How long is a piece of string? Depends on how many people they...

How long is a piece of string? Depends on how many people they have working, and how far the vent bag has to go into the tunnel. I work all over the world on tunneling projects and every site is different. It might take a couple of days in China but like here on this job I'm on in Sydney it can take a week just to get the necessary permits in place, safe working method statement, hot works permit, confined space permit, rescue plan etc, etc. Even when the fan arrives on site the power supply has to be installed, VFD, vent bag support attached to the tunnel, then the bag installed, etc, etc. Then it probably needs certifying that it moves enough air and a rubber stamp. Mining is an expensive and slow process.