Confirm whether this is grease duct, kitchen exhaust, lab exhaust, industrial exhaust, or normal exhaust.
Check the approved drawings/spec/submittal.
Look for cleanout/access, clearance, enclosure/wrap, weld/seal, slope/drainage, and inspection requirements.
Check whether access is missing, blocked, too small, or pointed the wrong way before cover.
Ask foreman
In Grease Duct, Kitchen Exhaust & Industrial Exhaust, I’m looking at: What do I do when access panel blocked after ceiling/wall close-up? What should I verify before I cut, drill, seal, cover, move, or install?
Do not
Do not assume normal galvanized duct rules apply. Do not cover, block, or delete cleanout/access locations.