I came across your forum while researching Christmas crackers. My company makes crackers here in the UK and we ship to the US and all over Europe using DHL and in 5 years have never had one box returned!
As someone previously mentioned as long as the crackers are boxed in retail packaging they should be ok be. I say should because things change all the time.
The largest quantity we shipped was 200 for a wedding in New York. No problems at all! I forget how many you need to be able to combine them to make a significant explosion but it's a staggering amount! The biggest deterrent to shipping crackers to the US is the shipping costs unfortunately and not the airlines.
Things are a little more complicated when you have to import 100,000 snaps on a boat into the UK from China!!! They can go off with a bang!
Phil