Much agreed Teebin, this stuff fascinates me as well.
You sure about the Transformers problem? I thought it was a valve that had broken and needed to be replaced?
I assume thickening means that something else is mixed with the nitrogen before it is released, probably gives the fog more 'form'.
It seems to me that the fog effect in transformers is different from what it use to be, it does not fill the room up quite as much, I have actually wondered if perhaps people complained that there was too much fog.