For a collocated test, if one monitor is above the action level and the other is below, are the results valid?

In a collocated test scenario where two radon monitors are placed in the same location to measure radon levels simultaneously, the validity of the results depends on specific criteria. The correct answer indicates that the results are considered valid as long as the higher reading is less than twice the lower reading. This guideline serves to ensure that any discrepancies in readings are within an acceptable range, reflecting the inherent variability of radon measurements.

When one monitor reads above the action level and the other below, it highlights that there could be fluctuations in radon levels influenced by factors such as ventilation, weather, or sampling errors. However, as long as the higher reading is not overwhelmingly greater than the lower reading (specifically, less than a 2:1 ratio), the results are deemed reliable for making informed decisions.

This approach balances the need for accuracy in radon testing with the understanding that measurements might naturally vary. Therefore, in the context of radon measurement practices, this answer reinforces the importance of examining the relationship between collocated monitor readings rather than dismissing them outright based on action level thresholds.