Er, you don't.
Rehearsals for this sort of situation were quite well publicised.
At the very least, there were a couple of dry runs in London, in the wake of the Twin Towers coming down.
( monster munch person, man, woman... camera... TV?, Thu 7 Jul 2005, 12:55, archived)

No...
he was refering to the comitters not the tidy up operation...
(Aquai, Thu 7 Jul 2005, 12:56, archived)

"He"?
Are you referring to yourself in the third person, so as to distance yourself from your ridiculous comment?
( monster munch person, man, woman... camera... TV?, Thu 7 Jul 2005, 12:59, archived)

No
The guy on tv... erm, i've forgotten his name >_<
He was talking on ITV
(Aquai, Thu 7 Jul 2005, 13:00, archived)

Oh, right.
Anyway, if you want to rehearse a terrorist attack, you do it when/where no one's looking. Basically, anywhere that isn't Iraq or Afghanistan.
( monster munch person, man, woman... camera... TV?, Thu 7 Jul 2005, 13:04, archived)

Ant & Dec?

( Johnny Catfish - Yowsa!, Thu 7 Jul 2005, 13:04, archived)

That's the one/two!

(Aquai, Thu 7 Jul 2005, 13:05, archived)