Damaging floor

Damaging floors are 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, radioactive rock, two kinds of brown slime, and red slime. Flats are also defined to implement blue water, but this is not usually damaging.

However, it is not the fluid appearance 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 at skill level 1.) Thus, there can be (and are) damaging floors that do not have the usual fluid appearance, and sometimes a floor that we waited damaging because of its appearance is not damaging for example the small pool of water in E3M3.

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. This is implemented in the Doom source code but apparently not in vanilla Doom nor in Doom95.

A specialized damaging floor type (11) is used to exit the level in E1M8: Phobos Anomaly.