What factor can increase the air plenum's risk regarding asbestos?

Obstructed airflow poses a significant risk concerning asbestos in air plenums. When airflow is obstructed, it can lead to stagnation of air, which can cause the accumulation of airborne asbestos fibers if they are present in the environment. This stagnation can result in areas where concentrations of these harmful fibers increase, making it more dangerous for individuals who might be exposed to the air that circulates through the plenum. Additionally, proper airflow is crucial for maintaining low levels of contaminants, including asbestos, and an obstruction can impede the effectiveness of filtration systems that are employed to reduce airborne hazards.

In contrast, low levels of moisture, high humidity, and clean air circulation typically do not contribute to the risk of asbestos exposure in the same direct manner. While humidity can affect the overall indoor air quality, it does not inherently increase asbestos risk like obstructed airflow does. Keeping air circulation clean is essential for reducing contaminants, thus directly contradicting the risks associated with obstructed airflow.