Natural gas consists primarily of methane and is normally colorless, tasteless and odorless but the utility company adds chemicals to give it a “rotten egg” smell to make it easily detectable as a safety precaution. More than half of American homes use natural gas for heat and cooking but a leak can be very dangerous to any in the vicinity.
The most dangerous factor of natural gas is that it is highly flammable. A buildup from a gas leak can be set off from something as simple as a static spark and can cause fire and explosions. Natural gas also contains methane and any leaks can release toxic levels of Carbon Monoxide.
If you suspect a gas leak in or near your home, evacuate the vicinity immediately. Call the Gas Company and emergency personnel from a safe outside location. Do not attempt to use or power any appliances on or off and do not smoke or light a flame.
Signs and symptoms of a natural gas leak: Smell similar to “rotten eggs” or sulfurNoises near gas appliancesPlants or grass outside the home that are dead or turning brown near buried gas linesAir bubbles in puddles outside the homeSymptoms of Carbon Monoxide poisoning.
More info:
http://www.ehow.com/info_8356201_signs-symptoms-natural-gas-leak.html