Not many roleplaying games have realistic damage mechanics. Most use hit points – when you get hit, you lose points. Lose all of them, die. The end.

Where did hit points (so ubiquitous in role-playing games) originate? The first RPG, Dungeons & Dragons has used hit points, an abstract resource representing loss of life, copied by Dave Arneson from a set of American Civil War naval game. It prevented players from losing their characters every time they lost a roll and was simple and easy.

And completely wrong. It reflects neither reality nor conventions from heroic literature and action movies. It is self-referential – it describes the reality of games, which use hit points, health bars and so on, all under the influence of previous games which use the same concept.

Unfortunately, the understanding of issues of survivability of injuries typical for role-playing games, that is, cuts and stabs and gunshot wounds is not common, so hit points or wounds which add up seem a sensible solution. And since role-playing games do not have to reflect reality, we should at first take a look at action movies – maybe hit point systems will be justified there?

In the movies mooks and background characters usually die or are incapacitated instantly when hit, whereas the main heroes (both the protagonists and the antagonists) will ignore hits, which are purely cosmetic. The main hero will survive until the end, his mentor will die, but his death will take long enough to say a few words of wisdom, the hero’s sidekick or romantic interest may either die to make the hero internally conflicted, or open their eyes after a dramatic pause, unbutton their jacket and show a bulletproof vest, whereas the main villain is allowed to die only at the end of a long final fight at the movie’s climax, no earlier. No hit points here (well, except for the boss-fight, perhaps).

Do roleplaying games need to behave in the same manner? The answer is, of course, “it depends”. If the game in question is, say, Hong Kong Action Theater, then of course yes – after all, HKAT is supposed to recreate the “reality” of Hongong action movies, and not real life. If we play D&D 3e, then not really, because we’re not looking for realism nor cinematic drama, but an increase of hit points, better magic items and fame and power (but mainly power), like in Baldur’s Gate. However, an RPG in a realistic convention, like CP2020 or Delta Green, requires something more researched. So how is it with killing people in reality?

Humans are simultaneously very fragile and very resistant. It is hard to kill them, and at the same time it is very simple. There is only one final and ultimate reason for death. It is the destruction of most cells of the central nervous system (to be exact, death of the brain cortex and brain stem). But it is necessary to kill most brain cells. Let’s take a widely known example of Phineas Gage, a railway employee in the United States, whose skull and brain was impaled by a steel rod in an accident while tamping explosive material. The rod has transfixed Gage′s head, passing through the frontal lobe, but after pulling it out Phineas was still able to act as normal (although supposedly his personality changed for the worse; this may or may not be true). There are many other examples of people who have survived brain damage and returned to full functionality. As it turns out, human brain is a very flexible device and functions of the damaged area may sometimes be taken over by another area.

Physical destruction of most of brain cells is not simple, because it is protected by a rather hard skull and by an impact-absorbing system of meninges. Yet there is a much simpler method of killing nerve cells. To kill a human, it is sufficient to stop his blood from circulating. Lack of oxygen kills brain cells very efficiently and rapidly – neurons are record-holders in oxygen and sugar consumption. Stopping the heart (or cutting off the brain’s blood supply in another manner, by cutting the throat, tearing the aorta etc.) causes rapid loss of consciousness and clinical death, and after three to five minutes, the beginning of necrosis of the cerebral cortex (cerebral decortication). Lack of supply of oxygen to brain cells for five to twenty minutes results in irreversible changes in the brain, and then cerebral decortication (more information may be found in an encyclopaedia or a forensic pathology manual). The only exception to this rule which may occur sometimes is the situation where the brain is placed in a very low temperature. For example, people fished out from under ice after a long time – something similar to hibernation occurs then. However, without advanced (technological or magical) medical aid biological death will occur within five to ten minutes after clinical death, and cardiopulmonary failure is sufficient to cause clinical death.

And it is rather simple to switch off a man’s circulation – shock may stop the heart even after being shot with a small .22 LR bullet. In the leg. The person who’s been shot may lose consciousness right away (for psychological reasons), or maybe only after a minute or two (due to blood loss), but if her heart stops, the brain will die.

