What substance is added to natural gas to provide an odour to it?

Natural gas is inherently odorless, which can pose a significant safety risk in case of a leak, as it would be difficult to detect without any smell. To make natural gas safer for consumers and to facilitate leak detection, an odorant is added. Mercaptan, which contains sulfur, is commonly used as the odorant for natural gas due to its distinctive smell, often described as similar to rotten eggs.

Mercaptan is effective in very low concentrations, making it a practical choice for ensuring even minute leaks can be detected by smell. This safety feature is critical for the prevention of fire hazards or explosions that could occur if gas leaks go undetected.

The other substances listed do not serve this purpose. Propane is a type of fuel but does not have the characteristic odor that mercaptan has. Ethanol is often used as a fuel or solvent and does not provide the necessary odor. Water (H2O) is not an odorant and does not contribute to the detection of gas leaks. Therefore, the addition of mercaptan to natural gas is essential for ensuring consumer safety.