LPG in a basement kitchen: a detector in the wrong place
At a rural gastropub, the kitchen is in a basement below street level. Two 47 kg propane cylinders stand in an external compound at ground level against the front wall; the 15 mm copper supply runs down through an unsealed duct into the basement and feeds a new 40 kW six-burner range. There is a ceiling-mounted combustible gas detector in the kitchen and no low-level ventilation opening. Staff report a gas smell near floor level and that the range flames are long, yellow and sooty; one cylinder is frosting on the outside. The kitchen extract fan is running but the make-up air grille has been boarded over. The cylinder regulator is a 37 mbar unit and the pipe run is 12 m. The pub has no emergency shut-off valve at the cylinder compound and no written emergency procedure.
1. Explain why the gas detector position and ventilation are inappropriate, with reference to the behaviour of propane.
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Propane vapour is about 1.5 times as dense as air, so leaks collect at low level in drains, ducts, floor voids and basements rather than dispersing at ceiling height. A ceiling-mounted detector will not see a low-level accumulation until the concentration is already widespread. It should be at low level, typically within a few hundred millimetres of the floor, and be appropriate for LPG.
Ventilation must also be low level. The basement has no low-level opening, and the boarded make-up grille prevents the extract from being replaced. Extract alone can depressurise the kitchen and pull vapour from the duct. The cylinder compound is outside, but the unsealed duct is a path for heavy vapour to run down into the basement. Cylinders must be upright, secured, away from openings, drains and ignition sources, and the compound needs ventilation and a clear emergency shut-off. The present arrangement defeats both detection and dilution.
2. What do the flame symptoms and cylinder frosting tell you, and what immediate actions are required?
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Long yellow, sooty flames indicate incomplete combustion and a lack of primary air or wrong injector/regulator pressure, not merely a dirty burner. Soot is a strong warning sign of CO risk. Frosting on a 47 kg cylinder at a 40 kW load suggests overdraw or liquid carry-over; propane vaporisation falls in cold weather and two cylinders may be marginal.
Immediate actions: shut the emergency control valve at the cylinders, avoid operating electrical switches, ventilate at low and high level, evacuate and call the gas supplier or emergency service. Do not relight to 'see if it clears'. The range must remain isolated until the regulator, injectors, air supply and pipework are checked by a competent LPG commercial installer. If anyone has symptoms, seek medical advice. A combustible-gas check at low level, not at the ceiling, should guide re-entry.
3. What permanent corrections and handover records should be required before the range is used again?
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Permanent corrections: seal the duct or re-route the pipe externally; provide low-level ventilation and restore make-up air; fit a low-level LPG detector with alarm and shut-off; install an emergency shut-off at the cylinder compound; ensure cylinders are correctly sited, secured and protected; check the regulator and pipe size for 40 kW; verify injectors and burner aeration; and carry out combustion analysis and a gas rate.
Handover records should include cylinder and regulator details, pipe run and test results, ventilation details, detector test, emergency procedure and the installer's RGII completion documentation. The range should only be returned after combustion readings are satisfactory and the extract and make-up air are proven. A warning notice should remain until then.