Barrel

The exploding barrel is quite common throughout the Doom levels. A barrel takes damage like a monster, but when its hit points reach zero, it explodes. The explosion inflicts damage to all objects within the blast radius of 128 units, including monsters, players, and even other barrels (exploding one barrel in a closely-arranged cluster of barrels often leads to a chain reaction of explosions). Each barrel starts with 20 hit points.

A useful tactic, sometimes called a "barrel frag", is to wait until one or more enemies are close to a barrel, and then shoot to explode the barrel (this tip is given in the user manuals).

Doom II added the burning barrel. However, these are just animated obstacles. They do not explode or inflict damage in any way.