How do I ensure fire-stopping is done correctly around duct penetrating a floor slab

Plain-English answer

Clean all debris out of the open annular air gap between the duct wall and the concrete cutout floor line.

Pack the space tightly with an approved dense mineral wool insulation batting (backing material), leaving a uniform 1-inch deep pocket at the top. Fill this top pocket completely with a thick, smooth layer of UL-classified intumescent fire-stop caulk or fire-rated mortar sealant until it is completely smoke-tight.

Field checklist

• Stop and verify the approved detail, manufacturer instructions, foreman direction, and project specs before touching it.
• Clean all debris out of the open annular air gap between the duct wall and the concrete cutout floor line.
• Pack the space tightly with an approved dense mineral wool insulation batting (backing material), leaving a uniform 1-inch deep pocket at the top. Fill this top pocket completely with...

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Verify before acting

Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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