Use whatever looks best to you. Sometimes we must make artistic choices that aren't realistic.
An explosion will vary a lot depending on the kind of explosion.
A gun will often flash faster than a frame. Unless you're firing something like a minigun that fires many bullets every second, often a regular gun can be fired a few times without a video camera even picking up the muzzle flash. And, when it is captured, the flash will only be there for one frame.
A camera flash will be there for one frame only.
A spark an be on screen for a few frames as it streaks across.
- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')
No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.