Welding health hazards: fumes, gases, radiation and PPE

Fire is not the only danger in hot work. Welders and the people around them breathe fumes and gases, are exposed to intense ultraviolet and infrared radiation, work with electrical equipment that can shock, handle hot metal that burns, and are often exposed to loud noise. Many of these effects are slow and invisible: lung damage, nervous system effects from manganese, cancers linked to hexavalent chromium and to welding fume itself. This lesson covers the main health hazards of hot work and how ventilation, work practices and personal protective equipment control them.

Welding fume

Welding fume is a mixture of very fine metal oxide particles formed when metal vaporizes in the arc or flame and condenses in air. The particles are small enough to reach deep into the lungs. The composition depends on the base metal, the filler metal or electrode, the coatings and the process. Mild steel fume is mostly iron oxide with some manganese; stainless steel fume contains chromium, including hexavalent chromium, and nickel; galvanized steel releases zinc oxide; old painted steel may release lead or cadmium.

In 2017 the International Agency for Research on Cancer classified welding fume as carcinogenic to humans (Group 1), based on evidence of lung cancer in welders. That classification applies to welding fume in general, not only to stainless steel. It means fume exposure should be kept as low as reasonably achievable, not just below a limit.

Exposure limits

Occupational exposure limits (OELs) in Canada are set by each province and territory, and by the federal government for federally regulated workplaces. Most jurisdictions adopt the threshold limit values (TLVs) published by the American Conference of Governmental Industrial Hygienists (ACGIH), or base their limits on them, sometimes with a delay or amendments. The ACGIH TLVs for some welding fume components are very low: for manganese, 0.02 mg/m³ for the respirable fraction and 0.1 mg/m³ for the inhalable fraction, and for hexavalent chromium compounds, 0.0002 mg/m³ (0.2 µg/m³) inhalable as an 8-hour average. Check your jurisdiction's OEL table, because the legal limit may differ from the current TLV.

Ventilation and fume control

The best way to control welding fume is to capture it at the source before it reaches the welder's breathing zone. Local exhaust ventilation uses a hood, slot or nozzle close to the arc, connected to a fan and filter. Fume-extraction guns build the extraction into the welding gun. General ventilation, which dilutes fume across a room, is much less effective for the welder and is mainly a back-up.

CSA W117.2 and provincial OHS regulations require ventilation adequate to keep exposures below the OELs, and several provinces specifically require local exhaust for welding on materials such as stainless steel or coated metals. Many designers use a capture velocity of at least about 0.5 m/s at the point of welding, which matches the long-standing US benchmark of 100 ft/min.

Capture velocity falls off sharply with distance from the hood, roughly with the square of the distance. A hood that captures well at 15 cm may do almost nothing at 45 cm. This is the most common reason local exhaust fails: the welder works too far from the hood, or the hood is not moved as the work moves.

Work practices matter too: keep the head out of the fume plume, weld with the plume rising away from the face, remove paint and coatings from the weld area before welding, never weld near chlorinated solvent degreasing, and choose processes and consumables that produce less fume where possible. In confined spaces, ventilation must be designed carefully, oxygen must never be used for ventilation, and air-supplied respirators may be needed.

Respiratory protection

Where ventilation cannot keep exposure low enough, respirators are needed as part of a program meeting CSA Z94.4: selection based on the hazard and exposure level, fit testing, training, maintenance and medical fitness where required. Filtering respirators for welding fume use particulate filters (such as N95 or P100 classes approved by NIOSH, which Canadian regulations generally accept), sometimes with ozone or acid gas protection. Powered air-purifying respirators built into welding helmets are popular because they are comfortable and provide higher protection. Respirators are the last line of defence and do not replace good ventilation.

Radiation: ultraviolet, visible and infrared

Welding arcs emit intense ultraviolet (UV), visible and infrared (IR) radiation. UV causes photokeratitis, known as arc eye or welder's flash: a painful inflammation of the cornea that feels like sand in the eyes, starting several hours after exposure. Repeated exposure can damage the lens and retina. UV also burns exposed skin like severe sunburn. IR heats the eyes and skin and contributes to cataracts. Bystanders can be injured by reflected and direct arc light, which is why welding screens and curtains are used.

Eye and face protection must follow CSA Z94.3, which classifies welding helmets and filters and gives guidance on filter shade numbers by process and current. Higher shade numbers are darker. A common approach is to start with a darker shade than needed and go lighter until the weld zone is visible without discomfort, without going below the minimum.

Electric shock, burns and noise

Arc welding uses electrical power. The open-circuit voltage of a welding machine is usually low enough to be safe in dry conditions, but in wet, hot or cramped conditions, sweat and damp clothing lower body resistance, and shocks become dangerous. A shock can also cause a fall from height. Precautions include dry gloves and clothing, insulating mats, keeping cables in good condition, connecting the work return lead close to the work, using voltage-reducing devices in high-risk locations and never coiling cables around the body.

Burns from spatter, slag and hot metal are the most common welding injuries. Flame-resistant clothing made of wool, leather or treated cotton, without cuffs or open pockets that catch sparks, protects the body. Synthetic fabrics can melt and stick to skin. Leather gloves, aprons, sleeves and safety boots, with trousers worn over the boots, complete the protection. Air carbon arc gouging and plasma cutting can exceed 100 dBA, so hearing protection is needed for many hot work tasks.

Health surveillance and long-term protection

For some welding hazards, regulations require health surveillance in addition to exposure control. Workers exposed to designated substances such as lead or to some carcinogens may need medical examinations, and workers who use respirators may need medical fitness assessments. Provincial occupational disease programs and workers' compensation boards recognize several welding-related diseases, including some lung cancers, occupational asthma and manganism. Keeping records of exposures, processes and materials helps workers make claims years later, when disease appears.

Helpers, fitters and other workers near welding are exposed to fume and radiation too, sometimes more than the welder, because they do not benefit from the welder's helmet or local exhaust positioned for the welder. Exposure assessments should include them, and screens, ventilation and work layout should protect everyone in the area, not only the person holding the torch.