Flue blockage and CO incident in a 16-storey gas-supplied apartment
A 16-storey apartment building in Yerevan receives natural gas at a measured pressure of 18 mbar at the riser, while the appliance rating plate requires 20 mbar. Several flats use instantaneous gas water heaters connected to individual flues. A resident reports headache and nausea; the fire service finds a carbon monoxide alarm at 95 ppm in one flat. Inspection shows that a satellite dish has been fixed across the terminal of that flat's flue, and that a later bathroom ventilator discharges into the same shaft. The management company wants to reset the alarm and adjust the gas regulator, arguing that the CO was caused only by low pressure.
1. Determine the likely causes of the CO incident and explain why adjusting the regulator alone is unsafe.
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Carbon monoxide is produced by incomplete combustion, and the evidence points to multiple causes. The satellite dish obstructing the flue terminal reduces draft, so combustion products spill back into the room. The bathroom ventilator discharging into the same shaft can reverse flow or dilute and recirculate products. The 18 mbar pressure is below the appliance requirement, which can affect gas-air ratio and flame stability, but low pressure is not the only cause and may not be the main one. Resetting the alarm treats the symptom and removes the warning. Adjusting the regulator without checking the whole shaft, the appliance combustion performance and room air supply could restore gas flow while leaving the blocked flue in place. The correct response is to shut off and tag the affected appliances, ventilate the flats, test the flue for integrity and draft, and verify combustion by instrument before any gas is restored.
2. Set out the corrective actions and allocate responsibilities among the management company, gas supplier and flat owners.
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The management company should immediately issue a building-wide notice, isolate the affected gas riser, remove the satellite dish and any other obstruction, and arrange a camera inspection of the shared shaft. The gas supplier should verify supply pressure and regulator setting against the appliance requirements and confirm that any pressure correction does not exceed safe limits. A competent gas installer should service the water heaters, measure CO and CO2 in the flue, check ventilation openings, and confirm that the ventilator no longer discharges into the flue. Flat owners must provide access, remove unauthorised alterations and replace nonconforming appliances. Re-commissioning should be documented appliance by appliance, with a signed certificate and a follow-up CO test under normal operating conditions. The incident should also trigger a survey of all identical flues in the building, because one blocked terminal suggests a systemic maintenance failure.