Confined Space Entry During Duct Installation
A two-person sheet metal crew is installing 600 mm × 400 mm galvanized duct in a converted below-grade mechanical room. Access is through a 750 mm × 750 mm floor hatch with a fixed ladder; the room measures 2.4 m × 3.0 m × 2.2 m high and has no mechanical ventilation. The crew is using a propane torch to braze a refrigerant line and applying solvent-based duct sealant. After about 40 minutes, one worker reports a headache and nausea. A portable gas monitor hung on the ladder reads CO 95 ppm, O2 20.6%, and LEL 2%. The foreman says to prop the hatch open and keep working because the monitor has not reached the alarm setpoint. The worker wants to finish the joint before leaving.
1. What immediate actions should be taken, and who should make the entry decision?
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Stop work immediately and evacuate both workers from the room. Do not re-enter to finish the joint. Move the affected worker to fresh air, keep them under observation, and arrange medical assessment because headache and nausea at 95 ppm CO indicate overexposure, not a harmless reading. Notify the site supervisor and the employer's confined-space entry supervisor.
The entry decision cannot be made by the foreman alone or by the worker who wants to finish. It must be made under the employer's confined-space program by a qualified person who has completed a hazard assessment, atmospheric testing, isolation, ventilation design, an attendant and a rescue plan. A reading of 95 ppm CO is above common occupational exposure limits and confirms that the existing natural opening is not adequate ventilation. The LEL of 2% from solvent vapour also matters because the propane torch is an ignition source.
Treat the space as a permit-required confined space until the assessment proves otherwise. Call emergency responders if the worker's symptoms worsen, loses consciousness, or cannot be moved safely. Do not use the worker's desire to finish the task as a reason to delay evacuation.
2. Identify the hazards and specify controls for the remaining work.
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The main hazards are carbon monoxide from the propane torch, solvent vapour from the sealant, fire/explosion from the torch and solvent, oxygen depletion from torch operation, heat and burns, poor access through the 750 mm hatch, and ergonomic strain from working in a 2.2 m high room.
Controls should follow the hierarchy. Substitute the solvent-based sealant with a low-VOC product if the specification allows it, and use a press-fit or mechanical joint instead of brazing where the design permits. If hot work is still required, issue a hot-work permit, remove or protect combustibles, provide a fire watch and a suitable extinguisher, and test the atmosphere before and during work. Provide mechanical ventilation from outside the space, sized for the room volume of about 15.8 m³; for example, a fan delivering at least 160 m³/h gives roughly 10 air changes per hour, but the actual rate must be confirmed by monitoring. Use continuous CO, LEL and oxygen monitoring with alarms set for the site program. Keep an attendant at the hatch with communications and a rescue plan, and use a full-body harness and retrieval line where the assessment requires it.
Do not rely on propping the hatch open as the only control. Re-test after ventilation and before any re-entry, and stop work if the monitor alarms.
3. What documentation and follow-up are required after the incident?
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Document the incident promptly: names of workers, time of exposure, symptoms, gas monitor readings, ventilation conditions, work being performed, and immediate actions taken. Preserve the monitor data if the unit logs readings. Record the entry decision, the hazard assessment, and any atmospheric test results. If medical treatment is provided, complete the workers' compensation and incident-reporting requirements.
Follow up with a formal investigation to determine why the work proceeded without adequate ventilation and why the foreman attempted to override the alarm. Review the confined-space program, hot-work permit process, gas monitor calibration, and training for supervisors and workers. Update the hazard assessment for this room and similar below-grade spaces. Hold a toolbox talk on CO and solvent hazards, and verify that a rescue plan and attendant are in place before the next entry. Notify the joint health and safety committee or worker representative as required. Re-inspect after corrective actions and keep records available for the regulator and the client.