Let’s get one thing straight: space is dangerous.

The depth of the health system will vary depending on the species of the character. Simpler entities may not have all of the following systems, for example it would be a waste of resources to simulate organs or blood for something tiny like insects.

The health system documented here assumes we are referring to the primary character type, humanoids, unless otherwise stated.

The health system is composed of many different and optional complex systems, which we will divide into Body Layers and Body Parts from now on.

Body Layers

One of the main systems of any biological character is the system of their tissue layers. Humans are generally made of muscle, connective, neural, bone and other types of tissues, each providing different functions and having different ways of being affected by the outside world.

Circulatory System

The circulatory system makes the heart pump the blood through the organism; blood goes through various organs in the torso and distributes oxygen and nutrients to other body parts, so the root of the system should be located in the Torso and depend on the heart.

This also means, that if the intermediate link in this hierarchy is damaged, the child link should have less blood delivered as well as the damaged part itself. The easiest way to imagine it is to think of it as a number of interconnected containers.

Nervous System

The nervous system is also connects all over the body, but the hierarchy is different:

Which also means that if the intermediate link in this hierarchy is damaged, the child link should have worse chance to provide sensory information or receive a brain's command to function as well as the damaged part itself. That means that if the NERVES are severed in some body part, it’s connection to the brain is lost along with the parts that are lower on the hierarchy. If NERVES for the body parts are damaged, the character’s ability to make precise movements is damaged as well, to a point of losing control of the body part completely, depending on the severity of the damage.

Below is a breakdown of players’ body parts, and what they do.

What's blood for?

Blood is circulating through the body, carrying oxygen, it's necessary for body parts that require oxygen.

The hazard players are most likely to face, likely result in some form of bleeding.

Many creatures you’ll encounter also rely on their blood levels to survive. In the average human’s body, all players start with around five liters of blood. Any attack with a sharp object, like a broken bottle, or a kinetic firearm, may form an open wound that causes blood loss relative to the severity of the wound.

Luckily, most living things (humans especially) are equipped with processes that slowly reduce the severity of most wounds, meaning blood loss will slow down and eventually stop. However, some wounds may be too severe, and cause fatal blood loss faster than the wounds can be naturally healed. A little blood loss is one thing, but a lot of blood loss is another thing.

Blood volume in the body

A human with an average body contains around 5 liters of blood, so if a human has an approximate volume of 65L, we have a ratio of approximately 0.077, blood on total volume. Applying this ratio to individual body parts we can deduce their blood volume (always assuming that blood is spreaded homogeneously in the body). Let's call B a body part and BV its blood volume, then :

$BV(B) = \text{Vol(B)} \times 0.077$

The blood a human can contain can be should then have a maximum volume capacity roughly equal to the sum of individual body parts blood volume. let's call this substance container volume $Vol(S_c)$, then

$Vol(S_c) = \sum_i BV(B_i)$

This simple formula will be used to always determinated the maximum amount of blood a human can contain, depending on what limb they have left.

This quantity will change if the player lost a limb, or any other parts. It is important because it can help to define the right amount of blood the player needs to have in its circulatory system, and it's drastically different if it's a whole healthy human or just a living head.

Absence of blood, global effects

Below is a chart of blood levels, and how they affect the player.

As a player can lost limbs, or even just be a brain, the player does not need the same amount of blood depending on its total volume.

Keep in mind the percentage below is expressing the amount of blood in the body, over the maximum amount of blood that could be in it.

Other effects, such as vision reduction may apply.

Absence of blood, local effects

Blood is essential to convey oxygen. If blood lacks too much, then oxygen starts to be difficult to conveys to organs and other body parts. This inexorably lead to oxygen damages.

Oxygen damage can eventually lead to body parts failing and dying, see more in :

Treating blood loss

Open wounds may be treated using medicines, just like most other injuries. Cauterization is also a potential solution, as well as bandages and sutures.

Because the amount of blood loss from open wounds needs to be tracked, each limb may need to track their own contained blood and wounds.

That said, bleeding damage shouldn’t be counted toward the total damage taken by a player, and instead should simply be an indicator of how much blood is being lost over time.

Blood can be drawn and injected with syringes and IV drips, can be lost from wounds and regenerated through chemicals. Blood regenerates slowly over time, and regenerates faster the better fed the character is.

There are also blood types, which follow the general real world rules. Lizardpeople have a special bloodtype, marked L, which can only receive from and donate to the L blood type. See

Heart is pumping blood and oxygen into body parts. One of its main role is actually to send oxygen contained in the circulatory system into each body parts reserve connected to it.

