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About this tool
How long an LPG or PNG leak takes to reach its flammable limit in your room, plus the detection and shut-down steps in the right order.
A gas leak is only dangerous once the room reaches the fuel's lower explosive limit — 1.9% by volume for a typical LPG blend, 5% for the methane in piped natural gas. This tool applies the standard single-zone room mass balance, C(t) = C_ss × (1 − e^(−ACH·t)), to work out how long a leak of a given size takes to get there in a room of your size and ventilation, and pairs it with the shut-down sequence and detector placement that follow from whether your gas sinks or rises.
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Add your input to the workspace.
Adjust the options until the result looks right.
Copy or download the output and put it to work.
Published LEL and UEL figures, blended with Le Chatelier's rule for cylinder LPG.
Uses the well-mixed room balance, so an open window changes the answer the way it does in reality.
Response steps are sequenced — valve before ventilation, no switches at any point.
LPG is heavier — a butane/propane blend has a vapour density around 1.9 times that of air, so it sinks, pools at floor level and flows into basements, drains and lift pits. Piped natural gas is methane at about 0.55 times air density and does the opposite, rising to the ceiling. That is why an LPG detector mounts near the floor and a PNG detector near the ceiling.
Do not touch any electrical switch, then shut the regulator knob and the cylinder or meter valve. Switch contacts arc when they move, so turning a light off is as much an ignition source as turning it on. After the valve is closed, open doors and windows, get everyone out, and call the emergency line from outside — in India that is 1906, which covers both LPG and piped gas.
Commercial LPG is flammable between roughly 1.9% and 8.8% by volume in air, and propane and butane individually span 2.1–9.5% and 1.8–8.4%. Below the lower figure the mixture is too lean to ignite and above the upper one it is too rich, though a rich room is still dangerous because the mixture passes through the flammable band at every doorway and window.
Brush soapy water over the regulator, hose and joints and watch for bubbles — never use a flame or a lighter. Also check the hose for cracks, stickiness or a past replacement date, commonly two years for a plain rubber tube and five for a reinforced type. If the smell is strong or you can hear hissing, do not test anything: shut the valve, leave, and call the supplier.