For short-term tests lasting fewer than 4 days, when must closed-building conditions be initiated?

For short-term radon testing lasting fewer than 4 days, it is essential to initiate closed-building conditions at least 12 hours prior to beginning the test. This time frame allows for the stabilization of indoor conditions, which is critical for obtaining accurate and consistent radon measurements. Closed-building conditions involve keeping windows and doors closed, minimizing the ventilation, and maintaining temperature stability, which helps to create a controlled environment that reflects typical living conditions.

Starting the closed-building conditions 12 hours before the test helps ensure that any external influences on radon levels, such as drafts or changes in temperature, do not affect the results. This period is a well-established guideline in radon measurement protocols, aiming to provide reliable data for assessment and mitigation efforts. It helps to avoid fluctuations in the radon concentration that could occur if the building remains open to outdoor air influences closer to the test start time.