Environmental Rules

Environmental hazards more specific to one kind of terrain (such as an avalanche, which occurs in the mountains) are found in the Wilderness article. Environmental hazards common to many settings are detailed below.

Acid Effects

Corrosive acids deals 1d6 points of damage per round of exposure except in the case of total immersion (such as into a vat of acid), which deals 10d6 points of damage per round. An attack with acid, such as from a hurled vial or a monster’s spittle, counts as a round of exposure.
The fumes from most acids are inhaled Poison. Those who come close enough to a large body of acid to dunk a creature in it must make a DC 13 or take 1 point of Constitution damage. All such characters must make a second save 1 minute later or take another 1d4 points of Constitution damage.
Creatures immune to acid’s caustic properties might still drown in it if they are totally immersed.

Cold Dangers

Cold and exposure deal nonlethal damage to the victim. This nonlethal damage cannot be recovered until the character gets out of the cold and warms up again. Once a character is rendered unconscious through the accumulation of nonlethal damage, the cold and exposure begins to deal lethal damage at the same rate.
An unprotected character in cold Weather (below 40° F) must make a Fortitude Save each hour (DC 15, + 1 per previous check) or take 1d6 points of nonlethal damage. A character who has the Survival skill may receive a bonus on this saving throw and may be able to apply this bonus to other characters as well.
In conditions of severe cold or exposure (below 0° F), an unprotected character must make a Fortitude Save once every 10 minutes (DC 15, +1 per previous check), taking 1d6 points of nonlethal damage on each failed save. A character who has the Survival skill may receive a bonus on this saving throw and may be able to apply this bonus to other characters as well. Characters wearing winter clothing only need check once per hour for cold and exposure damage.
A character who takes any nonlethal damage from cold or exposure is beset by frostbite or hypothermia (treat them as Fatigued). These penalties end when the character recovers the nonlethal damage they took from the cold and exposure.
Extreme cold (below -20° F) deals 1d6 points of lethal damage per minute (no save). In addition, a character must make a Fortitude Save (DC 15, +1 per previous check) or take 1d4 points of nonlethal damage. Those wearing metal armor or coming into contact with very cold metal are affected as if by a Chill Metal spell.

Ice Effects

Characters walking on ice must spend 2 squares of Movement to enter a square covered by ice, and the DC for Acrobatics checks increases by +5. Characters in prolonged contact with ice may run the risk of taking damage from severe cold (see above).

Darkness

Darkvision allows many characters and monsters to see perfectly well without any light at all, but characters with normal vision (or Low-Light Vision, for that matter) can be rendered completely Blinded by putting out the lights. Torches or lanterns can be blown out by sudden gusts of subterranean wind, magical light sources can be dispelled or countered, or magical traps might create fields of impenetrable darkness.
In many cases, some characters or monsters might be able to see, while others are Blinded. For purposes of the following points, a blinded creature is one who simply can’t see through the surrounding darkness.

• Creatures Blinded by darkness lose the ability to deal Precision Damage (for example, a sneak attack).
• Blinded creatures are hampered in their Movement, and pay 2 squares of movement per square moved into (double normal cost). Blinded creatures can’t Run or Charge.
• All opponents have total Concealment from a Blinded creature, so the Blinded creature has a 50% miss chance in combat. A Blinded creature must first pinpoint the location of an opponent in order to attack the right square; if the Blinded creature launches an attack without pinpointing its foe, it attacks a random square within its reach. For ranged attacks or spells against a foe whose location is not pinpointed, roll to determine which adjacent square the Blinded creature is facing; its attack is directed at the closest target that lies in that direction.
• A Blinded creature loses its Dexterity adjustment to AC and takes a -2 penalty to AC.
• A Blinded creature takes a -4 penalty on Perception checks and most Strength- and Dexterity-based skill checks, including any with an armor check penalty. A creature Blinded by darkness automatically fails any skill check relying on vision.
• Creatures Blinded by darkness cannot use a Gaze Attack and are immune to gaze attacks.

A creature Blinded by darkness can make a Perception check as a Free Action each round in order to locate foes (DC equal to opponents’ Stealth checks). A successful check lets a Blinded character hear an unseen creature “over there somewhere.” It’s almost impossible to pinpoint the location of an unseen creature. A Perception check that beats the DC by 20 reveals the unseen creature’s square (but the unseen creature still has total Concealment from the Blinded creature).

