Fume, radiation and electrical safety

Arc welding concentrates several kilowatts in a few millimetres, and the same intensity that melts steel creates its hazards. The arc vaporises some metal and flux, which condense into fine fume particles. It emits intense ultraviolet, visible and infra-red radiation. Its circuit carries enough voltage to drive a dangerous current through a person in the wrong conditions, and enough current to create strong magnetic fields. None of these hazards is new, but the understanding of the fume hazard in particular has changed sharply in recent years.

This chapter uses Safe Work Australia’s model code of practice on welding processes and recent changes to exposure standards to set out the hazards, and puts numbers on why the conveyor shop needed extraction at the source.

What welding fume is

Welding fume is a mixture of very fine particles, mostly metal oxides, formed when vapour from the arc condenses in the air, together with gases such as ozone, oxides of nitrogen and carbon monoxide. Safe Work Australia’s code notes that the amounts and types of fumes vary greatly with the process and materials, that many fumes and gases are invisible, and that generally fewer fumes are generated from gas welding than from electric welding processes. It lists effects including irritation, metal fume fever, lung damage, bronchitis, cancer, pneumonia and emphysema, and it sets out the controls.

Two changes have raised the importance of fume control:

• the International Agency for Research on Cancer, in its Monographs volume 118 published in 2018, classified welding fumes as carcinogenic to humans (Group 1), and also classified ultraviolet radiation from welding as Group 1;
• Safe Work Australia reduced the workplace exposure standard for welding fumes (not otherwise classified) from an eight-hour time-weighted average of 5 mg/m³ to 1 mg/m³, a change that becomes mandatory as each jurisdiction implements it in its work health and safety laws.

Exposure standards are being replaced by workplace exposure limits, and individual fume components such as manganese, chromium and nickel compounds have their own limits, so the current values should always be checked. Recall from Chapter 1 that the 1921 measurements found only a small proportion of the electrode vaporised; it is that small proportion, condensed into a plume of fine particles in the welder’s breathing zone, that causes the harm.

Why general ventilation cannot cope

The fume formation rate, the mass of fume produced per minute of arc time, depends on the process, the consumable, the current and the technique, and is measured by consumable makers and researchers. This is an illustration. Suppose the shop’s 4.0 mm low-hydrogen electrodes at 170 A produce fume at about 0.3 g per minute of arc time, an assumed figure for this calculation; the real value for any consumable should come from its maker or from measurement.

On a conveyor frame with 124 minutes of arc time, that is about 0.3 × 124 ≈ 37 g of fume per frame. More revealing is the rate during welding: 0.3 g per minute is 300 mg per minute. To dilute 300 mg per minute to the exposure standard of 1 mg/m³ by general ventilation alone, the workshop would need to supply and mix fresh air at 300 m³ per minute, which is 5 m³ per second, for one welder, and the dilution would have to be perfect.

Figure 1Fresh air needed to dilute one welder's fume to 1 mg/m³

Q = G ÷ C

Q

ventilation rate, m³/min

G

fume generation rate during welding, 300 mg/min (assumed)

C

exposure standard, 1 mg/m³ (eight-hour time-weighted average)

1. Q = 300 ÷ 1 = 300 m³/min
2. Q = 300 ÷ 60 = 5 m³/s for one welder

Even that understates the problem. The exposure standard is measured in the welder’s breathing zone, which for a welder is inside the helmet, and the fume plume rises from the arc directly towards it before it has a chance to mix with the room air. General ventilation dilutes the background but does little for the welder in the plume. The answer is to capture fume where it is made, with local exhaust ventilation: an extraction hood or arm positioned close to the arc, or extraction built into the welding gun for gas metal arc welding.

The controls in order

Safe Work Australia’s code applies the hierarchy of control. For fume, it starts with eliminating exposure as far as reasonably practicable. Where that is not possible, its examples of measures to minimise the risk include substituting a less hazardous chemical, reducing the quantity involved, for example by removing surface contaminants before welding, isolating the source, for example by welding in booths away from others, and engineering controls such as ventilation to capture or remove airborne contaminants, followed by administrative controls and respiratory protective equipment. It also suggests checking the consumables’ safety data sheets for the gases and fumes they release, points to the Welding Technology Institute of Australia’s fume minimisation guidelines, and sets out when air monitoring is needed, including to check whether exposure standards are being exceeded or approached.

Surface contaminants matter particularly on repair work. Old paint, primers, oil, plastic coatings and galvanising on a conveyor frame are vaporised by the arc along with the steel, adding their own fumes, some of them far more hazardous than steel fume. Zinc from galvanising causes metal fume fever, and some old paints contain lead. The shop’s site procedure requires coatings to be removed back from the weld area by grinding or other suitable means, with its own dust controls, before welding begins, and asks the site about the coating’s composition when it is unknown.

Figure 2The conveyor shop's fume controls, from most to least effective

1. 1Eliminate or reducefewer and smaller welds (Chapter 5); bolted site connections
2. 2Substitutelower-fume process and consumables where qualified
3. 3Capture at sourceextraction arms at each bay, positioned at the arc
4. 4Administrativewelding bays away from other workers; air monitoring
5. 5Personal protectionrespiratory protection as the risk assessment requires

Extraction only works if it is used properly. A hood that captures well at 150 mm from the arc may capture little at 500 mm, because the airflow it induces falls away rapidly with distance. Welders moving along a long rail weld must move the hood with them, and a hood pulled aside to see the weld better captures nothing. The shop’s supervisors check hood position during their rounds, and the extraction system’s airflow is tested at a set interval, because a blocked filter or a damaged duct can halve its capture without anyone noticing.

