Phoenix Journal · LEV Testing
One failed fume check on a mild steel bay was nearly the story that ended a small welding shop. Instead, it became the moment they took extraction and LEV testing seriously - and got it right.
LEV Testing
The scare did not come from a fire, a dropped load or a near miss with a forklift - it came from a health surveillance appointment, and a welder who could not do the breathing test he had passed the year before.
It is the kind of moment that quietly reshapes a business. A small fabrication shop, four bays, mostly mild steel work, the sort of place that had ticked along for years on the assumption that a couple of wall fans and an open roller door were doing the job. The welder was fine, in the end. But the occupational health nurse asked a simple question that nobody in the shop could answer with any confidence - how do you know your fume extraction is actually working? Not switched on. Working. Pulling the fume away from the breathing zone at the rate it was designed to.
Nobody could answer it, because nobody had ever tested it. And that gap, once you see it, is hard to unsee.
What made the difference for this shop was not a bigger extractor or a shinier torch. It was understanding what the law had already decided on their behalf. Since 2019, the Health & Safety Executive has treated all welding fume - including mild steel fume, which many welders still think of as harmless - as a human carcinogen. That reclassification followed evidence from the International Agency for Research on Cancer linking mild steel welding fume to lung cancer, and possibly kidney cancer. The practical upshot is blunt - there is no known safe level of exposure, so general ventilation is no longer accepted as adequate control for indoor welding. The HSE will not accept welding undertaken without suitable engineering controls in place, regardless of how short the job is.
That means Local Exhaust Ventilation, or LEV - a system designed to capture fume at or near the point it is created and take it away before anyone breathes it. On-torch extraction, an extracted bench, a moveable capture hood on an articulated arm - the form varies, but the principle is the same. Get the fume before it reaches the welder's face. Where LEV alone cannot bring exposure low enough, it has to be supplemented with suitable respiratory protective equipment for the residual fume. The shop in question already had extraction of a sort. What it did not have was any evidence the extraction did what it was supposed to.
The uncomfortable truth this shop discovered is that fume you cannot see is still doing damage. Welding fume is a fine mix of metal oxides and gases, and the finest, most dangerous particles are the ones that never form a visible plume. A bay can look clean, smell tolerable and still be sitting well above the limits set out in the HSE's EH40 guidance for individual fume constituents. There is no single Workplace Exposure Limit for welding fume as a whole - EH40 sets limits for the specific substances within it, such as manganese and various metal oxides - and because the fume is carcinogenic, exposure has to be reduced as low as reasonably practicable, not merely nudged under a number.
An extraction system also does not fail all at once. It fails slowly. Filters load up and airflow drops. A flexible duct kinks behind a bench. A capture hood drifts a few inches further from the arc than it was when someone commissioned it, and the capture velocity at the weld quietly halves. None of that announces itself. The welder feels no different on the day it stops protecting them. That is precisely why the law does not rely on how the system feels, and why it asks for something measured instead.
The rules in three numbers
Under the Control of Substances Hazardous to Health Regulations, an LEV system is not a fit-and-forget purchase. It has to be maintained, and it has to be examined and tested on a schedule that reflects the risk it controls.
Fourteen months is a ceiling, not a target. HSE guidance in HSG258 is clear that you match the interval to the contaminant and how quickly the system may degrade - and for a carcinogenic fume, many systems are examined more often than the maximum allows. The three-stage examination is what turns a hunch into evidence - a thorough visual check that the system is in good repair and clean, technical measurements such as hood capture and face velocities, duct velocities and static pressures compared against the original commissioning figures, and a final assessment - often using smoke or a dust lamp - that the fume is genuinely being pulled away from the welder rather than drifting past them.
What the shop did next is the part worth copying. They did not panic-buy equipment. They booked a proper LEV thorough examination and test, and let the results tell them where the real problems were. Two bays were fine. One had a partially blocked filter that had never been changed. One had a capture hood mounted so far back that, on paper, it looked like extraction but in practice it was ventilating the ceiling. Fixing those two issues cost a fraction of what a wholesale replacement would have, precisely because the testing showed them exactly what to fix.
The testing also settled an argument the shop had been having with itself for years - whether to rely on extraction pulled right to the torch or a broader capture arm over the bench. That choice is not academic, and the right answer depends on the work, the metal and how the welder moves. If you are weighing it up, it is worth reading our take on torch, arm or ambient fume extraction before you commit to a system, because the wrong capture method looks compliant and quietly is not. The same logic applies with far higher stakes inside tanks, vessels and other tight spaces, where fume has nowhere to go - our guide to welding in confined spaces covers why extraction and monitoring there are non-negotiable rather than nice-to-have.
A year on, the shop treats its fume control the way it treats its gas bottles - as something that gets checked, logged and trusted because it has been checked, not because it looks alright. The health surveillance appointments are no longer a source of dread. And the welder who could not do his breathing test that day is still welding, with extraction he can be confident about, because someone finally measured it.
That is the whole point. A scare is only wasted if nothing changes afterwards. This shop turned a bad appointment into a system it can actually stand behind - and every piece of that confidence traces back to one thing, a proper test that produced real numbers instead of reassuring guesses.
Questions
COSHH Regulation 9 requires a thorough examination and test of your LEV at least every 14 months. For welding fume, which is classed as carcinogenic, that 14 months is a maximum rather than a target - many systems are tested more frequently because the risk is high and airflow can degrade between visits. You must also keep each test record for at least five years.
Yes. Since 2019 the HSE has treated all welding fume, including mild steel fume, as a human carcinogen, following evidence linking it to lung cancer and possibly kidney cancer. There is no known safe level of exposure, so exposure has to be reduced as low as reasonably practicable. General ventilation such as open doors and wall fans is no longer accepted as adequate control for indoor welding.
Following HSG258, the test has three stages. First a thorough visual examination to confirm the system is in good repair and clean. Second, technical measurements such as hood capture and face velocities, duct velocities and static pressures, compared against the original commissioning figures. Third, an assessment - often using smoke or a dust lamp - to confirm fume is genuinely being drawn away from the welder's breathing zone.
No. There is no single Workplace Exposure Limit for welding fume as a whole - EH40 sets limits for individual constituents such as manganese and various metal oxides. Because the fume is carcinogenic, the HSE's position is that meeting a limit is not sufficient. Exposure must be reduced as low as reasonably practicable, which for indoor welding means suitable LEV, supplemented by RPE where residual fume remains.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.