• A Blinded creature can grope about to find unseen creatures. A character can make a Touch Attack with their hands or a weapon into two adjacent squares using a Standard Action. If an unseen target is in the designated square, there is a 50% miss chance on the Touch Attack. If successful, the groping character deals no damage but has pinpointed the unseen creature’s current location. (If the unseen creature moves, its location is once again unknown.)
• If a Blinded creature is struck by an unseen foe, the Blinded character pinpoints the location of the creature that struck them (until the unseen creature moves, of course). The only exception is if the unseen creature has a reach greater than 5 feet (in which case the Blinded character knows the location of the unseen opponent, but has not pinpointed them) or uses a ranged attack (in which case, the blinded character knows the general direction of the foe, but not their location).
• A creature with the Scent ability automatically pinpoints unseen creatures within 5 feet of its location.

Difficult Terrain

Difficult terrain hampers Movement. Each square of difficult terrain counts as 2 squares of Movement. You can’t Run or Charge across difficult terrain.
If you occupy squares with different kinds of terrain, you can move only as fast as the most difficult terrain you occupy will allow.
Flying and Incorporeal creatures are not hampered by difficult terrain.

Squeezing

In some cases, you may have to squeeze into or through an area that isn’t as wide as the space you take up. You can squeeze through or into a space that is at least half as wide as your normal space. Each move into or through a narrow space counts as if it were 2 squares, and while squeezed in a narrow space, you take a –4 penalty on attack rolls and a –4 penalty to Armor Class.
When a Large creature (which normally takes up 4 squares) squeezes into a space that’s 1 square wide, the creature’s miniature figure occupies 2 squares, centered on the line between the 2 squares. For a bigger creature, center the creature likewise in the area it squeezes into.
A creature can squeeze past a creature while moving but it can’t end its movement in an occupied square.
To squeeze through or into a space less than half your space’s width, you must use the Escape Artist skill. You can’t attack while using Escape Artist to squeeze through or into a narrow space, you take a –4 penalty to Armor Class, and you lose any Dexterity bonus to AC.

Falling

Falling Damage
The basic rule is simple: 1d6 points of damage per 10 feet fallen, to a maximum of 20d6.
If a character deliberately jumps instead of merely slipping or falling, the damage is the same but the first 1d6 is nonlethal damage. A DC 15 Acrobatics check allows the character to avoid any damage from the first 10 feet fallen and converts any damage from the second 10 feet to nonlethal damage. Thus, a character who slips from a ledge 30 feet up takes 3d6 damage. If the same character deliberately jumped, they take 1d6 points of nonlethal damage and 2d6 points of lethal damage. And if the character leaps down with a successful Acrobatics check, they take only 1d6 points of nonlethal damage and 1d6 points of lethal damage from the plunge.
Falls onto yielding surfaces (soft ground, mud) also convert the first 1d6 of damage to nonlethal damage. This reduction is cumulative with reduced damage due to deliberate jumps and the Acrobatics skill.
Falling into Water
Falls into water are handled somewhat differently. If the water is at least 10 feet deep, the first 20 feet of falling do no damage. The next 20 feet do nonlethal damage (1d3 per 10-foot increment). Beyond that, falling damage is lethal damage (1d6 per additional 10-foot increment).
Characters who deliberately dive into water take no damage on a successful DC 15 Swim check or DC 15 Acrobatics check, so long as the water is at least 10 feet deep for every 30 feet fallen. However, the DC of the check increases by 5 for every 50 feet of the dive.
Falling speed
How fast someone or something falls is dependent on the item. A small, heavy Object (or creature) can fall much faster than a large light one. To simplify, most items and creatures are categorized as light or heavy when they fall, and how far they fall each round is determined accordingly.
Light objects and creatures fall for 150 ft. in the first round they fall, then 300 ft. on each subsequent round. Light objects include things like clothing, empty bags, and other items of low density that have a lot of surface area to catch the air. Light creatures includes any creature with a non-magical means of Flight, and creatures of tiny size or smaller.
Heavy objects and creatures fall for 500 ft. in the first round they fall, then 1,000 ft. on each subsequent round. Heavy objects include things like books, rocks, swords, and other dense or aerodynamic objects. Heavy creatures includes any creature larger than tiny without a non-magical means of Flight.
Especially lightweight items, like paper, feathers, and leaves, fall much slower, and are ruled on an individual case (though typically will fall around 60 ft. per round)
As objects have no Initiative, they typically fall their full round's distance immediately when put into a falling state.
When Creatures Fall
While a creature falls 500 ft. in their first round of falling, it can be counterproductive to the agency of everyone involved to resolve the entirety of that fall immediately. When necessary, the increment of this fall can be broken up to allow for better versimilatude and more engaging interactions. If a creature begins falling when it is not their turn, they immediately fall 100 feet (this distance does not count towards the 500 feet a creature falls on their first round). This fall cannot be interrupted except through an Immediate Action (or contact with a solid surface). On that creature's next Initiative (a creature cannot delay their Initiative while falling), they fall a full 500 feet as their first round of falling.
Actions while Falling
A creature falling during their turn does not fall the entire distance instantaneously, and has a chance to react while doing so. On a creature's first round of falling, they fall 150 feet in the first half of their turn and the remaining 350 on the second half. Thus, a creature taking a Standard Action or Move Action in this time would resolve that action after falling 150 feet, then the rest of their action after falling another 350 feet. A Full-Round Action would not be resolved until they had fallen the full 500 feet. Similarly, a creature that wants to take an action after falling could not resolve a Full-Round Action after falling 150 feet or further, and cannot resolve a Standard Action or Move Action after falling the full 500 feet (unless they could begin that action before reaching that distance). For example, a Barbarian jumping off a cliff to attack a creature below could not perform a Full Attack action on that creature unless it was less than 150 feet down.
Many actions are more difficult to perform when falling, and may require additional checks to do. Notably, casting a spell with a somatic component while falling requires a Concentration check with a DC equal to 20 + the spell's level to cast.
Teleportation spells do not remove a subject's momentum unless explicitly stated, and thus do not prevent falling damage from distances already fallen when activated.

