Since the fans of the booth have been off for a couple of months. I had to clean everything from the dust. I started from the top shelves, wiping one by one all the objects. I moved the boxes made of paperboard out of the clean booth because paperboard  is known to produce dust. I cleaned the optical table and all the objects on it. Wiping with a wet tissue was not enough because the tissue releases fibers and dust. So I used the strong green lamp to watch the dust particles, the spray air to blow on the surfaces to make the dust fly and the vacuum cleaner to blow it up from the air. The vacuum cleaner was outside, I only brought the pipe inside.  After that, I measured again the particles number.