The first two steps link back to earlier chapters. Every kilogram of weld metal not deposited is fume not made, so the weld-size discipline of Chapter 5 is also a fume control. A change of process, such as from manual metal arc to gas metal arc welding, changes the fume and must be reassessed rather than assumed to be better.

The shop installed an extraction arm at each welding bay and trained welders to keep the hood close to the arc and to reposition it as they move along a weld. Air monitoring in the welders’ breathing zones, by an occupational hygienist, was used to check that the controls were working. Respiratory protection is provided where the risk assessment requires it, including for site work where extraction is not practicable.

Radiation

The code notes that electric arc welding emits ultraviolet, visible and infra-red radiation. Ultraviolet exposure of the eyes causes arc eye, or welder’s flash, a painful inflammation of the cornea that usually heals in one to two days but can lead to infection. The effects are often not felt until hours after exposure. Exposed skin is burnt by ultraviolet radiation in the same way as by severe sunburn. Bystanders, not only welders, are at risk.

The controls are screens and curtains around welding bays, a helmet or face shield with a filter of the right shade for the process and current, eye protection for people nearby, and clothing that covers the skin. The code refers to AS/NZS 1338.1 for filters for protection against radiation generated in welding; the filter shade depends on the process and current, and the helmet maker’s guidance gives it. Auto-darkening helmets must be kept in good order, because a filter that fails to darken exposes the eye at the moment the arc strikes.

Electric shock

Chapter 2 noted that open-circuit voltage is the voltage a welder can touch, and that the code considers the risk of electric shock lower for gas metal arc welding than for manual metal arc welding. The code’s controls for electric shock include:

• fully insulated electrode holders, never dipped in water to cool or placed on conductive surfaces;
• dry welding gloves, so that electrodes and wire are never touched with bare hands, and holders never held under the armpit;
• checking the work area for live structures and wet areas;
• installing a residual current device and inspecting all equipment before use;
• keeping terminals and cable connections clean and tight, and using cables fully insulated along their whole length;
• not connecting or changing welding cables without first switching off at the mains;
• using an appropriate hazard reducing device, and avoiding working alone in hazardous environments;
• minimising perspiration, standing or sitting on non-conducting material where practicable, and not leaning against the work.

The code points to AS 1674.2 for electrical safety in welding and to AS 60974.1 for hazard reducing devices on welding power sources. Moisture, heat and confined steel structures all raise the risk, which is why site work inside steel chutes, hoppers and tanks needs particular care.

Electromagnetic fields

The code also notes that electric arc welding produces strong electric and magnetic fields close to the power source and around the current-carrying cables, which can disrupt pacemakers, defibrillators and other medical devices. A worker with such a device may not be aware of the hazard until the device behaves irregularly. Medical advice should be sought before such a worker is exposed. The code’s suggested controls include barriers to keep people away, substituting a different process for workers with such devices, signs, and not standing close to the power source or draping cables around the body.

Fire and other hazards

Arc welding throws spatter and slag, and the work stays hot long after welding. Fires start from sparks landing in dust, rags, paint, conveyor belting and hidden combustible material on the other side of a wall or inside a structure. The shop’s site procedure includes a hot-work permit where the site requires one, removal or protection of combustible material, fire extinguishers at hand and a fire watch after welding. Noise, burns, manual handling and working at height complete the list, and the code addresses each.

A failure: welding inside the chute

This is an illustration. During a site repair, a welder spent most of a morning replacing a wear liner inside a conveyor transfer chute, a steel box about 1.5 m across with a small access opening. There was no extraction, because the extraction arm would not reach, and the welder relied on the chute’s open bottom for ventilation. By late morning the welder had a headache and felt unwell, and stopped work.

The investigation identified several failures together. The chute was effectively an enclosed space in which fume accumulated, so the welder’s exposure far exceeded anything in the open workshop, where the extraction arms worked. The site’s procedures for working in enclosed and confined spaces had not been considered when the job was planned, because it was thought of as a routine liner change. And the welder was working alone, inside a steel structure, with a manual metal arc set, which also raised the electric shock risk.

The shop changed its site planning. Any welding inside a chute, hopper or other enclosure is now assessed for confined-space requirements under the site’s procedures before work starts; portable extraction with ducting is taken to site for such jobs; respiratory protection suitable for the work is provided; a second person is present; and the welding power source is fitted with a hazard reducing device. The welder recovered, and the job was completed later with the new controls.

Exercise: two welders and a smaller electrode

Two welders work in the same bay, one using 4.0 mm electrodes producing fume at an assumed 0.3 g per minute and one using 3.2 mm electrodes at an assumed 0.2 g per minute, each with a 30% operator factor over an eight-hour day. Calculate the fume produced by each and in total over the day, and the general ventilation rate that would be needed, in m³/s, to dilute the combined fume to 1 mg/m³ while both are welding at once.

Each welder’s arc time is 0.30 × 480 = 144 minutes. The 4.0 mm welder produces 0.3 × 144 ≈ 43 g and the 3.2 mm welder 0.2 × 144 ≈ 29 g, about 72 g a day in total. While both are welding, fume is produced at 300 + 200 = 500 mg per minute, so dilution alone would need 500 m³ per minute, about 8.3 m³/s.

That is an impractical volume of air to move, heat or cool in a workshop bay, and it would still leave each welder in their own plume. The figures, built on assumed fume rates, make the same point as the code: capture fume at its source, and use general ventilation only to deal with what escapes.