Confined-space FCAW repair with rising CO2
A two-person crew is repairing a corroded bulkhead inside a 21.6 m³ steel compartment of a barge. The work uses FCAW with 1.2 mm E71T-1 wire and 100% CO2 at 15 L/min. A 0.75 kW blower with 12 m of 100 mm flexible duct supplies air; the duct outlet sits 2 m from the only access hatch. The CO2 cylinder and regulator are inside the compartment. A calibrated four-gas monitor clipped at the welder's chest reads O2 20.3%, LEL 0%, CO2 0.4% at 08:00. By 08:25 the CO2 reads 1.1% and the welder reports headache and shortness of breath. The hot-work permit lists a 30-minute gas test interval and half-mask P100 respirators. The hatch is 500 mm × 700 mm; the nearest rescue team is 25 minutes away. Production wants the repair finished before the 14:00 shift change.
1. What do the readings and symptoms indicate, and what immediate decision should be made?
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Decision: stop and evacuate. CO2 rose from 4,000 ppm to 11,000 ppm in 25 minutes. The 8-hour TLV is 5,000 ppm, so the reading is already above the occupational limit and still climbing; at 1.1% CO2 can cause headache, drowsiness and breathing discomfort, and the trend points to a gas release or poor ventilation, not a measurement error. O2 20.3% and LEL 0% do not make the space safe. A half-mask P100 filters particles, not CO2 gas, and a 30-minute test interval is too slow for a confined space with a live gas source. The welder should leave immediately, the attendant should account for both workers, and no one should re-enter until the space is ventilated, the source is found, and continuous monitoring shows a stable safe atmosphere.
2. Identify the missing controls and the corrective actions required before re-entry.
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Move the CO2 cylinder and regulator outside the compartment and route the hose through the hatch; leak-test the regulator, hose and torch with soap solution. Replace the blower arrangement so fresh air is drawn from outside and exhaust is discharged away from the intake - the current outlet 2 m from the hatch can recirculate CO2. Provide continuous forced ventilation and continuous monitoring with an alarm set below 5,000 ppm CO2; use an airline respirator or supplied-air hood inside, not a P100 half-mask. Add a competent attendant at the hatch, reliable communication, a rescue plan with practiced response inside 25 minutes, and a permit gas test before entry and after any break. Re-test O2, CO2 and LEL before re-entry, and stop if CO2 rises or the welder reports symptoms.
3. What environmental and housekeeping issues arise from the CO2 release and the FCAW operation, and how should the waste be handled?
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CO2 is an asphyxiant, not a flammable gas, so the LEL reading is not the main control; ventilate to outside and prevent accumulation in low areas. FCAW produces metal fume and fine particulate; use source extraction or supplied air and keep the plume away from the breathing zone. Collect spent flux, slag, wire ends, used filters and contaminated wipes in labeled containers; do not wash slag or wire residues into the bilge or storm drain. Recycle steel wire and contact tips where local arrangements exist, and record gas use and cylinder returns. Check local environmental rules for waste classification before disposing of mixed fume-filter and slag waste.