Be afraid, be very afraid. There is no telling what the next disaster will be. Another terrorist attack? A steam pipe explosion like the one that shut down several blocks of Lexington Avenue a year ago? Or perhaps a pandemic flu that would cripple New York City's economy by making people afraid to go to work or ride on subways and buses? That was the message at a daylong workshop conducted on Tuesday by the city's health and emergency management agencies, intended to give businesses tips on how to cope with the potential calamities.