" How It Starts
In the first few moments, the effects of an EMP
will be just like a power outage. Actually, most people won’t be able
to tell the difference between an EMP and any other power outage. There
is no obvious sign that an EMP has occurred, other than the loss of
power. In fact, most of the power generating stations and other services
won’t even recognize what had happened, instead thinking that the
problems they were experiencing were localized.
The first hours to a day of any EMP will look to everyone just as if
they were having a regional blackout. People will be surprised to see
that their whole city is blacked out, rather than just their
neighborhood. They’ll probably speculate about what has happened, but
few will think of suggesting an EMP....."
http://www.survivopedia.com/dominoemp/