What negative pressure level is required for a Visual Clearance Inspection?

• A. 0.01 inches of water
• B. 0.02 inches of water
• C. 0.03 inches of water
• D. 0.04 inches of water

Answer: (B)

Visual clearance inspections require maintaining a small negative pressure in the containment area relative to surrounding spaces. This keeps air flowing into the containment rather than out, helping prevent release of contaminants when openings are used. The minimum level specified for this check is 0.02 inches of water in negative pressure. In practice, you measure with a differential pressure device (like a manometer) between the containment and a clean area, and you must see at least this −0.02 in water tolerance to pass. Values smaller in magnitude (less negative) would not provide the required containment, while a more negative reading is acceptable but not required.