Sending oxygen to body parts

On each pulse, heart send oxygen to each connected body parts. Connected body parts are all parts linked to heart through a chain of circulatory layers present in adjacent body parts, including internal ones.

Heart uses the body part parent hierarchy to decide what is connected to it.

Indeed, on human, the torso is the root of the body part parent hierarchy.

Heart should check then what are the children of the torso to know which body parts are connected to it.

Stamina system is responsible for managing the player’s ability to run around. It is a single value which initially depends on character’s species and can be modified in the round by doing exercise (or reduced by getting fat, contracting an illness or getting injured). The amount of stamina available is reduced with running, fighting, carrying heavy objects or doing any other physical activity that can make people tired IRL, but is recovered over time to the maximum stamina amount.

Improving stamina is done by doing said physical activity, the max amount of stamina is increasing with every N spent stamina.

Stamina can be recovered quickly in a variety of ways as shown below, ordered from slow to fast recovery.

• Walking (instead of running)

• Staying still

• Sitting

• Lying

There’s a variety of ways the Max amount of stamina or it’s regeneration speed can be reduced. For example, the Max amount of stamina is reduced by (100-x)/2 where x = health of both lungs, and regeneration of the stamina is reduced by total OXY damage. (all numbers are placeholders, here and below)

For a healthy character stamina should regenerate fast enough to not matter much, and for combating, injured or tired character it can serve as a more flexible cooldown system. At least, that's the idea of how it should be balanced.

Lungs are the organs interfacing between the atmospherics and circulatory systems. They intake gases, including oxygen, and transfer a part of it into the circulatory system.

Lungs have a specific rate at which they do this intake. If the equilibrium between amount of oxygen needed by body parts and amount of oxygen available gets negative (e.g when too much blood is lost or when oxygen in air is low), then the intake rate may increase.

Lungs are working independently from each other, meaning a human can survive with only one lung left, even though it will be able to intake only half the amount of oxygen it needs, and so will have to breath two times faster.

Organs

Humanoids with organs can also suffer damage to specific organs, separate but still connected to the other damage types. To analyze organ damage, you need a health analyzer equipped with an organ scan upgrade, which will assess damage in these relative terms:

• 1-9: "Minor"

• 10-29: "Moderate"

• 30-64: "Significant"

• 65-99: "Critical"

• 100 and above: "Dead"

Usually, "Significant" and "Critical" are the most important ratings, for some organs cause extra problems upon reaching the "Critical" damage threshold.

If left untreated, these problems can cause the organ to fail completely and die, resulting in the same effects as lacking one. Dead organs cannot be healed back to full health and thus require transplants.

Below is a breakdown of players’ organs, and what they do.

While it may seem like a lot, the majority of the organs perform their functions by simply existing. It’s when the organs fail, die, or go missing, is when the effects kick in.

Organ failure occurs when an organ sustains 65% damage. Upon failing, the organ will slowly deteriorate, and eventually die, at which point a transplant is needed.

Damage

Damage, in general, measures how much health character can lose before dying or being rendered inoperable.

Historically, within SS13, a player’s overall damage is composed of 4 primary types: brute, burn, toxin, and oxygen.

Damage Subtypes

Proposition: expanding on the damage types by adding subtypes of damage might make more sense in the context of medical experience and in other spheres:

BRUTE: Brute damage is the most common: it's caused by being hit with physical weapons, pressure, explosion blasts, surgery, and so on. Subtypes:

• CRUSH: Damage for being hit with a blunt object (fists, toolbox, hammer)

• SLASH: Damage of being cut with a blade (sword, saw, cleaver)

• PUNCTURE: Damage if being pierced with a bullet or a stab with a blade (bullets, drill, spear)

• PRESSURE: Atmospheric pressure or lack thereof (depressurization, overpressurization)

ENERGY: Previously known as a burn damage type. The second most common damage, is usually dealt by lasers, hot weapons like welding tools, electric shocks, explosion heat waves, fire and cold. Subtypes:

• HEAT: Damage of being exposed to dangerously high temperatures (fire, laser burn, welding tool)

• COLD: Damage of being exposed to dangerously low temperatures (being stranded in space without env suit, being stuffed in the fridge, contact with liquid nitrogen)

• SHOCK: Damage of being exposed to electricity (taser, hacking failure, stun baton)

• RAD: Damage of being exposed to radioactivity (uranium, refined plasma, space exposure)

CHEMICAL: Previously known as a toxin damage type. The least common (normal) damage, it's caused mainly by, obviously, toxins, acid and miscellaneous poisoning. Subtypes:

• TOXIC: Damage of being exposed to viruses, poisons, bacteria or viruses, oxygen poisoning (too much O2 in the air) also counts as such (self-explanatory)

• ACID: Damage of being exposed to corrosive materials (acid, being devoured by slimes)

OXYGEN: Also known as suffocation, this damage is taken when not breathing

Сlarification: doctors don’t heal the damage subtype itself, but it’s effect on different organs/parts. Any damage taken will add to its corresponding category and subtract from part's health.

