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LEV testing - welding fume
Welding fume is a serious hazard - the HSE now treats all welding fume as capable of causing cancer, so it has to be properly controlled. But there's more than one way to extract it: on-torch (built into the welding gun), on-arm (a movable capture hood on an arm), or ambient (general extraction of the whole area). They capture the fume differently and suit different situations. Here is how the types compare, and where each fits. This is general information.
The short answer
Welding produces a fume that's now recognised as seriously hazardous - the HSE hardened its position so that all welding fume, including from mild steel, is treated as capable of causing cancer, meaning it has to be properly controlled with extraction (and often RPE too). But 'welding fume extraction' isn't one thing: there are three main approaches - on-torch, on-arm, and ambient - which capture the fume differently and suit different welding. Here's how they compare, and where each fits. This is general information. On-torch extraction: capture at the gun. On-torch extraction (also called on-gun, or high-vacuum-at-source) builds the extraction into or onto the welding gun itself, so it captures the fume right at the point it's created - at the arc - as the fume forms. This is the closest possible capture: the extraction is at the source, drawing the fume away the instant it's made, before it can rise into the welder's face. When set up and used well, it's very effective at capturing the fume at source. Its trade-offs: it adds to the gun (affecting handling and weight), and it has to be balanced so it doesn't disturb the shielding gas that protects the weld; and it suits certain welding processes and setups better than others. So on-torch is powerful source capture, with some practical trade-offs. On-arm extraction: a movable hood near the arc. On-arm extraction uses a capture hood on an articulated (movable) arm, which the welder positions near the arc to capture the fume in the area around it. As the welder moves to a different spot, they reposition the arm to keep the hood near the new arc. It's a flexible form of near-source capture - not right at the gun, but close to the arc - and it's effective when kept positioned close to the work. Its key dependency: it relies on the welder actually positioning it right - close to and over the arc. If the hood is left too far from the arc, or not repositioned as the welder moves, the capture drops, because capture falls off quickly with distance. So on-arm is flexible near-source capture that depends on being positioned well. Ambient extraction: treating the whole area. Ambient (or general) extraction treats the whole welding area or workshop air - extracting and removing fume from the general space, rather than capturing it at source. It dilutes and clears the fume from the area over time. Its role: it's a backstop or a supplement, not a substitute for source capture. Because it doesn't capture the fume before it reaches the welder's breathing zone - it deals with the fume once it's already in the general air - it doesn't protect the welder as well as source capture does. So ambient extraction has a place (dealing with residual fume that source capture misses, or large/variable areas), but as a supplement to source capture, not the primary control. Source capture first. The general principle across the three is that source capture - on-torch or on-arm - is preferred. Capturing the fume at or near the arc, before it reaches the welder's breathing zone, protects the welder better than treating the general air after the fume has spread. This follows the general hierarchy of controlling airborne hazards: capture at source beats general dilution. So on-torch or on-arm should be the primary control, with ambient as a supplement for residual fume or where source capture can't reach everything - not the other way round. A shop relying on ambient extraction alone, with no source capture, is generally not controlling the welder's exposure well. Matching to the work. Which approach (or combination) suits a given shop depends on the welding done: the process (some suit on-torch better), the mobility (a welder moving around large fabrications may need on-arm's flexibility, or the portability of certain systems), the workpieces (big structures vs small bench work), and the setup. So the choice is matched to the work, with source capture as the priority - often on-arm or on-torch as the primary control, sometimes with ambient support. And whichever is used, it has to actually capture the fume and be kept working: as an LEV controlling a carcinogenic fume, it must be thoroughly examined and tested regularly, and used correctly (positioned right, gun extraction not disabled). The approach matters, but so does it genuinely working (covered in the lev-testing-for-welding-fume-what-good-capture-looks-like page). The takeaway. So welding fume extraction comes in three main forms: on-torch (capture at the gun, the closest capture, with handling trade-offs), on-arm (a movable hood positioned near the arc, flexible but dependent on good positioning), and ambient (general extraction of the whole area, a supplement not a substitute). Source capture (on-torch or on-arm) is generally preferred, because it captures the fume before it reaches the welder; ambient is a backstop. The right choice is matched to the welding done, with source capture as the priority - and whichever is used, it has to actually capture the fume and be tested and kept working. This is general information. This is general information.
Key points
Why it matters
Getting welding fume extraction right matters because welding fume is a serious hazard. The HSE hardened its position so that all welding fume - including fume from mild steel, which was once thought lower-risk - is treated as capable of causing cancer. So welding fume has to be properly controlled with extraction (and often respiratory protection as well), for indoor welding in particular.
