Barrel

The exploding barrel is a relatively common hazard found throughout many Doom levels. It is a cylindrical metal barrel containing what appears to be a flammable, radioactive green slime or "nukage". Barrels form part of the "dangerous Doom environment" described in the game booklets:


 * Exploding barrels: Scattered around the base are drums containing toxic waste. If your shots hit one of these barrels, it's kablooey time! It might take several bullets to set off a barrel, but a single blast of any of the other weapons usually does the trick.

A barrel takes damage like a monster, and when its hit points reach zero, it explodes, accompanied by the sound effect DSBAREXP. 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, which is the same as the Zombieman.

A useful tactic, sometimes called a "barrel frag", is to wait until one or more enemies are close to a barrel, and then shoot the barrel to detonate it (this tip is given in the user manuals). Barrels are extremely effective and efficient weapons when used correctly: a well-timed chain reaction can produce thousands of hit points of damage from a single shotgun blast, for example.

Damage inflicted by an exploding barrel was long thought to be simply attributed to whoever last damaged it caused it to blow up -monster or player-, but after a more recent analysis of the source code this turned out not to be that simple. A barrel's map object doesn't get its 'inflictor' field set when it's actually exploding but only when it's damaged without exploding, therefore monsters or players that destroy barrels in a single attack do not cause the barrel's explosion to be attributed to them, and thus cannot cause infighting or be attributed a kill as a result of it.

E.g. if a monster A damages a barrel 'without' making it explode, and then a monster B damages it further and makes it blow up and hurting both itself and monster A, then monster B will start chasing after monster A, because the barrel survived one hit from monster A and thus A was registered as the damage's inflicter.

This trick can be used to trigger monster infighting even between monsters of the same species, e.g. between two imps. Their fireballs still do no damage, but once they get into melee range they will claw each other to death. However, this is harder than it sounds to achieve in practice because a barrel must survive at least one hit from a monster in order to result in infighting when exploding, otherwise the monsters are damaged but do not start infighting.

Versions
In versions v1.1 and older of Doom, the above infighting trick could also result in a monster to attack itself if it was damaged by its own barrel blast, resulting in the so called barrel suicide.

Doom II added the burning barrel. However, these are just animated obstacles. They do not explode or inflict damage in any way (except in Brutal Doom, as seen below).

The pods of Heretic and mushrooms of Hexen play the same role as Doom's exploding barrels. Strife also has exploding barrels.

Demo

 * [[Media:BLDYBRRL.WAD|A level demonstrating how an exploding barrel can leave bloody remains when crushed]] (file info). It features several such barrels placed under a crushing ceiling; walk over the silver touchplate to see the effect.