True or False: Short-term measurements lasting 90 days or less should be conducted under closed-building conditions.

Short-term measurements lasting 90 days or less should indeed be conducted under closed-building conditions to ensure accuracy in detecting radon levels. Closed-building conditions refer to maintaining windows and doors closed, and minimizing outside air infiltration, which helps to stabilize the indoor environment and allows for a true assessment of radon concentrations. This is particularly important because radon levels can fluctuate depending on various factors such as weather, ventilation, and occupancy.

By adhering to closed-building conditions during short-term measurements, it ensures that the results are reflective of the radon exposure that inhabitants would realistically experience, leading to more reliable data for assessing potential health risks. The recommendations for short-term measurements aim to provide an accurate snapshot of radon levels in a given environment to prompt necessary remediation actions if high levels are detected.