This leads to the conclusion that in a roleplaying game there are three possible effects of being hit. The least frequent is instant death, which in practice occurs only in the situations where brain is severely damaged (either by a bullet or by a sword blade, troll’s fist etc.). The remaining options are either an immediate loss of consciousness (due to pain or psychological reasons) or, in case of people hopped up on amphetamine, PCP, cocaine or plain, old, natural adrenaline (usually present in large quantities in the body during a fight), ignoring the damage until the blood loss becomes large enough to result in loss of consciousness. It is of course completely possible that until that time the fight will end, and the injured person (or his teammate) will be able to stop the blood loss, either using a mundane bandage, or an automatic nanomedical pack/′Cure Light Wounds′ wand. One can notice that the “bullet kills instantly, unless the character is important, then it has only a cosmetic effect” from Hollywood is much more realistic than hit points (“Rambo may ignore the first fifteen bullets, and the sixteenth will kill him”).

It is time to interrupt our deliberations on RPGs and their rulesets. Time for a short lecture on trauma medicine. There is something called “Abbreviated Injury Scale” (AIS). It is a medical system to assess the hazard caused by a wound. The AIS scale was created in 1969 and since then was updated many times and compared to the survivability data in order to provide accurate assessment of a given injury.

In AIS wounds are assessed on a scale of 1 to 6, where 1 covers small injuries (like cut skin, zero chance of death), 2 covers moderate injuries (e.g. fractured sternum, probability of death for AIS 2 is 1-2%), 3 covers serious injuries (open arm fracture, 8-10%) chance of death, 4-5 includes severe to critical injuries (punctured throat or ruptured liver, 5-50% chance of death), and 6 is a lethal injury. This scale demonstrates in a simplified manner the threat to survival presented by the injury, and is logarithmic.

What happens to a person who has suffered multiple injuries, a situation which hit points are supposed to represent in theory? Another system was created to assess the impact of multiple injuries, called ISS – Injury Severity Score. It is the only system used in medicine which correlates linearly with mortality, morbidity, hospital stay etc. In other words, it can be used to assess the impact of wounds suffered by characters to their chances of survival and healing time.

The ISS assessment has values of 0 to 75. If any injury is assigned an AIS of 6 (unsurvivable), then ISS will automatically become equal to 75. Unfortunately, even such a simple statistical tool as ISS can’t be used directly in an RPG system’s mechanics, because it’s overly complicated.

The ISS is calculated in the following manner: each wound receives an AIS level, and is assigned to one of six body areas: head and neck, face, chest, abdomen, extremities (including pelvis) and external (skin). For each area only the highest AIS is used. Then, take the AIS levels for three most severely injured areas, square them, and then add them to each other to obtain an ISS score. An example:

Head and neck: Concussion, AIS 3 (square: 9)
Face: no injury, AIS 0
Chest: flail chest, AIS 4 (square: 16)
Chest: minor contusion of liver, AIS 2
Chest: complex rupture of spleen, AIS 5 (square: 25)
Extremity: fractured femur, AIS 3
External: no injury, AIS 0
The total Injury Severity Score is 50, so the chances of death are quite high.

There is also another scale, which tells a lot about immediate survival chances, Revised Trauma Score. It does not take into account injuries of individual organs, only the condition of the patient at the moment of first contact with medical personnel, in three aspects: neurological damage described by the Glasgow Coma Score (most important element of the RTS, obtained by the test of “please open your eyes, please say something, a knock to the knee with a small hammer”), systolic blood pressure (second in importance, establishing whether the patient has bled out significantly and whether his heart is working correctly) and respiratory rate (the least significant element of RTS, since respiratory action is easiest to restore). As one can see, neurological damage is most dangerous, and bleeding out or having one’s heart stop is the second most important danger.

So what can gamers learn from medicine?

First, hit points from Dungeons & Dragons, or any other system where damage adds up (like wounds in World of Darkness or Shadowrun) are completely unrealistic. Chances of dying after fifteen shallow cuts are much lower than after one deep slash (which is rather intuitive: someone with his skin cut in fifteen places is in a lot of pain, whereas someone with a deep cut to the stomach is someone trying to keep his intestines from spilling out). Wounds do not add linearly. If each gunshot wound has, for example, a 15% chance of causing a significant bleeding and 2% chance for mortally damaging the spine (say, we’re shooting someone in the back with .22 LR), then putting 10 bullets in someone significantly increases the chance that one of them hits the spine or cuts through an important artery. But if not one of the bullets does it, then the person shot will not feel ten times worse than after being hit by one bullet. Similarly, after breaking an arm, a second break five centimetres along will not cause the arm to hurt twice as strong and it will not become two times less effective, nor will it take two times as long to heal.

