Three Welders, One Small Room, and a Clogged Extractor
A three-person crew is GMAW-welding 6 mm mild-steel brackets in a 4 m × 5 m room with a 2.7 m ceiling. Ventilation is one open window (0.6 m × 0.9 m) and a pedestal fan blowing across the bench. All three machines run CO₂ at about 18 L/min each. It is rainy season, so the roller door stays closed. After two hours, one welder reports headache and dizziness; another says the air tastes metallic. A portable fume extractor sits in the corner with a clogged filter and its hood is not positioned over the arc. Gas cylinders are chained, but a CO₂ regulator hose lies across the walkway and a grinder lead is coiled on the floor beside a puddle. The supervisor wants the batch finished before lunch.
1. The crew wants to keep welding and simply open the window wider. Assess the situation: what is the most likely hazard, what immediate actions are required, and how would you rule out other causes?
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Most likely hazard: CO₂ accumulation plus welding fume in a poorly ventilated room. Room volume is 4 × 5 × 2.7 = 54 m³. Three machines at 18 L/min release 54 L/min, or 3,240 L/h - about 6% of the room volume every hour. CO₂ is roughly 1.5 times heavier than air, so it pools at low level and displaces oxygen; headache, dizziness and shortness of breath fit early oxygen deficiency. The “metallic” taste is not diagnostic - it can come from fume or ozone - so do not use it to rule anything in or out.
Immediate actions: stop welding; move the affected welder to fresh air and have them medically assessed; do not re-enter until a calibrated meter shows O₂ ≥ 19.5% and CO₂ below the occupational limit; mechanically ventilate, preferably with exhaust at low level, not just a fan stirring the air. Rule out a leaking regulator or hose with a soap test, and check for galvanized or coated plate that could cause metal fume fever. Isolate the trip and electrical hazards before cleanup.
2. List the engineering, administrative and PPE controls required before restart, and state how you would verify each is working.
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Use the hierarchy of controls, not PPE first.
- Elimination/substitution: move this batch to a bay with open access, or schedule it when the roller door can be opened and make-up air is available.
- Engineering: repair or replace the extractor filter; position the hood within 150–300 mm of the arc; add low-level exhaust because CO₂ pools; ensure make-up air so the extractor does not merely recirculate. Fit a calibrated CO₂/O₂ monitor with an alarm.
- Administrative: written procedure for poorly ventilated welding, gas-flow checks at the start of shift, rotation and breaks, training on gas hazards, and a permit if the room meets a confined-space definition.
- PPE: welding helmet, FR clothing, gloves, safety glasses; a respirator only for residual fume after engineering controls, and only with fit testing.
Verification: smoke or tissue test at the hood, flow test at the nozzle (not just the regulator), monitor bump test, and a documented pre-start checklist. Correct the 5S issues - hose across the walkway, lead by the puddle, unsecured extractor - before any arc is struck.
3. The supervisor argues that issuing respirators to the three welders is enough. Explain why this is not acceptable and what you would tell him.
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Respirators protect the wearer only, and only if fit-tested and worn correctly; they do not reduce the asphyxiant gas load, do not protect the other two welders, and do not remove the source. CO₂ is an asphyxiant, not a particulate, so a particulate respirator gives no protection against it. The supervisor is also creating a false sense of control: the room still has low air changes, the extractor is still clogged, and the gas hoses are still a trip hazard. The correct message is that PPE is the last line, after ventilation, extraction, monitoring and housekeeping. If the engineering controls cannot be restored before lunch, the batch waits - production pressure is not a reason to accept an oxygen-deficient atmosphere.