The exploding barrel is a relatively common hazard found throughout many Doom levels; a cylindric metal barrel containing what appears to be 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 fuel, toxic waste, or some other volatile substance. 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 trooper.
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 is attributed to the last actor damaging the barrel without actually blowing it up. This requires a barrel to survive at least one hit, before being able to cause infighting. Destroying an undamaged barrel with one hit does not set the inflictor/target field of the barrel's mobj, and as such it does not propagate responsibility. This also makes it possible to deliberately set off a barrel previously damaged by a monster: this will cause retaliation against said monster, not the one actually destroying the barrel. If done correctly, this can lead to infighting even between monsters of the same type – for example, if an imp takes damage from an exploding barrel previously damaged by another imp's fireball, it will attack and the two will fight to the bitter end. Their fireballs still do no damage, but once they get into melee range they will claw each other to death.
Doom II added the burning barrel. However, these are just animated obstacles. They do not explode or inflict damage in any way.
- When a barrel is destroyed by a crushing ceiling before it can complete its explosion animation, it leaves behind a pool of blood and flesh. See also a demo of the phenomenon below.
- The burning barrel also exists in The Ultimate Doom version of the engine; however, its sprites are not correctly offset and it is never used.
- 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.
- Doom Oddities thread at the Doomworld forums
- Unofficial Doom Specs v1.666, section 22.214.171.124 (archived 🏛)