Falling Objects

Just as characters take damage when they fall more than 10 feet, so too do they take damage when they are hit by falling objects.
Objects that fall upon characters deal damage based on their weight and the distance they have fallen.
For each 200 pounds of an object’s weight, the object deals 1d6 points of damage, provided it falls at least 10 feet. Distance also comes into play, adding an additional 1d6 points of damage for every 10-foot increment it falls beyond the first (to a maximum of 20d6 points of damage).
Objects smaller than 200 pounds also deal damage when dropped, but they must fall farther to deal the same damage. Use Table: Fall Increments for Falling Objects to see how far an object of a given weight must drop to deal 1d6 points of damage.
For each additional increment an object falls, it deals an additional 1d6 points of damage.
Objects weighing less than 1 pound do not deal damage to those they land upon, no matter how far they have fallen.

Heat Dangers

Heat deals nonlethal damage that cannot be recovered until the character gets cooled off (reaches shade, survives until nightfall, gets doused in water, is targeted by Endure Elements, and so forth). Once rendered Unconscious through the accumulation of nonlethal damage, the character begins to take lethal damage at the same rate.
A character in very hot conditions (above 90° F) must make a Fortitude Save each hour (DC 15, +1 for each previous check) or take 1d4 points of nonlethal damage. Characters wearing heavy clothing or armor of any sort take a -4 penalty on their saves. A character with the Survival skill may receive a bonus on this saving throw and may be able to apply this bonus to other characters as well. Characters reduced to unconsciousness begin taking lethal damage (1d4 points per hour).
In severe heat (above 110° F), a character must make a Fortitude Save once every 10 minutes (DC 15, +1 for each previous check) or take 1d4 points of nonlethal damage. Characters wearing heavy clothing or armor of any sort take a -4 penalty on their saves. A character with the Survival skill may receive a bonus on this saving throw and may be able to apply this bonus to other characters as well. Characters reduced to unconsciousness begin taking lethal damage (1d4 points per each 10-minute period).
A character who takes any nonlethal damage from heat exposure now suffers from heatstroke and is Fatigued.
These penalties end when the character recovers the nonlethal damage they took from the heat.
Extreme heat (air temperature over 140° F, fire, boiling water, lava) deals lethal damage. Breathing air in these temperatures deals 1d6 points of damage per minute (no save). In addition, a character must make a Fortitude Save every 5 minutes (DC 15, +1 per previous check) or take 1d4 points of nonlethal damage. Those wearing heavy clothing or any sort of armor take a -4 penalty on their saves. In addition, those wearing metal armor or coming into contact with very hot metal are affected as if by a Heat Metal spell.
Boiling water deals 1d6 points of scalding damage, unless the character is fully immersed, in which case it deals 10d6 points of damage per round of exposure.

Catching On Fire

Characters exposed to burning oil, bonfires, and non-instantaneous magic fires might find their clothes, hair, or equipment on fire. Spells with an instantaneous duration don’t normally set a character on fire, since the heat and flame from these come and go in a flash.
Characters at risk of catching fire are allowed a DC 15 Reflex Save to avoid this fate. If a character’s clothes or hair catch fire, they take 1d6 points of damage immediately. In each subsequent round, the burning character must make another Reflex saving throw. Failure means they take another 1d6 points of damage that round. Success means that the fire has gone out (that is, once they succeed on their saving throw, they're no longer on fire).
A character on fire may automatically extinguish the flames by jumping into enough water to douse themselves. If no body of water is at hand, rolling on the ground or smothering the fire with cloaks or the like permits the character another save with a +4 bonus.
Those unlucky enough to have their clothes or equipment catch fire must make DC 15 Reflex saves for each item. Flammable items that fail take the same amount of damage as the character.

