What's measured
The most common and most dangerous assumption in any workshop is that because the fan is running and you can feel a draught, the extraction is working. A system can hum away, pull air, and still leave a worker breathing the very dust it was fitted to remove.
The short answer
The most common and most dangerous assumption in any workshop is that because the fan is running and you can feel a draught, the extraction is working. A system can hum away, pull air, and still leave a worker breathing the very dust it was fitted to remove.
The detail
A running fan proves only one thing: that a motor is turning. It says nothing about whether the hood is close enough and shaped right to catch the release, whether the duct behind it is leaking or silting up, whether the filter is choked, or whether a cross-draught is carrying the plume straight past the capture zone into the operator's face. Capture happens at the source, not at the fan, and every single link between the source and the fan can fail while the fan itself spins perfectly.
That is why a draught felt at the hood is reassurance rather than proof. You can feel air moving and still be nowhere near the velocity the process needs at the point the contaminant is released. The parts of the system you can sense - the hum, the pull - are the parts least likely to have failed; the parts that quietly defeat control are the ones you cannot feel at all.
What it means for you
Proving an LEV system works means measuring capture at the source and airflow through the system against its design, watching the air with smoke and the dust with a lamp, and checking every component from hood to discharge. That is the whole purpose of a thorough examination and test - to replace the comforting sound of a running fan with evidence that the contaminant is genuinely being caught before anyone breathes it.
Treat a running fan as the starting assumption to be tested, never the conclusion to be trusted. Every page in this cluster - capture velocity, hood design, ductwork, filters, the fan itself - is really one point seen from a different angle: the system controls exposure only when the whole chain works, and the only way to know the whole chain works is to examine it.
The service behind the guide
We prove control the only way that counts - measuring capture at the source against the design and checking every link from hood to discharge, with a clear report and remedial actions.
Questions
No. A running fan proves only that a motor is turning. It says nothing about whether the hood is catching the release, whether the duct or filter is sound, or whether a cross-draught is defeating capture.
At the source, where the contaminant is released - not at the fan. Every link between the source and the fan can fail while the fan itself runs perfectly.
No. You can feel air moving and still be well below the velocity the process needs at the point of release. A draught is reassurance, not proof of control.
Measuring capture at the source and airflow against the design, watching the air with smoke and the dust with a lamp, and checking every component from hood to discharge - in other words, a thorough examination and test.
Because it lets a system that looks and sounds healthy leave workers exposed. The parts you can sense are the least likely to have failed; the parts that quietly defeat control are the ones you cannot feel.
Phoenix Duct Clean · by the numbers
We prove control the only way that counts - measuring capture at the source against the design and checking every link from hood to discharge, with a clear report.