Natural gas poisoning can cause unconsciousness or death, but the levels of gas must be very high, according to Tox Town. Exposure to small amounts of natural gas is not harmful, but symptoms of exposure to nonlethal levels of natural gas include headache, dizziness, tiredness and irregular breathing.
These symptoms can come on gradually, explains Quality 1st Plumbing. The pain of a headache may intensify when a person enters a certain room in her house or whenever she comes home from work. Other members of the household may also suffer from unexplained headaches. Headaches that last longer than a day need to be investigated.
Being shut up in a room or car where there is a gas leak causes nausea, states Quality 1st Plumbing. A slow gas leak eventually lowers the oxygen content in the air. Because of this, members of the household can suffer seizures or long-term physical and mental problems such as amnesia, epilepsy or pneumonia. The asphyxia from high levels of gas in the air also cause chest pain and fatigue, reports Cristen Conger for HowStuffWorks.
Because natural gas can be dangerous if it leaks, gas companies add mercaptan to it, notes Sarah Alban for HowStuffWorks. It gives the gas an odor that warns people there is a leak. If a natural gas leak is suspected, the building should be evacuated right away, according to Conger. No one should pause to touch switches, unplug appliances or even use the telephone.