Also, this way the damage from the toolbox (CRUSH) and the knife (SLASH) would be different (because it logically should be), without directly manipulating the chances of causing bleeding, concussions and other effects for every weapon and item.

Damages are shared between the different body part layers on a body part. Getting a strong hit in the head will damage mainly the head's bone structure, but also its circulatory system. If the hit is strong enough, it can even affect the brain.

Certain types of damage, like burn and brute damage, may have a direct effect on specific areas of the body; different body parts may be damaged individually. For example, if your liver dies, you may start fainting and sustain toxin damage over time.

Damages can affect many things, from your ability to talk and walk to your ability to feel pain.

Every damage type has a way to be treated with professional help. Most of the damage can be negated or remedied by providing the damaged part with a substance designed to deal with it.

Substance Exposure

Reagents should be introduced into the bloodstream at various rates depending on the type of 'exposure'.

• Injecting: would instantly introduce reagents to the bloodstream. Requires IV stand, syringe or hypo applied to the bodypart (+ CIRCULATORY connected to it).

• Inhaling: introduces reagents fast, but not instantly. Requires at least one working lung (+ CIRCULATORY connected to it) and either breathing mask connected to a source of gas/dispersed reagent or said reagent introduced to the station’s atmosphere.

• Digesting: slowly extracts reagents located in intestines. Requires working intestines (+ CIRCULATORY connected to it).

• Topical: skin absorbs reagents very slowly. Requires a reagent or a patch/bandage/dandaid containing it applied to a bodypart with a not-dead MUSCLE layer (+ CIRCULATORY connected to it).

This way, for example, a combat stim patch would be good for negating the effect of a wound temporarily, a pill would be perfect for long engagements with a very low overdose risk and an autoinjector would be an ace up your sleeve at the risk of an overdose if the dosage is too high.

Pain is a (normally) unpleasant feeling often caused by intense or damaging stimuli. It's a transitory symptom of an underlying condition or problem in the life form’s body.

It triggers as a burst of pain, then it slowly fades away, causing varying effects depending on the level of pain and its localization. Pain is transferred over the Nervous system layer and is delivered into the brain (so there’s no need for several pain meters for each body part). There is the natural pain resistance every creature has, as a threshold the pain level must cross before causing any effect. Pain resistance is also the factor by which pain is reduced over time.

Pain effects

Pain can manifest in several ways, beside the action message, depending on the level of pain the life form is feeling. Some of those effects are:

• Mechanics: Temporarily disabling a body part, which can cause dropping things (in case of pain in arms) or inability to run (in case of pain in legs)

• Mechanics: Dizziness, Passing out (heavy stamina damage?)

• Mechanics: Vomiting

• Visual effects: Sudden red flashes on screen so show damage occurring

• Text: RP automated messages like *Twitches*, *Goes Pale*

• Sound: Involuntary vocal screaming, moaning, groaning or whimpering.

• Animation: Involuntary movement (spasms, twitching), momentarily violent muscle contraction (think of tasers)

Mitigation of pain

Pain can be controlled in several ways. First and most effective way is to fix the issue that is causing pain - take care of the wound, for example.

Drugs such as morphine can also relieve pain momentarily as the needed drug is delivered to the Nervous system via the Circulatory system, without fixing the underlying issue. And lastly there is intervention on the nervous system, affecting Nervous system directly through surgery or other means.

Some data regarding oxygen consumption in the body.

At rest a human consumes about 250 ml of oxygen each minute, 4.16 mL per second, so approximately 4.16/22.4 = 0.18 mmol per second (22.4 is the molar volume of oxygen under 1 atm and 25 degree celsius). https://www.britannica.com/science/human-respiratory-system/Interplay-of-respiration-circulation-and-metabolism

• Average volume of a human body : 65 L https://bionumbers.hms.harvard.edu/bionumber.aspx?s=n&v=3&id=109718

• One milliliter of body then consume 0.18/65/1000 = approximately 2.77*10^-6 millimoles per second. We'll call that MilliMolesOfOxygenPerMillilitersOfBody.

Oxygen needs of individual body parts

A body part might, or might not, need oxygen. At the basis, it's the layers composing it that needs oxygen. Generally, the formula will be very simple, let's call L a single layer and O() the function for the needed oxygen. O(L) is expressed in millimoles, Vol(L) in milliliters and MilliMolesOfOxygenPerMillilitersOfBody is the constant above (unit in the name). The volume of a layer is currently simply the volume of its body part.

