Originally posted by ahn1991:[..]
What you are asking for is pretty much impossible. Complete evacuation could take several hours, especially if they wanted to sweep the venue to ensure complete evacuation. Thorough screening would take an additional several hours and can only take place after the venue is confirmed to be empty. If they wanted to actually be thorough, they would need at the very least metal detectors, security officers trained to do proper pat-downs (your average rent-a-cop isn't trained to do that) and sniffer dogs. Before you say that this is overkill, anything short of this might as well be the equivalent of kicking everyone out and letting them all back in without doing checking a single person.
As for a group lawsuit, this is never going to happen. When you buy a ticket, you are automatically consenting to the possibility that your event might be cancelled or rescheduled. You can be refunded the price of your ticket, but definitely not travel costs.
