable. So the 20–50 ppm range best matches the idea of “readily detectable.”