Co2 in a small confined space can also be fatal as it induces a collapse (heart attack?) at high concentrations, thats why CO2 fire extinguishers always carry the warning "don't use in confined spaces".
That said, this is really a warning to others more than yourself as if you own a sizeable nightclub the levels will probably never reach dangerous concentrations unless you do a lot of fogging, won't make for great breathing though as it will lower oxygen levels.
As others have said though, a smoke machine might prove a better bet as then you have access to a whole variety of different smoke liquids with different densities and dispersal properties. There seems to be a trend towards water based liquids at the moment as they claim to leave no residue but I'm no expert.
This is one of the best smoke machines I've seen demo'ed but then again I'm haven't seen serious commercial equipment and don't own a machine:
http://www.youtube.com/watch?v=vxNICVgOv4g
Claimed output is 18,000 cubic feet per minute!!
Another outside demo!!!!!!:
http://www.youtube.com/watch?v=IQODJ...eature=related
Company: http://www.gvgdiscolighting.co.uk/pr...oke%20machines
Just to be clear, I have no connection with either the GVG or the company selling these.