The regular use of natural gas means no danger to man at all. Only the breakdown or irregular mode of operation of the gas equipment, chimneys or the ventilator, air supply systems may lead to suffocation, poisoning or an explosion.
Suffocation ensues if the concentration of the oxygen decreases in the air, that is if the concentration of the natural gas increases in the airspace. Natural gas in a concentration smaller than 0.5 % does not jeopardize man's health. It induces a suffocating effect in higher concentration, since it reduces the ratio of oxygen in the air.
Natural gas may only cause poisoning in an indirect manner since natural gas itself is not harmful to health. If the combustion of natural gas is incomplete, then the poisonous carbon monoxide (CO) appears as his by-product. Carbon monoxide in a concentration of already 0.2 % may cause death within two hours.
An explosion may arise if the proportion of natural gas attains the value of 5% and 15 % in the air. The explosion is ignited by a naked flame apart from this condition.
The inflammation temperature is the lowest temperature at which the mixture of natural gas and the air (oxygen) ignites. In function of the content of the gas, the pressure and the lower explosion limit, the lowest inflammation temperature of the natural gas is between 595 - 645 °C.