Air Duct Debris on a Duct Wall Caught Halfway Through Cleaning

A light sweeps across the inside wall of a sheet metal duct. Part of the panel is already pale, bare metal. The rest is still peppered with dark specks of debris, and toward one corner they thicken into a grey smudge where the dust hasn't been touched yet.

Then the camera turns down the trunk, the long main run off the system. A scatter of the same specks dots its walls on the way to the far end.

It's a raw phone clip from a July job, with nobody in the frame. Thirty-three minutes later on the same job, another clip shows the plenum and a trunk down to bright, bare metal.