Second, the only moment when the wound effects add up is when establishing the general condition and strength of the victim, and time needed to heal (and his can be done after he fight is over, when there is some free time). And even then the wounds do not add linearly – wounds to different parts of the body are most important.

Third, people usually don’t die at the moment of being stabbed with a sword, cut with a knife or being shot with a gun (or laser). Even with a cut throat you can live for a few seconds. In role-playing games characters either die instantly (because they received seven damage points or another severe wound, and they only had four hit points remaining or only one remaining moderate wound to mark off), or you can be certain they will survive. In reality, a disembowelled person will be dying for some time and modern medicine should have a chance save her, not to mention supertech or magical healing, while at the same time, a “moderately wounded” person can die of complications two weeks later, even though in an RPG a character who lost 4 hit points out of 10 is guaranteed to survive.

Four, some mechanism is necessary to reflect blood loss. This is a very important element. Although some wounds (shallow knife cuts) result in a very slow blood loss, there are many types of wounds which can cause rapid blood loss and loss of consciousness. They include both significant, extensive trauma which destroys multiple blood vessels (a sword cut pretty much guarantees high blood loss) and small, narrow wounds which have cut open an artery (a gunshot wound or a stab with a rapier, if the attacker is highly skilled or lucky). Blood loss or destroying the central nervous system are the only guaranteed methods of stopping a human assailant.

This means that studies which show “stopping power” of 90% and more for handguns are pure marketing, without a connection to reality. For interested reader: at http://www.firearmstactical.com/pdf/fbi-hwfe.pdf one can find an FBI report on efficiency of handgun bullets in stopping people. Summarising: most people hit by bullets are incapacitated, but a determined person can act effectively even after multiple hits, and the only way to stop a determined attacker is a hit to the brain or upper spinal cord.

Over large distances, damage caused by firearms is highly random, whereas at short distances it depends significantly on the shooter’s skill – a precise hit to the head from a small calibre .22 LR handgun is much more effective than breaking someone’s rib by .45 ACP slug. The definition of “short distance” depends on the weapon used, of course. For an M-16 it may be up to 80 or 90 metres in good conditions, and for a sniper equipped with a high quality rifle, match grade ammunition and good optics a quarter of a kilometre may be a “short distance”. This is the main advantage of long guns over handguns – much higher accuracy, which provides real stopping power.

We have many studies and analyses on the mortality of gunshot wounds. Generally, statistics indicate that GSW mortality is around 20%, with headshots having double that chance and shots placed elsewhere on the body having approx. 16% mortality. What about melee weapons?

This is somewhat more problematic. Modern medicine, autopsies in order to establish the precise cause of death, statistical analysis – this all came into being a long after blades were replaced by firearms. So there is a lack of an appropriately large sample for statistical studies, which in case of firearms was provided by criminals, law enforcement and the military.

However, there is one source of data on the effectiveness of melee weapons used on a mass scale in times before the firearm. This is paleopathology, the study of causes of death and general medical history conducted on skeletons dug out by archaeologists.

What does it tell us? For example, that swords used in the Middle Ages could easily cut someone’s arm or leg, but they didn’t always. The skeletons dug up and tested included warriors with cuts to the legs and the head slashed with a sword (combination of attacking under the shield and then killing the wounded enemy when he lowers the shield), people whose both legs were cut off with a single sword strike, and skeletons with remodelled injuries on skulls, tibia, ribs or arm bones, indicating healed injuries caused by swords or knives. This last item shows that people who were wounded, but not killed had a chance to survive, depending mainly on the strength of their immune system (and on whether the cut was clean, or did dirt get into the wound).

Of course, there was always the possibility of dying of infection. A stab wound to the stomach, or a deep cut to this area were almost a guaranteed death sentence, caused by the bacteria from the intestines getting out into the body. Richard the Third died of an infection from an arrow wound. However, in sword fights arms and legs are easier to hit than the body and the head, and wounding them is not as dangerous.

