Theatre?
I know beggars can’t be chosers, I and didn’t even read how this place was attacked, or what with, but I would be awefully nervous ‘sheltering’ in a theater or warehouse or anywhere with a long ceiling span. It may seem ideal for larger quantities of people, but it’s far from safe conditions
The safest place to shelter would be miles away. Failing that an underground bunker. Or a trench with overhead cover. A large auditorium or theater would be one of the worst places.
I feel the same way when we are requested to go to a gymnasium during bad tornado weather.