I will tell you what happened to US last year, and you can do what you want with it.
We were at my BIL house, his young (21?) GF is there, they had a whole sleu of fireworks they were going to put off later that night. She thought it would be fun to light a few bottle rockets, or whatever, RIGHT BEHIND MY 21 month old son, when he wasnt prepared, and wasnt even LOOKING. The sound made him crap himself. When it was time for the real fireworks, he was so shell shocked, my MIL was in the house with him, holding him the rocking position (like a newborn) while he shook and cried. (I was holding my then 7 month old) It was awful.
Im hoping he has completly forgotten that experience by now, and we are going to try to give both boys plenty of noitce and NO SURPRISES THIS YEAR. (BILs gf is history, so that should help

)