Phoenix Journal · LEV Testing
The right dust extraction unit protects your lungs, your machines and your compliance in one go - here is how to specify, size and test one properly for a UK woodworking workshop.
A dust extraction unit is one of the few pieces of workshop kit that protects your lungs, your machines and your legal position all at once - which is exactly why it pays to choose carefully rather than by price alone.
Whether you run a single panel saw in a small joinery or a bank of machines across a production floor, the goal is the same: catch wood dust at the point it is made, move it safely through ductwork, and collect it without letting the fine stuff drift back into the air you breathe. Get that right and the workshop stays cleaner, tools run cooler and the health risk drops sharply. Get it wrong and you are left with settled dust on every surface, blocked ducts and an extraction unit that looks busy while doing very little.
This guide walks through what actually matters when you are buying - the airflow and velocity figures that make or break capture, the filtration you need for fine dust, and the testing regime that keeps the whole thing legal once it is installed. None of it is complicated, but the details are where the money is either well spent or wasted.
The numbers that shape the choice
Before you compare units it helps to be clear about what you are controlling. Wood dust is not a nuisance to be tidied up later - it is a recognised occupational hazard. The Health and Safety Executive sets a workplace exposure limit of 3 mg/m³ for hardwood dust and 5 mg/m³ for softwood dust, both measured as an 8-hour time-weighted average. The hardwood figure was tightened to 3 mg/m³ in January 2020, and where hardwood and softwood are mixed the lower hardwood limit applies to the whole mixture.
Those limits are a ceiling, not a target. Under the Control of Substances Hazardous to Health Regulations you are expected to reduce exposure to as low a level as is reasonably practicable, so being just under the limit is not the finish line. It matters because wood dust of any species can cause occupational asthma and dermatitis, and hardwood dust is linked to a rare cancer of the nose and sinuses. It is one of the more common causes of occupational asthma reported in Britain, which is why extraction at the machine - properly called local exhaust ventilation, or LEV - is treated as a core control rather than an optional extra. If you want the fuller picture of why the fine fraction is so easily underestimated, our note on wood dust as a workshop hazard is worth a read alongside this one.
Most buyers fixate on the headline airflow figure, and it does matter - workshop units commonly range from around 1,350 m³/h for a single-bag machine up to roughly 5,000 m³/h for a four-bag unit serving several machines. But airflow on its own tells you very little. What counts is whether the system delivers the right velocity in two different places at once.
The first is capture velocity: the air speed at the tool where the dust is actually made. If the hood cannot pull the dust cloud in as it leaves the blade or sanding belt, nothing downstream will save you. The second is transport velocity: the speed of the air moving through the ductwork. Wood dust needs to stay suspended, and for dry wood dust that generally means keeping the air moving at or above 20 m/s. Drop below that and dust settles in the ducts, which chokes airflow, wrecks capture and quietly builds a fire and explosion risk inside the system. The HSE guidance document HSG258, "Controlling airborne contaminants at work", is the reference most competent designers work from, and it is the one to ask about if a supplier cannot explain their velocity assumptions.
A few things are worth pinning down before you commit:
It is also worth remembering that wood is not the only dust a mixed workshop generates. If you cut fibre-cement board, engineered stone or masonry alongside timber, that is a different and more dangerous problem - our overview of silica dust and its health risks explains why those materials should never simply be piped into a wood-dust unit.
An extraction unit is not a plug-and-play appliance. Its performance depends on how it is installed, commissioned and then kept in condition - and the law reflects that. A good supplier will commission the system on site, measure the actual airflow and velocity at each machine, and hand you a clear log of the figures the system is designed to hold. That commissioning sheet becomes your benchmark: it is the reference you compare against when you suspect performance has slipped.
From then on the regulatory clock is running. LEV systems used to control substances hazardous to health must undergo a thorough examination and test - often shortened to TExT - at least every 14 months, and in practice many workshops sensibly test annually so the date never drifts. That examination is more than a quick look: it checks that the system still achieves the capture and transport velocities it was designed for, that filters and fans are performing, and that the controls actually protect the operators using them. Keep the reports, keep the commissioning data, and keep a simple record of day-to-day checks such as blast gate use, filter condition and any loss of suction.
Treated this way, a dust extraction unit stops being a grudge purchase and becomes what it should be - a control you can prove is working, on paper and in the air. The cheapest unit that cannot hold its velocities or pass its examination is the expensive one; the right specification, properly tested, is what keeps people healthy and keeps the inspector satisfied.
Questions
It depends far more on how many machines run at once than on floor area. Size the unit around the total airflow needed to hold capture velocity at every machine that could be open together, while keeping duct transport velocity at or above 20 m/s. Workshop units commonly range from about 1,350 m3/h for a single machine to around 5,000 m3/h for a multi-bag unit, but the ductwork design matters as much as the fan, so have a competent supplier calculate it rather than guessing.
The HSE sets an 8-hour workplace exposure limit of 3 mg/m3 for hardwood dust and 5 mg/m3 for softwood dust, with the lower hardwood figure applying to any mixture of the two. The hardwood limit was tightened to 3 mg/m3 in January 2020. Under COSHH you must also reduce exposure to as low a level as is reasonably practicable, so staying just under the limit is not enough on its own.
Any LEV system controlling a hazardous substance such as wood dust must have a thorough examination and test, known as a TExT, at least every 14 months. Many workshops test annually so the deadline never slips. The examination confirms the system still meets its design capture and transport velocities and that it genuinely protects operators, and you must keep the reports as evidence.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.