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Local exhaust ventilation (LEV) works only when it captures welding fumes before they pass through your breathing zone. The hood does not need to be directly over the weld, but it does need a clear path to pull the smoke away from your face and toward the duct. A hood positioned several inches too far away can make a noticeable difference, especially with stainless steel, galvanized steel, painted parts, and flux-cored wire.
Start With the Fume Path
Before striking an arc, identify where the visible plume will travel. Welding fumes rise when the metal is hot, but the plume also follows room currents, torch movement, shielding gas, and the operator’s body position. Your face should never sit between the arc and the exhaust hood.
For most bench welding, position the hood slightly above and to one side of the weld. This lets it pull the plume away without interfering with the torch, electrode, or shielding gas. If you place the hood directly in front of the weld, the airflow can disturb MIG or TIG shielding and cause porosity. If you place it behind your head, it may pull fumes through your breathing zone before capturing them.
A practical starting point is to keep a movable hood about 4 to 8 inches from the arc, as close as the work allows without blocking the weld or disturbing shielding gas. Some high-volume systems can capture effectively from farther away, but distance rapidly reduces capture performance. If you must move the hood more than a foot away, use a larger hood or a system specifically designed for that reach rather than assuming a small shop vacuum will compensate.
Position the Hood by Welding Process
| Process | Useful hood position | Main positioning concern |
|---|---|---|
| MIG and flux-cored | 4–8 inches behind or to the side of the arc | Keep suction from pulling shielding gas away |
| TIG | 4–8 inches to the side or slightly above | Avoid drafts across the tungsten and weld puddle |
| Stick | As close as practical, usually above and to the side | Accommodate changing electrode angle and slag |
| Plasma cutting | Over the table, behind the cut, or through a downdraft table | Capture smoke, sparks, and hot particles safely |
Stick welding produces a plume that changes as the electrode burns, so a fixed hood can quickly become poorly aligned. A flexible-arm hood is usually more useful than a rigid overhead duct. For plasma cutting, a small movable welding hood is often inadequate. Use a cutting table with downdraft or water-table extraction, or a hood rated for the volume and spark load produced by the cutter.
Choose the Right Hood and Airflow
A movable capture arm is the most versatile choice for a home or small fabrication shop. Look for a hood that holds its position, has a reasonably wide opening, and connects to a filter or extractor designed for welding fumes. A welding fume extractor with a flexible arm is generally more useful than a bare fan because it captures at the source and filters the air.
Do not substitute an ordinary box fan placed across the room. It may dilute fumes, but it does not provide reliable source capture and can spread contaminants through the shop. A shop vacuum is also not automatically suitable. Many lack the airflow, filter arrangement, spark protection, or continuous-duty rating needed for welding. Never allow sparks and hot slag to enter a plastic vacuum or a filter not intended for them.
For a fixed welding bench, a canopy hood can work if it is positioned above the entire work area and has enough airflow. It is less efficient than source capture because the fumes have already risen through the operator’s breathing zone. Downdraft tables are effective for small parts and plasma cutting, but they can pull shielding gas away from a MIG or TIG weld unless the airflow is controlled.
Check Capture in Practice
Use visible smoke from a smoke pencil or theatrical smoke, not your face or lungs, to test airflow. With the extractor running, release smoke near the expected plume and watch whether it moves smoothly into the hood. It should not curl around your helmet or drift across the front of your body first.
Test with the hood at the actual working distance, with the workpiece, torch, and fixture in place. A hood that captures smoke from an empty bench may fail when a large plate blocks the airflow. Check several torch angles and weld positions. If the plume escapes whenever you reach around the part, reposition the arm or use a second capture point.
Keep doors, fans, and compressed-air lines from creating cross-drafts. Even a modest cross-draft can carry fumes past a small hood. If opening a garage door is necessary for cooling, place the welding station so incoming air does not blow from the arc toward your face. Shielding a draft with a partial screen may help, but do not create an enclosed space that traps fumes.
Avoid Common LEV Failures
- Hood too far away: Move it closer before buying a larger extractor. Capture effectiveness falls quickly with distance.
- Hood behind the operator: This often pulls the plume through the breathing zone. Position it to the side or in front of the plume, not behind your head.
- Blocked or crushed duct: Flexible hose loses airflow when kinked. Keep runs short, smooth, and free of sharp bends.
- Dirty filters: A loaded filter reduces airflow. Check the extractor’s airflow indicator, if fitted, and replace filters according to pressure or manufacturer guidance.
- Wrong filter: A particulate filter does not remove every gas or vapor from coatings, degreasers, or galvanized steel. Remove coatings where possible and follow the product’s filter specifications.
- Relying on LEV alone: Use a suitable welding respirator when the risk assessment calls for it, particularly in confined areas, during stainless or galvanized work, or when coatings cannot be removed.
What to Buy for a Small Shop
For occasional MIG or stick welding, a correctly positioned flexible-arm extractor is usually the best balance of cost and performance. A welding fume extraction hood is worthwhile when the arm can stay close to the arc without becoming a nuisance.
The cheaper option is acceptable when you weld briefly, work outdoors or in a genuinely well-ventilated open area, and can keep the plume completely out of your breathing zone. It is not a good substitute for LEV when welding indoors for long periods. For a regular fabrication setup, budget for a source-capture extractor, replacement filters, and a welding respirator with P100 filters where appropriate. Keep wearing the correct welding helmet, gloves, clothing, and eye protection: LEV controls fumes, not arc flash, sparks, noise, or hot metal.