What are common reasons an LEV system fails a test?

Poor maintenance is the root cause of many failures. Common issues include worn-out fans, clogged filters, and damaged ducting. Sometimes it is misused, such as when workers are not properly trained to use the system or when extraction hoods are too far from the work area.
Inadequate design is another factor. Some systems have been modified without retesting, or they were never robust enough for the hazard in the first place. Failure of an LEV is typically an indication of either system-task mismatch or negligence.