what is purging?

 what is purging? 

1) the introduction of inert gas into a tank already in the inert condition to further reduce the existing content or hydrocarbon gas content to a level below which combustion cannot take place if the air is introduced
2) introduction of oxygen into a take to a tank to a high level
3) using blowers to push oxygen into a tank 

Ans______1) the introduction of inert gas into a tank already in the inert condition to further reduce the existing content or hydrocarbon gas content to a level below which combustion cannot take place if the air is introduced