However, a large building relying on natural gas for space and water heating will often have a large gas heated boiler in the basement.

In the event of a large earthquake the gas pipe from where it enters the building at the demarcation point to the boiler can be many meters away and even on a different floor.

If this pipe ruptures, the building can become full of a combustible mixture of gas and air which is very easily ignited causing the demolition of the building and the loss of many lives.