Which statement correctly contrasts dilution ventilation with local exhaust ventilation?

• A. Dilution ventilation reduces room contaminant concentration by adding clean air; LEV captures contaminants at the source.
• B. LEV reduces room concentration by diluting the air; dilution ventilation captures at the source.
• C. Both approaches rely on identical filtration processes.
• D. Dilution ventilation is not effective for any hazard.

Answer: (A)

The key idea is how each ventilation approach handles contaminant control. Dilution ventilation works by introducing clean air into the space to lower the overall concentration of contaminants, relying on mixing and air changes to dilute what’s present. Local exhaust ventilation, by contrast, captures contaminants right at the source—before they spread—using hoods, ducts, and exhaust to remove them from the room. So the correct statement accurately reflects that dilution reduces room concentrations through added clean air, while LEV removes contaminants at the source.

This differs from the other ideas: LEV doesn’t reduce room concentration by diluting air; dilution ventilation doesn’t simply capture at the source; the two approaches don’t rely on identical filtration processes, since LEV emphasizes source capture and targeted removal rather than broad room dilution. And while dilution ventilation isn’t perfect for every hazard, it isn’t true that it’s not effective for any hazard at all.