Most professional fume extractors have alarms to tell you when there is a problem. However, Chau Vo, PAT Technology, says there are two major signs the extractor is not operating properly.
1. Smoke is not being evacuated fast enough from the laser enclosure
You should be able to see this through the glass door of the laser. This usually means that the dust filters are clogged and need replacing. Alternatively, it could be a sign that you have a leak in the ducting between the laser and the fume extractor.
2. Odors are getting stronger
This usually means that the gas filters are full and need replacing. As above, it can also mean that you have a leak in the ducting between the laser and the fume extractor.
Additionally, Brad Banfill, Purex Inc, says machine operators or other people near the process may complain of headaches, depending on the process and what fumes are being created.