How to Design Dust Extraction Into a Workshop

Designing extraction in, step by step

Good LEV design follows the air backwards - from the point where dust is made, through the ducts, to the collector and the fan. Work in this order and each choice sets up the next one cleanly.

1. Start with the process, not the fan. List every machine that will make dust and how much each one throws off - a wide-belt sander produces fine, respirable dust, while a planer or saw throws heavy chips and offcuts. Note which machines run at the same time, because that decides your simultaneous demand rather than simply adding every machine together. The Health and Safety Executive's guidance HSG258, Controlling airborne contaminants at work, is the reference every UK designer should be working from here.
2. Fix the capture at each source. Dust is easiest to control at the exact point it is created, so design a hood, enclosure or machine spigot that catches it before it enters the room air. HSG258 works in terms of capture velocity - the air speed you need at the dust source to draw it reliably into the hood - and a fine sander needs a very different approach from a heavy planer. Enclose as much of the process as you sensibly can, because a partial enclosure always outperforms an open hood held at a distance.
3. Size the ducts for transport velocity. Wood dust will settle and pack inside a duct if the air moving it slows down, so the branches and mains must be sized to hold a minimum transport velocity throughout. For wood dust that figure is high - commonly around 20 m/s - which is far more than you would need to shift a gas or fume. Ducts that are too big drop below that speed and silt up; ducts that are too small choke the flow, so this is a calculation, never a guess.
4. Route the runs to keep the air moving. Favour short, direct runs with smooth-bore ducting, long-radius bends and tapered junctions that bring branches into the main at a shallow angle. Every sharp elbow, blast gate and abrupt change of section adds resistance and creates a spot where dust drops out and builds up. Plan the route in three dimensions early, so ductwork is not fighting steels, lighting and services once the building is up.
5. Choose the collector and decide where the air goes. Match the filter or cyclone to your dust type and volume, and think hard about whether cleaned air is returned to the workshop or discharged outside. Recirculating filtered air saves heat but demands high-efficiency filtration and monitoring to stay within exposure limits, so weigh it carefully. Site the unit for easy filter changes and waste removal, not just wherever there happens to be a gap.
6. Design for fire and explosion from the start. Fine wood dust in suspension is an explosive atmosphere, which brings the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) into play alongside COSHH. Build in explosion relief, isolation and correct earthing to control static, and keep the collector position and ducting consistent with a proper DSEAR risk assessment. This is far cheaper to engineer in than to add afterwards.
7. Leave room to test, check and maintain. A system you cannot examine is a system that quietly fails, so design in test points, accessible ducting and clear airflow indicators from day one. Fit a simple pressure or airflow gauge at each machine so operators can see at a glance that capture is still working. Building this access in is what makes the statutory examination straightforward for years to come.

Where the law meets the layout

A well-drawn system is only half the job - it has to keep people below the legal exposure limits and prove that it does. Under the Control of Substances Hazardous to Health Regulations 2002 (COSHH), wood dust carries workplace exposure limits (WELs) measured as an 8-hour time-weighted average: 3 mg/m³ for hardwood dust and 5 mg/m³ for softwood. Where hardwood and softwood are mixed - which is most real joinery - the tighter hardwood limit of 3 mg/m³ applies to the whole mixture. Designing extraction that comfortably beats those numbers, rather than scraping under them, gives you headroom for the days when every machine is running at once.

Extraction is also only one layer of control. COSHH expects a hierarchy - enclose and extract at source first, then keep housekeeping tight, and only then reach for respiratory protective equipment as a top-up. Sweeping and compressed-air blow-down throw settled dust straight back into the breathing zone, so specify low-energy cleaning and a fixed vacuum point in the design rather than leaving it to a yard broom. Employers also have duties around health surveillance for workers exposed to wood dust, typically starting with a respiratory baseline and continuing with regular checks, so the system you design is protecting people the law is actively watching over.

None of this stays fixed once the workshop opens. Machines move, branches get added, filters load up and fans wear, so a system that was perfect at commissioning drifts over time. That is exactly why COSHH Regulation 9 requires a thorough examination and test of LEV by a competent person at least every 14 months, backed by operator checks in between. If you are fitting out or upgrading a joinery, it is worth reading alongside our guide to controlling dust in a joinery workshop, and if you are still choosing hardware, our buyer's guide to woodworking dust extraction units covers how to match a collector to the design you have drawn.