What is the main functional difference between dilution ventilation and local exhaust ventilation (LEV)?

• A. Dilution ventilation reduces contaminant concentration by bringing in clean air to dilute the pollutant; LEV directly captures contaminants at the source.
• B. Dilution ventilation uses localized capture near the emission source, while LEV dilutes the air in the room.
• C. Both strategies rely on activated carbon filtration to remove contaminants.
• D. Dilution ventilation creates negative pressure to contain contaminants.

Answer: (A)

The key distinction is where contaminants are removed. Dilution ventilation works by bringing in clean outdoor air and mixing it with the polluted room air, lowering the contaminant concentration throughout the space. Local exhaust ventilation (LEV) captures pollutants right at the emission source with a hood or capture device and exhausts them away, preventing spread into the room.

This means dilution ventilation relies on air changes and mixing to dilute pollutants, which is effective for widespread or lower-level emissions. LEV, by capturing at or near the source, protects workers more directly from exposure and can be more energy-efficient for localized, high-concentration emissions.

The other statements blur these roles: one incorrectly describes LEV as dilution, another wrongly states that both systems depend on activated carbon filtration, and another misstates that dilution creates negative pressure to contain contaminants. The fundamental idea is about where the removal occurs—at the source with LEV versus throughout the room with dilution.