This is why the choice of extraction approach - on-torch, on-arm or ambient - isn't just a technical preference but a matter of how well the welder is protected from a carcinogenic fume. An approach that captures the fume well (at or near the source, before it reaches the welder) protects better than one that doesn't. So understanding the three approaches, and that source capture is generally preferred, is about genuinely controlling a cancer-causing exposure, not just ticking a box. So why it matters - welding fume is treated as a carcinogen - sets the stakes: the extraction has to properly control a serious hazard, so the approach and its effectiveness matter. The three approaches follow. So the fume is a carcinogen, so the extraction must control it well. This is general information. This is general information.
On-torch extraction
On-torch extraction (also called on-gun, or high-vacuum-at-source) builds the extraction into or onto the welding gun itself, so it captures the fume right at the point it's created - at the arc - as the fume forms. This is the closest possible capture: the extraction is at the source, drawing the fume away the instant it's made, before it can rise into the welder's face. When set up and used well, it's very effective at capturing the fume at source.
Its trade-offs: it adds to the gun (affecting the handling and weight of the torch the welder holds), and it has to be balanced so the extraction doesn't disturb the shielding gas that protects the weld (too much extraction at the wrong point can pull the gas away and affect weld quality). And it suits certain welding processes and setups better than others. So on-torch is powerful source capture with some practical trade-offs to manage - the closest capture there is, but requiring the gun setup to be got right so it captures without harming the weld. So on-torch extraction - capture right at the gun - is the closest-source approach: very effective when set up and used well, with handling and shielding-gas trade-offs. On-arm extraction follows. So on-torch captures at the gun, the closest capture. This is general information. This is general information.
On-arm extraction
On-arm extraction uses a capture hood on an articulated (movable) arm, which the welder positions near the arc to capture the fume in the area around it. As the welder moves to a different spot on the workpiece, they reposition the arm to keep the hood near the new arc. So it's a flexible form of near-source capture - not right at the gun like on-torch, but close to the arc - suited to work where the welder moves around, and effective when the hood is kept positioned close to the work.
Its key dependency is that it relies on the welder actually positioning it right - close to and over the arc - and repositioning it as they move. If the hood is left too far from the arc, or not moved when the welder shifts to a new spot, the capture drops sharply, because capture velocity falls off quickly with distance from the hood (a hood that's too far away captures little). So on-arm extraction is only as good as its positioning: kept close, it captures well; left far, it doesn't. This makes the welder's habit of repositioning it (and training on that) important. So on-arm extraction - a movable hood positioned near the arc - is flexible near-source capture that depends on good positioning: effective when kept close to the arc, weak when it isn't. Ambient extraction follows. So on-arm captures near the arc, if positioned well. This is general information. This is general information.
Ambient extraction
Ambient (or general) extraction treats the whole welding area or workshop air - extracting and removing fume from the general space, rather than capturing it at source. It dilutes and clears the fume from the area over time. So it deals with the fume once it's already in the general air, rather than catching it at the arc before it spreads.
Its role is as a backstop or a supplement, not a substitute for source capture. Because it doesn't capture the fume before it reaches the welder's breathing zone - the welder still breathes the fume as it rises from the arc, before the ambient system clears it from the wider area - it doesn't protect the welder as well as source capture does. So ambient extraction has a place (dealing with residual fume that source capture misses, or clearing large or variable areas where source capture can't reach everything), but as a supplement to source capture, not the primary control. A shop relying on ambient extraction alone, with no source capture, is generally not controlling the welder's exposure well - the welder is still breathing the fume at the arc. So ambient extraction - treating the whole area, a backstop - is the supplementary approach: useful for residual fume and general clearance, but not a substitute for capturing at source. Why source capture comes first follows. So ambient clears the area but doesn't protect the welder at the arc. This is general information. This is general information.
Source capture first
The general principle across the three approaches is that source capture - on-torch or on-arm - is preferred. Capturing the fume at or near the arc, before it reaches the welder's breathing zone, protects the welder better than treating the general air after the fume has already spread. This follows the general hierarchy for controlling airborne hazards: capture at source beats general dilution. So on-torch or on-arm should be the primary control, with ambient as a supplement for residual fume or where source capture can't reach everything - not the other way round.
