Shooting survivors?
Other people mentioned in another thread that it's probably ammo of the security team exploding in fire. They probably had between them a couple thousand rounds.
Three things...
1. The fire and heat is setting off small arms.
2. They are firing warning shots.
3. They are shooting surviors.
The laughter could be asscociated with any of these three scenarios.
And it would not take to have missing bodies for #3 to happen.