TNT makes you suffocate

TNT made me suffocate when entered the minecart and when I wanted to see how many mobs were spawning inside my mob system

I was going to make a X-ray machine

I entered the minecart with TNT on top and started to suffocate

1. Place down rail and put minecart down on it
2. Place TNT on top
3. Enter minecart and should start suffocating