allhandsofsorrow :
when I play Titanfall and i'm next to a explosion my fps drops to 40 it is usually 60 constant.
GPU: Gtx 760
CPU:amd fx 6300
Most visual effects, explosions included, are entirely GPU dependant.
There are a number of mechanisms for visual effects such as explosions. The most primitive of which involves stencilling sprites (two dimensional textured objects) in the area, while the most complex involve a chain of vertex -> geometry -> pixel shaders. Regardless of the mechanism, it's almost always done on the GPU unless the game performs those operations entirely in software for other reasons.
Many games will often tie nice visuals in with gameplay action, such as an explosion hurling a barrel across the street which may or may not kill the player on impact. These are two independent operations, the rendering of the explosion through a shader mechanism, and the calculation of the barrel's position over time using rigid body dynamics. The former is done on the GPU, while the later is traditionally done on the CPU.