My first show in this space was Les Misérables. During Javert's suicide I had C02 fog shooting across the stage. In rehearsals it worked great flowing across the stage, awesome effect. Well, opening night comes and Javert's scene, fog starts to flow and bam hits an invisible wall center stage and flows into the pit. On the headsets everyone started to question the problem. knowing what is happening I started to laugh. During rehearsals the HVAC system wasn't running so no effect on the fog. I ended up putting the fog machine in the orchestra pit and placing the outlet tube on the DS center edge and shooting the fog upstage. Also, found out that the smoke detectors go off with chemical fog.