Which soil gas is commonly considered in indoor air quality assessments due to potential intrusion from the ground?

• A. Oxygen
• B. Radon, leakage from underground fuel tanks, pesticides
• C. Nitrogen
• D. Water vapor

Answer: (B)

Gases migrating from the ground into a building are a key issue in IAQ, and radon stands out as the most commonly evaluated soil gas because it originates in soil and readily infiltrates through foundations and openings. Radon is a colorless, odorless gas produced by the natural decay of uranium in soil and rock, so it can accumulate indoors without you noticing. Long-term exposure to elevated radon levels is a known lung cancer risk, which is why radon testing is a standard part of many IAQ assessments and why mitigation often focuses on reducing soil-to-indoor entry, such as sealing cracks or using sub-slab depressurization.

The other options aren’t the typical soil-gas concern for ground intrusion in IAQ. Oxygen and nitrogen are the major components of air and don’t indicate ground-origin pollution. Water vapor relates to humidity and moisture issues rather than a problem sourced from the ground.