All windows, outside vents, and doors should be closed for how many hours before and during the measurement period?

The requirement to keep all windows, outside vents, and doors closed for 12 hours before and during the radon measurement period is crucial for obtaining accurate readings. This practice minimizes the influence of outdoor air, which can dilute indoor radon levels and lead to misleading results. By sealing the building for this specified duration, you ensure that the measurement reflects the radon concentration resulting from indoor sources rather than being affected by external atmospheric conditions.

This 12-hour period aligns with standard protocols in radon measurement to ensure consistency and reliability. It provides a stable environment where radon can accumulate and be detected without interference, allowing technicians to gauge the actual radon levels that occupants might be exposed to over time. Maintaining this closed environment helps create a controlled setting for precise measurement.