$O(L) = \text{MilliMolesOfOxygenPerMillilitersOfBody} \times \text{Vol(L)}$

Now for each layers present in the body part, we just compute the average of their need in oxygen to get the need of the bodypart itself.

Oxygen reserve of individual body parts

The amount of oxygen a single body part can hold will rely on its volume and on a factor that user can pass in parameter.

$R_o(B) = \text{MilliMolesOfOxygenPerMillilitersOfBody} \times \text{Vol(B)} \times \text{ReserveFactor}$

The reserve factor is here to allow the user to set different amount of oxygen reserves for body parts, thus making some dying faster than others.

Some data regarding blood and oxygen volume in a human

The maximum volume of oxygen which the blood can carry when fully saturated is termed the oxygen carrying capacity, which, with a normal haemoglobin concentration, is approximately 20 mL oxygen per 100 mL blood.

Of course, oxygen doesn't circulate in the body like in the air. In blood, it is densely packed into haemoglobin. We can safely consider that haemoglobin makes up 2% of blood volume, so oxygen is packed by a factor ten compared to normal atmospheric conditions.

Upon being taken in atmos by lungs, oxygen should turn into haemoglobin, so that there's no actualy oxygen into blood.

Surgical Access

Several problems require immediate surgery to save the patient, some of which concern their extremities or internal organs, in which case the patient must be "opened" in order to directly interact with the part that needs doctor's attention. The overall organ access order (by body parts) should look as such:

That means, while Eyes, Ears and Speech organs (Tongue) can be directly accessed and treated without surgical intervention, to treat the brain the doctor should first cut through the skin of the patient’s head and through the skull bone. Or, in other words, they should cut through the MUSCLES and BONES layers of the Head body part.

The dotted line means that there’s no need in any sort of incisions to access the needed organ, the parent organ just should be moved (Made for simplicity and cartoonish style, don’t try this at home, author knows nothing of real anatomy or surgery or medicine in general. Applicable to the whole document, actually.)\

Surgical transplantation

In order to be removed, the organs should be surgically accessed and disconnected from MUSCLES, CIRCULATORY and NERVES of their body part.

Example: In order to extract the brain, the doctor should first cut off the top of the head, open the skull, cut the nerve endings, cut off (and cauterize, depending on the situation) the blood vessels and extract the brain. In order to install a different brain in it’s place, the doctor should basically perform the procedure in reverse: place the brain in the head, reconnect blood vessels of the new brain and the body, reconnect the nerves, close the skull and staple the head back.

Surgical tools

Surgeon uses a variety of tools

• Tools for incisions (TI) - the tools to cut through the soft tissues of the organism, used primarily on MUSCLES, CIRCULATORY, NERVES and ORGANS. The most convenient one is Scalpel, but any item/weapon that can do slash damage might work (the more the characteristics of the item differ from the scalpel, the worse it is as a tool for surgery, i.e. being too heavy, making too much/not enough slash damage, etc.).

• Tools for bone cutting (TBC) - tools to cut BONES. Bone-saw is an obvious choice, but other types of slash damage items might work (but even worse than the incision tools).

• Tools for retraction (TR) - opens the incisions wide, holds the skin and MUSCLES in place and doesn't allow it to close on the doctor while they operate. Surgical retractors are made for this purpose, but wire-cutters or wrench can be used in case of emergencies.

• Tools for cauterizing (TC) - burns the CIRCULATORY to stop blood loss from a specific vessel, for example, after ORGAN removal. Cautery is the choice for this job, but any item that can provide a similar HEAT damage can possibly work.

• Tools for manipulation (TM) - for moving organs tissues and bones around without harm for the patient. Might also be used to close the CIRCULATORY vessels (to be reconnected later). Hemostat is the intended tool, but wire-cutters can be used to achieve the same effect with a certain chance of failure.

• Tools for bone merging (TBM) - for setting BONES back together after fracture of surgical procedures. Bone gel can make bone tissue ductile, after which the bone parts can be mended back together with TM, but it can be partially substituted with surgical tape or a regular adhesive material for worse results.

• Tools for wound closing (TWC) - for sawing MUSCLES wounds back together or bandaging the wound. Depending on the severity of the wound/incision, medical gauze or surgical tape might be enough, but the wound might reopen if the application is removed too early. Surgical suture is more time consuming and works only for incisions, but needs no removal. There are ghetto versions for both, being adhesive tape and cloth for the first option and regular sewing thread or wire for the second.

