What is the maximum exposure limit for a 12-month period in terms of radon concentration?

The correct choice reflects the established standard for radon exposure limits, specifically referring to the unit of measure known as Working Level Month (WLM). One WLM corresponds to the exposure to radon decay products at a concentration of 1 Working Level (WL) over a period of 173 hours. For a 12-month period, the maximum exposure limit is defined as 4 WLM, which is equivalent to approximately 5,700 pCi/L/Days.

This standard is significant as it sets a guideline for acceptable radon exposure to minimize health risks associated with long-term radon inhalation, which has been linked to lung cancer. Understanding this limit enables radon mitigation specialists to effectively evaluate indoor air quality and implement necessary remediation strategies when concentrations exceed these thresholds, ensuring health and safety for occupants.

The other options do not align with established safety standards, helping clarify why Option B is the accurate answer.