Why is natural gas dangerous to life?
“Natural gas” - methane - is not really any more “dangerous” to life than most of the things on the planet.
There are innumerable ways that life of various sorts and stages can be endangered by other natural phenomena. In “nature” - undisturbed by man, natural gas is relatively benign. It requires both a specific concentration in air and an ignition source to burn, and an explosion would be very unlikely.
Natural generation of natural gas can be trapped underground in higher concentrations, and only appears on the earth’s surface when there is a vent – as with a volcano – or when it comes from decaying or digested organic material – swamp gas and animal flatulence.
Swamp gas may occasionally ignite spontaneously (“Will ‘o the Wisps” in folklore), but rarely causes any damage. Digestive emissions are rapidly dispersed without any ill effect or potential for harm.
When humans modify the environment by mining or drilling, the potential for releases of much higher volumes and concentrations of natural gas occur. These can indeed be hazardous to the people working in the area (mining in particular) due to the high probability of ignition and explosion in many cases.