Diagnostics & problems
A shop vac, a domestic fan and a length of flexible hose can move air and feel like extraction. Under a thorough examination it rarely holds up, because moving air and controlling exposure to a standard are two very different things.
The short answer
Improvised extraction is common: a workshop vacuum, a domestic or agricultural fan, a homemade hood and some flexible hose taped into a run. It moves air, it feels like it is doing something, and it is far better than nothing in the eyes of the person who built it. Under a thorough examination it rarely passes, and the reason is not snobbery about kit. It is that a thorough examination measures whether a system controls exposure to a recognised standard and can prove it, and improvised extraction is almost never built to meet either half of that test.
The detail
The gaps are structural. There is usually no capture-velocity calculation behind the hood, so it is a guess whether it draws the contaminant in at the source or merely nearby. The air speed in narrow domestic hose is often below the transport velocity needed to keep dust suspended, so material settles and the run silts up. The hood is frequently the wrong type or too far from the work, the fan is not sized to overcome the system's resistance, and many rigs simply recirculate poorly filtered air back into the room or discharge it in the wrong place. Each of these is a reason the system does not actually control exposure, however busy it sounds.
The harder problem is proof. A thorough examination compares live readings to the system's commissioning data, the figures recorded when it was proven to control. Improvised extraction has no commissioning data and no design specification, so there is no benchmark to test against. The examiner is left to judge it against recognised guidance such as HSG258 and their own competent assessment, and against that yardstick a rig that was never designed almost always falls short. The examination itself must be carried out by a competent person, in the UK typically someone holding the BOHS P601 qualification, precisely so that judgement is sound.
What it means for you
So the honest position is that DIY extraction may move some air but rarely controls exposure to the standard, and just as importantly cannot demonstrate that it does. That matters beyond the test, because the ability to show control is what protects an employer if exposure is ever questioned. A system that cannot be benchmarked cannot be defended.
The route to a system that passes is the same route that makes it effective in the first place: a proper design based on the substance and the process, installation to that design, commissioning that records the performance actually achieved, and examination against those figures. That does not always mean expensive kit, but it does mean designed kit. Where an examination finds improvised extraction, the useful output is not just a fail but a clear statement of the gap between what is installed and what the work needs, so it can be put right rather than patched.
The service behind the guide
We assess what is actually installed against recognised good practice and tell you plainly where it stands, so an improvised rig gets a real verdict and a clear path to a system that both works and can prove it.
Questions
Because it is rarely built to control exposure to a standard or to prove that it does. There is typically no capture-velocity calculation, the transport velocity is too low, the hood and fan are not properly sized, and there is no commissioning data to test against.
It may move some air, but moving air is not the same as controlling exposure at the source. An improvised rig can leave contaminant escaping into the breathing zone while sounding like it is working, so it should not be relied on as control.
A thorough examination compares live readings to the figures recorded when a system was proven to control. With no commissioning data there is no benchmark, so the examiner must judge the rig against guidance such as HSG258, where it usually falls short.
A competent person, in the UK typically someone holding the BOHS P601 qualification. The competence requirement exists so the assessment against the standard is sound, especially where there is no design to test against.
A proper design based on the substance and process, installation to that design, commissioning that records the achieved performance, and examination against those figures. It need not be expensive, but it must be designed rather than improvised.
Phoenix Duct Clean · by the numbers
If your extraction was improvised rather than designed, an examination will show honestly where it stands against the standard. Call to book a test and a clear report of what it takes to comply.