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, 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 is to wait until one or more enemies are close to a barrel, and then shoot to explode the barrel. (This is a tip 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.

The doom engine uses the same code for exploding barrels as for exploding rockets, and even the same sound effect. The blast radius is 128 units, and all objects within that radius are examined. For each object that can be damaged, the distance to the barrel is calculated as the greater of the x-distance and the y-distance of the centers, less the radius of the object. The line-of-sight is checked, and if the view of the object from the barrel is obstructed, no damage is inflicted. Otherwise, damage is equal to 128 hit points less the distance.

Cyberdemons and Spider Masterminds are immune to blast damage.