I believe most of the victims of the theatre gas event where elderly. In the school case, however, the use of gas would have caused the bombs to detinate. The trigger relied on constant depression of the switch (releasing the switch causes ignition).
If we could only find a way to disable an assailant while simultaneously freezing the pressure on a switch that keeps a circuit open...
Thanks for the comments. I hadn't considered the elderly in the theater situation. As for the pressure sensitive triggers, you've got a point there. I don't think it was very wise to use those types of triggers for extended time. In the end, that may be what caused the initial explosions.
It's a little tough to keep pressure on a device for days on end.