A grease duct installed within a rated enclosure shall maintain an air pressure of at least _____ water column positive pressure for _____ minutes when an air test procedure is used.

A grease duct installed within a rated enclosure shall maintain an air pressure of at least _____ water column positive pressure for _____ minutes when an air test procedure is used.

• A. 0, 10
• B. 2.0, 20
• C. 1.0, 20
• D. 0.5, 10

Answer: (C)

The key idea here is verifying the enclosure’s airtightness by applying a defined positive air pressure and holding it long enough to reveal leaks. For a grease duct inside a rated enclosure, the air test requires maintaining at least 1.0 inch water column of positive pressure for 20 minutes. This specific pressure level is chosen because it is sufficient to detect leaks in joints, closures, and penetrations without imposing excessive stress on the structure. Holding it for 20 minutes provides a reliable window to uncover slow leaks that might not show up in a shorter test, ensuring the enclosure can contain grease-laden air under normal operation and during testing. Why the other options don’t fit: zero or no positive pressure wouldn’t test the enclosure’s tightness; a higher pressure like 2.0 in wc isn’t the specified requirement and could exaggerate test results; a shorter duration such as 10 minutes wouldn’t meet the required test length to reliably detect leaks.

The key idea here is verifying the enclosure’s airtightness by applying a defined positive air pressure and holding it long enough to reveal leaks. For a grease duct inside a rated enclosure, the air test requires maintaining at least 1.0 inch water column of positive pressure for 20 minutes. This specific pressure level is chosen because it is sufficient to detect leaks in joints, closures, and penetrations without imposing excessive stress on the structure. Holding it for 20 minutes provides a reliable window to uncover slow leaks that might not show up in a shorter test, ensuring the enclosure can contain grease-laden air under normal operation and during testing.

Why the other options don’t fit: zero or no positive pressure wouldn’t test the enclosure’s tightness; a higher pressure like 2.0 in wc isn’t the specified requirement and could exaggerate test results; a shorter duration such as 10 minutes wouldn’t meet the required test length to reliably detect leaks.