Damaging floor

Damaging floors appear in Doom, Heretic, Hexen, and Strife. They form part of the "dangerous Doom environment" described in the game booklets:
 * Slime and other radioactive waste: Many of the areas in Doom contain pools of dangerous liquids that will damage you if you walk through them. There are several varieties of waste, each doing increasing damage. If it looks fluid, beware!

Despite the damaging effects, it is often necessary to cross a damaging floor during gameplay. Crossing as quickly as possible minimizes the damage. If the player has armor, then the damage is split between health and armor. Also, the radiation suit protects the player from damaging floors for a limited time.

Monsters are not affected by damaging floors.

Technical information
The fluid appearance is implemented using animated flats. These include nukage, lava, blood, etc. Flats are also defined to implement blue water, but this is not usually damaging.

It is not the fluid appearance, however, that makes a floor damaging. The level designer assigns a special type value to make the floor of a sector damaging when the player is within the typed sector. (Damage is halved, rounded down, at skill level 1.) Thus, there can be (and are) damaging floors that do not have the usual fluid appearance, and sometimes a floor expected to be damaging because of its texture is not damaging.

For the 20% damage types (4 and 16), there is a small chance (6/256 = 2.3%) that the damage will penetrate the radiation suit during a given second.

A specialized damaging floor type (11) is occasionally used in the last room of a level (e.g. E1M8: Phobos Anomaly). Damage is inflicted as with type 5, but when the player's health drops below 11%, the level ends. Play then proceeds to the next level, if applicable, with the player's health restored to 1% if it has fallen to 0% or lower. These sectors cancel the invulnerability bestowed by the God mode cheat, although the invulnerability power-up is not affected.