Unaccounted Fume, a Missing Guard and a Monday Fever
At a fabrication shed, a worker shears 1.2 mm galvanised iron sheet on a treadle shearing machine whose fixed guard was taken off last week "to see the cut line better". The same worker welds the corners of GI boxes with MMA at about 90 A in a corner of the shed, while a pedestal fan blows across the bench to keep him cool. After two days he complains of fever, chills, a dry cough and a metallic taste. The symptoms fade over the weekend at home and return on Monday afternoon. A helper cleans swarf off the bench with a compressed-air nozzle at 6 bar. The 600 mm roof extractor is switched off because it is noisy, and 12 workers share one first-aid box with no eyewash. The supervisor wants production to continue and asks you, as the trade supervisor, what should be done.
1. List the unsafe conditions and unsafe acts in this shed, then rank the corrective actions using the hierarchy of control. Which single action must be completed before any further shearing?
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Unsafe conditions: treadle shear running without its fixed guard; foot pedal unguarded; local extraction not working; welding done in a corner with a fan that stirs air instead of removing fume; no eyewash; one first-aid box for 12 workers; compressed-air nozzle available at the bench.
Unsafe acts: guard removed and not replaced; fan used to "clear" fume; compressed air used for cleaning; welding galvanised steel without stripping the coating; recurring symptoms ignored and not reported.
Hierarchy of control applied to this shed:
- Elimination – stop welding galvanised sheet in that corner; use mechanical joints (rivets, self-drilling screws, folded seams) wherever the design allows.
- Substitution – grind off the zinc coating 50–75 mm each side of the weld zone so the arc does not vaporise zinc; use a lower-fume process for the same joint.
- Engineering – interlocked fixed guard on the shear, extraction hood at the arc, roof extractor kept running, welding screens, vacuum or brush for swarf.
- Administrative – written SOPs, training, job rotation, 5S, health surveillance, first-aid and eyewash provision.
- PPE – face shield and goggles, welding helmet, suitable respiratory protection, gloves, hearing protection.
Action before any further shearing: isolate and lock off the shear (LOTO) and refit/adjust the fixed guard. An unguarded treadle shear is the highest-severity immediate risk in the shed – a single mis-step on the pedal can amputate fingers – so it outranks the fume problem, which builds up over a shift, in urgency.
2. The worker's symptoms appear a few hours after welding and clear at weekends. Explain what is happening, and state what must change so that the problem does not return.
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Reasoning: the pattern is the classic one for metal fume fever. Welding galvanised steel at the arc temperature vaporises zinc; the vapour oxidises in air to fine zinc oxide fume, which is inhaled and reaches the alveoli. Symptoms – fever, chills, thirst, metallic taste, dry cough, aching – typically start 4–8 hours after exposure, peak at night, and settle within 24–48 hours. They disappear away from work and return on the next exposure, which is why it is nicknamed "Monday fever". It is not a true allergy and it confers no immunity, so the worker can be affected again and again; repeated heavy exposure can lead to chronic respiratory effects and lost workdays.
What must change, in order:
- Remove the zinc at the joint (grinding back the coating) so less fume is generated at source.
- Capture fume at the arc with local exhaust ventilation; the extractor must run during welding, not be switched off for quiet. A fan blowing across the bench only spreads fume through the shed.
- Keep the head out of the plume and weld in a screened bay away from other workers.
- Use suitable respiratory protection as the last line, not as the only line.
- Record the case, refer the worker for medical assessment, and train all welders to recognise the symptoms so cases are reported instead of being treated as ordinary flu.
3. Why is the 6 bar compressed-air nozzle on the bench a serious problem, and what should replace it?
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Compressed air at 6 bar carries enough energy to drive chips, scale and grit through the skin and into the eye at high speed; eye injuries from air-blast cleaning are common in sheet metal shops. Air can also be forced into a small cut and, in the worst case, into the bloodstream. The nozzle also raises dust and metal particles into the breathing zone of everyone nearby, adding to the fume load.
Replacement: a soft brush and dustpan for coarse swarf, a vacuum cleaner with a suitable filter for dust, and a proper chip tray under the shear. If air must be used for a machine-cleaning task, fit a safety nozzle that limits pressure and use eye and face protection, but for bench cleaning in this shed the correct answer is brush and vacuum.
The wider judgement point is that this is the same management system that removed the shear guard and switched off the extractor: small daily shortcuts are being accepted because nothing has gone wrong yet. The corrective action is not just to remove the nozzle, but to make the supervisor's walk-round check guard, extraction and cleaning equipment every shift.