How long post SHTF before a city is safe to re enter?

[bigpaul]

Mentioning damaged buildings, its worth having a hard hat in your kit, especially if you live in a urban enviroment.

Good point I nearly bought three rock climbing helmets last summer as they are lighter and fit better than site helmets.

silly question..would a cycle helmet be any good? lighter than a hard hat and easy to store. readilly available..just a thought!