Zinc Fume and Porosity on Galvanized Columns
Ridgeway Metal Works is welding stiffener plates to galvanized transmission columns for a utility contract. Three FCAW welders work inside a 40 ft x 20 ft bay with a 14 ft ceiling; ventilation consists of one 2 ft roof fan and a roll-up door 30 ft away that stays closed in cold weather. On day two, welder A reports headache, nausea, and a metallic taste by mid-shift. Two seams on column 7 show clustered porosity and white powdery residue in the crater. The crew runs E71T-1 with CO2 at 35 cfh, 26 V, 250 A, and grinds only the weld toes, not the faying surfaces. The utility's third-party inspector arrives tomorrow at 0700, and 9 of 22 columns are complete. The project manager wants the crew to "weld through it" because the columns ship Friday and daily overhead is $4,800. You are the CWS on the floor, and the welders are asking whether they should keep going.
1. What do you do in the next 30 minutes? Name the hazard and the quality cause the evidence points to, and justify the control you choose first.
Read the worked answer
Stop the work, then control by hierarchy, not by handing out respirators.
Hazard: welding through zinc coating generates zinc oxide fume. The symptoms (headache, nausea, metallic taste, onset a few hours into the shift) are the classical metal fume fever pattern, and three welders in a 40 x 20 x 14 ft bay with one roof fan and a closed door is an enclosed-exposure profile. The CO2 shielding gas also reduces the oxygen margin in a tight bay.
Actions, in order:
- Halt welding in the bay. Open the roll-up door and run the roof fan, but treat general dilution as a supplement, not the control.
- Put portable fume extraction at the arc and verify capture at the plume. Where geometry prevents capture, supply air or a PAPR with P100 particulate filters is interim protection until engineering controls are in place.
- Fix the source: grind zinc off the faying surfaces and 1-2 in. beyond the weld zone to bare metal on both members. Zinc vaporizes around 1,660 F, far below arc temperature, so it both fumes and blows through the pool - one action addresses exposure and porosity.
- Check gas delivery with a flowmeter at the nozzle and a soap test. Air pulled in by the fan strips shielding and adds to the porosity.
- Send the symptomatic welder for medical evaluation and start personal air sampling so the exposure is documented rather than debated.
Welding does not resume until fume capture is demonstrated and the faying surfaces are bare.
2. How do you handle the nine completed columns before the inspector walks in at 0700?
Read the worked answer
They are potentially nonconforming in two ways: the porosity itself, and undocumented quality.
- Treat the two porous seams as a nonconformance, not a cosmetic issue. Excavate to sound metal, confirm with PT or by visual after grinding, and repair under a qualified WPS. Clustered porosity in FCAW is gas entrapment; with zinc still present it will recur, so the repair is wasted unless the coating is removed first.
- Look at all nine columns yourself before the inspector arrives. 100% visual against the D1.1 fillet acceptance criteria, plus PT on the suspect seams. Record what you found, the serial numbers, and the disposition. Presenting work as conforming without your own inspection is what turns a repairable defect into a credibility problem with the utility.
- Raise an NCR with the root cause (zinc contamination plus shielding disturbance), the affected columns, and the repair record. If the inspector finds repairs he was never told about, the utility can require re-inspection of the whole lot at your cost.
- Cost the rework honestly: grinding, re-weld, re-inspection, and the lost production hours. That number becomes the argument in your conversation with the PM.
3. The project manager repeats the instruction to weld through it. How do you handle that direction?
Read the worked answer
Frame it as cost and liability, because schedule language alone will lose.
- Give the PM the arithmetic. A couple of hours of rework per affected column is cheap next to a shipment rejected after the utility's inspector writes it up, or a fume-related illness recordable. One lost-time case or citation under the general industry welding ventilation requirements costs more than the schedule slip.
- Put the stop-work in writing, one page: symptoms reported, bay conditions, zinc on faying surfaces, the porous seams, the corrective actions, and the date they clear. Verbal stop-work requests get overridden on the shop floor; dated documents backed by evidence do not.
- Offer a recovery path so the answer is not simply "no." While the ventilation is being set up, the crew can grind faying surfaces on the remaining 13 columns - productive work that also removes the contamination source.
- If the PM still directs welding to continue, escalate to EHS and operations in writing the same day. That is not insubordination; it is the supervisor's duty, and it also protects the PM from a decision he will later have to defend.