Stainless tank entry: Cr(VI) and argon purge exposure
A welder is working inside a 3 m diameter stainless steel tank, welding 316L internal attachments with GTAW and SMAW. The tank has one 500 mm manhole and no forced ventilation. A fume extractor is placed at the manhole, 4 m from the arc. Personal air sampling over 6 h gives Cr(VI) 0.012 mg/m³ and total welding fume 8 mg/m³; the project OEL for Cr(VI) is 0.005 mg/m³ as an 8-h TWA. The welder wears a disposable FFP2 respirator and reports headache and metallic taste. Argon is used for purging the adjacent compartment and the purge gas line passes through the tank. The entry permit records oxygen 20.9% at the start but no continuous monitoring. The job is behind schedule, and the supervisor wants to continue with the same controls.
1. Evaluate the exposure and the adequacy of the existing controls against the hierarchy of controls.
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The Cr(VI) result is more than twice the project OEL (0.012 vs 0.005 mg/m³), so the existing controls are inadequate. The fume extractor at the manhole is too far from the arc and does not capture fume at the plume. An FFP2 is not adequate for Cr(VI) or welding fume; it has a low assigned protection factor and poor fit.
The argon purge line through the tank is an asphyxiation hazard, and the headache/metallic taste may indicate fume or oxygen deficiency. The hierarchy requires elimination/substitution, engineering controls (local exhaust at the arc, supplied air), then administrative controls and PPE.
2. Set out the immediate actions and the revised safe system of work.
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Immediate:
- stop work, evacuate, ventilate;
- test the atmosphere (oxygen, LEL, Cr(VI)/fume);
- do not re-enter without a permit and rescue plan;
- reroute the argon purge line outside the tank;
- add continuous oxygen monitoring and an alarm;
- provide local exhaust at the arc and supplied-air respiratory protection for the welder;
- rebrief the crew, restrict entry and record the exposure.
3. What air monitoring and health surveillance would you require before restart?
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Before restart:
- personal 8-h sampling for Cr(VI) and total fume with the welder in the actual posture;
- area sampling;
- continuous oxygen and LEL monitoring;
- fit testing and training for RPE;
- health surveillance including respiratory symptoms and skin checks;
- review of exposure records.
Restart only when the measured Cr(VI) is below 0.005 mg/m³ or the RPE program is fully effective.