Galvanized Handrail: Fume Symptoms and Porosity Before a Customer Audit
Your shop is fabricating 48 galvanized steel handrail sections to ASTM A123, 1/8 in. wall, 1.5 in. square tube. Two GMAW welders work in a 30 ft by 40 ft bay with a 24 ft overhead door open about 2 ft. They run 0.035 in. ER70S-6 with 75Ar/25CO2 at 180 A. By Thursday both report headache, metallic taste, and flu-like aching; one leaves early. An industrial hygienist's area sample shows 4.2 mg/m3 zinc oxide fume, below the 5 mg/m3 PEL. Visual inspection finds porosity on about 12 percent of fillets, concentrated at starts and stops, with coating burn-back about 1/4 in. from the weld toe. The customer's inspector arrives Friday. Production is two days behind. Your boss asks whether to keep welding, add respirators, or stop.
1. What immediate safety and quality actions do you take before the customer inspector arrives?
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Do not treat 4.2 mg/m3 as a green light. The PEL is not a safe-harbor line, and two symptomatic welders plus visible coating burn-back indicate overexposure and a process problem. My immediate decision is to stop galvanized welding in that bay until controls are in place, or move it to a bay with local exhaust at the arc. Actions: open the overhead door fully; use portable fans only to dilute after capture is established, not to blow fume across the shop; position a fume extractor hood within about 12 in. of the arc; issue fit-tested PAPRs with P100 filters; have the IH resample the personal breathing zone during actual welding; send symptomatic welders for medical evaluation. For quality, quarantine all 48 sections, mark suspect fillets, and perform 100 percent visual inspection plus penetrant testing on the porosity areas. Notify the customer inspector before arrival with a containment plan. Deadline pressure does not justify welding known suspect product.
2. What is the most likely cause of the porosity, and what would you change in the procedure?
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The location of the porosity at starts and stops, with only 1/4 in. of coating burn-back, points to zinc vapor and unstable shielding at initiation rather than a random gas-flow problem. Zinc boils at about 907 C, well below the arc temperature, so any coating left in the weld zone vaporizes through the pool. Grind both faying surfaces and the weld toe area to bare metal at least 1 in. beyond the intended weld, use a dedicated grinding wheel, and clean with solvent before welding. At starts, use run-on and run-off tabs or backstep technique; set gas preflow of about 0.5 to 1 s and adequate postflow; maintain contact-tip-to-work distance and gun angle within the WPS. Verify gas flow at the nozzle with a flowmeter, not just at the regulator. If porosity persists, qualify a revised procedure on a test coupon with visual and penetrant testing before releasing production.
3. How do you balance the customer deadline with the safety findings? Give a decision and rationale.
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I would negotiate a partial shipment rather than ship everything or miss the date entirely. Release only sections that pass 100 percent visual and penetrant inspection and have documented coating removal and fume controls. Hold the suspect sections for rework under a qualified repair procedure. Present the customer with the IH sample, the symptom reports, the containment plan, and a realistic recovery date. Ask for two to three working days. If the customer refuses, escalate to management in writing: shipping product made with uncontrolled zinc fume and known porosity is both a safety and a quality risk. Use the incident to update the job safety analysis and the purchasing specification so galvanized work requires coating removal, local exhaust, and respiratory protection by default, not by exception.