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Why does natural gas smell?

Natural gas is colourless, odourless, and non-toxic. Pure natural gas is very safe and non-flammable, but when it is mixed with the right concentration of air, between 5% and 15%, it becomes highly flammable; both when we want it to be (inside our appliances) and when we don't want it to be, as in the case of a leak. Since natural gas is highly flammable when mixed with air, but odourless, no one would be able to detect a gas leak without the right equipment. Therefore before natural gas is sent to customers an odourant called mercaptan is added to it to give it a smell. Some say, after mercaptan has been added to natural gas, it smells like rotten eggs.

This smell then enables consumers to detect a natural gas leak and alert the right people to correct the leak before trouble occurs. An interesting fact is when natural gas is burned the odourant mercaptan is burned off completely leaving the natural gas odourless again.