Which approach (or combination) suits a given shop depends on the welding done: the process (some suit on-torch better), the mobility (a welder moving around large fabrications may need on-arm's flexibility), the workpieces (big structures vs small bench work), and the setup. So the choice is matched to the work, with source capture as the priority - often on-arm or on-torch as the primary control, sometimes with ambient support. And whichever is used, it has to actually capture the fume and be kept working: as an LEV controlling a carcinogenic fume, it must be thoroughly examined and tested regularly, and used correctly (positioned right, on-torch extraction not disabled). The approach matters, but so does it genuinely working (covered in the lev-testing-for-welding-fume-what-good-capture-looks-like page). So source capture first - capture at the arc, then match to the work - is the guiding principle: prioritise on-torch or on-arm, match the choice to the welding, and keep whatever's used tested and working. So prioritise source capture, match it to the work, keep it tested. This is general information. This is general information.
Questions
Three main approaches: on-torch (extraction built into the welding gun, capturing at the arc), on-arm (a movable capture hood on an arm, positioned near the arc), and ambient (general extraction of the whole area) - the first two capture at or near the source, while ambient treats the general air as a backstop. There are three main ways to extract welding fume, which capture it differently. On-torch extraction (also called on-gun, or high-vacuum-at-source): the extraction is built into or attached to the welding gun itself, capturing the fume right at the point it's created - at the arc - as it forms. This is the closest possible capture. On-arm extraction: a capture hood on an articulated (movable) arm, which the welder positions near the arc to capture the fume in the area around it, repositioning it as they move. This is flexible near-source capture. Ambient (or general) extraction: extraction that treats the whole welding area or workshop air, removing fume from the general space rather than capturing it at source - it dilutes and clears the fume from the area over time. The first two - on-torch and on-arm - are source capture (or near-source), catching the fume at or close to the arc before it reaches the welder. Ambient treats the general air after the fume has spread. Source capture is generally preferred, because it protects the welder better; ambient is a backstop or supplement, not a substitute. The right choice is matched to the welding done, with source capture as the priority. So the three are on-torch, on-arm and ambient. So on-torch, on-arm (source capture) and ambient (general). This is general information. This is general information.
Source capture - on-torch or on-arm - is generally preferred, because it captures the fume at or near the arc before it reaches the welder's breathing zone, protecting the welder better than ambient (general) extraction, which treats the air after the fume has spread; which of on-torch or on-arm suits depends on the welding done. There's no single 'best' welding fume extraction for every situation, but there's a clear general principle: source capture - on-torch or on-arm - is preferred over ambient extraction. This is because source capture catches the fume at or near the arc, before it reaches the welder's breathing zone, whereas ambient (general) extraction deals with the fume only once it's already spread into the general air - by which time the welder has breathed it. Capturing at source protects the welder better, following the general hierarchy for airborne hazards (capture at source beats general dilution). So the primary control should be on-torch or on-arm, with ambient as a supplement for residual fume, not the main control. Between on-torch and on-arm, which is best depends on the welding done: on-torch gives the closest capture (right at the gun) but adds to the gun and suits certain processes; on-arm is flexible (good for a welder moving around larger work) but depends on the welder positioning the hood close to the arc. So the choice is matched to the work - the process, the mobility, the workpieces. And whichever is chosen, it has to actually capture the fume and be tested and kept working - the best approach on paper doesn't protect if it's not working or not used right. So source capture is best in principle, with on-torch vs on-arm matched to the work. So source capture (on-torch/on-arm), chosen to fit the welding. This is general information. This is general information.
Generally no - ambient extraction treats the general air rather than capturing fume at source, so it doesn't catch the fume before it reaches the welder's breathing zone; it's a backstop or supplement for residual fume, not a substitute for source capture, so a shop relying on it alone usually isn't controlling the welder's exposure well. Generally no - ambient (general) extraction is not enough on its own to control a welder's exposure. Ambient extraction treats the whole welding area or workshop air, removing and diluting the fume from the general space over time - but it doesn't capture the fume at source. The problem is that it deals with the fume only once it's already in the general air, after it's risen from the arc; by that point, the welder - standing right over the arc - has already breathed it. So ambient extraction doesn't protect the welder at the moment and place the fume is most concentrated (at the arc, in their breathing zone). This is why ambient extraction is a backstop or a supplement, not a substitute for source capture: it has a role in dealing with residual fume that source capture misses, or clearing large or variable areas, but it should sit alongside source capture (on-torch or on-arm), not replace it. A shop relying on ambient extraction alone, with no source capture, is generally not controlling the welder's exposure well - the welder is still breathing the fume at the arc, and welding fume is treated as a carcinogen. So ambient extraction should supplement source capture, not stand in for it. So no - ambient alone doesn't capture the fume at the welder; it's a supplement. So generally no; it's a backstop, not a substitute for source capture. This is general information. This is general information.
