I seriously question the artistic choice of
fog for 70 minutes straight. Not only is it a very difficult thing to do, I think the audience will get annoyed with it quickly and it will just be a distraction. This is theater right? There is a reason you've never seen this done before. Is this show about acting or about
fog? Continuous
fog is just going to be a distraction for the audience as it slowly gets more and more out of control. Use some dry ice
fog to set the mood for 5 minutes then cut it and let the actors do their job. The purpose of theater tech is to create the world that the
play exists in while staying out of the way of the audience's experience. Any time you do some sort of over the top
effect like this you better have a REALLY good reason for it, because you run a high risk of annoying the audience.
Creating a lighting
effect which could be dialed back as the setting is established is a great idea.
If you are stuck on
fog you could try a chemical fogger with a chiller and
LeMaitre's extra quick dissipating fog juice. Maybe it will dissipate fast enough to not
block the audience's view.
What's your budget? The best option would be to create a 6"
platform on top of the
stage. Run duct work into it to let the
fog out and then create a perimeter of ducting to suck the
fog back out as it reaches the
edge. This would be complicated, time consuming, and expensive to do right.