• Tools for drilling (TD) - for making holes in BONES or teeth to insert pills/patches into a resulting cavity. The medical drill can be used for it, but the cavity can also be dug with other drills like mining one (why) or meticulously scratched using needles or scalpel.

Surgical description (in-system)

Surgical operations should be described in the same way as basic crafting recipes (see Crafting Design Document (WIP)), in a sense that every interaction of the tool with a certain layer or organ should describe the target, the tool and the result of the basic interaction.

{
  "type": "surgery",
  "result": " [ { "bones_access", 1 } ]
  "time": "10 s",
  "tool": "saw_circ",
  "component": [ [ [ "head", "bones", "bones_access", 0, "muscles_access", 1 ] ] ]
} 

This “recipe” describes that if a circular saw is used on a patient head’s skull when the skin in the head is already cut, then after this interaction 10 seconds (of animation) should pass and the skull would also be opened.

Death is a (semi)permanent disability, suffered by biological characters. Character is counted as Dead upon death of a brain (or an alternative organ/device responsible for higher neural/computational functions). The general order of a natural death of the body (or brain removal) is as follows:

1. Neural activity stops, the body is unable to move. Remedied by brain reconnection or implantation with an AI tech.

2. Heart stops, blood flow stops. Remedied by Torso surgery to connect the Circulatory system to the medical blood pump.

3. Organs and all other layers stop receiving O2 and nutrients. Remedied by surgical removal of the organs prior to their death and connecting them to life support containers. (Organs not connected to the Circulatory system start taking oxygen damage)

4. Organs and all other layers take oxygen damage. Systems that require nutrients to sustain regenerative functions stop doing that. Blood starts being replaced with a substance “Stale blood”, that cannot be used for transfusions. Blood staleness is prevented by pumping it out of the body and storing it in a cold place.

5. Organs’ health lowers. Organs that deplete their health die and cannot be used as functional transplantation organs. Not remedied

6. The Muscular, Circulatory, and Nervous systems continue taking damage as they rot. At the point of 0 health they cannot be used as a transplant (limb transplant, for example). Not remedied unless transplanted before death of a layer or removed from the body and stored in a life support container.

7. The Muscular system continues to lose health down to -100, at which point the muscles cannot be harvested as human meat and cooked. Remedied by storing the body in a cold storage prior to this point or harvesting meat immediately.

As stated, the death of the brain is the death of the character. But it might not be the end! Possible options to continue the game are becoming a ghost to fly freely over the station in spectator mode or taking a role for a ghost, such as an AI for a personal PDA, little robots or possible poltergeist antagonist. See Ghosts in Roles section for more info.

Players can also be cloned/resurrected/regenerated. The brain (or the body with one) can be thrown into a cloning vat to be rebuilt and restored. For balancing, this process might require a lot of energy or nutrients to do its magic. For RP balancing, the lore of the game claims a short term amnesia is a constant side-effect of the revival, so players can’t just wait for someone to clone their character back and use their knowledge prior to their death to point at the antagonist who (most likely) killed them.

This data is useful as it gives us some rough rough idea about things such as the volume of blood in a given body part, if we make the simple approximation that blood quantity is homogeneous in the body (obviously untrue, but good enough for SS3D).

• Average volume of a human body : 65 L https://bionumbers.hms.harvard.edu/bionumber.aspx?s=n&v=3&id=109718

• Volume of intestines : https://bionumbers.hms.harvard.edu/bionumber.aspx?s=n&v=2&id=111759

• Volume of Heart, lungs and liver : https://bionumbers.hms.harvard.edu/files/Mass%20and%20volume%20of%20the%20organs%20of%20the%20human%20body.pdf

• Volume of stomach : https://en.wikipedia.org/wiki/Stomach

• Volume of limbs :

  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769678/

Using those sources, we can approximate the volume for each body part :

For the torso and its organs :

• Total Torso = 50 % of 65L = 32.5L

• Heart = 0.3 L

• Lower and upper Intestines = 1 L each

• Liver = 1.5L

• Lungs = 0.7L each

• Stomach = 2L

• Total volume of Torso without organs = 32.5 - 0.3 - 1 - 1 - 1.5 - 0.7*2 - 2 = 25.3 L

For the limbs :

• left/right arm = 4% of 65 L = 2.6L

• left/right hand = 1% of 65 L = 0.65L

• left/right leg = 14% of 65 L = 9.1L

• left/right foot = 2% of 65 L = 1.3L

For the head and its organs :

• total head = 8% of 65L = 5.2L

• Brain = 1.3L

• Eyes = 0.03 L each

• head without organs = 5.2 -1.3 - 0.06 = 3.8L