// Machinery

Welding - Ventilation

Where can I find some general guidelines for welding ventilation? Ventilation is used for three general purposes: Remove air contaminants from a worker's breathing zone and work area,Prevent the accumulation of flammable or combustible gases or vapours; and,Prevent oxygen rich or oxygen deficient atmospheres.

What types of ventilation can be used to remove air contaminants from a welder's breathing zone?

Ventilation strategies fall into three general categories:

context Natural Dilution Ventilation (least effective)
context Mechanical Dilution Ventilation
context Local Exhaust Ventilation (most effective)

Natural Dilution Ventilation

context Dilution ventilation adds new fresh air to an area and can be accomplished by non-mechanical means, such as opening windows and doors, or mechanical means, such as wall and roof exhaust fans.
context Weld out of the plume. Use a tight-fitting welding helmet to shield you from the plume. By opening doors, windows and other openings in a building's structure, fresh air can be added to an area to decrease the concentration of an airborne contaminant and eventually remove it. This type of ventilation is generally considered the least effective because there is no direct control of how the airborne contaminants will move through the work area.
context Natural dilution ventilation should not be used to ventilate confined spaces in areas that have structural features that prevent or obstruct natural airflow, or when the airborne contaminant contains a carcinogenic substance, or other substance of high toxicity. See CSA W117.2 for specific guidance.

Mechanical Dilution Ventilation

context Mechanical dilution ventilation uses wall fans, roof exhaust fans, or other mechanical means to prevent airborne contaminants from entering a worker's breathing zone.
context See the OSH Answers on Industrial Ventilation for more information.

Local Exhaust Ventilation

context Local exhaust ventilation (LEV) is always the preferred method of removing welding fumes and gases. It exhausts or removes the toxic gases, fumes, dusts, and vapours before they can mix with the room air.
context A well-designed welding helmet can help reduce a welder's exposure to welding fumes by diverting the plume away from the welder's breathing zone.

What are some examples of Local Exhaust Ventilation?

Downdraft Bench

context A downdraft bench has an open grid work surface. Air is drawn downward through the grid, drawing contaminants into exhaust ducting. Air speed must be great enough to prevent contaminants from accumulating and rising into the breathing zone. If workpieces are too large, they may block the ventilation airflow or cause pockets of high-velocity air (which could affect shielding gases).

Moveable Hood

context Flexible ducting allows the capture hood to be moved where required. Provide an air velocity of at least 100 ft/min (0.5 m/s) across the welding arc. Place the hood as close as practical to the work. The optimal location for the hood is about 1 duct diameter from the arc.

Fume Extraction Welding Guns

The contaminants are removed very close to the source of generation and are drawn through a hose into the exhaust system. They can be very effective on flat and vertical surfaces or in corners and around flanges.