Fans in Reverse

What happens when a Centrifugal Fan (3 phase) is wired so that it runs in the opposite direction to normal (ie in Reverse)?
It has been estimated that around 7% of all centrifugal fans are running in Reverse!
How can that possibly be?
Wouldn't it be opposite that it was running in Reverse?
Ahh! See this video for some possible explanations.
Brought to you by OXYL8 (see websites www.oxyl8.com and www.oxyl8training.com for more information, support and LEV Training Courses information)

Видео Fans in Reverse канала OXYL8 Ltd