What is the minimum duration for a long-term radon sample?

• A. 30 days
• B. 2 days
• C. 7 days
• D. More than 90 days

Answer: (D)

Long-term radon sampling is meant to capture a representative indoor radon concentration by spanning periods that include seasonal changes. Radon levels indoors can vary with the time of year, weather, and how the space is ventilated or used, so a short test may not reflect the year-long average. Because of those fluctuations, the minimum duration for a long-term sample is more than 90 days, typically at least three months or longer. Extending the sampling period reduces the impact of unusual short-term conditions and yields a more reliable estimate of sustained radon levels. Short-term tests are useful for quick screening, but they don’t provide the long-term average.