Phoenix Journal · LEV Testing
The position of a hood, a doorway or a cross-draught decides whether your extraction captures contaminants or misses them - often more than the fan ever does. Here is how workshop layout shapes real-world LEV performance.
Extraction & workshop design
Where you put a bench, a bay or a doorway changes how well your extraction actually works - long before anyone reaches for the fan switch.
It is tempting to treat local exhaust ventilation as a bolt-on: buy the hoods, run the ducting, book the annual test and move on. In practice, the layout of the room does more to decide whether contaminants are captured than almost any other single factor. A well-specified hood sitting in the wrong place, fighting a cross-draught from an open shutter, will fail to control dust and fume no matter how much air the fan moves. The guidance that examiners work to - the HSE's HSG258, Controlling airborne contaminants at work - is clear that capture happens over a very short distance, and that short distance is exactly what layout either protects or destroys.
There are broadly two ways to approach this. You can design the workshop around fixed capture points, or you can keep the floor flexible and bring extraction to the work. Both are legitimate; both have trade-offs. Understanding them helps you get more from every pound spent on plant, and makes the annual thorough examination and test far more likely to pass first time.
In a source-led layout, the extraction comes first. You decide where welding, grinding, spraying or solvent work will happen, fix the hoods and enclosures at those points, and then arrange benches, storage and walkways to suit. The dirty processes are pinned to the building; everything else flows around them.
Where it wins
Where it costs you
The alternative keeps the floor open and adaptable. Benches move, bays are reconfigured for the job in hand, and extraction is brought to the work using articulated capture arms, mobile units or portable on-tool extraction. The building serves the process of the day rather than the other way round.
Where it wins
Where it costs you
Layout is not a matter of taste once you put figures against it. These are the thresholds that decide whether a hood in a given position can genuinely control exposure, and they are the same benchmarks an examiner will hold your system to.
Two practical points fall out of these figures. First, siting a hood is a battle over centimetres, not metres: gaining a little distance from the source costs you a lot of capture. Second, the room around the hood matters as much as the hood itself - roller shutters left open, pedestal fans pointed at a welding bay, make-up air rushing in to replace what the extraction removes, and even foot traffic can all generate the 0.5 m/s that undoes an otherwise sound design. Getting make-up air planned deliberately, rather than letting it sneak in through the nearest gap, is one of the biggest layout wins available. The same layout-first thinking applies well beyond engineering: if you are planning a kitchen layout around extraction and gas, the discipline of fixing the capture points before the equipment is identical.
None of this shows up in a quick glance at the fan. It shows up when air feels wrong despite the kit running - which is worth understanding in its own right if you have ever wondered why your workshop air feels dusty despite extraction. Records of each examination must be kept for at least five years, so a layout that quietly drifts out of compliance leaves a paper trail that inspectors can follow.
Questions
Yes, often dramatically. Capture velocity falls away very quickly with distance - by roughly one hood diameter from the opening you are down to about 10% of the velocity at the face. Move a workpiece even a couple of hundred millimetres further from the hood, or shift a bench into a cross-draught, and a hood that comfortably controlled fume can stop capturing it altogether, even though the fan is unchanged.
Very little. Air movement of around 0.5 m/s - the sort of breeze from an open roller shutter, a pedestal fan or someone walking past - can be enough to peel contaminant away before the hood draws it in. This is why layout has to account for doorways, make-up air paths and general ventilation, not just the position of the hood itself. Planning where replacement air enters the room is as important as siting the extraction.
An LEV thorough examination and test under COSHH Regulation 9 - due at least every 14 months - checks that contaminants are actually being controlled in normal use, not simply that air is moving. A fixed, source-led layout gives the examiner stable, repeatable test points to measure against the design. A flexible layout with moveable arms can still pass, but the examiner has to be satisfied the hoods are positioned correctly in day-to-day practice, so how your team actually uses them matters.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.