🔍 Key Concepts

• Properties of hydrogen sulfide (H2S), especially its odor at low vs. high concentrations • Limitations of human senses as gas detectors in hazardous atmospheres • Why industrial safety rules require gas detectors instead of relying on smell

💭 Think About

• At what concentration range is H2S known for having a strong, characteristic smell, and what happens to that smell at higher concentrations? • In a confined space or tank, would you trust your nose alone to decide if an area is safe, or would regulations require an instrument? Why? • Which option describes a specific effect H2S has on the body that would make smell unreliable as a warning sign?

✅ Before You Answer

• Compare each choice with known facts: H2S is famously associated with a particular strong odor at low levels—does that rule out any options? • Ask: does any option describe why your nose could stop warning you even when dangerous levels are present? Focus on that effect. • Remember: Safety doctrine says “never trust your senses” for toxic gas detection—look for the answer that explains a physiological reason your nose can’t be trusted.