Because it catches the fume at or near the arc, before it rises into the welder's breathing zone - protecting the welder from the most concentrated fume at the point it's created; treating the general air (ambient) only removes the fume after it's spread, by which time the welder has already breathed it, so source capture protects better. Capturing welding fume at source is better because it catches the fume at or near the arc - the point it's created, and where it's most concentrated - before it rises into the welder's breathing zone. The welder stands right over the arc, so the fume rises straight up towards their face as it's produced. Source capture (on-torch, right at the gun, or on-arm, close to the arc) draws that fume away at or near the moment and place it's created, so it never reaches the welder's breathing zone in the first place. This is the most effective protection, because it deals with the fume at its source. Ambient (general) extraction, by contrast, removes the fume only after it's already spread into the general workshop air - by which time the welder, standing over the arc, has already breathed the concentrated fume. So ambient protects the welder much less well, even though it clears the wider area. This is an instance of the general principle for controlling airborne hazards: capturing a contaminant at source is more effective than diluting or removing it from the general air after it's dispersed. Since welding fume is treated as capable of causing cancer, protecting the welder well - with source capture - matters. So source capture is better because it catches the fume before the welder breathes it. So because it catches the fume at the arc, before the welder breathes it. This is general information. This is general information.
Yes - on-arm extraction relies on the welder positioning the movable hood close to and over the arc, and repositioning it as they move; capture falls off quickly with distance, so a hood left too far from the arc captures little - which makes positioning it correctly (and training on that) essential to it working. Yes - on-arm extraction relies on the welder positioning the movable hood, and this is its key dependency. On-arm extraction uses a capture hood on an articulated (movable) arm, which the welder positions near the arc to capture the fume. As the welder moves to a different spot on the workpiece, they have to reposition the arm to keep the hood close to the new arc. So the system's effectiveness depends on the welder actually doing that - positioning the hood close to and over the arc, and moving it as they move. This matters because capture velocity falls off quickly with distance from the hood: a hood positioned close to the arc captures the fume well, but a hood left too far away captures little, because the pull of the extraction weakens rapidly with distance. So if the welder leaves the hood too far from the arc, or doesn't reposition it when they shift to a new spot, the capture drops sharply and the welder is left breathing the fume - even though the extraction is running. This is why positioning is essential to on-arm extraction working, and why training the welder to position and reposition the hood correctly matters. It's also something LEV testing and good practice check - that the on-arm system, used as intended, captures the fume. So yes - it has to be positioned right by the welder to work. So yes; it only captures if the welder keeps it close to the arc. This is general information. This is general information.
Yes - whichever approach (on-torch, on-arm or ambient), it's an LEV controlling a fume treated as carcinogenic, so it must be thoroughly examined and tested regularly (at least every 14 months) to confirm it captures the fume as it should, and be used correctly; the approach matters, but so does it actually working. Yes - welding fume extraction needs testing whichever type it is. On-torch, on-arm and ambient extraction are all forms of LEV controlling welding fume, which is treated as capable of causing cancer - a serious health exposure. So whichever approach a shop uses, it must be thoroughly examined and tested regularly (at least every fourteen months for most systems) to confirm it's still capturing the fume as it should and controlling the exposure. The choice of approach affects how the fume is captured, but every approach has to actually work, and testing is how you confirm it does. The test measures the real performance - for source capture, whether it's genuinely capturing the fume at or near the arc; for ambient, whether it's clearing the area as intended - rather than just whether it's running. Testing also matters because each approach has ways it can fail or be undermined: on-torch extraction can be disabled or its capture reduced; on-arm depends on positioning (which affects real-world capture); ambient can be inadequate for the fume load. So confirming the system genuinely captures the fume, in use, is essential whatever the type. Alongside testing, the extraction has to be used correctly (positioned right, not disabled) and maintained. So the approach you choose matters, but so does keeping it tested and working - a good approach that isn't working doesn't protect the welder. So yes - every type must be tested to confirm it captures the fume. So yes; whichever type, test it to confirm it works. This is general information. This is general information.
Whichever welding fume extraction you use - on-torch, on-arm or ambient - it only protects the welder if it actually captures the fume; we thoroughly examine and test welding fume LEV, confirming it captures the fume at or near the arc as it should, so a carcinogenic fume is genuinely controlled, as COSHH requires. Ask us to test your welding extraction. This is general information.
