Author Topic: [PoC] Atmospheric Conditions  (Read 1679 times)

Offline Garryl

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[PoC] Atmospheric Conditions
« on: September 07, 2014, 12:42:17 AM »
Atmospheric Conditions
Different environments can have different atmospheric conditions. Even on Earth, the air is distinctly thinner at high altitudes.



Atmosphere Thickness
Each breathable atmosphere has a thickness, relating to its atmospheric density or chemical composition relative to a baseline atmosphere. Characters native to a given atmosphere can be acclimatized to thicker or thinner atmospheres.

  • Thick: In a thick atmosphere, a character must make a Fortitude save (DC 10, +1 per previous check) each hour or be fatigued until returning to a normal atmosphere. Characters acclimatized to thick atmospheres are not at risk.
  • Normal: Characters can breathe and function normally in a normal atmosphere. On an Earth-like planet, this type of atmosphere occurs at or below altitudes of 5000 feet.
  • Thin: In a thin atmosphere, a character must make a Fortitude save (DC 15, +1 per previous check) each hour or be fatigued until returning to a normal atmosphere. Characters acclimatized to thin atmospheres are not at risk. On an Earth-like planet, this type of atmosphere occurs at or between altitudes of 5000 and 15000 feet.
  • Very Thin: In a very thin atmosphere, a character is at risk of fatigue as described above for thin atmospheres (even if acclimatized) and must further make a Fortitude save (DC 15, +1 per previous check) every 6 hours or take 1 point of ability damage to each ability score. This represents the physical and mental effects of long-term oxygen deprivation. Characters acclimatized to thin atmospheres gain a +4 competence bonus on the saves against the fatigue and ability damage. On an Earth-like planet, this type of atmosphere occurs above altitudes of 15000 feet.
Non-breathing characters are unaffected by atmosphere thickness.



Atmosphere Contents
A given atmosphere can have multiple types of usual or unusual contents. An atmosphere can, for example, be both breathable and toxic at the same time.
  • Breathable Atmosphere: The atmosphere contains breathable air. This may be effectively thinner or thicker than normal atmospheres even with the same atmospheric pressure due to different proportions of molecules.
  • Corrosive: A corrosive atmosphere deals 1d4 acid damage per hour to unprotected objects, ignoring hardness. To unprotected creatures, the atmosphere deals 1d4 acid damage each round instead.
  • Toxic: A toxic atmosphere has toxic components to it. The air functions as an inhaled poison of some sort.
Vacuums
Environments with no atmosphere at all are vacuums. Breathing creatures are at extreme risk in a vacuum. Unlike being underwater or in an unbreathable atmosphere, there is no atmospheric pressure at all in a vacuum. Despite some popular myths, moving into a vacuum does not cause the body to explosively decompress, nor does it cause instant freezing as heat bleeds away from the body. Rather, the primary hazards of surviving in the vacuum of space is the lack of air and air pressure.

Starting on the third round of exposure to vacuum, a creature must succeed on a Fortitude save (DC 15, +1 per previous check) each round or suffer from aeroembolism (“the bends”). A creature that fails the save experiences excruciating pain as small air bubbles form in its bloodstream; such a creature is stunned for 1 round. A creature that fails two consecutive Fortitude saves falls unconscious and remains so until returned to breathable atmospheric pressure.

The real danger of vacuum comes from suffocation, though holding one’s breath in vacuum damages the lungs. A character who attempts to hold his breath must make a Constitution check against suffocation every round (DC 10, +1 per previous check), and on a successful check the character takes 1 point of Constitution damage (from the pressure on the linings of his lungs). If the check fails, or when the character simply stops holding his breath, he begins to suffocate. In the next round, he falls unconscious with 0 hit points. The following round, he drops to –1 hit points. On the third round, he drops to –10 hit points and dies. Unlike holding one's breath underwater, the character must start making checks immediately in a vacuum, rather than after twice his Constitution score in rounds have elapsed.

Since there is no atmosphere in a vacuum, most normal fires can't burn. Fires brought into a vacuum go out, barring flames that can burn without atmospheric oxygen, such as burning magnesium and some magical flames. Firearms and fire effects still function normally otherwise, however. Even magical and cybernetic effects that produce magical flames over sustained periods still function, as they burn through different mechanisms.

A lack of atmosphere also means that air pressure waves can't propagate. Verbal communication is impossible through the vacuum; the lack of sound propagation means that creatures exposed directly to the vacuum are effectively deafened and cannot speak to provide the verbal component for spells and command word items. Further, most sonic effects are negated in a vacuum. Vacuum blocks line of effect for sonic effects that propagate from the user to the target via pressure waves, such as language-dependent effects employed through speech and a yrthak's sonic lance. For sonic effects that simply apply upon the target or in the targeted area without need to travel from the user, such as a sound burst spell, a vacuum blocks line of effect only when determining the area in which a sonic effect applies, not for the purpose of aiming the sonic effect. Sonic effects transmitted through physical contact, such as a thundering weapon, are transmitted through said physical contact, and so can largely bypass the vacuum's effects upon them. In a vacuum, sonic area spells and cybernetic effects can be employed as single-target effects instead, targeting a single creature or object (as applicable) in the spell or effect's normal range.



