Positive ventilation is defined as which configuration?

• A. Exhaust off/low, supply high in surrounding areas
• B. Exhaust off, supply low in surrounding areas
• C. Exhaust high, supply low in affected space
• D. Exhaust high, supply high in surrounding areas

Answer: (A)

Positive ventilation aims to keep contaminants out by creating a higher pressure inside the protected space than in the surrounding areas. This is done by pushing in a lot of air (high supply) while keeping the outflow (exhaust) minimal, so the pressure builds rather than being relieved. That’s why a setup with exhaust off or low and a strong supply is the configuration that achieves positive pressure. If exhaust were high or supply was low, the space wouldn’t maintain a positive pressure differential, and contaminants could still enter. Supplying air to surrounding areas without building pressure in the protected space wouldn’t achieve the desired protective effect either.