This is from the front page of the instructions for the 4684
Personal casualty and theft losses attributable to a federally declared disaster are subject to the $100 per casualty and 10% of your adjusted gross income (AGI) reductions unless they are attributable to a qualified disaster loss. Personal casualty and theft losses attributable to a qualified disaster loss are not subject to the 10% of the AGI reduction and the $100 reduction is increased to $500.