Past Best Practices
To prepare for site interruption:
For larger companies, arrange for an automatic dial-up in the event of the need for an urgent contacting of all employees. (e.g.: site closing). For smaller companies, have a "call" hierarchy whereby each senior manager calls the next-level direct reports, and so forth. For any size company; have an emergency call-in number so employees can check as to whether the site is open in the event of bad weather, etc.