Negative ventilation is characterized by which action?

Negative ventilation is characterized by which action?

• A. It lowers the pressure inside the structure
• B. It raises the pressure inside the structure
• C. It seals all openings
• D. It relies on natural drafts

Answer: (A)

Negative ventilation creates a pressure deficit inside the structure compared with the outside, so air is drawn in from outside through openings to replace the smoky, hot air. This inward air flow lowers interior pressure and helps vent smoke and heat out by exchange. It’s the opposite of increasing interior pressure (positive‑pressure ventilation) and sealing openings would stop ventilation. While natural drafts can contribute, the defining action is deliberately reducing interior pressure to pull fresh air in.

Negative ventilation creates a pressure deficit inside the structure compared with the outside, so air is drawn in from outside through openings to replace the smoky, hot air. This inward air flow lowers interior pressure and helps vent smoke and heat out by exchange. It’s the opposite of increasing interior pressure (positive‑pressure ventilation) and sealing openings would stop ventilation. While natural drafts can contribute, the defining action is deliberately reducing interior pressure to pull fresh air in.