Near the end, Carrie and Al are pulling the detonators out of the C4 before the lit fuses reach them, to prevent them from exploding. However, all they do is pull the detonators out of the blocks of C4 without pulling the burning fuses from the detonators. Thus, the detonators should still have gone off, making a loud "bang", at the very least.
When Al goes down into the sewer with Carrie & the sewer hiker, he has no flashlight. When he goes around the first turn he has one.