Ridiculous.
I spent 22 years in the US Air Force doing Nuclear Defense. There is not going to be a continent-wide fire. Not even when both we and the Soviets had twice as many nuclear weapons as now.
Please provide a reputable source for such a claim!
Sorry that was long before there was such a thing as the internet. I know, if there is no link going back to events 60 years ago, the past never happened. Here are no links to what was going on in Rome 2,000 years ago. So that never happened either.
So just forget it.