Radiation (Fallout 3)

Radiation is a major environmental hazard in Fallout 3, in contrast to earlier games. At max level, it will cause instant death. Radiation only applies to the player: Any non-player characters do not gain rads.

Overview
Radiation is accumulated from a variety of sources, including exposure to its sources, micronuclear explosions (such as Fat Man detonations or cars), swimming in irradiated water, and eating and drinking contaminated food. While radiation never directly affects the current hit point level, the player will receive progressive penalties to SPECIAl, until they reach a total of 1000 rads and die.

There are five major stages of radiation poisoning at 200, 400, 600, 800, and 1000 rads. The game helpfully displays the current irradiation at the status screen and on the Pip-Boy 3000's dosimeter in the upper right on the HUD and on the Pip-Boy itself when the player accesses it.

Radiation exposure in the environment is generally limited and comes mostly from water sources and polluted environments, such as near the White House in D.C. There are a handful of exceptions:
 * The entrance at Vault 87 peaks at 3 932 rads per second, virtually instant death.
 * The river below the Pitt Bridge reaches 600 rads per second, and is fatal due to a lack of ability to leave.
 * Vault 87 GECK chamber peaks at roughly 400 rads per second, as does the blast furnace in the steelyard.

The player can moderate radiation exposure by increasing radiation resistance with Rad-X (effectiveness scales with Medicine) and radiation suits. The Lead Belly perk also reduces exposure to radiation by halving the amount of rads obtained while drinking. The Cyborg also provides an increase to radiation resistance.

Notably, the player can earn the Rad Regeneration perk by electing to complete the optional 600 rad challenge for the The Wasteland Survival Guide.

The accumulated radiation can be removed in a variety of ways:
 * Most doctors will flush the rads for 100 caps.
 * RadAway will reduce irradiation. Its effectiveness depends on the player's medicine skill.
 * Rad Absorption confers a constant radiation removal effect.
 * Nuclear Anomaly clears the radiation count.
 * My First Infirmary can be used to remove all rads once per day.
 * Certain consumables, such as cave fungus or wild and refined punga fruit (in Point Lookout) reduce the radiation count.

Radiation can be resisted by equipping certain types of apparel, such as radiation suits or power armor. A dose of the chem Rad-X also grants the player a radiation resistance based on his or her Medicine skill, but the effects do not stack. This resistance is applied to all sources of radiation, from the external environment to irradiated consumables.

High radiation areas

 * Vault 87 entrance: Maximum ~3999 rads/second, the highest level of radiation found in the game.
 * The Pitt's Monongahela River: 600 rads/second
 * Near the G.E.C.K in Vault 87 (1-400 rads/second).
 * Delta IX rocket wreckage near the Statesman Hotel: Around 40 rads/second near the front of the rocket).
 * The chamber inside Project Purity during the quest Take it back!: Around 17-30 rads/second.
 * The Hole: Around 17 rads/second.
 * Megaton Ruins' perimeter if the player blew it up in The Power of the Atom (1-13 rads/second).
 * Holy Light Monastery and Olney Powerworks in Broken Steel, if the radiation traps are active: 9-15 rads/second.
 * Wheaton Armory: Inside the silo, up to 13 rads/second.

Behind the scenes

 * The instant death is handled by a script that instantly applies a -10 000 HP effect to the player character and inverts stimpak functionality, so that they cause damage, rather than heal.