Which action directly obstructs transmission pathways of indoor air contaminants?

• A. Remove the source
• B. Obstruct modes of transmission
• C. Control humidity
• D. Ventilate with fresh air

Answer: (B)

The main idea is interrupting the ways contaminants move through indoor air to reach people. Blocking the transmission routes directly stops contaminants from traveling from their source to occupants, using barriers and containment, targeted filtration, and local exhaust or zoning to keep contaminants contained and out of people’s breathing zones. This direct obstruction of movement is why obstructing modes of transmission is the best choice.

Removing the source reduces how much contaminant is released, which helps overall exposure, but it’s about stopping generation rather than blocking the path to people. Controlling humidity can influence how long particles stay suspended or how certain contaminants behave, but it doesn’t by itself block the routes they would take to reach someone. Ventilating with fresh air dilutes contaminants and lowers exposure, but it changes concentration rather than creating a direct barrier to transmission pathways.