This means that although melee weapons may destroy much larger amounts of tissue than firearms, but the basic reactions of the organism on being wounded are the same. Only being hit in the heart, spine or head guarantees immediate death. Well, almost immediate – the brain will survive a minute or more, which should be taken into amount. This means that in a fantasy world effective healing magic, whether in the form of Last Chance Amulets or Bloodstones, effective prayers of good priests or a healing tub of a skilled watercrafter can save most victims, if provided fast enough.

If you think about it, a dead character in a fantasy system could be saved by a priest or a wizard even a few minutes after “dying”. Magical medicine in most fantasy world seems much more effective than modern medicine in healing wounds. Why shouldn’t it have prayers or spells of Transfuse Blood, Oxygenate, Resuscitate or Protect Mind at it disposal, to preserve the brain against brain death until other spells of Cure Severe Wounds knit back severed tissues, repair punctured heart and return the almost-dead victim back to normal life? And of course a Restore Health spell, which exorcises the invisible demons of pestilence (microbes) from the wound, removing the risk of infection.

In science fiction games saving critically wounded characters can also be much simpler than in modern times. Oxygen-transporting nanoparticles in the blood may increase oxygen contents of blood multiple times, nanobots or implants which automatically release smart clotting agents may protect against bleeding, and as a last resort the head with an undamaged brain (protected by a carbon nanofibre reinforced skull) may be placed in a box which will automatically find the blood vessels and will pump synthetic, oxygenated blood-substitute into the brain, preserving it.

As this example shows, realistic approach to damage is better even in completely unrealistic heroic fantasy systems. A powerful barbarian or experienced warrior will be truly hard to defeat, since small wounds don’t add up, especially if the character has a magical item for stopping blood loss. And at the same time it avoids the problem of D&D 3e, where characters are alive, alive, alive, alive, and then fall down and within at most 10 rounds (so, one minute), or frequently even shorter are completely absolutely dead and require resurrection. The remaining characters from the group can stand guard over the fallen body of their comrade, while the group’s clerics or mages can save him with their spells. And if we ignore or significantly slow the bleeding-out process we get real fantasy badasses, which in combination with great dodging or parrying ability (and appropriate reserve of Destiny Points or other Ass Saver Points) reflects the “reality” of heroic fantasy much better than slow scraping of heroes to death in D&D.

And in a system with realistic damage mechanics creatures which do not bleed, such as zombies, skeletons or other cyborgs turn out to be much more dangerous in a natural manner, without requiring artificial rules like “zombies have additional armour against damage other than slashing”.

To summarise: good damage tracking mechanics in an RPG should take into account five factors. First, psychology: an average human who is wounded will fall down or even lose consciousness, but people with extraordinary training and/or determination (which is usually true for Player Characters) may fight even with multiple wounds, until they are incapacitated by blood loss, or until they receive a wound that is instantly incapacitating (destruction of brain or spine). Second, wounds do not add up linearly – multiple small wounds are less hazardous to health and will heal faster than a single severe wound. Third, wounds have little impact on ability to fight (mainly impairing a wounded limb and causing general fatigue from loss of blood) until adrenaline and endorphins wear off, at which point pain becomes rather distracting (however, pain thresholds are highly individual and depend on psychological factors). Fourth, the bigger the gun or sword and the higher advantage of attacker’s skill against defender’s skill, the higher the chance of instant incapacitation regardless of the defender’s determination and pain threshold (or used drugs). A stab with a rapier through the eye socket, a decapitation with a sword or a headshot into the brainstem from a handgun will instantly kill the toughest guy alive. And finally, fifth is that death occurs at the moment of killing blow only for most lethal wounds, hits to the head and spine. A character does not die when stabbed with a sword for 8 damage points when it only has 6 points remaining. A character stabbed with a sword for 8 out of 10 possible damage points will most probably die in the nearest future, but advanced medicine or magic can still save them.

Are there RPG systems with realistic damage mechanics? Of course, for example HarnMaster for fantasy, Blue Planet for SF, Millenium′s End for a contemporary gun-oriented mechanics, and CORPS from universal systems. (GURPS, unfortunately, fails completely here, because it is a very old system with Hit Points, and regardless of the amount of optional rules grafted on the linear, additive HPs still lurk underneath)

Unfortunately, they’re rare, because it’s much easier to copy hit points from one set of mechanics to another. Thanks for nothing, Dave Arneson and Gary Gygax.