Lava Effects

Lava or magma deals 2d6 points of damage per round of exposure, except in the case of total immersion (such as when a character falls into the crater of an active volcano), which deals 20d6 points of damage per round.
Damage from magma continues for 1d3 rounds after exposure ceases, but this additional damage is only half of that dealt during actual contact (that is, 1d6 or 10d6 points per round).
An immunity or resistance to fire serves as an immunity to lava or magma. However, a creature immune to fire might still drown if completely immersed in lava.

Dim Light (Shadowy Illumination)

While not complete darkness, areas of dim light are dimly lit, and are difficult to see through for those without Darkvision. Creatures within this area have Concealment, and can make Stealth checks to hide from foes. Creatures with Low-Light Vision suffer the same difficulty seeing into dim light, but consider the radius of bright and dim light from light sources to be twice as far.

Smoke Effects

A character who breathes heavy smoke must make a Fortitude Save each round (DC 15, +1 per previous check) or spend that round choking and coughing. A character who chokes for 2 consecutive rounds takes 1d6 points of nonlethal damage.
Smoke obscures vision, giving Concealment (20% miss chance) to characters within it.

Starvation And Thirst

Characters might find themselves without food or water and with no means to obtain them. In normal climates, Medium characters need at least a gallon of fluids and about a pound of decent food per day to avoid starvation. (Small characters need half as much.) In very hot climates, characters need two or three times as much water to avoid dehydration.
A character can go without water for 1 day plus a number of hours equal to their Constitution score. After this time, the character must make a Constitution check each hour (DC 10, +1 for each previous check) or take 1d6 points of nonlethal damage.
A character can go without food for 3 days, in growing discomfort. After this time, the character must make a Constitution check each day (DC 10, +1 for each previous check) or take 1d6 points of nonlethal damage.
Characters who have taken nonlethal damage from lack of food or water are Fatigued. Nonlethal damage from thirst or starvation cannot be recovered until the character gets food or water, as needed—not even magic that restores hit points heals this damage.

Suffocation

A character who has no air to breathe can hold their breath for 2 rounds per point of Constitution. After this period of time, the character must make a DC 10 Constitution check in order to continue holding their breath. The save must be repeated each round, with the DC increasing by +1 for each previous success.
When the character fails one of these Constitution checks, they begin to suffocate. In the first round, they fall Unconscious (0 hit points). In the following round, they drop to -1 hit points and are Dying. In the third round, they suffocate and die.

Slow Suffocation

A Medium character can breathe easily for 6 hours in a sealed chamber measuring 10 feet on a side. After that time, the character takes 1d6 points of nonlethal damage every 15 minutes. Each additional Medium character or significant fire source (a torch, for example) proportionally reduces the time the air will last. When a character falls unconscious from this nonlethal damage, they drop to -1 hit points and are dying. In the next round, they suffocate.
Small characters consume half as much air as Medium characters. A larger volume of air, of course, lasts for a longer time.

Water Dangers

Any character can wade in relatively calm water that isn’t over their head, no check required. Similarly, swimming in calm water only requires skill checks with a DC of 10. Trained swimmers can just take 10. (Remember, however, that armor or heavy gear makes any attempt at swimming much more difficult.)
By contrast, fast-moving water is much more dangerous. On a failed DC 15 Swim check or a DC 15 Strength check, it deals 1d3 points of nonlethal damage per round (1d6 points of lethal damage if flowing over rocks and cascades), and the character goes under.
Very deep water is not only generally pitch black, posing a navigational hazard, but worse, it deals water pressure damage of 1d6 points per minute for every 100 feet the character is below the surface. A successful Fortitude Save (DC 15, +1 for each previous check) means the diver takes no damage in that minute. Very cold water deals 1d6 points of nonlethal damage from hypothermia per minute of exposure.

Drowning

Any character can hold their breath for a number of rounds equal to twice their Constitution score. After this period of time, the character must make a DC 10 Constitution check every round in order to continue holding their breath. Each round, the DC increases by 1. See also: Swim skill description.
When the character finally fails their Constitution check, they begin Drowning. In the first round, they fall Unconscious (0 hp). In the following round, they drop to -1 hit points and are Dying. In the third round, they drown.
It is possible to drown in substances other than water, such as sand, quicksand, fine dust, and silos full of grain.