I understand that there is still a fair amount of development as far as graphical lag is concerned, and others may have voiced this concern before. I just wanted to give a detailed account of the massive lag experienced when the fire vents are shooting flames.
I play on a macintosh, which may or may not make a difference as far as the client is concerned. But I have experienced significant lag when playing on any level where fire vents are visible, even on the lowest graphics settings, when I have nearly no lag anywhere else. I have asked others about it, with some people having significant lag, and some others having next to none. This lag makes it next to impossible to play on tier 3 floors with fire vents, at least in the small portions of the levels that have them.
I have a 12 MBps high speed internet connection, an i5 intel processor, and a mid-top level graphics card. I have an excellent ping with test servers, so I can't imagine its an internet speed or processor issue. Feel free to message me about it, as I'd love to get it fixed as soon as possible! I occasionally, but not always, have similar problems with the render of the explosions of tier 2 "bomb gremlins"