First of all, you should examine the damaged currency and if the notes are identifiable more than fifty percent then you are safe as you can redeem it without facing any hassle.
Contact the U.S Treasury Department after examining the condition of burnt currency notes. They will deal this matter and if your currency has an approximately fifty percent damage, then there is a great chance that you will get it back.
You should email or go personally by taking the mutilated currency to the U.S Treasury Department’s section of Federal Bureau of Engraving and Printing. Their experts will carefully examine the condition of damaged currency.
You should take the money carefully by packing it up in an appropriate box. Make sure you have not folded it after burning. Keep it in the similar condition which will help the examiner to check with ease.
Carefully separate the coins, if any, from the damaged money and take the currency notes to the concerned authority.
Make sure you have not rolled the notes and also do not unfold the notes which were folded when they caught fire.
Write a letter to the concerned authority stating the estimated worth of your damaged money and also write details explaining how the money became damaged.