What criteria are used for exiting an airplane in an emergency?
Per 14 CFR 25.803:


  For airplanes having a seating capacity of more than 44 passengers, it
  must be shown that the maximum seating capacity, including the number
  of crewmembers required by the operating rules for which certification
  is requested, can be evacuated from the airplane to the ground under
  simulated emergency conditions within 90 seconds


Appendix J to Part 25 specifies exactly how the evacuation tests should be done. It's too long to quote here, but it includes requirements for lighting levels, number of passengers, minor obstacles, infants on board etc.

I have no idea whether or not those simulated conditions are reasonable and effective, but they at least set a standard.