Sudden Decompression
The sudden decompression of a starship, vehicle, or other object can be dangerous to creatures inside. Whenever a sealed environment within a vacuum is breached, all of the air inside rushes out quickly to equalize the air pressure. Creatures within the decompressing environment must succeed on a Fortitude save or be thrust toward the breach (and possibly beyond it) by the air flow; this functions much like extreme winds in a normal atmosphere.

A creature blown or pushed into a breach may pass through it. If the creature's size category is equal to or smaller than the breach’s size category, the creature passes through the opening and is blown out into the vacuum. If the creature's size category is one size category larger than the breach’s size category, the creature is still blown out into the vacuum but also takes 1d6 points of damage from battering as it gets pushed through the breach. In either case, the creature is allowed a Reflex save at the effective wind's normal Fortitude save DC to hold on to something around the edge of the breach and avoid being pulled though entirely. If the creature is pulled through, it floats away at a rate of 60 feet per round unless it has some method of controlling its momentum in the vacuum.

If the creature is two or three size categories larger than the breach's size category, the creature blown into the breach isn’t thrust into the vacuum but takes 2d6 points of damage as it slams against the area around the breach. It takes another 2d6 points of damage each round until the air completely evacuates from the decompressed compartment or until the creature pulls itself away from the breach with a successful Fortitude save or Strength check (at the effective wind's DC). Creatures four or more size categories larger than the breach are not adversely affected except by the high effective winds.

The time it takes for all of the air to evacuate from a compartment depends on the size of the breach and the volume of the decompressing compartment, as shown in Table: Decompression. Once the air has completely rushed out through the breach, the pressure equalizes and the interior environment becomes a vacuum.

Table: Decompression

Breach Size

Decompression Time
Effective
Wind Force
Effective
Wind Speed
Ranged Attacks
Normal/Siege Weapons1

Creature Size2
Wind Effect
on Creatures
Fort
Save DC
Fine (3-inch square)1 round per 5-foot cube of air
(8 rounds per 10-foot cube of air)
Severe40 mph-4/--Tiny or smallerBlown Away15
SmallKnocked Down
MediumChecked
Large or largerNone
Diminutive (6-inch square)1 round per 10-foot cube of airWindstorm70 mphImpossible/-4Small or smallerBlown Away18
MediumKnocked Down
LargeChecked
Huge or largerNone
Tiny (1-foot square)1 round per 15-foot cube of air
(3 10-foot cubes of air per round)
Hurricane130 mphImpossible/-8Medium or smallerBlown Away20
LargeKnocked Down
HugeChecked
Gargantuan or largerNone
Small (2.5-foot square)1 round per 25-foot cube of air
(16 10-foot cubes of air per round)
Tornado190 mphImpossible/impossibleLarge or smallerBlown Away25
HugeKnocked Down
GargantuanChecked
Colossal or largerNone
Medium (5-foot square)1 round per 40-foot cube of air
(64 10-foot cubes of air per round)
Tornado225 mphImpossible/impossibleHuge or smallerBlown Away30
GargantuanKnocked Down
ColossalChecked
Larger than colossalNone
Large (10-foot square)1 round per 65-foot cube of air
(275 10-foot cubes of air per round)
Tornado255 mphImpossible/impossibleHuge or smallerBlown Away30
GargantuanKnocked Down
ColossalChecked
Larger than colossalNone
Huge (15-foot square)1 round per 85-foot cube of air
(625 10-foot cubes of air per round)
Tornado275 mphImpossible/impossibleHuge or smallerBlown Away30
GargantuanKnocked Down
ColossalChecked
Larger than colossalNone
Gargantuan (20-foot square)1 round per 100-foot cube of air
(1000 10-foot cubes of air per round)
Tornado290 mphImpossible/impossibleHuge or smallerBlown Away30
GargantuanKnocked Down
ColossalChecked
Larger than colossalNone
Colossal (30-foot square)1 round per 135-foot cube of air
(2500 10-foot cubes of air per round)
Tornado300 mphImpossible/impossibleHuge or smallerBlown Away30
GargantuanKnocked Down
ColossalChecked
Larger than colossalNone
1. The siege weapon category includes ballista and catapult attacks as well as boulders tossed by giants.
2. Flying or airborne creatures are treated as one size category smaller than their actual size, so an airborne Gargantuan dragon is treated as Huge for purposes of wind effects.

Checked: Creatures are unable to move forward against the force of the wind. Flying creatures are blown back 1d6×5 feet.

Knocked Down: Creatures are knocked prone by the force of the wind. Flying creatures are instead blown back 1d6×10 feet.

Blown Away: Creatures on the ground are knocked prone and rolled 1d4×10 feet, taking 1d4 points of nonlethal damage per 10 feet. Flying creatures are blown back 2d6×10 feet and take 2d6 points of nonlethal damage due to battering and buffeting.

Note: Due to the sonic barrier, wind speeds do not increase beyond 315 mph regardless of the size of the breach.

Note: The wind effects presented here do not perfectly match those presented in the DMG. This is intentional in order to produce smoother scaling of decompression's dangers up from the smallest breaches to the largest ones.



Sidebar: Different Atmospheres for Different Races
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« Last Edit: June 15, 2022, 10:39:14 PM by Garryl »