Why is everything exploding?

While playing MW3, I have noticed a frustrating trend of random things exploding and killing me. Not enemy lethal equipment, but map objects like cars, barrels, and what look like blown, sparking fuseboxes. Each of these deaths (and occasionally kills - last night on Dome I happened to shoot through a wall when moving to cover, blowing up a barrel inside and killing two people) gets it's own kill icon, as well.

Usually these are triggered by some sort of damage (shooting a barrel, grenading a car, etc.), but as far as the fuseboxes, I have no idea why they explode (I've never even seen a grenade nearby when they exploded).

Is any quick way to know what will and won't explode? Obviously most intact cars will, some barrels (probably a particular color) will, and I've learned that sparking fuseboxes are also apparently a deathtrap. How can I tell?

For barrels and cars, you can tell that they will explode if they are flaming. Sparking fuseboxes etc explode only when they have taken some damage. This is true of all exploding objects. Observe a fusebox at the very beginning of a game. As you shoot it, it sparks and smokes more until it explodes.