Carbon Monoxide and Confined-Space Conditions in an Occupied Basement
A three-person crew is installing 24-gauge galvanized supply duct in a 14 ft by 22 ft basement mechanical room of an occupied duplex. The room has an atmospherically vented 80,000 Btu/h natural-gas water heater and a condensing furnace; the only opening is a 30 in. door to a finished hallway. The crew is using a propane-fired soldering torch to sweat a condensate line, and a portable generator is running outside with its exhaust near a window well. After 40 minutes, the apprentice reports a headache and nausea; a personal CO monitor worn by the journeyman reads 38 ppm and rising. The general contractor wants the duct sealed and the system started the same day. The crew has a 20 in. box fan, a 25 ft extension cord, and one 4-gas meter. No confined-space permit has been issued, and the basement stair is a straight ladder.
1. What is the immediate hazard, and what should the crew do in the first 10 minutes?
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The symptoms, the 38 ppm CO reading, the open-flame torch, and the generator exhaust near a window well point to carbon monoxide exposure, not a simple case of poor ventilation. The crew should stop work immediately, move everyone to fresh air, and call 911 if symptoms persist or worsen. Do not run the box fan in a way that pulls generator exhaust or combustion products into the basement; place the fan to supply clean air from an uncontaminated opening and keep the exhaust path downwind. Shut down the torch and the generator. Use the 4-gas meter to check CO, oxygen, and combustible gas at several heights before anyone re-enters. Notify the general contractor and building owner that the basement is unsafe until CO is below the action level and the source is controlled. A rising 38 ppm reading is not a wait-and-see condition in an occupied dwelling.
2. Does this basement meet the criteria for a permit-required confined space, and what controls would that require?
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A basement with a straight ladder, limited egress, and atmospheric hazards can meet the OSHA 1910.146 definition of a permit-required confined space if it is not designed for continuous employee occupancy and contains a hazard capable of causing death or serious physical harm. The crew should not assume the space is exempt simply because it is a mechanical room. If entry is required, the employer must issue a permit, test the atmosphere before entry and continuously during entry for oxygen, flammables, CO, and hydrogen sulfide, provide forced ventilation, station an attendant at the entry, and have a rescue plan and retrieval equipment. The 4-gas meter alone is not a rescue plan. Until those controls exist, entry should be prohibited and the work rescheduled or performed from outside the space.
3. Recommend engineering and administrative controls to prevent recurrence before the duct work restarts.
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Eliminate the generator from the immediate intake zone by moving it at least 20 ft from doors, windows, and window wells and directing exhaust away from the building. Replace the propane torch with electric soldering or perform hot work outside the basement. If open flame is unavoidable, use a written hot-work permit, a fire watch, and local exhaust ventilation. Provide positive-pressure ventilation from a clean source and verify with the 4-gas meter that CO stays below the action level during work. Add continuous CO monitoring with an alarm, and give the crew a pre-task briefing covering symptoms, evacuation, and shutdown authority. The general contractor should also confirm that the water heater and furnace are not back-drafting when the basement is depressurized. The schedule should be adjusted to allow ventilation and testing, not compressed to meet the same-day startup.